US2456294A - Underwater sound transmitter or receiver - Google Patents

Description

Dec. 14, 1948.. F. MASSA UNDERWATER SOUND TRANSMITTER 0R RECEIVER Filed May 15, 1946 2 shgetsesheet 1 INVENTOR- FRANK ASSA By Wu A ORN F. MASSA UNDERWATER SOUND TRANSMITTER 0R RECEIVER 2 Sheets$heet 2 Filed May 15, 1946 ATTO R INVENTbR. FRANK MASSA Patented Dec. 14, 1948 I UNDERWATER SOUND TRANSMITTER OR RECEIVER Frank Massa, ClevelandHelghts, Ohio, assignor to The Brush Development Company,- Cleveland, Ohio, a corporation of Ohio Application May '15, ms, Serial No. 669,761

. 1 e My invention pertains to transducers of transelectric crystals wherein the crystal assemblies are mounted in the transducer with particular orientation, I This application is a continuation-in-part of my previous application Serial No. 436.304, now abandoned, and is related to my application Serial No. 519,069, which is a division of Serial No.

436,304, and which claims-the crystal unit per se.-

An object of my invention is to provide a-piezoelectric crystal assembly capable of being used with greater efliciency. l

Another object of my invention is to provide a piezoelectric crystal assembly which will not transmit certain undesired low frequency sound pressures.

A further object of my invention is to Prov d a fluid-filled transducer device utilizing my piezoelectric crystal assembly, and in which certain undesirable low frequency sound pressures are substantially prevented -from"be ing hydrostatically transmitted.

Still another object of my invention is'to provide a transducer device which is sensitive to cer tain desirable low frequency electric fields and/or pressure variations.

It is another object of my invention to provide a speaker device which has sharp directional characteristics.

It isanother object of my invention to provide an underwater speaker and/or microphone which will withstand high pressures, and wherein lowfrequency signals will .not cancel out within the speaker or microphone housing. Y

Aiurther object of my invention is'to so mount one or more of the crystal assemblies disclosed and claimed in Serial No. 519,069 that the maximum efficiency of transmission or reception is obtained. I

And still another object ofmy invention is'to provide a piezoelectric crystal transducer wherein each individual crystal is subjected to substantially uniform static pressure on all of itsfaces and to.alternatin g pressures on some only of its faces.

Other objects and a fuller understanding of my invention will be had by referring to the following description and claims readin conjunction with the drawing wherein Figure 1 is a sectional view taken along line i-l of Figure 2 showing a-transdllcer utilizing a number of the crystal units of Figure 3.

Figure 2 is a sectional view taken along line 2-2 of Figure 1.

Figure 3 is an isometric view of a, crystal unit constructed in accordance with the teachings of my application Serial No. 519,069.

Figures 4 and 5 are isometric views or two crystal elements, and

mitting and/or receiving typesutilizing piezo-' 2 Claims. (01. 177-386) Figures 6 and 7 are-sectional views taken along lines G-6 and 1-1 of Figures '7 and'6, respectively, of a transducer which utilizes the crystals shown in'Figures 4 and 5.

In the use of piezoelectric crystals for underwater microphones and speakers it is desirable to fill the housing surrounding the crystal with oil, such as castor oil, in order to seal the housing against ingress of humidity and in order to couple the crystals through a vibration transmitting portion of the housing to the water outside.

Crystals which may be used arequartz, Rochelle salt, primary ammonium phosphate, primary potassium phosphate and the like. In fact,

any crystal out which has more than one face which vibrates may be treated-in accordance with my invention.

