US2691749A - Vibrating reed assembly with damping - Google Patents

Description

Oct. 12, 1954 J. D. puRKEE 2,691,749

VIBRATING REED ASSEMBLY WITH DAMPING Filed April 22. 1952 2 Sheets-Sheet l gam/es D. Barlow Arrow/5v5 Oct. l2, 1954 Filed April 22. 1952 51 7/ INVENTOR 7 James .wr]ee l 65 I Y//d maf/1111@ J. D. DURKEE VIBRATING REED ASSEMBLY WITH DAMPING 2 Sheets-Sheet 2 ATTORNEYS Patented Oct. 12, 1954 UNITED srA'r s VIBRA'ING REED ASSEMBLY WITH DAMPING Application April 22, 1952, Serial No. 283,626

The present invention relates to improvements in vibrating reed assemblies in which one or more vibrating reeds are caused to vibrate at their natural mechanical or resonant frequency. Such assemblies have many fields of utility. One field of utility in which I am particularly interested is the reception of signals in telecommunication systems. In such systems a frequency sensitive reed or reeds may be caused to vibrate electromagnetically by the now of alternating current through a coil having a core pro vided with pole pieces adjacent the free end or ends of the reed or reeds. A reed will be caused to vibrate when current having a frequency equal to the resonant frequency of the reed is caused to flow through the coil With which the reed is associated.

A system of telecommunication developed by me involves the transmission of a plurality of impulses of different frequencies. The nature of the combinations of such impulses determines the character of intelligence transmitted. For example, a given combination of frequencies may designate a particular letter of the alpha bet While a different combination of frequencies may designate a different letter of the alphabet. The impulses may be simultaneously or sequentially received at a receiving station. thus received composite signal may be fed to the coil associated with a plurality of reeds having dif ferent resonant vibrating frequencies. Those reeds having frequencies corresponding to the frequencies of the various impulses making up the composite signal will be vibrated, while reeds having other frequencies will not be affectedby n the particular composite signal under consideration. Subsequently received signals composed of impulses of other frequencies will, of course, cause other reeds to vibrate. The number of reeds in a signal receiving apparatus should preferably correspond to the number of different frequencies which may be used in various cornbinations in making up the composite signal. It Will be apparent that with this system a large number of different characters may be trans mitted and received by the use of various combinations of impulses of the different frequencies.

It is frequently important for the apparatus used in the reception of signals according to the foregoing system to be compact, simple in construction, and inexpensive. It is frequently necessary for the receiving apparatus to be portable or capable of being used on moving air, wa-

ter or land craft. It is also essential to speed of transmission and reception that the reeds be capable of very rapidly beginning to vibrate at their resonant frequency upon the passage of current corresponding to their resonant frequency through the associated driving coil. It is also essential that the vibration of the reeds cease abruptly or quickly after termination of flow of current corresponding to their frequency through the associated coil. In order to realize the full benets of their frequency selectivity, the reeds should completely or substantially cease vibrating before the next signal is received in order to eliminate the possibility that the reeds vvill respond to impulse currents of other than their resonant frequencies.

One of the primary objects of my invention is to provide an electromagnetically driven vibrating reed assembly in which a reed can very quickly begin vibrating at its resonant fre quency upon passage of an electric current corresponding to its resonant frequency through its associated coil.

Another important object of the invention is to provide mechanical damping means which will cause a vibrating reed to quickly cease its vibration after its driving force has been removed.

Still another object of the invention is to provide mechanical damping means for a vibrating reed which provides a minimum of interference to vibration of the reed at its resonant frequency, but which quickly clamps the vibration after removal of that force tending to drive the reed.

Still another important object of the invention is to provide an assembly Which includes a plurality of reeds having diiferent resonant frequencies and in which a single coil is used as a driving coil for all of the reeds. This arrangement contributes greatly to the simplicity, cornpactness, and economy of apparatus involving a plurality of electromagnetically driven vibrating reeds. The use of a single .coil concentrates in the eld kof the single coil the energy necessary to 'drive all of the reeds rather than supplying that energy to each of a plurality of coils.

