EP0040559B1 - Piezoelectric convolution device using elastic waves - Google Patents

Piezoelectric convolution device using elastic waves Download PDF

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Publication number
EP0040559B1
EP0040559B1 EP81400686A EP81400686A EP0040559B1 EP 0040559 B1 EP0040559 B1 EP 0040559B1 EP 81400686 A EP81400686 A EP 81400686A EP 81400686 A EP81400686 A EP 81400686A EP 0040559 B1 EP0040559 B1 EP 0040559B1
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Prior art keywords
substrate
convolver
convolver device
electrode
strips
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German (de)
French (fr)
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EP0040559A1 (en
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Hervé Gautier
Charles Maerfeld
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Thales SA
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Thomson CSF SA
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06G—ANALOGUE COMPUTERS
    • G06G7/00—Devices in which the computing operation is performed by varying electric or magnetic quantities
    • G06G7/12—Arrangements for performing computing operations, e.g. operational amplifiers
    • G06G7/19—Arrangements for performing computing operations, e.g. operational amplifiers for forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions
    • G06G7/195—Arrangements for performing computing operations, e.g. operational amplifiers for forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions using electro- acoustic elements

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  • the invention relates to convolvers using the propagation of acoustic waves in piezoelectric solids.
  • counterprogressive elastic waves which propagate in a region of the surface of the support where they interact non-linearly are excited at the ends of a support made of piezoelectric material. generate a double frequency electric field.
  • This electric field is collected by an integrating electrode covering the interaction region and this collecting electrode provides an electric signal whose modulation represents the convolution function of the two incident electric signals.
  • the modulation function of one of the two incident signals has undergone a time inversion before being applied to one of the inputs of the convolver device, the emerging signal represents a correlation function.
  • the invention applies more particularly to convolvers capable of analogically processing signals characterized by a product f. T high.
  • the guide convolvers produced so far have a response which tends to deviate from the mathematical expression of the convolution integral. Indeed, when the length L of the collecting electrode becomes large with respect to the electromagnetic wavelength, which corresponds to a product fT of high value, it is necessary to take account of the electromagnetic losses which create disturbances at the level of interaction. The signal from the interaction is no longer spatially uniform. As the electric charges are no longer induced in phase, they do not add up in an equiphase manner in the interaction region. In addition, the resistance of the collecting electrode eventually becomes appreciable with respect to the output impedance of the convolutor, which leads to a deterioration of the response. It should also be mentioned that disturbances at the interaction level also appear, even if the length L of the collecting electrode is small compared to the electromagnetic wavelength, when the resistance-capacitance product of the guide is not small enough before period 1 / f.
  • the invention as it is characterized in the claims, aims to collect the convolution signal by samples taken step by step along the interaction region of the elastic waves. contraprogressive, without these samples being able to disturb the propagation of acoustic waves by their presence.
  • the interval between two successive samples is chosen so that the difference in uniformity of the interaction remains small when the samples are brought back to the outlet of the convolutor.
  • FIG. 1 represents the diagram of a convoluting device of known type.
  • a support made of piezoelectric material 10 are arranged at the two ends two transducers 11 and 12 in the form of interdigitated combs forming the two inputs e 1 and e 2 of the convolver.
  • the two signals for which the convolution function is to be obtained are modulated around a central carrier frequency f equal to several tens of megaherts. These two signals are sent to the inputs e 1 and e 2 so as to generate two counterprogressive elastic waves propagating in two directions opposite to the surface of the support 10 with more or less penetration depending on the type of waves generated.
  • the support 10 acts not only as a propagating medium but also as a non-linear medium where there is a non-linear interaction of the two waves which creates a signal of double carrier frequency. This signal is theoretically spatially uniform over the interaction zone and it is detectable by means of a uniform electrode 15 placed on the interaction zone.
  • This electrode 15 forms a capacitor with a counter electrode consisting for example of two side plates 16 connected to each other by a connection 17 to the electrical ground.
  • the plate 15 thus collects the electric charges induced by the non-linear interaction of the two waves and provides at its output s a signal C (t) at the frequency 2f.
  • the two contraprogressive waves emitted are of the form: and where x is the axis of propagation of waves at speed v, ⁇ the pulsation 2 ⁇ f and k the number of waves ⁇ / v.
  • a signal is obtained at the output s: where K is related to energy efficiency.
  • the modulation of the signal C (t) represents the convolution function of the signals F (t) and G (t) compressed in time by a ratio 2, and over a time interval corresponding to the duration during which the two signals interact over the entire length L of the plate 15.
  • These devices are capable of processing signals of several tens of Megahertz of bandwidth B and of a few tens of microseconds of duration T. They are of great interest by their great simplicity of implementation, their high processing speed, their volume and their very low consumption.
  • the waves must be guided in this width W and the plate 15 is simply used, the guidance being obtained by the effect of slowing down of the waves caused by the short-circuit of the acoustic field at the surface.
  • the device of FIG. 1 can be implemented as follows.
  • the frequency f is equal to 156 MHz and the duration T to 12 s.
  • the beam compressors are produced by couplers with conductive bands.
  • the electrodes 15 and 16 constitute a portion of the electromagnetic transmission line in which the propagation speed of the electromagnetic waves VEM is low because of the high value of the permittivity of the substrate. Effects of propagation losses appear when the length L of the output plate is greater than about 0.1 of electromagnetic wavelength ⁇ EM equal to v EM / 2f. These effects introduce on the one hand phase shifts between the sources of the charges and the contact points and on the other hand reflections at the points of electrical discontinuity.
  • the condition L / ⁇ Em > 0.1 corresponds to: going is the speed of the acoustic waves.
  • the device described has a central frequency equal to 156 MHz for a band of 50 MHz.
  • the factor M (a), function of r is due to the non-uniformity of the interaction and the signal H (t) no longer represents the function of convolution of the two signals F (t) and G (t) .
  • the convolver device according to the invention illustrated in FIG. 2 comprises an output electrode 15 provided with several contacts distributed over its entire length along the axis of propagation of the acoustic waves and connected together to form the output s of the convolutor, the maximum interval between the contacts being chosen to obtain a low error of uniformity of the interaction.
  • the transmission line 20 comprises n equidistant sockets 21 connected at a common point by wires 22 introducing a negligible phase shift.
  • the short-circuit current I cc at the output is then evaluated as a function of the abscissa of an acoustic generator 23 of charge I, the abscissa x being identified with respect to the middle of the interval between two taps, for example the taken 1 and 2.
  • FIG. 4 represents the variations of I cc / I in amplitude, solid line, and in phase, dotted line, in the case where the half-distance between taps is equal to O, 075, lEM and for 3 values of the attenuation a by y ⁇ EM in Néper.
  • the resistance R is given by if r is the plate resistivity and the capacitance C depends on the distance between the positive and negative electrodes and it can be adjusted.
  • the loss a is known and the maximum spacing between taps can be determined to obtain the required uniformity error.
  • the maximum distance between taps is of the order of 0.1 ⁇ a to 0.22 ⁇ a for a phase error and of amplitude limited respectively to 10 ° and 1 dB, ⁇ a denoting the acoustic wavelength at the surface of the substrate.
  • the contacts on the outlet plate must be made so as not to disturb the propagation of the acoustic waves. Given the high operating frequencies, the dimensions are very small, the plate being able to measure a few tens of microns in width, and several production techniques can be used.
  • the contacts are made by soldering or by direct bonding of a conductive wire 40 on the outlet plate 41 placed on the surface of the substrate 45.
  • the dimensions of the welding point 42 or the adhesive point 43 do not exceed one tenth of the acoustic wavelength.
  • welding is carried out either by thermocompression or by ultrasound. As for bonding, it is obtained cold using either indium or electrically conductive epoxy resin.
  • the contacts can be made by welding or gluing next to the plate so as to be able to increase the size of the welding point or the point of glue. For this, the contacts are made at a distance from the plate such that the energy of the acoustic waves is practically zero, this distance being of the order of a few wavelengths.
  • connection blocks 52 are arranged along the plate 55 on the surface of the substrate. They are electrically connected to the plate by conductive strips 50 whose width is less than / ! A / 5 to disturb the propagation of the acoustic waves as little as possible, their length being equal to Z chosen to sufficiently distance the blocks from the plate. These bands are connected to the blocks by wider bands 51 making it possible to reduce the electrical resistance. These strips 51 can be flared from the strips 50 to the blocks 53 as shown in FIG. 8. Referring to FIG. 7, the ground electrodes 54 are notched to receive the blocks 52, this discontinuity not affecting the uniformity of interaction.
  • Electrodes can also be distant enough from the plate to remain uniform if the width of the substrate allows it. These electrodes can also be placed on the lower surface of the substrate.
  • the spots of solder or glue 53 made on the pavers can be produced using all the conventional techniques since there are no longer any dimensional constraints. Although in the example represents each contact is ensured by two blocks, we could use only one on one side or the other.
  • each metal strip 51 and each block 52 are placed on a thin layer of an electrically insulating material 60 such as resin or Si0 2, thus significantly reducing the coupling between the substrate and the metallized parts .
  • an electrically insulating material 60 such as resin or Si0 2
  • FIG. 9 shows another technique making it possible to suppress coupling by the conductive strips of connections 50.
  • Each strip is metallized on a material which is then eliminated so as to leave an air gap 70 between substrate and the strip. Note that this technique is known in particular for producing an acoustic filter.
  • the guide 55, the strips 50 and 51 and the blocks 52 are for example metallized by deposition, by evaporation or spraying using a mask produced by photolithography.
  • Another embodiment consists in placing an electrode in the form of a plate opposite the guide and similar to the latter. The connections to the output circuit are made on this electrode.
  • FIG 10 shows in section an embodiment by capacitive coupling.
  • a first substrate 85 has on its surface the devices for generating the acoustic waves and the guide 80; it can also include the ground electrodes 82.
  • a second substrate 86 is applied to the surface of the first substrate 85.
  • the two substrates are preferably made of the same material.
  • the substrate 86 has a recess 83 provided with the output electrode 81 placed opposite the guide 80 and at a predetermined distance h. This distance h is chosen so as to capacitively couple the electrode to the guide without reducing the efficiency of the convolver. For this the capacitance C brought back must be large compared to the capacitance Cp of the piezoelectric substrate.
  • the value of the capacitance Cp is of the order of the permittivity 8 p of the substrate while the value of the capacitance C is equal to ⁇ o where ⁇ o is the permittivity of the air, these values being counted per unit of length along the axis of propagation of the waves.
  • the substrate 85 includes the recess such as 83 provided with the acoustic guide 80 while the other substrate is planar.
  • Figures 11 and 12 show two other alternative embodiments for which the guide is not metallized: sout it is produced by profiling the substrate to give it a greater thickness opposite the output electrode as shown in Figure 11 at 90, either it is produced by modifying the structure of the substrate opposite the output electrode by an ion implantation as shown in FIG. 12 at 100.
  • the faces of the two piezoelectric substrates 85 and 86 are polished and brought into contact and then held by gluing or mechanically by pressing, or else by adhesion obtained by a seal.
  • FIG. 13 shows an embodiment comprising metal studs 110 produced between the metal guide and the outlet electrode.
  • the height of the recess 83 can be notably greater than for the constructions with capacitive coupling and it is therefore less critical.
  • the lateral dimension of each stud is small in front of ⁇ a, around 0.1 ⁇ a; in addition, these studs 110 are distributed along the guide randomly to avoid cumulative effects, the average distance between studs being of the order of 100 ⁇ a.
  • the pads are produced beforehand either on the guide 80 or on the electrode 81, for example by photoengraving, the two substrates then being assembled according to one of the techniques seen above.
  • FIG. 14 An embodiment by profiled guide is shown in FIG. 14.
  • the guide 120 is profiled in thickness transversely to the axis of propagation of the waves to present a central zone 121 and two lateral zones 122.
  • the central zone has a thickness greater than the two lateral zones causing, by mechanical load effect on the substrate 125, a slower propagation speed under this central zone and consequently guiding the waves.
  • the speed in the free zone of the substrate 123 is also greater than that of the lateral zones by the effect of an electric short circuit on the surface of the substrate.
  • the lateral zones 122 are produced so as to present a large electrical conduction.
  • the profiling of the guide is obtained for example by ionic machining. It can also be obtained by adding a conductive or insulating material over a prior metallization.
  • the electrical contacts 124 are made at the outer edges of the lateral zones outside the zone of presence of the acoustic energy.
  • the guide 130 is homogeneous in thickness and has a structure transverse to the axis of propagation of the waves, leading to the creation of a central guiding zone 131 and two lateral zones on which the electrical connections are made.
  • the central zone is continuous while the two lateral zones are discontinuous and produced by cutting the guide into strips (132) perpendicular to its axis.
  • the central zone thus makes a total short-circuit on the surface of the substrate which slows down the waves relative to the lateral zones which make a partial short-circuit.
  • the spacing p between bands (132) is chosen to be less than ⁇ a / 2 to avoid the known effects of "stop band” and thus maintain a large bandwidth B.
  • the guide is for example obtained by photoengraving or photolithography.
  • the electrical contacts are made at the ends of the strips.
  • the guide has a width W of 30 ⁇ and a length L of 35 mm. It has four equidistant sockets of 1, two of which are located at the ends so that the I / ⁇ Em ratio is close to 0.16, the frequency band being equal to 100 MHz.
  • Figures 16 and 17 schematically represent the convolver and output circuit assembly.
  • FIG. 17 makes it possible to distinguish the detail of the connections at the level of a socket.
  • the metallized studs 146 are connected to the guide 145 and are connected to each other and to the ends of the tracks 142 of the output circuit by gold wires a few millimeters in length 148.
  • the ground electrodes 147 are connected to the parts of the output circuit connected to ground at 149.
  • the arrangement of the tracks 142 makes it possible to connect the four sockets to the output cable 143, of impedance generally equal to 50 ⁇ , by connections of identical lengths, thus making it possible to add the signals from the sockets in phase. Note that this realization is possible because the speed of the electromagnetic waves in the guide is low compared to that of the conventional transmission lines constituted by the tracks 142.
  • the output circuit can also be produced on the acoustic substrate previously metallized and covered with a insulating layer with the lowest permittivity possible.
  • such an embodiment makes it possible to obtain a uniformity of the amplitude response of less than 1 dB and a uniformity of the phase of less than 15 °. With only the two extreme sockets connected, the result is amplitude uniformity to within 5 dB and phase uniformity between 80 and 90 degrees.

