WO2008125071A1 - Micromechanical sound emission measurement system - Google Patents
Micromechanical sound emission measurement system Download PDFInfo
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- WO2008125071A1 WO2008125071A1 PCT/DE2007/000657 DE2007000657W WO2008125071A1 WO 2008125071 A1 WO2008125071 A1 WO 2008125071A1 DE 2007000657 W DE2007000657 W DE 2007000657W WO 2008125071 A1 WO2008125071 A1 WO 2008125071A1
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- WO
- WIPO (PCT)
- Prior art keywords
- measuring system
- acoustic emission
- micromechanical
- sound
- sound emission
- Prior art date
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H13/00—Measuring resonant frequency
Definitions
- the invention relates to a micromechanical measuring system and a method for measuring acoustic emissions emitted by a solid.
- the term sound emission is understood to mean a signal that can be caused by distortions of a grating in solids. Such a sound emission is also frequently referred to by the English term “acoustic emission” and describes the following phenomenon: External influences can cause tension in the material on the lattice plane. These tensions of material represent a storage of potential energy. If the tensions exceed a certain threshold, they dissolve and a conversion of the potential energy into kinetic energy occurs. The kinetic energy releases itself in the form of stress waves, which spread in the material. Since the tension in the material relax abruptly, the stress waves have a broad spectrum with frequency components up to the megahertz range.
- Acoustic emission monitoring is a very efficient way to monitor components subject to wear in an industrial environment to reduce equipment downtime. By measuring Acoustic Emission, wear and defects of production equipment can be detected early on, since Acoustic Emission directly tracks the damage process and does not indirectly evaluate its consequences. On the other hand, an analysis of frequencies in the audible range of an analysis of acoustic emissions is preferable for the detection of already existing, no longer changing damage.
- piezoelectric sensors are used, which are designed for the ultrasonic range.
- a sound emission detected with such a special sensor is amplified by a preamplifier.
- the amplified signal is then evaluated, either derived from the measured and amplified time signal characteristics or complex spectral algorithms are applied to extract the relevant frequencies.
- Object of the present invention is to enable the most cost-effective measurement of acoustic emission.
- a sound emission sensor having at least one first micromechanically manufactured oscillatable Structure having a first resonance frequency in the ultrasonic range, first means for deriving at least one threshold value from a first sound emission measured by the acoustic emission sensor, a memory for storing the threshold value and second means for comparing a second sound emission measured with the acoustic emission sensor with the threshold value.
- the object is achieved by a method for monitoring sound emissions with the following method steps, which are carried out with a micromechanical measuring system:
- Micromechanics refers to a field of microengineering that deals with micrometer-sized mechanical structures.
- known processes are frequently used from semiconductor process technology, in particular microchip production.
- the invention is based on the knowledge that shock-shaped excitations, as they are caused when dissolving material stresses in the form of sound emissions, generate a broadband frequency spectrum that is particularly easy to detect in the ultrasonic range.
- ultrasound is meant here and throughout the document the frequency range between 20 and 2000 kHz.
- the advantage of a detection of the sound emissions by a measurement in the ultrasonic range is that a disturbing background noise in the spectrum of the excitation at such high frequencies has already subsided. These interference signals can arise, for example, due to structural resonance of the measurement object. In a measurement in the ultrasonic range, therefore, only the signals of interest are detected, which are responsible for the phenomenon
- Acoustic Emission and may be characteristic of damage. This allows a simplified evaluation, since no spectral distinction of measurement signal and superimposed background noise is necessary.
- a sound emission sensor for the ultrasonic range is manufactured micromechanically.
- Micromechanically produced acoustic emission sensors have the advantage over piezoelectric emissions that the geometric parameters of the corresponding oscillatable structures can be realized, for example, by processing methods such as lithography with very narrow tolerances. The ability to set these parameters in very tight tolerances, the resonant frequency and the bandwidth of such a vibratory structure can be dimensioned extremely accurate. As a result, the micromechanical sensors can therefore also be adapted very easily to a specific application.
- micromechanically manufactured oscillating structures is considerably smaller than the size of commercially available piezoelectric sensors. This allows a high degree of integration when multiple vibration structures to be integrated on a sound emission sensor.
