US3194209A - Ultrasonic generator - Google Patents

Description

ARCH R SUBSTITUTE FOR MISSING XR July 13, 1965 A. NELKIN ETAL ULTRASONIC GENERATOR 2 Sheets-Sheet 1 Filed Jan. 31, 1962 NGDAL DIAMETER d SECTOR A SECTOR c INVENTORS Anhur Nelkin Robert A. LesIer Roberf H. Whittaker 8-IYohn H. Thompson ATTORNIZY wmuzssss: gLWWJ A. NELKIN ETAL ULTRASONIC GENERATOR July 13, 1965 2 Sheets-Sheet 2 Filed Jan. 31, 1962 United rates 3,194,209 ULTRASONIC GENERATOR Arthur Nelkin, Pittsburgh, Robert A. Lester, Pitcairn, Robert H. Whittaker, Export, and John H. Thompson, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 31, 1962, Scr. No. 170,157 5 Claims. (Cl. 1l6137) The present invention relates to a transmitter for generating ultrasonic signals and more specifically to a flexural mode mechanical resonator to generate ultrasonic signals of the predetermined frequency in the supersonic or ultrasonic range.

The requirements for usable mechanical resonators is that they can vibrate with sufficient amplitude and also sufficient duration. .In addition, if these resonators are to be used as ultrasonic transmitters they must be capable of producing such signals of a frequency within a range of frequencies so that the ultrasonic receiver will be able to accurately detect the transmitter signal despite various other signals which may be present. Such a desirable range would be in the order of 30 kilocycles to 60 kilocyclcs where there is a minimum of extraneous sound signals from such things as squeaky door hinges, ripping of paper, and also a minimum of extraneous electromagnctic signals such as from radio station transmitters, etc. Further in this frequency range the air absorption is relatively low. In addition the resonator should be relatively small.

The types of vibration which bars or plates assume after they are actuated have been known for many years. Examples of various types of modes are illustrated in the book Acoustical Engineering" by Olson published by D. Van Nostrand Co., 1957. Page 65 of this book illustrates various types of fiexural modes of a disc or plate while on page 67 of this book longitudinal vibrations of a rod are illustrated. 'Many of the modes illustrated in this book have been found unsatisfactory for use as a mechanical resonator or an ultrasonic transmitter either because the discs, rods or plates cannot be or have not been satisfactorily mounted to provide sufficient output from the resonating element. More specifically, most heretofore known mounting means for many of these resonators, absorbs most of the vibratory energy so that amplitude and ring time of the vibrations or the resonating elements are very small.

A complete theory of the vibration of a plate suspended in air was described in a celebrated memoir by Kirchhoff in 1850. In this memoir, it was described that the gravest of all normal modes has no nodal circle but rather vibrates with at least two nodal diameters in a flexural mode. It is stated in this memoir and other works that a circular plate and a square plate has its gravest mode with two nodal lines that cross each other through the center of the circular or square plate. Since the Kirchhoff grave mode is predicated upon a circular plate or square plate being suspended in air with no suspension or contact or very little suspension contact, it has heretofore been found to be impractical to utilize such a vibrating resonator for producing ultrasonic signals.

Accordingly, it is an object of the invention to provide a new and improved ultrasonic generator utilizing a flexural mode resonator having at least two nodal diameters to generate ultrasonic signals of a predetermined frequency.

A further object of the invention is the provision of a 3,1942% Patented July 13, 1965 new and improved Kirchhoff grave mode resonator for generating ultrasonic signals.

It is a still further object of the invention to provide a fiexural mode resonator in the form of a plate which can produce ultrasonic signals of the predetermined frequency having relatively large amplitude and duration.