Other objects and advantages of the invention will be apparent from the following detailed description of exemplary forms of my invention. This description has reference to the accomn panying drawings, wherein:

Figure 1 is a side elevational View of a form of my invention involving a single vibrating reed;

Figure 2 is a top plan view of the apparatus shown in Figure l;

Figure 3 is a side elevational View of a form of apparatus embodying the invention and in cluding a pair of vibrating reeds having a single y driving coil;

Figure 4 is an end elevational view of the apparatus shown in Figure 3;

Figure 5 is a top plan view of the apparatus shown in'Figures 3 and 4;

Figure 6 is a vertical sectional view taken in the direction of the arrows along the line 6 6 of Figure 5;

Figure '7 is a View similar to Figure 4, but i1- lustrating mechanical vibration damping means to dampen vibration of the reeds;

Figure 8 is a fragmentary detail view in side elevation illustrating one of the reeds and its associated damping means;

Figure 9 is a top plan view of a further apparatus embodying the invention and including six vibrating reeds having a single driving coil; and

Figure l is a sectional View taken in the direction of the arrows along the line I--I of Figure 9.

The form of the invention illustrated in Figures 1 and 2 includes the principal features of the apparatus disclosed in my copending application Serial No. 229,975, filed June 5, 1951, entitled Polarized Relay (now abandoned) of which this application is a continuation-in-part. A base il of non-magnetic and insulating material is provided at one end with an upwardly eX- tending reed supporting standard I2 of nonmagnetic but electroconductive material. The reed supporting standard I2 may be of tubular form and may be secured to the base I I by means of a bolt I3. A vibrating reed I4 of magnetic and conductive material has one of its ends fixed at I5 to the reed supporting standard I2. The reed I4 extends generally parallel to the base l I and is capable of vibrating in a plane which is parallel to that base.

A permanent magnet I6 extends upwardly from the base i I and may be secured thereto by any suitable means such as a bolt I'I. The permanent magnet Iii has one of its poles positioned closely adjacent the approximate midportion of the reed. rEhe opposite pole of the magnet I6 is adjacent the base II and is positioned a substantial distance from the reed I4.

The flux paths induced by the permanent magnet I6 are illustrated by the dot-dash lines I8 and I9. The location of one pole of the permanent magnet i6 adjacent the mid-portion of the reed I4 and the location of the opposite pole of the magnet remote from the reed, plus the fact that the polar axis of the permanent magnet I6 extends at approximately a right angle to the longitudinal axis of the reed I4 serves to establish magnetic flux of the same polarity in both ends of the reed I4. This positioning of the permanent magnet l5 also serves to provide substantial symmetry of ux distribution longitudinally of the reed i4. The maximum amplitude of vibratory movement of the reed I4 occurs at the free end 2) of the reed. This amplitude of movement diminishes greatly toward the midportion of the reed, and I have found that there is very little amplitude of vibratory movement of that portion of the reed I4 immediately overlying the adjacent pole of the permanent inagnet i6. For this reason, vibration of the reed causes very little disturbance of a symmetrical distribution of the lines of flux laterally of the reed I.

A core supporting block 2I of non-conducting and non-magnetic material extends upwardly from the base II. A generally U-shaped flux core 22 is supported at the upper end of the member ZI and is secured thereto and to the base by means of bolts 23 and 24. A coil 26 is positioned around the closed end of the flux core 22. The ux core is provided with pole pieces 21 and 28 disposed on opposite sides of the free end of lil (ill

the reed I4 and in the plane of vibration of the reed.