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  • Mathematical Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Acoustics & Sound (AREA)
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Description

L'invention se rapporte aux convoluteurs utilisant la propagation des ondes acoustiques dans les solides piézoélectriques. Etant donné deux signaux électriques incidents de durée T et de fréquence porteuse f, on excite aux extrémités d'un support en matériau piézoélectrique des ondes élastiques contraprogressives qui se propagent dans une région de la surface du support où elles interagissent non-linéairement de façon à engendrer un champ électrique à fréquence double. Ce champ électrique est recueilli par une électrode intégratice recouvrant la région d'interaction et cette électrode collectrice fournit un signal électrique dont la modulation représente la fonction de convolution des deux signaux électriques incidents. Cette technique est notamment décrite dans un article de C. S. KINO intitulé »Acoustoelectric interactions in acoustic- surface-wave devices« et publié dans les Pro- ceedings of the IEEE, mai 1976, vol. 64, N° 5, pages 724-748. Lorsque la fonction de modulation de l'un des deux signaux incidents a subi une inversion de temps avant d'être appliquée à l'une des entrées du dispositif convoluteur, le signal émergent représente une fonction de corrélation. L'invention s'applique plus particulièrement aux convoluteurs capables de traiter analogiquement des signaux caractérisés par un produit f. T élevé.The invention relates to convolvers using the propagation of acoustic waves in piezoelectric solids. Given two incident electrical signals of duration T and carrier frequency f, counterprogressive elastic waves which propagate in a region of the surface of the support where they interact non-linearly are excited at the ends of a support made of piezoelectric material. generate a double frequency electric field. This electric field is collected by an integrating electrode covering the interaction region and this collecting electrode provides an electric signal whose modulation represents the convolution function of the two incident electric signals. This technique is described in particular in an article by C. S. KINO entitled "Acoustoelectric interactions in acoustic-surface-wave devices" and published in the Protections of the IEEE, May 1976, vol. 64, No. 5, pages 724-748. When the modulation function of one of the two incident signals has undergone a time inversion before being applied to one of the inputs of the convolver device, the emerging signal represents a correlation function. The invention applies more particularly to convolvers capable of analogically processing signals characterized by a product f. T high.