An ultrasonic generator embodying the present invention includes a resonator which vibrates in a flexural mode with a plurality of nodal diameters which diameters inter- Cept at a reference point to form an axial reference through the resonator. A mounting pin is integral with the plate and positioned concentric with the reference axis. The pin extends outwardly from the plate so that the vibrations of the plate travel a short distance down the integral pin and are cancelled so that there is no vibratory energy at the lower mounting portion of the pin and hence no energy is lost to the mounting. Means are applied to the outer edges of the plate to impart energy to the plate to initiate oscillations of. the flexural mode resonator. To further increase the output of the ultrasonic resonator, a housing is employed around the resonator and Is spaced parallel with the resonator surfaces a distance wherein is the wave length of the ultrasonic signals caused by the vibration of the resonator and N equals any integer or zero. This housing includes apertures therein so that the phase of the ultrasonic signals coming out of the housing are substantially in phase whereas the energy from the quadrants in the other phase of vibration are not transmitted into space so as to prevent cancellation of the first named phase vibrations.

These and other advantages of this invention will be more clearly understood from the following description when read in conjunction with the accompanying drawings in which:

FIG. 1 is an isometric exploded view of an assembly layout of an ultrasonic generator constructed in accordance with the present invention;

FIG. 2 is a top view of the device illustrated in FIG. 1;

FIG. 3 is a cross-sectional view taken along lines III shown in FIG. 2;

FIG. 4 is a top view of the resonant plate illustrated in FIG. 1 with the housing illustrated therein shown in dotted lines;

FIG. 5 is an isometric view of the resonant plate and mounting member of the resonator shown in FIG. 1;

FIG. 6 is a cross-sectional view of the mounting pin of the resonator illustrated in FIGS. 1 through 5;

FIG. 7 is a side view of another embodiment of the invention; and,

FIG. 8 is an isometric view of a third embodiment of the invention.

FIG. 1 shows an assembled isometric view of an ultrasonic generator constructed in accordance with the present invention. This generator comprises generally a resonator 10 which is mounted on a base member 20. The resonator 10 shown is a plate, shown as circular in FIG. 1, which when energy is imparted near the periphery thereof, will vibrate in a flcxural mode having at least two nodal diameters so as to provide opposite sectors on the plate which are in phase during vibration as shown in FIG. 4. As shown in FIG. 4, the plus sign indicates sectors B and D on the disc which will be traveling toward the viewer whereas the negative sections A and C will be traveling away from the viewer at point in time during the vibration of the plate. This type of vibration is characteristic of a resonator which is suspended in free air contacting no other external structure. Ordinarily mounting such a plate to produce such a vibration absorbs such a great amount of the vibratory energy in the mounting means that ultrasonic signals transmitted to the air are negligible. In the present invention, however, a mounting means which was found to produce or effect relatively large amplitude and duration vibrations is employed. The mounting means which enables one to utilize the vibration characteristic of an air suspended plate is a pin or mounting means which is integral with the vibratory plate. When such a plate suspended in free air vibrates, the vibrations are described by nodal diameters al and (1 shown in FIG. 4. The diameters define sectors of vibrations or movement up and down. These nodal diameters intersect at a vibratory reference point V on the plate and define a reference axis extending through and normal to the plate. The mounting pin for such a resonator is integral with the plate with the axis of the pin intersecting the above described reference axis at a point which is in the plane of intersection of the two members. In this fashion, the sections of vibrations of the plate are transmitted down the integral pin so that the plus and minus vibrations or up and down vibrations transmitted down the pin are equal and opposite and at some point before the mounting portion of the pin these vibrations are completely canceled so as to provide no transmission of energy outwardly from the pin. Hence, there is substantially no loss of energy from the resonator except to the free air.

It has been discovered that in order to effect substantially no loss to the mounting portion of the mounting pin, the mounting pin and the resonator must be integral and preferably made of the same piece of material as the plate. Integral, however, is not meant necessarily to mean that the pin is constructed from the same piece of material or metal as the resonator but rather is meant to include any similar connection such as where the pin is alloyed to the resonator.