The reed I4 is a tuned reed which vibrates at a resonant frequency or at its natural mechanical period of vibration. When alternating current of a frequency corresponding to the resonant frequency of the reed I4 is supplied to the coil 26, the reed will very quickly begin to vibrate at its resonant frequency. If, however, alternating current of a frequency different from the resonant frequency of the reed I4 is supplied to the coil 25, the reed will not begin to vibrate. The reed is thus selective in that it will vibrate only when alternating current corresponding to its resonant frequency is supplied to the coil 26. Composite signals involving a plurality of different frequencies can be supplied to the coil 26 and the reed M will vibrate only whenv the signal includes a component of the frequency corresponding to the natural or resonant frequency of the reed.

Vibration of the reed can be detected by the opening and closing of an electric circuit during vibration of the reed. The circuit to be opened and closed can be connected as shown at 29 to the reed supporting standard I 2. The circuit can also be connected as indicated at 3D or 3I to either or both of the pole pieces 21 and 28. Current can thus iiow through the reed and the pole pieces at any time that the reed is in contact with either pole piece 21 or 28, and under such conditions the circuit will be closed. The circuit will, of course, be open while the free end 2C of the reed is not in contact with either pole piece.

The manner in which applicants permanent magnet I6 is positioned and arranged relative to the reed I4 provides several important advantages. The symmetry of distribution of the lines of flux induced by the permanent magnet I6 have been mentioned above. I find that this symmetry is not appreciably interfered with by the presence of the pole pieces 2'I and 28 of the core 22. Those pole pieces 2'I and 28 are pre- Y vented from receiving any substantial magnetic lines of force from the permanent magnet I6, except those lines of force which pass through the reed I4. In this way applicants pole pieces are not influenced by the permanent magnet I6 except by the flux passing through the reed. Those pole pieces are, however, inuenced by the magnetic condition of the free end of the reed, which magnetic condition tends to be substantially constant. The substantially constant magnetic condition of the free end of the reed enables the reed to be delicately responsive to the changing magnetic conditions of the pole piece resulting from the flow of alternating current through the coil 26. Since the pole pieces 2l and 28 are not influenced by the permanent magnet I6 except by the flux passing through the reed, the pole pieces are readily able to change their polarity or magnetic condition in response to the flow of feeble current through the coil 2S. These features have been found to be of extreme importance in permitting the reed to be rapidly started and effectively driven with a minimum of power in the coil 26. It has also been found that there is no tendency for the reed to freeze to either pole piece. There is no strongly effective permanent magnetic eld between the pole pieces 2l and 28 which can influence the free end of the reed. This absence of an effective permanent magnetic field permits applicants reed to be driven at its true mechanical frequency which tends toward frequencyy stability.

The foregoing factors contribute to the rapid beginning or onset of vibration of the reed I4 whenv alternating current of a frequency corresponding to the resonant frequency of the reed is caused to flow through the coil 26. It is 'also essential, as pointed out above, to cause vibration of the reed to rapidly cease or decay when current of a frequency corresponding `to 'the resonant frequency of the reed ceases to ow through the coil 26. The rapid onsetand rapid decay of vibration is essential to speed of transmission and reception in the telecommunication system in which the assembly is intended to be used. .It is, therefore, advisable to provide means for .effectively damping vibration of the reed immediately upon cessation of the driving force.

. This damping of vibration must be accomplished without effectively interfering with the ability of the reed to vibrate, without altering its resonant frequency and without interfering with the rapid onset of vibration of the reed. I have found that such damping can be accomplished by positioning a plurality of generally Parallel, flexible, filamentary energy absorbing elements in positions such that at least some of those elements are contacted by and absorb energy from the reed during its vibration. This absorptionof energy quickly dissipates the residual energy stored in the reed after the driving force has been removed. Such ilamentary energy absorbing elements are designated generally by the reference numeral 32. They preferably take the form of nylon bristles, although other filamentary substances may be used. The energy absorbing elements are bundled at one end in the mannerof a brush by means of a filament holder 33. The filament holder is preferably of flexible metal, and it may be secured to the upper end of the reed supporting standard l2 by means of the bolt i3. The flexibility of the filament holder 33 permits the position of the filaments 32 to be adjusted to obtain the appropriate degree of damping action. The filaments 32 are illustrated in Figures 1 and `2 as being generally parallel to the reed M with the free ends of the filaments lying on either side of the reed in the plane of vibration thereof.