Les convoluteurs à guide réalisés jusqu'ici ont une réponse qui tend à s'écarter de l'expression mathématique de l'intégrale de convolution. En effet, lorsque la longueur L de l'électrode collectrice devient grande vis à vis de la longueur d'onde électromagnétique, ce qui vorrespond à un produit fT de valeur élevée, il faut tenir compte des pertes électromagnétiques qui créent des perturbations au niveau de l'interaction. Le signal issu de l'interaction n'est plus spa- tialement uniforme. Comme les charges électriques ne sont plus induites en phase, elles ne s'additionnent pas de manière équiphase dans la région d'interaction. En outre, la résistance de l'électrode collectrice finit par devenir appréciable par rapport à l'impédance de sortie du convoluteur, ce qui entraine une détérioration de la réponse. Il faut également mentionner que des perturbations au niveau de l'interaction apparaissent également, même si la longueur L de l'électrode collectrice est petite devant la longueur d'onde électromagnétique, lorsque le produit résistance-capacité du guide n'est pas assez petit devant la période 1/f.The guide convolvers produced so far have a response which tends to deviate from the mathematical expression of the convolution integral. Indeed, when the length L of the collecting electrode becomes large with respect to the electromagnetic wavelength, which corresponds to a product fT of high value, it is necessary to take account of the electromagnetic losses which create disturbances at the level of interaction. The signal from the interaction is no longer spatially uniform. As the electric charges are no longer induced in phase, they do not add up in an equiphase manner in the interaction region. In addition, the resistance of the collecting electrode eventually becomes appreciable with respect to the output impedance of the convolutor, which leads to a deterioration of the response. It should also be mentioned that disturbances at the interaction level also appear, even if the length L of the collecting electrode is small compared to the electromagnetic wavelength, when the resistance-capacitance product of the guide is not small enough before period 1 / f.

En vue de pallier les inconvénients énumérés ci-dessus, l'invention telle qu'elle est caractérisée dans les revendications, vise à recueillir le signal de convolution par des prélèvements effectués de proche en proche le long de la région d'interaction des ondes élastiques contraprogressives, sans que ces prélèvements puissent perturber par leur présence la propagation des ondes acoustiques. L'intervalle entre deux prélèvements successifs est choisi de manière que l'écart d'uniformité de l'interaction reste faible lorsque les prélèvements sont ramenés à la sortie du convoluteur.In order to overcome the drawbacks listed above, the invention as it is characterized in the claims, aims to collect the convolution signal by samples taken step by step along the interaction region of the elastic waves. contraprogressive, without these samples being able to disturb the propagation of acoustic waves by their presence. The interval between two successive samples is chosen so that the difference in uniformity of the interaction remains small when the samples are brought back to the outlet of the convolutor.

L'invention sera mieux comprise au moyen de la description ci-après et des figures annexées parmi lesquelles

  • la figure 1 représente un dispositif convoluteur de type connu;
  • la figure 2 représente un dispositif convoluteur selon l'invention;
  • la figure 3 est un schéma explicatif;
  • la figure 4 est un diagramme explicatif;
  • les figures 5 et 6 illustrent une première variante réalisation des prises de contact;
  • la figure 7 illustre une seconde variante de prise de contact;
  • la figure 8 illustre une troisième variante de prise de contact;
  • la figure 9 illustre une quatrième variante de prise de contact;
  • la figure 10 représente un mode de couplage capacitif;
  • les figures 11 et 12 représentent des variantes du mode de couplage illustré sur la figure 10;
  • la figure 13 représente un mode de couplage galvanique par plots;
  • la figure 14 illustre un dispositif convoluteur à guide profilé;
  • la figure 15 représente une variante de réalisation du dispositif de la figure 14;
  • la figure 16 montre les connexions reliant les contacts avec la sortie du dispositif convoluteur;
  • la figure 17 représente un détail de la figure 16.
The invention will be better understood by means of the description below and the appended figures among which
  • FIG. 1 represents a convoluting device of known type;
  • FIG. 2 represents a convoluting device according to the invention;
  • Figure 3 is an explanatory diagram;
  • Figure 4 is an explanatory diagram;
  • Figures 5 and 6 illustrate a first alternative embodiment of the contact points;
  • FIG. 7 illustrates a second variant of making contact;
  • FIG. 8 illustrates a third variant of making contact;
  • FIG. 9 illustrates a fourth variant of making contact;
  • FIG. 10 represents a mode of capacitive coupling;
  • Figures 11 and 12 show variants of the coupling mode illustrated in Figure 10;
  • FIG. 13 represents a mode of galvanic coupling by studs;
  • FIG. 14 illustrates a convoluting device with a profiled guide;
  • Figure 15 shows an alternative embodiment of the device of Figure 14;
  • FIG. 16 shows the connections connecting the contacts with the output of the convolver device;
  • FIG. 17 represents a detail of FIG. 16.

La figure 1 représente le schéma d'un dispositif convoluteur de type connu. Sur un support en matériau piézoélectrique 10 sont disposés aux deux extrémités deux transducteurs 11 et 12 sous la forme de peignes interdigités formant les deux entrées e1 et e2 du convoluteur. Les deux signaux dont on veut obtenir la fonction de convolution sont modulés autour d'une fréquence centrale porteuse f égale à plusieurs dizaines de Méga- herts. Ces deux signaux sont envoyés sur les entrées e1 et e2 de manière à générer deux ondes élastiques contraprogressives se propageant suivant deux directions opposées à la surface du support 10 avec plus ou moins de pénétration suivant le type d'ondes générées. Le support 10 agit non seulement comme milieu propagateur mais également comme milieu non linéaire où il se produit une interaction non linéaire des deux ondes qui crée un signal de fréquence porteuse double. Ce signal est théoriquement spatiale- ment uniforme sur la zone d'interaction et il est détectable au moyen d'une électrode uniforme 15 placée sur la zone d'interaction.FIG. 1 represents the diagram of a convoluting device of known type. On a support made of piezoelectric material 10 are arranged at the two ends two transducers 11 and 12 in the form of interdigitated combs forming the two inputs e 1 and e 2 of the convolver. The two signals for which the convolution function is to be obtained are modulated around a central carrier frequency f equal to several tens of megaherts. These two signals are sent to the inputs e 1 and e 2 so as to generate two counterprogressive elastic waves propagating in two directions opposite to the surface of the support 10 with more or less penetration depending on the type of waves generated. The support 10 acts not only as a propagating medium but also as a non-linear medium where there is a non-linear interaction of the two waves which creates a signal of double carrier frequency. This signal is theoretically spatially uniform over the interaction zone and it is detectable by means of a uniform electrode 15 placed on the interaction zone.

Cette électrode 15 forme une capacité avec une contre-électrode constituée par exemple de deux plaques latérales 16 reliées entre elles par une connexion 17 à la masse électrique. La plaque 15 collecte ainsi les charges électriques induites par l'interaction non linéaire des deux ondes et fournit à sa sortie s un signal C(t) à la fréquence 2f.This electrode 15 forms a capacitor with a counter electrode consisting for example of two side plates 16 connected to each other by a connection 17 to the electrical ground. The plate 15 thus collects the electric charges induced by the non-linear interaction of the two waves and provides at its output s a signal C (t) at the frequency 2f.