A housing 30 is constructed around the disc and a striker means 40 is secured to the housing so as to impart energy to the disc to initiate vibrations thereof. The housing is spaced at odd quarter wave lengths from the sides of the disc or the plate so as to effect storage of energy back to thedisc which it is not desired to utilize. As shown in FIG. 1, apertures are provided in the housing 30 which are opposite vibrating surfaces of the plate that are in phase and hence utilizing only one phase of ultrasonic energy coming from the resonant disc 10. Still another aperture is provided in the housing which in the embodiment of FIG. 1 is a striker mounted on a spring to impart mechanical energy to the outer edges of the disc to initiate oscillations thereof.

In the embodiment of the invention illustrated in FIG. 1, the resonator 10 comprises a circular disc 11 having an upper major surface 12 and a lower major surface 13 with a circular outer peripheral side edge 14. Extending downwardly from the vibrating plate 11, as shown in FIG. 5, is an integral cylindrical pin 15 having a mounting portion with screwthreads 16 at the free end thereof to define a mounting portion for mounting the vibrator. The pin 15 is integral with the plate 11 and is concentric with the periphery of the plate 11. In a preferred form for optimum or greatest ultrasonic output, the pin 15 and the plate 11 are formed out of the same piece of material such as by constructing the pin 15 by taking a cylindrical body and turning down one portion thereof with a lathe to produce the pin 15.

The pin 15 is shown as extending from the lower major surface 13, however, a similar pin could also extend from the upper major surface 12. Such a pin must also be integral with resonator 11 and concentric with the reference axis described by the nodal diameters (1 and d FIG. 4 illustrates a top view of the resonator 11. This view illustrates a typical tlcxural mode vibration of the disc which is describedby two nodal diameters 41 and 11 As shown in FIG. 4, when the plate 11 vibrates, it will describe four vibrating sections A, B, C and D. In this configuration where'thc plate is a circular disc, these four sections are sectors. As shown in FIG. 4, sector A and sector C are in phase and are designated as such with a minus sign whereas the sector B and sector D are also in phase designated as such by a plus sign. That is, at a given point in time the sectors A and C are going away from the viewer whereas the sectors B and D are out of phase with the sectors A and C and are coming up toward the viewer of the drawing. As can be understood, the maximum point of vibratory amplitude is in the center of the sectors and these vibrations are produced about the two nodal diameters d and The vibration illustrated in FIG. 4 is descriptive of a vibration of a circular disc which is in free air and has no structural contact with any other element. As described above, this is the gravest mode of a plate although as explained above, the problem of mounting such a vibratory system without losses to its support has heretofore been quite unsatisfactory. In addition, it is possible under some conditions and with certain dimensions and modulates of elasticity to produce a flcxural mode of vibration where there is more than two nodal diameters. The particular mounting means disclosed in the embodiment of the invention, however, will work satisfactorily with any fiexural mode resonator having at least two or more nodal diameters. Further the resonator can be a circular plate or cylinder or a square or rectangular plate or block.

The particular vibrations illustrated in FIG. 4 are produced by imparting energy such as by a mechanical striker or a piezoelectric crystal, to either surface 12, 13 or 14. The point at which the energy is applied to the resonator determines the location of the nodal diameters 11 and (1 with a, being 45 in one direction from this point and d being 45 in the opposite direction from this point. In order to provide a maximum of energy transfer from the actuating means, such as a striker mounted on a spring, the striker should hit the outer peripheral edge 14 or should hit the surfaces .12 and 13 of the vibrating plate 11 near the periphery thereof. The closer the energy is applied to the center of the disc the less the amplitude and duration of the vibrations. If the energy is applied to the surface of the resonator at a point in actuating planes PI and P2 nodal diameters (l and (1 will be set up as shown in FIG. 4.

More specifically, when the disc is struck by a striker, this point on the disc preferably substantially outwardly from the center of the disc, then sets up nodal diameters at 45 extending radially from the center of the device, from the point at which the energy was imparted to the disc. If the vibrating plate 11 is struck near the center thereof, very little vibrating will be initiated since only a very small amount of the deflection of the vibrating plate 11 will be effected.