- the micromechanical measuring system is suitable for measuring sound emissions that propagate from a solid body.
- the micromechanical measuring system can be used for monitoring numerous components subject to wear, for example in the field of industrial automation and drive technology.
- An example of this is a bearing of an electric machine, which triggers a sound wave through self-excited or externally excited shocks. Depending on the characteristics of such a sound emission, this may indicate a destruction or damage to the camp.
- the micromechanical measuring system therefore comprises means for comparing a measured noise emission with a threshold value. Based on this comparison, a statement can be made as to whether the measured sound emission indicates damage or not.
- the micromechanical measuring system comprises the first means with which the said threshold value is determined on the basis of a first sound emission.
- the first sound emission is measured as a reference.
- a threshold value is derived, which may not be exceeded by the second acoustic emission or a value derived from the second acoustic emission.
- the type of threshold depends, among other things, on the process to be monitored.
- the threshold value may be a time-dependent threshold curve, a time average, or the value of a act short-term integral of the second acoustic emission.
- a micromechanical measuring system is provided with which the "normal state" of a structure-borne sound-producing process can be determined on the basis of a first acoustic emission measurement and monitoring can be carried out in further process cycles by comparing further sound emissions with the reference process.
- the first means for smoothing the time course of the first acoustic emission are set up over a time interval. By smoothing the time course, high-frequency noise is suppressed, thus creating a basis for determining the threshold value.
- an embodiment of the invention may be advantageous in which the first means for forming an envelope for the time course of the first acoustic emission over a time interval are set up. Whether an envelope or a smoothing of the chronological progression of the first acoustic emission is more suitable for determining the at least one threshold depends on the process to be monitored or the component to be monitored.
- the first means for deriving a time-dependent upper threshold curve for the time interval are set up, and the second means for detecting a Ü exceeded the upper threshold curve by the second acoustic emission or by a time average of the second acoustic emission within the time interval set , If such a threshold curve is exceeded by the temporal course of the acoustic emission or by its time average, this indicates, for example, damage to a product. dumiesstoffs or a workpiece to be machined.
- a successful production process may be characterized by a sound emission exceeding a certain lower limit in the implementation of this process.
- an embodiment of the invention may be advantageous in which the first means for deriving a time-dependent lower threshold curve for the time interval are established and the second means for detecting an undershooting of the lower threshold curve by the second acoustic emission or by the time average of the second Noise emission are set up within the time interval.
- the first oscillatable structure is made of a wafer of semiconducting material.
- the semiconductor industry there are a large number of technological processes that permit the exact production of the smallest vibratory structures.
- this offers silicon for cost reasons.
- the use of a substrate material of Galiummarsenit or silicon carbide, etc. is also conceivable.
- the first oscillatory structure is manufactured by means of silicon bulk mechanics and / or silicon surface micromechanics.
- silicon bulb mechanics freestanding mechanical structures are obtained from a silicon wafer by etching on both sides.
- Silicon surface micromachining records that freestanding mechanical structures are created by multiple etching and deposition processes on the wafer surface.
- the first oscillatable structure oscillatable parallel to the wafer plane it may be expedient to make the first oscillatable structure oscillatable parallel to the wafer plane.
- the direction of oscillation of the first oscillatable structure can be selected with many degrees of freedom.
- a very simple detection of impulsive excitations can be achieved if the acoustic emission sensor has third means for determining the acoustic emission on the basis of a measurement of the time-dependent electrical capacitance of the first oscillatable structure in a state excited by the acoustic emission.
- the first vibratable structure may be configured to form a capacitor whose capacitance is dependent on the deflection of the structure. The relationship between the capacity of the vibratable structure and its deflection can be adjusted by the geometry of the structure. From a measurement of the capacitance of the first oscillatable structure, the deflection of the oscillatable structure can be determined in this way, in order in turn to draw conclusions about the pulsed excitation.
- a corresponding electronic system which performs such an evaluation can be integrated very well, particularly in the case of a micromechanical implementation of the acoustic emission sensor on a semiconductor chip.