Si F(t) et G(t) sont les deux signaux dont on veut obtenir la convolution, les deux ondes contraprogressives émises sont de la forme:

Figure imgb0001
et
Figure imgb0002
où x est l'axe de propagation des ondes à la vitesse v, ω la pulsation 2πf et k le nombre d'ondes ω/v. On obtient à la sortie s un signal:
Figure imgb0003
où K est lié au rendement énergétique. La modulation du signal C(t) représente la fonction de convolution des signaux F(t) et G(t) comprimés dans le temps d'un rapport 2, et sur un intervalle de temps correspondant à la durée pendant laquelle les deux signaux interagissent sur toute la longueur L de la plaque 15.If F (t) and G (t) are the two signals whose convolution we want to obtain, the two contraprogressive waves emitted are of the form:
Figure imgb0001
 and
Figure imgb0002
 where x is the axis of propagation of waves at speed v, ω the pulsation 2πf and k the number of waves ω / v. A signal is obtained at the output s:
Figure imgb0003
 where K is related to energy efficiency. The modulation of the signal C (t) represents the convolution function of the signals F (t) and G (t) compressed in time by a ratio 2, and over a time interval corresponding to the duration during which the two signals interact over the entire length L of the plate 15.

Ces dispositifs sont capables de traiter des signaux de plusieurs dizaines de Mégahertz de largeur de bande B et de quelques dizaines de microsecondes de durée T. Ils présentent un grand intérêt par leur grande simplicité de réalisation, leur grande vitesse de traitement, leur volume et leur consommation très réduite.These devices are capable of processing signals of several tens of Megahertz of bandwidth B and of a few tens of microseconds of duration T. They are of great interest by their great simplicity of implementation, their high processing speed, their volume and their very low consumption.

Le rendement de tels dispositifs est d'autant plus grand que, pour une puissance des signaux d'entrée donnée, la largeur des faisceaux d'ondes acoustiques W qui interagissent est faible. Aussi ces dispositifs utilisent généralement en sortie des transducteurs 11 et 12 des compresseurs de faisceaux schématisés sur la figure 1 par les deux rectangles 13 et 14. Ces compresseurs peuvent être réalisés de différentes façons et en particulier à l'aide de bandes conductrices à pas ou largeurs variables comme décrit dans le brevet français de C. MAERFELD N°2.269.237 déposé le 7 Août 1973 au nom de THOMSON-CSF. De plus en sortie des compresseurs, les ondes doivent être guidées dans cette largeur W et on utilise simplement la plaque 15, le guidage étant obtenu par l'effet de ralentissement des ondes provoqué par le court-circuit du champ acoustique en surface. Ces dispositifs permettent alors d'obtenir une dynamique de l'ordre de 60 à 80 dB.The efficiency of such devices is all the greater when, for a given power of the input signals, the width of the beams of acoustic waves W which interact is small. Also, these devices generally use, at the output of the transducers 11 and 12, beam compressors shown diagrammatically in FIG. 1 by the two rectangles 13 and 14. These compressors can be produced in different ways and in particular using pitch or variable widths as described in the French patent of C. MAERFELD N ° 2.269.237 filed on August 7, 1973 in the name of THOMSON-CSF. Furthermore, at the output of the compressors, the waves must be guided in this width W and the plate 15 is simply used, the guidance being obtained by the effect of slowing down of the waves caused by the short-circuit of the acoustic field at the surface. These devices then make it possible to obtain a dynamic range of the order of 60 to 80 dB.

A titre d'exemple non limitatif le dispositif de la figure 1 peut être rélisé comme suit. La fréquence f est égale à 156 MHz et la durée T à 12 s. Les compresseurs de faisceaux sont réalisés par des coupleurs à bandes conductrices. Les électrodes 15 et 16 constituent une portion de ligne de transmission électromagnétique dans laquelle la vitesse de propagation des ondes électromagnétiques VEM est faible à cause de la valeur élevée de la permittivité du substrat. Des effets de pertes de propagation apparaissent lorsque la longueur L de la plaque de sortie est supérieure à environ 0,1 de longueur d'onde électromagnétique λEM égale à vEM/2f. Ces effets introduisent d'une part des déphasages entre les sources des charges et les points de contacts et d'autre part des réflexions aux points de discontinuité électrique.By way of nonlimiting example, the device of FIG. 1 can be implemented as follows. The frequency f is equal to 156 MHz and the duration T to 12 s. The beam compressors are produced by couplers with conductive bands. The electrodes 15 and 16 constitute a portion of the electromagnetic transmission line in which the propagation speed of the electromagnetic waves VEM is low because of the high value of the permittivity of the substrate. Effects of propagation losses appear when the length L of the output plate is greater than about 0.1 of electromagnetic wavelength λ EM equal to v EM / 2f. These effects introduce on the one hand phase shifts between the sources of the charges and the contact points and on the other hand reflections at the points of electrical discontinuity.

La condition L/ÂEm > 0,1 correspond à:

Figure imgb0004
va étant la vitesse des ondes acoustiques.The condition L / Â Em > 0.1 corresponds to:
Figure imgb0004
 going is the speed of the acoustic waves.

Le dispositif décrit a une fréquence centrale égale à 156 MHz pour une bande de 50 MHz. Par ailleurs les valeurs types sont va = 3500 m/s et VEM = 4,3107 m/s dans le cas où le matériau piézoélectrique utilisé est du LiNb03. Avec ces valeurs l'inégalité 3 conduit à tenir compte des effets de propagation lorsque fT devient supérieur à 600.The device described has a central frequency equal to 156 MHz for a band of 50 MHz. In addition, the typical values are va = 3500 m / s and VEM = 4.310 7 m / s in the case where the piezoelectric material used is LiNb0 3 . With these values the inequality 3 leads to take account of the propagation effects when fT becomes greater than 600.

En raison des effets de propagation, le signal obtenu à la sortie s est:

Figure imgb0005
Due to the propagation effects, the signal obtained at the output s is:
Figure imgb0005

Dans cette expression le facteur M(a), fonction de r, est dû à la non uniformité de l'interaction et le signal H(t) ne représente plus la fonction de convolution des deux signaux F(t) et G(t).In this expression the factor M (a), function of r, is due to the non-uniformity of the interaction and the signal H (t) no longer represents the function of convolution of the two signals F (t) and G (t) .

L'inconvénient est donc très important et cela d'autant plus qu'il n'est pratiquement pas possible de corriger le terme M(τ) a posteriori.The disadvantage is therefore very important, and all the more so since it is practically impossible to correct the term M (τ) a posteriori.

Le dispositif convoluteur suivant l'invention illustré sur la figure 2 comporte une électrode de sortie 15 munie de plusieurs contacts répartis sur toute sa longueur suivant l'axe de propagation des ondes acoustiques et reliés entre eux pour former la sortie s du convoluteur, l'intervalle maximum entre les contacts étant choisi pour obtenir une erreur d'uniformité de l'interaction faible.The convolver device according to the invention illustrated in FIG. 2 comprises an output electrode 15 provided with several contacts distributed over its entire length along the axis of propagation of the acoustic waves and connected together to form the output s of the convolutor, the maximum interval between the contacts being chosen to obtain a low error of uniformity of the interaction.

L'intervalle maximum entre contacts ou prises, peut être évalué par un calcul. Pour effectuer ce calcul la plaque de sortie 15 est assimilée à une ligne de transmission électromagnétique avec pertes, la constante de propagation étant de la forme γ = (― a + 2jπ)/λEM où a est l'atténuation par longueur d'onde dans la ligne (en Neper). En se reportant à la figure 3, la ligne de transmission 20, comporte n prises 21 équidistantes connectées en un point commun par des fils 22 introduisant un déphasage négligeable. On évalue alors le courant de court-circuit Icc en sortie en fonction de l'abcisse d'un générateur acoustique 23 de charge I, l'abscisse x étant repérée par rapport au milieu de l'intervalle entre deux prises, par exemple les prises 1 et 2.The maximum interval between contacts or sockets can be evaluated by a calculation. To perform this calculation, the output plate 15 is assimilated to an electromagnetic transmission line with losses, the propagation constant being of the form γ = (- a + 2jπ) / λ EM where a is the attenuation by wavelength in the line (in Neper). Referring to FIG. 3, the transmission line 20 comprises n equidistant sockets 21 connected at a common point by wires 22 introducing a negligible phase shift. The short-circuit current I cc at the output is then evaluated as a function of the abscissa of an acoustic generator 23 of charge I, the abscissa x being identified with respect to the middle of the interval between two taps, for example the taken 1 and 2.