When the disc or plate 11 commences to vibrate as shown in FIG. 4, the nodal diameters (f and (1 describe a point of vibratory reference 1' and a reference axis at the inner section thereof. On the lower major surface 13 of the disc 11, this point as projected on the lowermajor surface is also the symmetrical center of the mounting pin 15 with the intersection of the disc 11. More specifically, the reference axis, in the embodiment of the invention, is the center about which the in 15 is mounted on disc 11.

FIG. 6 illustrates the pin 15 with a cross section taken through the plane at which the pin 15 joins the lower major surface 13 of the vibratory plate 11.

The motion imparted to the pin 15 by the sectors A and C will be equal and opposite to the motion imparted by the pin body sectors B and D. Consequently, equal and opposite motions will oppose each other and cancel out a short distance down pin 15 so as to retain the energy within the disc 11 and not allow this energy to be dissipated in the mounting on the disc.

' it has been discovered that the pin must be integral with the vibratory plate 11. Forcing the pin into a hole on the disc 11 will not produce satisfactory vibrations and much of the energy will be dissipated down through the mounting portion or threads 16 on the pin 15 so as to provide an unsatisfactory resonator. In short, the pin 15 must be secured to the disc 11 in such a manner so that the transmission of energy down pin 15 by sectors B and D must be equal (and opposite) to the energy transmitted up the pin 15 by the sectors A and C. This can only be accomplished by having a continuity of material between the pin 15 and the disc 11.

As shown in FIG. 1 and FIG. 3, the resonator 10 can be mounted by the mounting portion having screw-threads 16 on a circular mounting disc 20 having a threaded hole 21 in the center thereof. Threaded apertures or holes 22 are provided in the circular mounting base 20 to receive screws for mounting a housing 30. As will be explained later, this housing increases the ultrasonic output of the resonator over and above the use of the resonator 10 in open air.

The housing 30 includes a cylindrical section 31 having holes for receiving screws that will screw into the apertures 22 of the mounting base 20. At the upper end of the housing 30 is a fiat planar top 32 which is perpendicular to the cylindrical section 31. This top cover is secured to the cylindrical section 31 and has two diametrically opposed apertures 33 therein with another aperture 34 to provide an opening for the actuating mechanism that imparts energy to the disc. As shown in FIG. 3, the actuating mechanism includes a leaf spring 41 having a striker 42 near the outer end thereof. The leaf spring 41 is secured to the top cover 32 by a screw 43. The leaf spring 41 is of such a resiliency so that when the leaf spring is forced upwardly a predetermined distance lllC striker 42 will move into contact and impart one striking blow or tap to the resonant plate 11. to thereby initiate ultrasonic output, the material of resonator 11 should have a Q of at least 5,000 to 10,000. Some aluminum base metals as well as other metals have Q5 of at least this amount.

Although the side walls of the housing are spaceda predetermined distance from the resonator, there are, as shown in FIG. 1, two apertures 33 in the top cover 32. These apertures in the top cover 32 are located above sectors of vibration having the same phase since the hole 34 is 90 from hole 33. More specifically, as shown in FIGS. 4 and 1. these apertures are located above sectors 13 and D. Hence, practically all the ultrasonic signals which come out of the housing 30 are of the same phase. Consequently, cancellation due to opposite phase of the signals coming from the vibrator to the free air is minimized. Although the hole 34 is to accommodate the striker 42 in the upper top plate 32 is over a sector A which is of the opposite phase of sectors B and D, there will be very little cancellation therefrom due to its being covered substantialy by the spring 41 and the striker 42. Hence, the housing 30 enables the ultrasonic signals of the first phase described emanating from sectors A and C to be effectively stored back in the disc and without allowing them to effect any substantial cancellation of the second phase of the vibration emanating from the sectors B and D. Hence the energy from the ultrasonic signals of the phase emanating from sectors A and C is conserved and the output of the transmitter itself will be that of the energy having the second phase from the sectors 13 and D.