Rochelle salt andprimary ammonium and potassium phosphate crystals in the expander plate form'have two pairs of parallel faces which vibrate, and, inasmuch as this type of crystal is used extensively in underwater transducers the detailed description which follows will refer thereto. It is to be remembered, however, that the principle involved is applicable to all crystalline materials and cuts therefrom which exhibit more than one face which vibrates in accordance with a properly applied alternating voltage, and is applicable to all crystalline materials and cuts therefrom which produce an alternating voltage upon the proper application of an alternating pressure.

change in fluid pressure; and in a microphone if the oil surrounds the crystal completely, any pressure change on one pair of crystal faces will generate a voltage; and the same pressure change on the other pair of faces will generate, a cancelling voltage thus greatly reducing sensitivity of the device. A single crystal or multiple separated crystals completely surrounded by oil may be inoperative particularly in the region of frequencies in which the wave length is large compared to the size of the crystal,

To eliminate or reduce the transfer of undesired alternatingpressures to certain of the piezoelectrically active faces of the crystal, I have found that it is desirable that there exist adjacent 3 to these faces, a material or a structure that is relatively compressible compared to the crystal material. This substantially eliminates alternating pressures on the certain crystal sides but applies the static pressure-thereby maintaining the sensitivity of the device at a higher level than would be obtained if a differential static pressure were present on only two of the faces of the crystal.

The use of oil inside the transducer housing esaeaaaos low frequencies and 1 characteristics.

tablishes under high water pressures an internal pressure on the housing which enables the transducer to withstand higher water pressures. In other words, the housing being fluid fllled is in effect substantially solid and can withstand high external pressures.

With reference to Figure 1 my invention comprises a plurality of crystal units It, positioned in a housing of a speaker or microphone adapted to operate underwater. Each crystal unit is made of an expander slab I of piezoelectrically active material with an electrode l2 at one end of the slab, an electrode It at the other end of the slab, and two pieces of sheet cork ll, or other such material cementedv on or held closelyadlacentto'two of the side faces whichvibrate piezoelectrically.

A very-suitable material has.been found to be a molded composition of cork and rubberkn'own as corprene. However, any material having a mechanical impedance which is low compared to the mechanical impedance of the'crystal and the liquidand which will not absorb substantial quantities'of the oil will operate successfully. Sponge rubber will also servethe purpose.. g v fire-slab ofcry tal ii and the' electrodes1i2 and l3'are adapted to .be connected'into an electric circuit in the well-known manner,.andare operable when subjeetedto an alternatingcurrent to establish an. alternating mechanical pressure.

The-units are also operablewhen subjected to an alternating mechanical pressure to establish an alternating electric potential. Thus the units may be utilized as motors such as in a loud-- speaker, or as generators such as in a microphone. My invention is applicable to both motor and generator devices but because it has found wideparallel faces does not interfere with the signal. In a substantially incompressible fluid such as oil,

however, the vibration of the other two faces may cause considerable distortion in the directional pattern of the transmitted signal, and may cause a reduction in output. It is the nature of the crystals that at any instant, upon being subjected to an alternating electric signal, one pair of parallel faces will tend to establish an increase in pressure to the surrounding fluid, while the other pair of parallel faces will tend to establish a decrease in pressure to the surrounding fluid. When the surrounding fluid is oil which readily transmits" the slightest variation in pressure, the oil coupling of all four vibrating faces to the external transmitting fluid (such as water) causes loss of site the first polarity- When the microphone I obviate these undesirable characteristics by fastening decoupling means to one pair of parallel vibrating faces to decouple substantially those faces from the oil inthe speaker, thereby substantially preventing the transmission of a signal from those faces, and I orient each crystal within the housing so that the other pair of parallel vibrating faces is parallel to the base upon which the crystal is mounted. Thus the plane of the decoupling means is substantially perpendicular to the base of the transducer, and one of the vibrating faces which is not covered by a decoupling member is cemented to the housing base and the other uncovered vibrating'face faces the vibration transmitting portion of the housing whereby directional vibrational waves are beamed out of the housing.

when a crystal microphone device of the oil-- filled type is submerged in water and subjected. to alternating pressures due to audio orsuperaudio waves. the piezoelectric'crystal has the property. nf-being; vibrated'in two directions, and