La figure 4 représente les variations de Icc/I en amplitude, trait plein, et en phase, trait pointillé, dans le cas où la demi-distance entre prises

Figure imgb0006
est égale à O,075,lEM et pour 3 valeurs de l'atténuation a par yÏEM en Néper. Cette atténuation a est telle que a = RCf si R et C sont la résistance et la capacité pour un
Figure imgb0007
 du guide. La résistance R est donnée par
Figure imgb0008
si r est la résistivité de plaque et la capacité C dépend de la distance entre les électrodes positive et négative et elle peut être ajustée.FIG. 4 represents the variations of I cc / I in amplitude, solid line, and in phase, dotted line, in the case where the half-distance between taps
Figure imgb0006
 is equal to O, 075, lEM and for 3 values of the attenuation a by yÏ EM in Néper. This attenuation a is such that a = RCf if R and C are the resistance and the capacity for a
Figure imgb0007
 of the guide. The resistance R is given by
Figure imgb0008
 if r is the plate resistivity and the capacitance C depends on the distance between the positive and negative electrodes and it can be adjusted.

Pour des valeurs de W, L, r et C, la perte a est connue et on peut déterminer l'espacement maximum entre prises pour obtenir l'erreur d'uniformité requise.For values of W, L, r and C, the loss a is known and the maximum spacing between taps can be determined to obtain the required uniformity error.

En pratique la valeur de a dépasse rarement 6 Nepers et en se reportant à la figure 4, la distance maximum entre prises est de l'ordre de 0,1λa à 0,22λa pour une erreur de phase et d'amplitude limitée respectivement à 10° et 1 dB, λa désignant la longueur d'onde acoustique à la surface du substrat.In practice the value of a rarely exceeds 6 Nepers and with reference to FIG. 4, the maximum distance between taps is of the order of 0.1λa to 0.22λa for a phase error and of amplitude limited respectively to 10 ° and 1 dB, λ a denoting the acoustic wavelength at the surface of the substrate.

Les contacts sur la plaque de sortie doivent être réalisés de manière à ne pas perturber la propagation des ondes acoustiques. Compte tenu des fréquences élevées de fonctionnement les dimensions sont très petites, la plaque pouvant mesurer quelques dizaines de microns en largeur, et plusieurs techniques de réalisation peuvent être employées.The contacts on the outlet plate must be made so as not to disturb the propagation of the acoustic waves. Given the high operating frequencies, the dimensions are very small, the plate being able to measure a few tens of microns in width, and several production techniques can be used.

Comme représenté sur les figures 5 et 6, les contacts sont réalisés par soudure ou par collage directs d'un fil conducteur 40 sur la plaque de sortie 41 placée à la surface du substrat 45. Pour éviter les effets de diffraction, et limiter la charge mécanique, les dimensions du point de soudure 42 ou du point de colle 43 ne dépassent pas le dixième de la longueur d'onde acoustique.As shown in FIGS. 5 and 6, the contacts are made by soldering or by direct bonding of a conductive wire 40 on the outlet plate 41 placed on the surface of the substrate 45. To avoid the effects of diffraction, and limit the load mechanical, the dimensions of the welding point 42 or the adhesive point 43 do not exceed one tenth of the acoustic wavelength.

La soudure est réalisée soit par thermocompression, soit par ultrasons. Quant au collage il est obtenu à froid en utilisant soit de l'indium, soit de la résine époxy électriquement conductrice.Welding is carried out either by thermocompression or by ultrasound. As for bonding, it is obtained cold using either indium or electrically conductive epoxy resin.

Les contacts peuvent être réalisés par soudure ou collage à côté de la plaque de manière à pouvoir augmenter la taille du point de soudure ou du point de colle. Pour cela les contacts sont faits à une distance de la plaque telle que l'énergie des ondes acoustiques soit pratiquement nulle, cette distance étant de l'ordre de quelques longueurs d'onde.The contacts can be made by welding or gluing next to the plate so as to be able to increase the size of the welding point or the point of glue. For this, the contacts are made at a distance from the plate such that the energy of the acoustic waves is practically zero, this distance being of the order of a few wavelengths.

Un exemple de réalisation est représenté sur la figure 7 dans le cas du convoluteur à trois plaques de la figure 2. Plusieurs pavés de connexion 52 sont disposés le long de la plaque 55 à la surface du substrat. Ils sont reliés électriquement à la plaque par des bandes conductrices 50 dont la largeur est inférieure à /!a/5 pour perturber le moins possible la propagation des ondes acoustiques, leur longueur étant égale à Z choisie pour éloigner suffisamment les pavés de la plaque. Ces bandes sont reliées aux pavés par des bandes 51 plus larges permettant de diminuer la résistance électrique. Ces bandes 51 peuvent s'évaser depuis les bandes 50 jusqu'aux pavés 53 comme représenté en figure 8. En se reportant à la figure 7, les électrodes de masse 54 sont échancrées pour recevoir les pavés 52, cette discontinuité n'affectant pas l'uniformité de l'interaction. Ces électrodes peuvent aussi être éloignées suffisamment de la plaque pour rester uniformes si la largeur du substrat le permet. Ces électrodes peuvent aussi être placées à la surface inférieure du substrat. Les points de soudure ou de colle 53 effectués sur les pavés peuvent être réalisés en utilisant toutes les techniques classiques puisqu'il n'y a plus aucune contrainte de dimensions. Bien que dans l'exemple représente chaque contact soit assuré par deux pavés, on pourrait n'en utiliser qu'un seul d'un côté ou de l'autre.An exemplary embodiment is shown in Figure 7 in the case of the three-plate convolver of Figure 2. Several connection blocks 52 are arranged along the plate 55 on the surface of the substrate. They are electrically connected to the plate by conductive strips 50 whose width is less than / ! A / 5 to disturb the propagation of the acoustic waves as little as possible, their length being equal to Z chosen to sufficiently distance the blocks from the plate. These bands are connected to the blocks by wider bands 51 making it possible to reduce the electrical resistance. These strips 51 can be flared from the strips 50 to the blocks 53 as shown in FIG. 8. Referring to FIG. 7, the ground electrodes 54 are notched to receive the blocks 52, this discontinuity not affecting the uniformity of interaction. These electrodes can also be distant enough from the plate to remain uniform if the width of the substrate allows it. These electrodes can also be placed on the lower surface of the substrate. The spots of solder or glue 53 made on the pavers can be produced using all the conventional techniques since there are no longer any dimensional constraints. Although in the example represents each contact is ensured by two blocks, we could use only one on one side or the other.

Avec cette technique, il existe un couplage acousto-électrique des surfaces métalliques avec le substrat qui engendre des effets parasites comme en particulier une perte de sensibilité accrue au niveau des connexions.With this technique, there is an acousto-electric coupling of the metal surfaces with the substrate which generates parasitic effects such as in particular an increased loss of sensitivity at the level of the connections.

Comme représenté sur la figure 8, chaque bande métallique 51, et chaque pavé 52 sont placés sur une couche mince d'un matériau isolant électriquement 60 tel que de la résine ou du Si02 réduisant ainsi notablement le couplage entre le substrat et les parties métallisées. Cette technique permet de disposer de pavés de grandes dimensions et d'électrodes de masse uniformes, le cas échéant en regard des pavés.As shown in FIG. 8, each metal strip 51 and each block 52 are placed on a thin layer of an electrically insulating material 60 such as resin or Si0 2, thus significantly reducing the coupling between the substrate and the metallized parts . This technique makes it possible to have pavers of large dimensions and uniform mass electrodes, where appropriate facing the pavers.

Sur la figure 9 on a représenté une autre technique permettant de supprimer le couplage par les bandes conductrices de connexions 50. Chaque bande est métallisée sur un matériau qui ensuite est éliminé de manière à laisser un intervalle d'air 70 entre substrat et la bande. Notons que cette technique est connue notamment pour la réalisation de filtre acoustique.FIG. 9 shows another technique making it possible to suppress coupling by the conductive strips of connections 50. Each strip is metallized on a material which is then eliminated so as to leave an air gap 70 between substrate and the strip. Note that this technique is known in particular for producing an acoustic filter.