Figures 3 to 'l illustrate a modification of the invention in which the features and advantages of the form of the invention described above are retained, but in which the apparatus includes a pair of vibrating reeds in a compact assembly. Compactness and economy are achieved by utilicing a single permanent magnet and a'single driving coil. The vibrating reeds have different resonant frequencies, and theywill respond to different frequencies of current Which may be supplied to the coil.

A base dii is provided with a reed supporting sub-base 1li which is secured to the base by means of a screwllZ. Vibrating reeds i3 and 44 have their lower ends secured in opposite ends of the sub-base di. The reeds 43 and ftd extend upwardly in parallel relationship. A magnet holder t5 is secured to the base 4U and sub-base il.' by means of a threaded lower end lit and a nut lll. A permanent magnet 48 is supported within an opening 49 in the upper end of the magnet support t5 and is rigidly held therein by means of a set screw Eil. The magnet 48 has one `of its poles positioned adjacent the midportion of reed i3 while its opposite pole is positioned adjacent the mid-portion of the reed 44. The magnet is disposed at right angles to both of thereeds and is also disposed at right angles to the planesof vibration of the reeds. The base lill, the sub-base 4I and the magnet support should be of non-magnetic, electroconductive material. In all illustrated forms of the invention the reeds are both magnetic and electroconductive.

A pair of spaced core supporting standards 5i and 52 extend through the base d@ and are rigidly secured thereto bymeans of nuts 53 and 54. The core supporting standards 5i and 52 extend upwardly from the base in parallel relationship to each other. A coil supporting bar 55 of insulating material extends from the upper end of the standard 5I tothe upper end of the standard .52 and is rigidly secured to those standards by'cap screws 55 and 5l. A generally U- shaped core 58 ispositioned above the coil supporting bar 55 and is provided with adjustable pole pieces in the form of screws 5S and 60 which are'threaded into the free ends of the core 53. The pole pieces 59 and 6B are positioned on opposite sides of the free upper end of the reed lill. A similar generally U-shaped core 6l is positoned beneaththe coil supporting bar 55. The core 5l is provided with adjustable pole pieces GZ'and 63 which are similar to the pole pieces 5s and I5@ described above. The pole pieces E2 @Ii are positioned on opposite sides of the free upper end of the reed d3. A coil 544 surrounds the coil supporting bar 55 and the closed end of each of the cores 58 and BI.

The manner of operation of the form of the invention illustrated in Figures 3 to '7 is essentially the same as that described above. When alternating current of a frequency corresponding to the resonant frequency of the reed 43 is fed to 'the coil S4, the reed 43 will be caused to vibrate at its resonant frequency while the reed ftd will not vibrate. Conversely, the reed 5d will be caused to vibrate when alternating current'corresponding to its resonant frequency is Afed to the coil 6d. The apparatus may be used to open and close a pair of electrical circuits. A contact which is common to both circuits may be connected to the base 4i! by any suitable means such as 'by clamping between the nut kSi! and the lower surface of the base. The current can flow from such connection to both of the reeds 43 and lill. The individual circuits areconnected respectively to the cores 53 and'l by any suitable .means such as by soldered contacts and E6. In this manner the circuit connected to the core Bl will be intermittently closed during vibration of the reed d3, while the circuit connected to the core 58 will be intermittently closed during vibration of the reed d4.