Although the housing 30 as described above increases the ultrasonic output of the generator, the resonator 10 can be utilized without such a reflective or resonant housing and still produce a substantial ultrasonic signal such as shown in FIG. 7, the lower portion of pin 15 is secured to a base having only a very small reflecting surface. In addition as shown in FIG. ii, energy can be transmitted to the virbratory disc 11 by means other than a mechanical striker such as by a piezoelectric crystal which has an AC. applied thereto by a source 52 through loads 51.

vibration therein. As will be understood, this striker 40 The frequency of source 52 is the same as the resonant could be mounted to impart a striking force to either frequency of the resonator 11. The crystal is secured to the side edges 14 or the lower major surface 13 of. the the surface of the vibrator 11 by some suitable conductftuexural disc or plate 11. When the resonator or transing adhesive. One of the leads 51 is electrically conmitter is assembled as shown in FIG. 3, the mounting base r nected to the upper side of crystal 50 and the other lead 20 is parallel to the lower major surface 13 of the flexural 51 is electrically connected to the mounting pin 15. mode plate 11 a distance S3 whereas the cylindrical section As stated previously, the most desirable frequency 31 of the housing 30 is spaced a distance S2 from the perange for ultrasonic signals is between 30 kilocyclcs and ripheral edges 14 of the vibrating plate. The top cover 32 kilocyclcs since in this frequency hand there is a miniof the housing 30' is parallel to and spaced :1 distance S1 r mum of interference due to extraneous electromagnetic from the upper major surface 12. These distances SI, waves and sonic waves. The following resonator was S2 and S3, for optimum performance of the embodiment constructed with systems Qs in free air of about 35,000 illustrated in the drawings, are distances which are odd made of 7075ST6 and 606lS-T6 aluminum discs. None quarter wave lengths of the frequency of vibration of the of these units lost any energy through the mounting porvibratory plate 11. More specifically these distances S1, tion (the threaded portion of the pin 15). No housing S2 and S3 are equal to was employed in the tests on these models. Other tests NA were made with housings and a substantial output in- +7 crease was realized.

In these tables f is frequency of output. in kiloeycles, where N is any whole integer (1,2, 3, 4 etc.) or zero. D is diameter of disc in inches, and r is thickness of disc In order for the resonator 11 to provide any usable in inches.

TABLE I Data for 606lS-T6 aluminum dis/ts Mounting l'nlhreadml Point D/t; D. t, f, kc. f-D lt, fD, pin post. po t length, inches inches kc.-iu. kerin. 1lia.,in. in.(linl5) (Pin 15) 2. 5s 1.125 are its 57 .300 .0113 4.0 1.02s 111.12 17s 44.3 .300 .219 4. 36 1.11s 37.0 ms 42. 1 .140 .195 4.3a 1.11s 14am lss 43.2 .360 .1114 4.50 1.1511 31:.74 m 42.2 .3011 .191 tan 1.500 25.5 ms 3x2 .360 .191 6.36 1.5110 10.8 2a.? .140 .305

Point D/t D, t, l, kc. LD /t, [1), Post dia., Post length,

inches inches kc.-in. ke.-in. in. in.

2.15 1. (115 37. (it) 12-4 59. 6 .1 10 250 3 1. 500 33.31 150 511.3 .141) 151) 4 1. .25 40.61 lti'i '11. 7 Ht) 1!)? 4.35 1.118 35. U 170.8 39.1 Ht) .197 6. 5 1. 615 l 28. f 110 250 3 1. 500 51 50. l 2. 03 1. 290 50. 6 3 1. 120 50. 3 2 1. r 02 N ,4 threaderl- 1. 5 1. 120 an gf' jjgff 24" non 1 75 7 inch. scr. threaded While particular embodiments of the invention have been shown and described, it is apparent that modifications and alterations may be made, to cover all such modifications as they fall within the true scope and spirit of the invention.