Pour ces réalisations le guide 55, les bandes 50 et 51 et les pavés 52 sont par exemple métallisés par dépôt, par évaporation ou pulvérisation à l'aide d'un masque réalisé par photolithographie.For these embodiments, the guide 55, the strips 50 and 51 and the blocks 52 are for example metallized by deposition, by evaporation or spraying using a mask produced by photolithography.

Une autre forme de réalisation consiste à disposer une électrode en forme de plaque en regard du guide et semblable à celle-ci. Les connexions vers le circuit de sortie sont effectuées sur cette électrode.Another embodiment consists in placing an electrode in the form of a plate opposite the guide and similar to the latter. The connections to the output circuit are made on this electrode.

La figure 10 représente en coupe une réalisation par couplage capacitif. Un premier substrat 85 comporte à sa surface les dispositifs de génération des ondes acoustiques et le guide 80; il peut comporter aussi les électrodes de masse 82. Un deuxième substrat 86 est appliqué à la surface du premier substrat 85. Afin d'éviter les problèmes dûs aux contraintes thermiques, les deux substrats sont de préférence constitués du même matériau. Le substrat 86 comporte un évidement 83 muni de l'électrode de sortie 81 placée en regard du guide 80 et à une distance h prédéterminée. Cette distance h est choisie de manière à coupler capacitivement l'électrode au guide sans diminuer le rendement du convoluteur. Pour cela la capacité C ramenée doit être grande devant la capacité Cp du substrat piézoélectrique. Dans le cas d'un dispositif tel que représenté sur la figure 2, la valeur de la capacité Cp est de l'ordre de la permittivité 8p du substrat tandis que la valeur de la capacité C est égale à εo

Figure imgb0009
où εo est la permittivité de l'air, ces valeurs étant comptée par unité de longueur suivant l'axe de propagation des ondes. La condition C > Cp s'écrit donc
Figure imgb0010
Par exemple W = 50 µ et εP/εo = 50 ce qui donne h 1 µ et h sera de l'ordre de 0,1 micron. Suivant une variante de réalisation, le substrat 85 comporte l'évidement tel que 83 muni du guide acoustique 80 tandis que l'autre substrat est plan.Figure 10 shows in section an embodiment by capacitive coupling. A first substrate 85 has on its surface the devices for generating the acoustic waves and the guide 80; it can also include the ground electrodes 82. A second substrate 86 is applied to the surface of the first substrate 85. In order to avoid the problems due to thermal stresses, the two substrates are preferably made of the same material. The substrate 86 has a recess 83 provided with the output electrode 81 placed opposite the guide 80 and at a predetermined distance h. This distance h is chosen so as to capacitively couple the electrode to the guide without reducing the efficiency of the convolver. For this the capacitance C brought back must be large compared to the capacitance Cp of the piezoelectric substrate. In the case of a device such as re presented in FIG. 2, the value of the capacitance Cp is of the order of the permittivity 8 p of the substrate while the value of the capacitance C is equal to ε o
Figure imgb0009
 where ε o is the permittivity of the air, these values being counted per unit of length along the axis of propagation of the waves. The condition C> Cp is therefore written
Figure imgb0010
 For example W = 50 µ and ε P / ε o = 50 which gives h 1 µ and h will be of the order of 0.1 micron. According to an alternative embodiment, the substrate 85 includes the recess such as 83 provided with the acoustic guide 80 while the other substrate is planar.

Les figures 11 et 12 représentent deux autres variantes de réalisation pour lesquelles le guide n'est pas métallisé: sout il est réalisé en profilant le substrat pour lui donner une épaisseur plus importante en regard de l'électrode de sortie comme représenté sur la figure 11 en 90, soit il est réalisé en modifiant la structure du substrat en regard de l'électrode de sortie par une implantation ionique comme représenté sur la figure 12 en 100.Figures 11 and 12 show two other alternative embodiments for which the guide is not metallized: sout it is produced by profiling the substrate to give it a greater thickness opposite the output electrode as shown in Figure 11 at 90, either it is produced by modifying the structure of the substrate opposite the output electrode by an ion implantation as shown in FIG. 12 at 100.

Dans ces réalisations les faces des deux substrats piézoélectriques 85 et 86 sont polies et amenées en contact puis maintenues par collage ou mécaniquement par pressage, ou encore par adhérence obtenue par joint obtique.In these embodiments, the faces of the two piezoelectric substrates 85 and 86 are polished and brought into contact and then held by gluing or mechanically by pressing, or else by adhesion obtained by a seal.

La figure 13 représente une réalisation comportant des plots métalliques 110 réalisés entre le guide métallique et l'électrode de sortie. Pour cette réalisation, la hauteur de l'evidement 83 peut être notablement plus importante que pour les réalisations à couplage capacitif et elle est donc moins critique. Pour ne pas perturber la propagation des ondes acoustiques, la dimension latérale de chaque plot est faible devant Âa, environ 0,1λa; en outre ces plots 110 sont répartis le long du guide aléatoirement pour éviter les effets cumulatifs, la distance moyenne entre plots étant de l'ordre de 100Âa.FIG. 13 shows an embodiment comprising metal studs 110 produced between the metal guide and the outlet electrode. For this embodiment, the height of the recess 83 can be notably greater than for the constructions with capacitive coupling and it is therefore less critical. In order not to disturb the propagation of the acoustic waves, the lateral dimension of each stud is small in front of Âa, around 0.1λa; in addition, these studs 110 are distributed along the guide randomly to avoid cumulative effects, the average distance between studs being of the order of 100Âa.

La réalisation des plots est effectuée au préalable soit sur le guide 80, soit sur l'électrode 81 par exemple par photogravure, les deux substrats étant ensuite assemblés suivant l'une des techniques vues précédemment.The pads are produced beforehand either on the guide 80 or on the electrode 81, for example by photoengraving, the two substrates then being assembled according to one of the techniques seen above.

Une réalisation par guide profilé est représentée sur la figure 14. Le guide 120 est profilé en épaisseur tranversalement à l'axe de propagation des ondes pour présenter une zone centrale 121 et deux zones latérales 122. La zone centrale a une épaisseur plus grande que les deux zones latérales entrainant par effet de charge mécanique sur le substrat 125 une vitesse de propagation plus lente sous cette zone centrale et en conséquence un guidage des ondes. La vitesse dans la zone libre du substrat 123 est en outre plus grande que celle des zones latérales par effet de court-circuit électrique à la surface du substrat. Les zones latérales 122 sont réalisées de manière à présenter une conduction électrique grande.An embodiment by profiled guide is shown in FIG. 14. The guide 120 is profiled in thickness transversely to the axis of propagation of the waves to present a central zone 121 and two lateral zones 122. The central zone has a thickness greater than the two lateral zones causing, by mechanical load effect on the substrate 125, a slower propagation speed under this central zone and consequently guiding the waves. The speed in the free zone of the substrate 123 is also greater than that of the lateral zones by the effect of an electric short circuit on the surface of the substrate. The lateral zones 122 are produced so as to present a large electrical conduction.

Le profilage du guide est obtenu par exemple par usinage ionique. Il peut aussi être obtenu en rapportant un matériau conducteur ou isolant par dessus une métallisation préalable.The profiling of the guide is obtained for example by ionic machining. It can also be obtained by adding a conductive or insulating material over a prior metallization.

Les contacts électriques 124 sont effectués au niveau des bords extérieurs des zones latérales en dehors de la zone de présence de l'énergie acoustique.The electrical contacts 124 are made at the outer edges of the lateral zones outside the zone of presence of the acoustic energy.