- a further advantageous embodiment of the invention is characterized in that the acoustic emission sensor has at least one second micromechanically manufactured having oscillatory structure with a second resonant frequency in the ultrasonic range. If the first resonance frequency differs from the second resonance frequency, two measurement frequencies in the ultrasonic range are available for later evaluation.
- the first oscillatable structure has a first measuring range which partially overlaps with a second measuring range of the second oscillatable structure.
- the overlap may e.g. be adjusted by appropriate choice of the quality of the oscillatory structures. If the first and second oscillatable structures have a relatively low quality, an overlapping of the measuring ranges can be achieved even if the first and second resonant frequencies are relatively far apart. In this way it is possible to cover a relatively large frequency spectrum in the ultrasonic range with two oscillatory structures.
- Vibration directions are detected.
- the acoustic emission sensor has a third oscillatable structure whose oscillation direction is substantially orthogonal to both the oscillation direction of the first and to the oscillation direction of the second structure.
- a complete three-dimensional vector space is spanned by the vibration directions of the first, second and third oscillatable structures. This enables the detection of shock-shaped excitations from all three spatial dimensions.
- the first and second means are designed as the digital processing unit, and the measuring system has an analog circuit for analog signal conditioning of the sound emissions measured with the acoustic emission sensor.
- analog and digital circuits can be integrated directly into the micromechanical measuring system. Conceivable here is an integration as a so-called system-on-chip.
- the sound emission sensor and the electronics can be integrated on a common substrate, in particular monolithically.
- methods such as Siliciumbulkmechanik or silicon surface micro-mechanics find use, if said substrate consists of silicon.
- a non-monolithic integration is possible in which the analog and digital components are arranged in the form of individual chips on a common substrate made of silicon or ceramic together with the acoustic emission sensor.
- the wire bonding technique or alternatively the so-called flip-chip technology.
- Such a system on chip design can generally achieve higher reliability of the measurement system than is the case with conventional wired designs.
- an embodiment of the invention is advantageous in which the micromechanical measuring system has a further oscillatable structure which has a first resonant frequency in a frequency range audible to humans.
- damage that is not or only badly detectable with an acoustic emission analysis can be additionally detected.
- An example is an imbalance of rotating parts. Damage already caused is usually noticeable by frequencies in the audible range, while progressive damage emits frequencies in the ultrasonic range.
- a measuring system according to the mentioned embodiment a distinction can be made between damage already incurred and progressive damage.
- a first acoustic emission which is measured with a micromechanical measuring system according to an embodiment of the invention during a teach-in, derived based on the first acoustic emission threshold curves, a first example of a second acoustic emission, a first performed with the micromechanical measuring system testing, a second example of a second acoustic emission, a second test carried out with the micromechanical measuring system, a third example of a third acoustic emission, a third test carried out with the micromechanical measuring system, a noise emission sensor with a first structure that can oscillate perpendicular to the wafer plane, a sound emission sensor with a second, parallel to the wafer plane oscillatory structure, a schematic representation of a sound emission sensor with an array oscillatable structures with different resonance frequencies, a frequency response of Schallemissio nssensors with the array oscillating structures with different resonance frequencies, a schematic representation of a sound emission sensor with an array of different structures with different directions of vibration and a
- 16 shows a micromechanical measuring system as a printed circuit board stack
- 17 shows a micromechanical measuring system in Star-Flex printed circuit board technology.
- FIGS. 1 and 2 show a teach-in process, which is carried out with a micromechanical measuring system according to an embodiment of the invention.
- FIGS. 1 to 8 are based on an application of the micromechanical measuring system in which, for example, crimp connections of metal caps to ceramic insulators are tested.
- the amount of crimping is crucial to the result. If too much crimping, the ceramic breaks. On the other hand, if the crimping is too weak, the connection will not last.
- the strength of the crimp can be determined by measuring the acoustic emission generated during crimping. With a normal crimping, only a slight acoustic emission level is created, whereas an excessive crimping force leads to breakage of the ceramic, which in turn results in a significantly increased acoustic emission level.
- the system In order to be able to perform such a crimp monitoring with the micromechanical measuring system, the system must first be taught in, as shown in FIGS. 1 and 2.