. has two faces perpendicular-to each of the two directions.- Accordingly, as in the speaker, there arefour vibrating faces. In the usual air-filled microphone the relative movement between any two vibrating parallel faces is utilized to establish "an alternating potential, and the vibration of the 1 other two parallel faces doesnot-interfere with the alternating potential; Whenwthe microphone is filled, withf'a substantially incompressiblefluid pressure wave hits all 1 four crystalfaces the vibration of twofaces gensuch as oil, however, and a crates a voltage, and the vibration of the-other two faces generates a. cancelling volt'agei This is due to'theaoiltransmitting substantially equal pressures to all four vibrating faces and'materi ally reduces the sensitivity of; the microphone. It is the nature of these piezoelectric crystals that at any instant upon-being subjected to a pressure on one pair-of parallel faces the crystal will tend to establish a potential of a first polarity and when that same instantaneous pressure is applied to the other pair of parallel faces the crystal will tend to establish a potential of a polarity oppotwo threaded openings 2| and 22. The base portion 20 maybe circular-and has an upstanding peripheral edge' portion 23, andan annular shoul- I der 24 near its center. Positioned against the base 20 and against-the shoulder 24- is a-contact ring 25, and connected to the contact ring 25 by means of rivets 261s an inside contact strip2l which has a plurality of contact fingers 28, onefor each crystal unit. Connected to the upstanding edge 23 of the base portion 20 by means of rivets 29 is a somewhat similar outside contact strip 30 having a plurality of contact fingers 3i, one for each crystal unit crystal units iii are positioned with one ofthe piezoelectric vibrating faces against the base 20, and with electrode, is against an outside contact of desired directional patternin the I 0. The plurality of flnger ii, and with electrode of moisture around the cable 35. ,The'wrires 35 and 31 are connected at one end to an amplifier. and wire 88 is connected at its other end to-inner contact strip 21 by means of one of therivets 20. The wire 31 is connected at its other end to the base 20 of the microphone by means of a screw 39. The electrical path may, therefore, be traced from wire 31 through the base 20 to the upstanding edge 23, to rivets 29, to contactor strip 30,

and through contact fingers 8|. to the electrode it of each crystal unit i|l.-- The contact ring 25 as shown is made of an insulating material, or it Y may be made of metal andinsulated from the base 20 to prevent a shunt circuit.

The waterproof connection means 38 is comprised of a cable clamp bushing 40, a washer 4|, and a cable clamp nut 42. The nut 42 threads into the threaded opening 22 and presses the washer 4| against the bushing 40 to effect the waterproof seal. A nut 43 may be provided on a threaded extension of the base 20 for attaching the microphone to a support, and a layer of cork- 34 or other vibration absorbing material may be applied to the bottom of the microphone (or speaker) to isolate it from vibrations in the support.

After the microphone has been assembled a rubber cover 44 having a downwardly extending edge portion 45 is placed over the top of the crystal units In with the edge portion 45 outside of the upwardly extending edge portion 23 .of the metal base 20. A clamping ring 46 is placed around the outside of the edge portion 45 of the cover 44 and is pulled tightand-clamped by means of a clamp".

After the 'cover 44 has-been connected to the upstanding edge 23 to prevent the ingress of moisture, the air within the speaker is evacuated and the air is replaced by castor oil admitted through the threaded opening 2|. This is preferably done in a position with the rubber cover 44 downward, and by using a vacuum pump. When all of the air is out and oil has replaced it, a threaded plug 48 is used to close the opening 2 l.