Figures 7 and 8 illustrate the manner in which the mechanical damping means can be applied to the form of the invention illustrated in Figures 3 to 6. A brush of filaments similar to those described above is attached to the mid-portion of either side of the base itil. A brush designated generally by the reference numeral 6l is secured to the 'base by means of the screw (i8 and is positioned so that portions of its laments lie on either side ofthe reed 43 and in the plane of vibration thereof. A similar brush 69 is secured tothe opposite side of the Abase by means of a screw lil, and is similarly positioned with respect to the reed ed. The brushes 6l and Ei@ may be provided with hoops ll which surround the filaments and which are slidable longitudinally thereof. Adjustment of vthe hoops 'H along the length of the filaments effects adjustment 7 of the energy absorbing capacity and damping characteristics or the brushes 61 and 69.

A further form of the invention is illustrated in Figures 9 and 10. in this form of the invention the number of Vibrating reeds has been increased to six. Three permanent magnets are associated with the vibrating reeds while a single coil is used to, drive the reeds. The reeds have different resonant frequencies, and any given reed will be vibrated when an alternating current corresponding to its frequency is supplied to the coil which is common to all of the reeds.

A base plate Si) is constructed of non-ma.,- netic and non-conductive material. Reed supporting standards 8l, 82, 83, 84, 85 and 86 are secured to the base SI) by any suitable means such as screws 8'! and these standards extend upwardly from the base in parallel equally spaced relationship, as best illustrated in Figure 9., Each of the standards SI to 86 has a vibrating reed secured thereto, these reeds being designated by the reference numerals 9i, 52, S3, 912-, and respectively. A magnet support 97 extends upwardly from the base 80 between the reeds 9! and 95. The magnet support 91 rigidly supports a permanent magnet S8. One pole of the permanent magnet 98 is disposed adjacent the mid-portion of the reed SI While the opposite pole of the magnet is disposed adjacent the mid-portion of the reed 85. The polar axis or" the magnet 93 extends at substantial angles to the longitudinal axes of the reeds Gl and 3&3 and also extends at substantial angles to the planes of vibration of those reeds. A magnet support QS supports a permanent magnet IBB in a similar position between the reeds 92 and 93 while a magnet support IGI supports a permanent magnet Ici between the reeds Qll and 95. In spite of the fact that the permanent magnets not strictly at right angles to their associated reeds. arrangement subjects all of the to magnetic effects similar to those discussed above in connection with the description or" the Jform of the invention illustrated in Figures l and The reeds 9| to 96 are provided with mechanical means IGB which are similar to those described above and which are secured to the upper ends of the reed supporting standards.

All of vibrating reeds 9! to 9E point toward the center of the base 89 and a driving coil with appropriately positioned pole pieces is positioned above the center of the base. The coil is designated by the reference numeral lIIl and is provided with a laminated magnetic core III in the form of a coiled strip of magnetic material. An upper pole plate H2 is positioned above the coil i i9 while a lower pole plate I I3 is positioned below the coil. A spacer member H4 is positioned between the lower pole plate H3 and the base 8G. A bolt IIS extends through the pole plates H2 and IIB, through the laminated core I I I, the spacer member I IA and the base 8G, and these elements are rigidly clamped together by means of a nut IIB. The bolt I I maintains the ends of the laminated core III in intimate contact with the magnetic pole plates I I2 and I I3.

rEhe pole plates I I2 and I I3 are vprovided with a. pair of adjustable pole pieces for each of the reeds 9| and 96. Since these pole pieces are identical it will be suicient to described one pair of the pole pieces in detail. An adjustable pole piece Iil is threadedly secured in the upper pole plate II2 and extends downwardly to terminate adjacent the free end of the reed 9|. A lock nut 8 H8 may be used to retain the pole piece II'I in its adjusted position. A lower pole piece IIB is threadly secured in the lower pole plate I I3 and extends upwardly to terminate beneath the free end of the reed Si.