- the micromechanical measuring system is taught how the amplitude pattern of the acoustic emission during a "normal" crimping runs.
- a reference crimping is performed in which a first acoustic emission 24 is formed.
- the illustrated level profile of the first acoustic emission 24 is stored in a memory of the micromechanical measuring system.
- a smoothing of the measured acoustic emission curve is carried out, as can be seen in FIG. Based on this smoothed material becomes an upper threshold curve 28 and a lower threshold curve 32 defined.
- These two threshold curves 28, 32 define a limit range for subsequent crimping operations, in which the sound emissions resulting from further tests must be in order to be rated as "good" by the micromechanical measuring systems.
- FIGS. 3 and 4 show a first test procedure carried out with the micromechanical measuring system, which is carried out after the said system has been taught in, as shown in FIGS. 1 and 2.
- a second sound emission 25 is measured by means of the oscillatory structure of the micromechanical measuring system.
- a smoothing in the form of a sliding average value 29 is performed. It turns out that this mean value 29 is within the range defined by the lower and upper threshold curves 28, 32 and thus the crimping process is found to be good.
- FIGS. 5 and 6 show a second test procedure performed with the micromechanical measuring system, in which the detected second acoustic emission 26 has a too low amplitude characteristic within the examined time interval. Again, the measured acoustic emission curve 26 is smoothed, so that an average curve 30 is present. It can be seen that the mean 30 is below the corridor defined by the lower and upper threshold curves 28, 32, and therefore the force applied at crimping is considered to be too low.
- FIG. 6 and 7 show a third test procedure carried out with the micromechanical measuring system, in which, in turn, a further second sound emission curve 27 is recorded. Also of this acoustic emission curve 27, the average value 31 is formed and compared with the lower and upper threshold curve 32, 28. In this Case, the average value 31 is above the corridor spanned by the lower and upper threshold curve 28, 32, which indicates destruction of the ceramic due to excessive crimping. Accordingly, the micromechanical measuring system can be equipped with a warning device, which indicates such destruction of the ceramic.
- FIG. 9 shows a noise emission sensor with a first structure, which can be oscillated perpendicularly to the wafer plane.
- a first chip 3 having a seismic mass 1 has been produced from a first wafer and is movably supported by spring elements 2.
- This first chip 3 has been connected by means of silicon fusion bonding to a second chip 4 which has been produced on a second wafer.
- the silicon fusion bonding makes it possible to first process the first chip 3 and the second chip 4 on separate wafers and subsequently to bond them together so that a firm bond 5 is formed between the two semiconductor chips 3, 4.
- the second chip 4 is e.g. mounted on a circuit board 6 via a solder joint.
- the preferred direction of the illustrated oscillatable structure is in this case perpendicular to the wafer plane. This is also called an out-of-plane arrangement.
- the seismic mass 1 is moved relative to the second wafer 4.
- the partial structures fabricated on the first and second chip form an electrical capacitance whose value is dependent on the deflection of the seismic mass 1 relative to the second chip 4.
- This change in capacitance can be measured, for example, by applying metallized contacts 7 on the first and second chip, which are contacted to the circuit carrier 6 via bonding wires 8.
- On the circuit carrier there is an amplifier circuit with which the Umladeströme generated by the dynamic capacitance changes can be amplified.
- an evaluation circuit is provided on the circuit carrier ⁇ , with which the pulse-shaped excitations, which excite the illustrated acoustic emission sensor for oscillating, can be determined on the basis of the measured charge-reversal currents.
- the measuring range of the illustrated acoustic emission sensor is in the ultrasonic range.
- the resonant frequency of the oscillatory structure has been dimensioned to the ultrasonic range.
- a dimensioning of the resonance frequency can be achieved for example by appropriate design of the spring element 2 and by selecting the seismic mass 1. The heavier the seismic mass 1, the lower the resonant frequency of the oscillatory structure.
- FIG. 10 shows a noise emission sensor with a second structure which can be oscillated parallel to the wafer plane.
- the illustrated acoustic emission sensor has likewise been produced from two silicon wafers with the aid of silicon bulk mechanics or silicon surface micromechanics and serves to determine impulsive excitations in the ultrasonic range.