Une réalisation par guide d'épaisseur homogène est représentée sur la figure 15 en vue de dessus. Le guide 130 est homogène en épaisseur et présente une structure transversale à l'axe de propagation des ondes aboutissant à créer une zone centrale 131 guidante et deux zones latérales sur lesquelles sont effectuées les connexions électriques. La zone centrale est continue tandis que les deux zones latérales sont discontinues et réalisées en découpant le guide en bandes (132) perpendiculaires à son axe. La zone centrale fait ainsi un court-circuit total à la surface du substrat ce qui ralentit les ondes relativement aux zones latérales qui font un court-circuit partiel.An embodiment by homogeneous thickness guide is shown in Figure 15 in top view. The guide 130 is homogeneous in thickness and has a structure transverse to the axis of propagation of the waves, leading to the creation of a central guiding zone 131 and two lateral zones on which the electrical connections are made. The central zone is continuous while the two lateral zones are discontinuous and produced by cutting the guide into strips (132) perpendicular to its axis. The central zone thus makes a total short-circuit on the surface of the substrate which slows down the waves relative to the lateral zones which make a partial short-circuit.

On obtient ainsi deux zones ayant des densités de métallisation différentes. L'espacement p entre bandes (132) est choisi inférieur à Âa/2 pour éviter les effets connus de »bande d'arrêt« et ainsi conserver une grande largeur de bande B.Two zones are thus obtained having different metallization densities. The spacing p between bands (132) is chosen to be less than  a / 2 to avoid the known effects of "stop band" and thus maintain a large bandwidth B.

Cette réalisation est plus simple à mettre en oeuvre que la précédente: le guide est par exemple obtenu par photogravure ou photolithographie. Les contacts électriques sont effectués aux extrémités des bandes.This embodiment is simpler to implement than the previous one: the guide is for example obtained by photoengraving or photolithography. The electrical contacts are made at the ends of the strips.

Les contacts électriques pour ces deux derniers types de réalisation peuvent être faits en bordure des zones latérales:

  • - sout par soudure ou par collage directement;
  • - soit par métallisation de plots 133 avec ou sans isolant.
The electrical contacts for these last two types of embodiment can be made at the edge of the lateral zones:
  • - support by welding or by gluing directly;
  • - Either by metallization of studs 133 with or without insulation.

A titre d'exemple non limitatif, on a réalisé un convoluteur à plusieurs prises de sortie ayant pour caractéristiques f = 300 MHz et T = 10 µs. Le guide a une largeur W de 30 µ et une longueur L de 35 mm. Il comporte quatre prises équidistantes de 1 dont deux sont situées aux extrémités de sorte que le rapport I/ÂEm est voisin de 0,16, la bande de fréquence étant égale à 100 MHz.By way of nonlimiting example, a convolutor has been produced with several output sockets having the characteristics f = 300 MHz and T = 10 μs. The guide has a width W of 30 µ and a length L of 35 mm. It has four equidistant sockets of 1, two of which are located at the ends so that the I / Â Em ratio is close to 0.16, the frequency band being equal to 100 MHz.

Les figures 16 et 17 représentent schématiquement l'ensemble convoluteur et circuit de sortie. Sur la figure 16, on distingue les quatre prises de sortie 141 placées sur le substrat 144 au voisinage duquel est rapporté le circuit de sortie 140 constitué par exemple d'un circuit imprimé de quelques dixièmes de mm d'épaisseur.Figures 16 and 17 schematically represent the convolver and output circuit assembly. In FIG. 16, a distinction is made between the four output sockets 141 placed on the substrate 144 in the vicinity of which is connected the output circuit 140 consisting for example of a printed circuit a few tenths of a mm thick.

La figure 17 permet de distinguer le détail des connexions au niveau d'une prise. Los plots métallisées 146 sont reliés au guide 145 et sont connectés entre eux et aux extrémités des pistes 142 du circuit de sortie par des fils d'or de quelques millimètres de longueur 148. De même les électrodes de masse 147 sont connectées aux parties du circuit de sortie reliées à la masse en 149.FIG. 17 makes it possible to distinguish the detail of the connections at the level of a socket. The metallized studs 146 are connected to the guide 145 and are connected to each other and to the ends of the tracks 142 of the output circuit by gold wires a few millimeters in length 148. Similarly, the ground electrodes 147 are connected to the parts of the output circuit connected to ground at 149.

L'agencement des pistes 142 permet de relier les quatre prises au câble de sortie 143, d'impédance en général égale à 50 Ω, par des connexions de longueurs identiques permettant ainsi de sommer en phase les signaux issus des prises. Notons que cette réalisation est possible car la vitesse des ondes électromagnétiques dans le guide est faible devant celle des lignes de transmission classiques constituées par les pistes 142. Le circuit de sortie peut être également réalisé sur le substrat acoustique au préalable métallisé et recouvert d'une couche isolante de permittivité aussi faible que possible.The arrangement of the tracks 142 makes it possible to connect the four sockets to the output cable 143, of impedance generally equal to 50 Ω, by connections of identical lengths, thus making it possible to add the signals from the sockets in phase. Note that this realization is possible because the speed of the electromagnetic waves in the guide is low compared to that of the conventional transmission lines constituted by the tracks 142. The output circuit can also be produced on the acoustic substrate previously metallized and covered with a insulating layer with the lowest permittivity possible.

En accord avec le choix de l'espacement entre les contacts, une telle réalisation permet d'obtenir une uniformité de la réponse en amplitude inférieure à 1 dB et une uniformité en phase inférieure à 15°. Avec seulement les deux prises extrêmes connectées, le résultat est une uniformité en amplitude à 5 dB près et une uniformité en phase comprise entre 80 et 90 degrés.In accordance with the choice of spacing between the contacts, such an embodiment makes it possible to obtain a uniformity of the amplitude response of less than 1 dB and a uniformity of the phase of less than 15 °. With only the two extreme sockets connected, the result is amplitude uniformity to within 5 dB and phase uniformity between 80 and 90 degrees.

Claims (36)