Upon an alternating pressure signal of One potential being applied to two parallel and piezoelectrically active faces of a crystal in a microphone, a voltage is generated. When the same pressure is applied to the other two parallel and piezoelectrically active faces -a voitag'eis generated.- If these pressures are applied at the same time the two voltages tend to cancel each other thereby reducing the signal output. Except for the presence of the decoupling means l4 on onepair of moving faces the fluid within the microphone would apply substantially equal pressures on all four piezoelectrically active faces at substantially the same instant. "This is notdesirable. Ac-

cordingly, I provide decoupling means such as cork, corprene, or sponge rubber l4 to prevent the pressures (both positive and negative) from being applied to more than one pair of piezoelectrically active faces. The piezoelectrically active faces of a crystal plate are those faces which are perpendicular to a direction of direct crystalline expansion and contrs ction when the crystal plate is properly subjected to an alternating electric field.

Figure 3 is an enlarged view of one of the exj pander crystals made according to my invention, and shows the decoupier l4 connected to two of the four faces which vibrate piezoelectrically when the crystal is subjected to alternating mechanical pressures, or when the crystal is subjected to alternating potentials. The electrode i3 is' shown connected to one of the uncovered faces and'another electrode l2 (not shown in Figure 3) is connected to theuncovered face which is parallel to the face upon which electrode 13 is placed.

For operation as a microphone, the alternatin pressure is applied to two parallel faces which are piezoelectrically' active, that is to two faces which cause the generation of an electromotive force upon being moved toward or away from each other, and the voltage appears between the electrodes l 2, l3. The other two parallel faces which are plezo'electrically active are decoupled from the surrounding medium by a rubber impregnated cork material l4. 5 W;

For operation asa speakerythe alternatin voltage is applied to the two electrodes l2, l3

thereby causing the two pairs of piezoelectrically active faces to move. One pair of piezoelectrically active faces is covered with the rubber impre nated cork l4 and is therefore uncoupled from the surrounding medium. The other pair of piezoelectrically active faces is notcoveredwith the rubber impregnated cork l4, and accordingly is closely coupled to the surrounding medium. When an alternating voltage. is applied to the electrodes i2, i3, the uncovered faces transmit an alternating signal'pressure to the surrounding fluid, and the covering on the other faces serves to prevent the vibrations from sending a signal into the surrounding fluid. 1

- The lmes l-I, 2-2, and 3-3 in Figure 3 illustrate the direction of the crystallographic axes of the unit. If the line l-i is the :c (or A) axis, then line 2-2 may be' the y (or B) axis and line 3-3 may be the 2 (or C) axis. If the line i--| is the y axis, then lines 2-2 and 3-3 become the other two axes and the piezoelectrically active faces are at 45 degrees with respect to them. Ii line l-l is the z axis, then lines 2--2 and 3- -3 represent the other two axes of the crystal. In any expander cut of crystal of Rochelle salt or primary ammonium phosphate types the direc tions of piezoelectric expansion are at 45 degrees with respect to two of the axes. The arrow 4 indicates one direction of expansion and contrac tion of the crystal, and arrow 5 indicates the other direction of expansion and contraction. It is desired that the amplitude of movement of the crystal faces in direction 4 be as small as possible, and that the amplitude of movement in direction 5 be as large as possible.

If it is desired that the pattern of the trans- ,du-cer be directional and in order that a good sigcompared to the diameter thereof. For example,

in Figure 1, if the device is four inches in diame- .ter it will be directional at about 60 km. in water.

if one of the directions of expansion and contraction extends out through the vibration transmitting portion of the housing.

It is not essential in order to practice my invention to aflix the sheet of decoupling material directly to certain faces of a crystal as the same result may be achieved by the mean shown in Figures 6 and 7, which is described as a speaker but which will also operate as a microphone.