- a pit 9 has been etched in a first wafer.
- a second wafer was bonded by silicon fusion bonding on the first wafer and thinned to the desired structural height.
- the second wafer was partially completely etched by dry etching (DRIE), so that a freely movable seismic mass 1 is formed above the pit 9.
- DRIE dry etching
- FIG. 11 shows a schematic illustration of a sound emission sensor with an array of oscillatable structures 11... 18 having different resonance frequencies, wherein all resonant frequencies lie in the ultrasonic range.
- the respective seismic masses 1 of the individual oscillatable structures 11... 18 of the array are shown schematically. All oscillatable structures 11 ... 18 are realized on a single silicon chip. By selecting the seismic masses 1, the resonant frequency of each individual oscillatory structure can be adjusted. In this case, a first oscillatable structure 11 has the largest seismic mass 1 and thus has the lowest resonance frequency.
- the structure has eight seismic masses 1, wherein the seismic masses continuously decrease from the first oscillatable structure 11 via a second and third oscillatable structure 12, 13 up to an eighth oscillatable structure 18.
- Larger seismic masses 1 are represented here by larger rectangles, smaller seismic masses 1 by smaller rectangles.
- the resonance frequencies of the individual oscillatable structures 11... 18 of the array are arranged in a stepped manner in order to be able to cover a complete frequency range in the ultrasonic range.
- the illustrated eight oscillatable structures 11... 18 of the array cover a frequency range between 30 and 100 kHz, the individual resonant frequencies differing by 10 kHz each.
- FIG. 12 shows the frequency response of the acoustic emission sensor with the array of oscillatable structures 11... 18 with different resonance frequencies, which is shown in FIG.
- the quality of these individual oscillatable structures of the array has been chosen such that their respective frequency ranges overlap. In this way, a frequency window in the ultrasonic range can be detected almost continuously.
- FIG. 13 shows a schematic representation of a sound emission sensor with an array of oscillatable structures with different vibration directions. By way of example, only two oscillatable structures are shown here, the preferred directions of the two oscillatable structures being oriented orthogonally to one another. With such an arrangement, it is possible to detect jerky excitations, wherein a resolution with respect to two spatial dimensions can be achieved. In order finally to be able to image the third spatial dimension, the vibration measuring system shown here could be supplemented by a further oscillatable structure whose preferred direction is aligned orthogonal to the direction of vibration of both oscillatory structures shown here.
- FIG. 14 shows a layout of a micromechanically produced acoustic emission sensor.
- This is an in-plane oscillator, i. the preferred direction of the oscillatable structures is aligned parallel to the wafer plane.
- the acoustic emission sensor comprises a comb-like running seismic mass 1, which engages on two sides at least partially in measuring electrons 10, which are also comb-like.
- the seismic mass 1 is suspended on four spring elements 2.
- the resonance frequency of the illustrated acoustic emission sensor in the ultrasonic range is adjusted over the length of the spring elements 2 and the weight of the seismic mass 1.
- the signal is obtained by evaluating the capacitance change between the seismic mass 1 and the measuring electrons.
- the dimension of such a vibratable structure is about 500 x 500 microns.
- FIG. 15 shows a micromechanical measuring system 23 as a hybrid system.
- the measuring system 23 comprises a sound emission sensor 19, which is one of the previously written embodiments corresponds and is shown here only schematically.
- the micromechanical measuring system 23 has an analog signal processor 20 and a digital signal processor 21. All three components 19, 20, 21 are on a common substrate 22, which may consist of silicon, ceramic or Leitplattenmaterial (FR 4) applied.
- FR 4 Leitplattenmaterial
- On the substrate 22 are copper tracks, with which the acoustic emission sensor 19 and the analog signal processing 20 is connected via bonding wires 8.
- the analog signal processing 20, which is provided for amplifying and filtering the signal detected by the acoustic emission sensor 19, is finally followed by the digital signal processing 21.
- One or more chips provided for digital signal processing are applied to the substrate 22 by means of the so-called flip-chip bonding technology.
- the chips of the digital signal processing 21 are connected with their electrically active side via so-called bumps 29 to the substrate 22 serving as the circuit carrier.