1. A convolver device based on the propagation of acoustic waves at the surface of a piezoelectric solid and comprising
- a piezoelectric substrate (10),
- means (112) for exciting two counter-progressing acoustic waves at the grequency f,
- at least two elongated electrodes (15, 16) extending parallelly to the propagation axis of the acoustic waves between the excitation means (11, 12), one electrode (16) being connected to ground and the other (15) being placed on that side of the substrate which bears the excitation means (11, 12), in order to collect the signal at the frequency 2f, said signal being produced as a result of the non-linear interaction of the two acoustic waves,
characterized in that said signal is collected at that electrode (15) through a plurality of electrical contacts (42) connected togehter to the output (S) of the device and disposed alon the length of the electrode, the spacing between these contacts on the one hand being small compared with the length of the electromagnetic wave ÂEM = VEM/2f, where VEM is the velocity of the electromagnetic waves within the electrode, and on the other hand being chosen so as to ensure that the product of resistance and capacitance of the electrode portions between two contacts is of low value in comparison with the period 1/f.
2. A devise according to claim 1, characterized in that said device comprises means (11, 12) for compressing the acoustic wave in the transversal direction, and means for guiding the compressed waves under the collector electrode (15).
3. A convolver device according to claim 2, characterized in that the collector electrode is a metallization layer deposited on the surface of the substrate (10).
4. A convolver device according to claim 3, characterized in that the electrical contacts (42) are formed directly on the collector electrode (15) by welding or by gluing, the dimension of the weld spot or glue spot being smaller than 0,1 times the acoustic wavelength Âa equal to va/2f, where va is the velocity of the acoustic waves.
5. A convolver device according to claim 4, characterized in that the weld spot (42) is obtained by thermocompression.
6. A convolver device according to claim 4, characterized in that the weld spot (42) is obtained by ultrasonic vibrations.
7. A convolver device according to claim 4, characterized in that the gluing (42) is carried out with indium or with a conductive epoxy resin.
8. A convolver device according to claim 4, characterized in that the electrical contacts (52) extend laterally with respect to the collector electrode (55).
9. A convolver device according to claim 8, characterized in that metallic chips (52) extending alongside the collector electrode (55) are deposited in a recessed situation in order to receive the electrical contacts (53) and are connected to said electrode (55) by means of first metallic strips (50), the width of said first strips being smaller than λa/5, where λa is the wavelength of the acoustic wave which propagates on the surface of the substrate.
10. A convolver device according to claim 9, characterized in that the connection chips (52) are connected to the first strips by means of strips (51) which increase in width at a distance from the collector electrode (55).
11. A convolver device according to claim 10, characterized in that said device comprises a thin film (60) of insulating material between the surface of the piezoelectric substrate and the assembly consisting of widened strips and connection chips.
12. A convolver device according to claim 1, characterized in that it further comprises another ground electrode (16) and that both ground electrodes (16) are deposited at the surface of the substrate (10) on each side of the collector electrode (55).
13. A convolver device according to any one of claims 9 to 12, characterized in that each electrical contact is associated with two connection chips (52) placed on each side of the collector electrode (55).
14. A convolver device according to any one of claims 9, 10 and 12, characterized in that the ground electrode (16) is deposited on the surface of the substrate (10), said ground electrode being cut out around each connection chip (52).
15. A convolver device according to claim 9, characterized in that the first strips (50) are deposited on the surface of the substrate (10).
16. A convolver device according to claim 9, characterized in that the first strips (50) are in the form of stirrup-pieces whose ends rest on the surface of the substrate.
17. A convolver device according to claim 8, characterized in that the contacts (42) are formed by one of the following means: welding by thermocompression, welding by ultrasonic vibrations, gluing with indium and gluing with an electrically conductive epoxy resin.
18. A convolver device according to claim 2, characterized in that the dimensions of the collector electrode (81) are similar to those of the guide means (80), said electrode being located at a predetermined distance h W/(εP/εo) above said guide means, where W is the length of the electrode and so and 6p are the dielectric constants of the air and of the substrate.
19. A convolver device according to claim 18, characterized in that said device comprises a second substrate (86) applied to the surface of the first substrate (85) which supports the guide means (80), and a recess (83) is formed in said second substrate and fitted with the collector electrode (81).
20. A convolver device according to claim 19, characterized in that the contact faces of the first (85) and second substrate (86) are polished and then held together either by gluing or by mechanical pressing or by adhesion obtained by means of an optical joint.
21. A device according to claim 18, characterized in that a recess is formed in the first substrate (85) and fitted with the guide means, a second substrate (86) being applied to the surface of the first substrate (85).
22. A convolver device according to any one of claims 19 or 21, characterized in that the guide means (80) are formed by depositing a metallization layer on the surface of the first substrate (85) over the width W.
23. A convolver device according to claim 19 or 21, characterized in that the guide means (90) are formed by means of an overthickness of the first substrate (85) having a width W.
24. A convolver device according to claim 19 or 21, characterized in that the guide means (100) are formed by modifying the structure of the surface of the first substrate (85) over the width W by ion implantation.
25. A convolver device according to claim 3, characterized in that the guide means (120) are shaped in thickness transversely to the axis of propagation of the acoustic waves so as to present a thick central zone (121) having a width W and at least one lateral zone (122) of smaller thickness, the electrical contacts (124) being formed at the level of the outer edges of the laterial zone or zones (122).
26. A convolver device according to claim 25, characterized in that the shaping of the guide means (120) is performed by overlaying a material having a widh W on a metallization layer previously formed.
27. A convolver device according to claim 25, characterized in that shaping of the guide means (120) is performed by machining the metallization layer.
28. A convolver device according to claim 25, characterized in that the guide means (120) are shaped so as to present two lateral zones (122) having the same width on each side of the central zone.
29. A convolver device according to claim 3, characterized in that the guide means (130) are made of a full central zone (131) having a width W for guiding the waves, and of at least one recessed lateral zone having the same thickness and constituted by strips (132) extending away from the axis of the guide means (130), the electrical contacts being formed at the ends of said strips, the relative spacing of the strips not exceeding ia/2 and the width of the strips being small compared with said spacing, where 2a is the length of the acoustic wave on the surface of the substrate.
30. A convolver device according to claim 29, characterized in that said device comprises a lateral zone (132) on each side of the central zone (131).
31. A convolver device according to any one of claims 25 or 29, characterized in that the electrical contacts (124) are formed by one of the following means: welding by thermocompression, welding by ultrasonic vibrations, gluing with indium and gluing by means of an electrically conductive epoxy resin.
32. A convolver device according to any one of claims 25 or 29, characterized in that the electrical contacts consist of metallized chips (133) on the surface of the substrate (125).
33. A device according to any one of claims 25 or 29, characterized in that the metallized chips (133) are separated from the surface of the substrate by a thin film (60) of insulating material.
34. A convolver device according to claim 3, characterized in that metallization (15) is obtained as a result of deposition performed by evaporation of the metal.
35. A convolver device according to claim 3, characterized in that metallization (15) is obtained as a result of deposition performed by sputtering of the metal.
36. A device according to claim 1, characterized in that the electrical contacts (141) are connected to the output by means of tracks (142) of equal lengths of a printed circuit (140) placed in proximity to the substrate (144).
EP81400686A 1980-05-20 1981-04-30 Piezoelectric convolution device using elastic waves Expired EP0040559B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8011225 1980-05-20
FR8011225A FR2483143B1 (en) 1980-05-20 1980-05-20 ELASTIC WAVE PIEZOELECTRIC CONVOLVER DEVICE

Publications (2)

Publication Number Publication Date
EP0040559A1 EP0040559A1 (en) 1981-11-25
EP0040559B1 true EP0040559B1 (en) 1984-08-08

Family

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Application Number Title Priority Date Filing Date
EP81400686A Expired EP0040559B1 (en) 1980-05-20 1981-04-30 Piezoelectric convolution device using elastic waves

Country Status (7)

Country Link
US (1) US4388599A (en)
EP (1) EP0040559B1 (en)
JP (1) JPS5718115A (en)
CA (1) CA1177126A (en)
DE (1) DE3165355D1 (en)
FR (1) FR2483143B1 (en)
NO (1) NO154365C (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58196712A (en) * 1982-05-12 1983-11-16 Nec Corp Elastic convolver
JPS598075U (en) * 1982-07-07 1984-01-19 三菱電機株式会社 Heat exchanger
US4592009A (en) * 1983-11-17 1986-05-27 E-Systems, Inc. MSK surface acoustic wave convolver
US4870376A (en) * 1983-12-15 1989-09-26 Texas Instruments Incorporated Monolithic elastic convolver output circuit
US4584475A (en) * 1984-05-29 1986-04-22 Allied Corporation Surface acoustic wave infrared line imaging array
US4675839A (en) * 1985-04-10 1987-06-23 Allied Corporation Receiver for a spread spectrum communication system having a time-multiplexed convolver
JPS61296807A (en) * 1985-06-25 1986-12-27 Clarion Co Ltd Surface acoustic wave device
GB2197559B (en) * 1986-08-22 1990-03-28 Clarion Co Ltd Bias voltage circuit for a convolver
US4894576A (en) * 1987-04-10 1990-01-16 Clarion Co., Ltd. Surface-acoustic-wave convolver
JP2911893B2 (en) * 1987-05-15 1999-06-23 クラリオン株式会社 Surface acoustic wave device
US5440155A (en) * 1987-10-15 1995-08-08 Electronic Decisions Incorporated Acoustic charge transport convolver, method of use and fabrication
JP2520136Y2 (en) * 1988-02-15 1996-12-11 クラリオン株式会社 Surface acoustic wave device
JPH02199910A (en) * 1989-01-27 1990-08-08 Clarion Co Ltd Surface acoustic wave device
JPH03162103A (en) * 1989-11-21 1991-07-12 Fujitsu Ltd Micro strip line whose effective line length is changed
US5357225A (en) * 1992-12-23 1994-10-18 Alcatel Network Systems, Inc. Method and apparatus for adjusting the impedance of a microstrip transmission line
DE69525937D1 (en) 1995-06-09 2002-04-25 Canon Kk Surface acoustic wave device and transmission system using the same

Also Published As

Publication number Publication date
DE3165355D1 (en) 1984-09-13
NO154365B (en) 1986-05-26
US4388599A (en) 1983-06-14
JPS5718115A (en) 1982-01-29
EP0040559A1 (en) 1981-11-25
CA1177126A (en) 1984-10-30
FR2483143B1 (en) 1988-02-05
NO811707L (en) 1981-11-23
FR2483143A1 (en) 1981-11-27
JPH031847B2 (en) 1991-01-11
NO154365C (en) 1986-09-03

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