The arrangement illustrated in Figures 9 and 10 can be used to control the periodic opening and closing of six circuits. A Contact common to all six of the circuits may be electrically connected to the pole plates I I2 and I I3 by connecting it to the bolt IIE. This common contact is thus electrically connected to all six sets of pole pieces. Contacts which are individual to each circuit may be connected in electrical contact with the reeds QI and 96 by connecting those contacts to the reed supports BI and S6, respectively.

Except for the greater number of reeds and magnets involved and the fact that more circuits are controlled, the operation of this form of the invention is the same as that described above.

I have illustrated and described what I now consider to be the preferred embodiments of my invention. It will be understood, however, that various modifications and alterations may be resorted to without departing from the broader scope of the invention as dened by the following claims.

Having thus described my invention, I claim:

1. In a polarized relay, a. pair of spaced movable members of magnetic material each of which is xedly supported at one end and free to move at the other end, both of said movable members lying in a common plane and being free to vibrate in separate planes perpendicular to said common plane, a magnet stationarily positioned with its polar axis in said common plane and with a rst pole thereof in juxtaposition to an intermediate portion of the length of one of said movable members and with the second pole thereof in juxtaposition to an intermediate portion of the other of said movable members, the polar axis of said magnet being disposed at a substantial angle to the longitudinal axis of each of said movable members, and means for inducing movement of the free end of each movable member, said movement inducing means comprising a core having pole pieces disposed on opposite sides of each movable member near the free end and in the plane of movement thereof, and a coil surrounding said core.

2. A vibrating reed assembly comprising a pair of spaced vibratile reeds of magnetic material each of which is iixedly supported at one end, said movable members lying in a common plane and being free to vibrate in separate planes perpendicular to said common plane, a magnet stationarily positioned with its polar axis in said common plane and with a iirst pole thereof in juxtaposition to an intermediate portion of the length of one of said reeds and with the second pole thereof positioned adjacent an intermediate portion of the length of the other of said reeds, the polar axis of said magnet being disposed at substantial angles to the longitudinal axes of said reeds to thus establish magnetic fluxes of like polarity in both ends of each of said reeds but with the flux in the ends of one reeds being of opposite polarity to the flux in the ends of the other reed, and electromagnetic means for inducing vibration of said reeds.

3. A vibrating reed assembly comprising a pair of parallel vibratile reeds of magnetic material fixedly supported at one of their ends, said reeds lying in a common plane and being capable of vibrating in spaced parallel planes perpendicular to said common plane, a magnet stationarilypositioned with its polar axis lying in said common plane perpendicular to the planes of vibration of said reeds, a rst pole of said magnet being in juxtaposition to an intermediate portion of the length of one of said reeds and the second pole of said magnet being in juxtaposition to an intermediate portion of the other of said reeds, to thus establish magnetic fluxes of like polarity in both ends of each reed but with the ilux in the ends of one reed being of opposite polarity to the flux in the ends of the second reed, electromagnetic pole pieces on opposite sides of said reeds near the free ends thereof and in the planes of vibration of the reeds, and an electrical conductor surrounding the magnetic flux paths through said electromagnetic pole pieces.

4. A vibrating reed assembly as 4described in claim 3 in which each of said vibratile reeds is a tuned reed Which is caused to vibrate only upon passage through said electrical conductor of an alternating current having a frequency corresponding substantially to the tuned frequency of the reed.

5. A vibrating reed assembly as defined in claim 3 including mechanical means for damping vibration of each of said vibratile reeds, said damping means comprising a plurality of flexible, lilamentary, energy absorbing members in generally parallel relationship and so positioned that at least a portion of said filamentary members contacts the reed during vibration thereof.

6. A vibratory reed assembly comprising a plurality of pairs of vibratile reeds disposed in a common plane and iixedly supported at their outer ends with their free inner ends converging toward but stopping short of a central axis perpendicular to said plane, said reeds 4being free to vibrate in planes perpendicular to said common plane, a magnet stationarily positioned with its polar axis in said common plane between the reeds of each pair With the first pole of the magnet being adjacent a mid-portion of one of the reeds of the associated pair and with the second pole of the magnet being adjacent the second reed of the pair, an electrical coil having a core coinciding with said -central axis, and pole pieces on opposite sides of the free inner end of each reed, said pole Apieces being in the path of flux induced by flow of current through said coil.