- the flip-chip bonding technology is an elegant alternative to wire bonding technology, as it allows an even more compact design to be realized and in general, a higher reliability and lower susceptibility can be achieved.
- the illustrated microsystem measuring system can finally be housed in an IC housing customary in microelectronics.
- micromechanical measuring system shown represents only one exemplary embodiment of a sound emission measuring system which has integrated signal processing.
- Micromechanical sound sensors, analog signal processing 20 and digital signal processing 21 can both be realized as discrete components on discrete silicon chips and then connected to one another by means of a suitable bonding technique. be connected electrically as well as monolithically integrated on a single chip.
- a micromechanical measuring system 23 as a printed circuit board stack.
- a sound emission sensor 19 an analog signal processing 20 and a digital signal processing 21 are implemented on individual carriers, wherein the carriers are stacked on each other to reduce the volume.
- a base material for the stack construction board material (FR4) or ceramic can be used as a base material for the stack construction board material (FR4) or ceramic.
- FIG. 17 shows a micromechanical measuring system 23 in Star-Flex printed circuit board technology.
- a sound emission sensor 19 an analog signal processor 20 and a digital signal processor 21 are also implemented to reduce the overall build volume on stacked carriers using Star-Flex printed circuit board technology.
- the connection between the individual functional layers is done here via flexible printed circuit boards in contrast to FIG 16, where the connection of the individual functional layers has been realized via a rigid frame.
Abstract
Description
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Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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PCT/DE2007/000657 WO2008125071A1 (en) | 2007-04-16 | 2007-04-16 | Micromechanical sound emission measurement system |
DE112007003547T DE112007003547A5 (en) | 2007-04-16 | 2007-04-16 | Micromechanical sound emission measuring system |
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PCT/DE2007/000657 WO2008125071A1 (en) | 2007-04-16 | 2007-04-16 | Micromechanical sound emission measurement system |
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WO2008125071A1 true WO2008125071A1 (en) | 2008-10-23 |
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PCT/DE2007/000657 WO2008125071A1 (en) | 2007-04-16 | 2007-04-16 | Micromechanical sound emission measurement system |
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WO (1) | WO2008125071A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20120017683A1 (en) * | 2009-03-31 | 2012-01-26 | Marco Dienel | Vibrating micromechanical system having beam-shaped element |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6092422A (en) * | 1995-09-29 | 2000-07-25 | International Business Machines Corporation | Mechanical signal producer based on micromechanical oscillators and intelligent acoustic detectors and systems based thereon |
US20020017834A1 (en) * | 2000-07-06 | 2002-02-14 | Macdonald Robert I. | Acoustically actuated mems devices |
US6359367B1 (en) * | 1999-12-06 | 2002-03-19 | Acuson Corporation | Micromachined ultrasonic spiral arrays for medical diagnostic imaging |
US20070068266A1 (en) * | 2005-09-26 | 2007-03-29 | Tsukasa Fujimori | Sensor and sensor module |
-
2007
- 2007-04-16 DE DE112007003547T patent/DE112007003547A5/en not_active Ceased
- 2007-04-16 WO PCT/DE2007/000657 patent/WO2008125071A1/en active Application Filing
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US6092422A (en) * | 1995-09-29 | 2000-07-25 | International Business Machines Corporation | Mechanical signal producer based on micromechanical oscillators and intelligent acoustic detectors and systems based thereon |
US6359367B1 (en) * | 1999-12-06 | 2002-03-19 | Acuson Corporation | Micromachined ultrasonic spiral arrays for medical diagnostic imaging |
US20020017834A1 (en) * | 2000-07-06 | 2002-02-14 | Macdonald Robert I. | Acoustically actuated mems devices |
US20070068266A1 (en) * | 2005-09-26 | 2007-03-29 | Tsukasa Fujimori | Sensor and sensor module |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20120017683A1 (en) * | 2009-03-31 | 2012-01-26 | Marco Dienel | Vibrating micromechanical system having beam-shaped element |
US8887571B2 (en) * | 2009-03-31 | 2014-11-18 | Siemens Aktiengesellschaft | Vibrating micromechanical system having beam-shaped element |
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