We claim as our invention:

1. A mechanical resonator comprising, a vibrating plate resonant in a fiexural mode with a plurality of nodal diameters, said plate having a pair of parallel planar major surfaces with peripheral edge surfaces extending perpendicular to the planes of said major surfaces, a cylindrical pin extending outwardly from one of said major surfaces and being concentric with said peripheral surfaces, said pin being integral with said plate, and means for applying energy to said plate to actuate said plate into resonant vibration in a fiexural mode with a plurality of nodal diameters.

2. A mechanical resonator comprising. a vibrating plate resonant in a flexural mode with a plurality of nodal diameters, said plate having a pair of parallel planar major surfaces with peripheral edges extending therebetween, a pin extending outwardly from the center of one of said major surfaces, said pin being integral with said plate, a reflecting surface spaced from one of said major surfaces :1 distance equal to where A equals the wave length of the ultrasonic waves produced by the said vibrating plate and N being any integer or zero, means for applying energy to said plate to actuate said plate into resonant vibration with a plurality of nodal diameters, said reflecting surface having an aperture therein with said aperture delining a projective surface on said one of said major surfaces with said projected surface being located within an area between two adjacent nodal diameters.

3. A mechanical resonator comprising, a vibrating plate rcsonantin a flexural mode with a plurality of nodal diameters, said plate having a pair of parallel planar major surfaces and an outer minor peripheral surface transverse to the plane of said major surfaces, a circular pin extending outwardly from one of said major surfaces and concentric therewith, said pin being integral with said circular plate, and means for applying energy to said plate near the outer periphery thereof to actuate said plate into resonant vibration in a flexural mode with -a plurality of nodal diameters.

4. A mechanical resonator comprising, a vibrating plate resonant in a tlexural mode with a plurality of nodal diameters. said plate having a major and a minor surfacewith said minor surface comprising the peripheral edges thereof, mounting means for said plate comprising a mounting pin, means connecting said pin to the center of said major surface to apply equal and opposite vibratory forces to said pin, and means for applying energy to said plate to actuate said plate into resonant vibration in a flexural mode with a plurality of nodal diameters.

5. A mechanical resonator comprising. a vibrating late resonant in a flexttral mode with a plurality of nodal diameters, said plate having a pair of parallel planar major surfaces with peripheral edge surfaces therebctwcen, a mounting pin, connecting means providing an undampcd connection between said pin and the center of one of said major surfaces, and means for applying energy to said plate to actuate said plate into resonant vibration in a fiexural mode with a plurality of nodal diameters.

FOREIGN PATENTS 11/22 Germany. 1/24 Germany.

OTHER REFERENCES Publication, Grits and Grinds," January 1951, vol. 42, Issue 1, pages 1012.

LOUIS J. CAPOZI, Primary Examiner.

ARNOLD RUEGG, LEO SMILOW, Examiners.

Claims (1)

1. A MECHANICAL RESONATOR COMPRISING, A VIBRATING PLATE RESONANT IN A FLEXURAL MODE WITH A PLURALITY OF NODAL DIAMETERS, SAID PLATE HAVING A PAIR OF PARALLEL PLANAR MAJOR SURFACES WITH PERIPHERAL EDGE SURFACES EXTENDING PERPENDICULAR TO THE PLANES OF SAID MAJOR SURFACES, A CYLINDRICAL PIN EXTENDING OUTWARDLY FROM ONE OF SAID MAJOR SURFACES AND BEING CONCENTRIC WITH SAID PERIPHERAL SURFACES, SAID PIN BEING INTEGRAL WITH SAID PLATE, AND MEANS FOR APPLYING ENERGY TO SAID PLATE TO ACTUATE SAID PLATE INTO RESONANT

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