'7. A vibrating reed assembly as described in claim -6 in which each of said vibratile reeds is a tuned reed lwhich is caused to vibrate only upon passage through said electrical conductor of an alternating current having a frequency corresponding substantially to the tuned frequency of the reed.

8. A vibrating reed assembly as dened in claim 6 including mechanical means for damping vibra-J tion of each of said vibratile reeds, said damping means comprising a plurality of flexible, lamentary, energy absorbing members in generally parallel relationship and so positioned that at least a portion of said lamentary members contacts the reed during vibration thereof.

9. A vibrating reed assembly comprising a vibratile reed of magnetic material fixedly supported at one end and free to vibrate in a plane, a magnet stationarily positioned With its polar axis lying in a plane perpendicular to said plane of vibration and with a iirst pole thereof in juxtapostion to an intermediate portion of the length of said reed and with the polar axis of said mag- Anet disposed at a substantial angle to the longitudinal axis of said reed to thereby position the second pole of said magnet a substantially greater distance than said first pole from said reed to thus establish a magnetic flux of like polarity in each end of said reed, electromagnetic means for inducing vibration o1" said reed, and mechanical damping means for said reed comprising a plurality of fiexible, ilainentary, energy absorbing members in generally parallel relationship and so positioned that at least a portion of said filamentary members contacts said reed during vibra tion thereof.

10. A vibrating reed assembly comprising a vibratile reed of magnetic material xedly supported at one end and capable of vibrating in one plane, a magnet stationarily positioned with its polar axis lying in a plane passing through said reed and perpendicular to the plane of vibration of said reed, said polar axis of said magnet forming a substantial angle With the plane of vibration of said reed, a rst pole of said magnet being in close juxtaposition to an intermediate portion of the length of said reed but slightly displaced from the plane of vibration thereof, and the second pole of said magnet [being spaced from the plane of vibration of said reed a substantially greater distance than said rst pole to thus establish a magnetic flux of like polarity in each end of said reed, electromagnetic pole pieces on opposite sides of said reed near the free end thereof and in the plane of vibration of the reed, and an electrical conductor surrounding the magnetic flux path through said electromagnetic pole pieces.

ll. A vibrating reed assembly comprising -a vibratile reed of magnetic material xedly supported at one end and capable of resonant vibration in one plane, electromagnetic pole pieces on opposite sides of said reed near the free end thereof and in the plane of vibration of the reed, a magnet stationarily positioned with its polar axis lying in a plane passing through said reed and perpendicular to the plane of vibration thereof, said polar axis forming a substantial angle with the plane of vibration of said reed, a rst pole of said magnet being in juxtaposition to the approximate mid-portion of the length of said reed but slightly spaced from the plane of vibration thereof, and the second pole of said magnet being spaced from said reed and from said pole pieces a substantially greater distance than said first pole to thus establish a magnetic ux of like polarity in each end of said reed, and an electrical y, conductor surrounding the magnetic flux path through said electromagnetic pole pieces to cause said reed to vibrate at its resonant frequency upon passage of alternating current of such frequency through said conductor.

References Cited in the file of this patent UNITED STATES PATENTS 1,159,189 Dempster Nov. 2, 1915 1,226,775 Koenig May 22, 1917 2,126,562 Lakatos Aug. 9, 1938 2,356,229 Dunlap Aug. 22, 1944 2,448,298 Fligue Aug. 31, 1948 2,494,451 Olson Jan. 10, 1950 FOREIGN PATENTS Number Country Date 169,465 Switzerland Aug. 16, 1934 261,384 Great Britain Oct. 6, 1927 699,782 Germany Feb. 10, 1942

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