The loudspeaker comprises a base portion 85 having a raised outside edge portion 88. Positioned between the edges 88, and resting against the base 85, there is a circular spider 82 which has a plurality of openings into which a plurality of electroded crystals fit. The crystals 88 are arranged in a ring with one of the two unelectroded narrow faces 88 or 80 in engagement with the base 85 and the other unelectroded narrow face extending slightly above the top of the spider 82. The spider 82 is made of some material such as a molded mixture of rubber and cork, or other such material which will serve to decouple the broad faces of the crystal units 88 from the oil in the speaker. A cover 8i is connected at its downwardly extending outside edges to the raised edge portion 88 of the base by means of a clamping ring 88 and a clamp 84 to establish a seal. A threaded opening is provided in the base 85 through which all of the air inv the speaker may be withdrawn and replaced by a fluid such as oil which will transmit fluid pressure to the crystals 88 but which will not affect the crystalline substance. The threaded plug 85 seals the oil within the speaker. A cable 88 comprised of two wires 81 and 88 is brought into the speaker through sealing means 88, and wire 88 is electrically connected to the base 85 of the speaker by means of the screw I00. The wire 81 is connected to a spring contactor strip IIII. The contactor strip fits in a slit I02 in the top surface of the spider 82 and electrically engages each of the electrodes I08 on the inner ends of all of the crystals 88. The outer crystal electrodes I84 each engage one of a plurality of U-shaped spring' clips I05. Each clip I05 has two legs and one of the legs is in engagement with a crystal electrode I04 and the other leg is in engagement with the raised edge portion of the base 85. Accordingly, an electric circuit is established from wire 81 to the spring contactor strip IN, to the inner end of each of the crystals 88 through the crystals 88 to each of the U-shaped clips I05, thence to the speaker edge 85 and base 85, and then to the wire 88. Upon an alternating potential being applied across the crystals 88, the crystals will expand and contract in a direction substantially normal to the base 85, and in a direction substantially normal to the planes of the large crystal faces. The expansion in the latter direction will not materially affect the pressure in the surrounding fluid as the two large crystal faces are in engagement with the spider and accordingly are decoupled from the fluid. The expansion and contraction in the direction normal to the base 85 will cause an alternating pressure to -be established in the oil unit within the speaker, and the cover 8i will transmit the pressures to the water outside the speaker. The waterproof cable connection means 88 may be the'same type as used in Figure 1, and cork insulating means 34 may be positioned on the bottom of the speaker if it is so desired to isolate any transmission through the base of the speaker housing.

From my description, it will be seen that in a fluid-filled transducer the operating characteristics may be improved by providing certain of the crystal faces with an adjacent compressible material, and by orienting the crystal to obtain the maximum beneficial results. If the compressible material contains trapped air such as in sponge rubber, cork, or similar material, then the sensitivity of the device at low frequencies may be substantially the sensitivity of an air-filled unit. The structure may be oil filled but the decoupling -means prevents sound pressures from being if the hydrostatic pressure were only present on one or two of the piezoelectrically active faces.

Although I have described my invention with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be made without departing from the spirit and scope of the invention as hereinafter claimed.

I claim as my invention:

1. In a piezoelectric transducer device adapted to operate underwater, a water-tight enclosure having a vibration transmitting portion, a liquid medium within said housing having a mechanical impedance comparable to the mechanical impedance of the water in which said piezoelectric device is adapted to operate, a compressible body having a slot therein mounted within said watertight enclosure and in contact with said liquid medium, said body having lower mechanical impedance than said liquid medium, and piezoelectric expander crystal means having at least two faces which vibrate with piezoelectric action mounted in the slot with one but not all of said faces directly against said compressible means to decouple said face from the surrounding liquid medium, said other face which vibrates being substantially coupled to said liquid medium to effect a differential alternating pressure of the liquid medium on the said two faces when the crystal unit operates piezoelectrieally.

2. A piezoelectric transducer device as set forth in claim 1, further characterized by said compressible body having a plurality of radially extending slots and by a plurality of expander crystal means, one of said crystal means being mounted in each of said slots.

FRANK MASSA.

REFERENCES CITED I The following'references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,384,465 Harrison Sept. 11, 1945 2,406,767 Hayes Sept. 3, 1946

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