US2405186A

US2405186A - Piezoelectric vibrator

Info

Publication number: US2405186A
Application number: US414132A
Authority: US
Inventors: Benioff Hugo
Original assignee: Submarine Signal Co
Current assignee: Submarine Signal Co
Priority date: 1941-10-08
Filing date: 1941-10-08
Publication date: 1946-08-06
Anticipated expiration: 1963-08-06

Description

Aug. 6, 1946. BENIOFF 2,405,186

PIEZOELEC'IRIG VIBRATOR Filed Oct. 8, 1941 INVENTOR Patented Aug. 6, 1946 FFEC PIEZOELECTBIC VIBRATOR Hugo Beniofl", La. Canada, Calif., assignor to Submarine Signal Company, Boston, Mass, a

corporation of Maine Application October s, 1941, Serial No. 414,132

11 Claims.

The present invention relates to a piezoelectric vibrator of the general type described and claimed in my copending applications Serial Nos. 386,583, filed April 3, 1941, and 344,363, filed July 8, 1940. closed a vibrating unit in which th piezoelectric crystals are secured to channels or recesses in the side walls of the vibrating unit, the unit itself forming a vibrating element in which the end acts as a acoustic radiating face. Where the unit is attached to a diaphragm, the diaphragm forms a part of the section of the unit. One of the limita tions encountered in the operation of devices employing piezoelectric crystals is that the crystals are limited in their power-handling capacity and while these factors are not detrimental when the devices are acting as receivers, however, they may seriously interfere with th utility of piezoelectric crystals in their use for transmitting increased acoustic power.

In the present invention a plurality of vibrators are used in which the individual vibrating units have a plurality of nodes and loops corresponding in efiect to a vibratory system of two or more wave lengths. In these units the crystals are mounted in recesses at th sides of th units and are cut and mounted such that the polarities of successive crystals provide expansion and contraction nodes in the corresponding crystals alternately longitudinally along the vibratory structure. This action is reciprocal inasmuch as the expansion and contraction along the vibratory structure generate potentials across the crystal electrodes which cooperate together in the electrical circuit. Various specific means may be employed to accomplish this result. In one case the crystals may be arranged so that the potentials generated by alternate crystals under contraction and expansion produce the same potential on all the exposed electrodes of the vibrator and similarly the same but opposite potential on all the unexposed or grounded electrodes of the vibrator, each group being opposite in potential to the other group at an instant. In another arrangement the crystals may have a parallel series connection, in which case successive crystals have their external electrodes alternately poled. In the latter case th impedance will be four times the impedance of the first case and will under certain conditions not be as preferable as the first-mentioned arrangement.

By the use of either of these arrangements the driving forces may be applied at many points along the vibrator, thus substantially reducing the power which each individual crystal needs to In each of these applications there is discarry. Due to the fact that the damping losses of the sound or mechanical wave in metal is very slight and that by proper choice of the mass elements in the system the amplitudes efiective upon the crystals may be accurately chosen, it i possible to design the longitudinal vibrator members in such a manner that all the crystals operate synchronously for transmission and reception without exceeding in any way the power which the crystal is capable of handling.

In the piezoelectric harmonic vibrator of the present design it has been possible by these expedients to obtain from the impressed electrical energy to th sound energy transmitted to the water an overall efficiency of approximately at frequencies well within the supersonic range. The so-called harmonic vibrator of the present invention may be nested together for projecting a beam of compressional wave energy and for directively receiving compressional wave energy in the Water or other medium. The harmonic vibrator may, however, also be used as a linear structure in which one or more long vibratory elements may be used independently or together. These long vibratory structures may have a length of twelve or more wav lengths and may be used under various circumstances for directive or partially directive transmission and reception.

Various further objects and advantages of the present invention will be understood from the description given in the specification below in connection with the illustrations in the drawing showing an embodiment of the invention in which Fig. 1 is a sectional view of the invention taken longitudinally through the vibrating elements on the line ll of Fig. 2; Fig. 2 is a sectional view taken on the line 22 of Fig. 1; Fig. 3 shows a modification of the form of oscillator used in Fig. 1 in which the vibrator units are double the length shown in Fig. 1; Fig. 4 shows a fragmentary section taken on the line i4 of Fig. 3; Fig. 5 shows an end view of one of th vibrating units; Fig. 6 shows a detail of an insulating support in perspective; Fig. 7 shows the same detail in elevation; Figs. 8 and 9 show circuit connections for the crystal elements of the vibrator; Fig. 10 shows one of the oscillating units in a longitudinal view partly in section; and Fig. 11 shows a horizontal section taken on the view of Fig. 10.

In the arrangement indicated in Figs. 1 and 2 there are provided a number of longitudinal vibrators I, l, I, etc., which are mounted on a diaphragm or plate 2 which is exposed to the compressional Wave or sound-propagating medium which may be air, water or other medium, the il- 3 lustration in Figs. 1 and 2 being more particularly adaptable for a liquid medium. As indicated more clearly in Fig. 2 the vibrators I, l, I, etc., may be nested together oVer substantially the whole surface of the plate 2, thus applying the vibrations of the longitudinal vibrators simultaneously over the Whole area of the plate. The plate 2 is provided with a thin peripheral flange 3 supporting the plate 2 to the casing, flange or wall 4. The wall or flange 4 may be joined in any suitable manner to the supporting casing 5 which, in turn, is supported by a plate 6 for mounting to any desired structure.

As indicated in Figs. 1 and 2 the longitudinal units I are positioned between shoulders I, I, 1, projecting slightly from the rear of the plate 2. These shoulders act to locate accurately the vibrating units and to space them slightly apart from each other. The Vibrating units are each cemented to the plate 2 and also bolted and screwed down by means of the screw 8 which is located in the longitudinal hole 9 and extends through the base of the vibrator into the plate 2. Each screw head is provided with a suitable flange so that the vibrator is securely held in place.

Referring to Fig. l, the crystal elements I0, [2 and I3 are of the piezoelectric type, preferably Rochelle-salt crystals or crystals having similar piezoelectric action. These crystals are so cut that compression on the upper and lower end surfaces produces electrical potentials across the crystal electrodes the inner ones l4 |5, |6 and I! of which are grounded to the metal of the longitudinal vibrating bar or element The outer electrodes |8,- I9, 20 and 2|, on the other hand, may all have the same potential when excited oppositely or they may be so faced that distance between successive crystal edges, as,

the potential of the group of the pair l8 and I9 is opposite to that of the

pair

20 and 2| as illustrated by the circuit arrangement of Figs. 8 and 9. The electrodes of the exposed surfaces of the crystals, that is, the outer electrodes, are connected by means of a conductive ribbon 22 which may be an extension of the electrodes to the bus wire 23. The ribbon 22 extends around the sides of the crystals through a channel 24 which is cut out of the metal of the vibrating unit. This channel 24 joins the verticalchannel 25 in which the bus wire 23 is positioned.

The bus wire 23 is supported away from the channel by an insulating bridge which is shown in Figs. 6 and 7 and in section in Fig. 10. This insulating bridge or support for the wire 23 comprises an insulating piece 26 made of a suitable product, such as that known by the trade name Bakelite, and which has a cross section in the form of a rather flat C, the bus wire 23 passing through the end elements of the C and supporting the wire away from the sides and base of the channel. The internal electrodes l4, Hi, It and I1 are grounded to the metal of the vibrating unit by leading the conducting ribbon which may form a part of the inner electrode over a channel 21 similar to the channel 24 and joining the end 28 of this conducting ribbon to a terminal connection 29 positioned in the vertical channel 30 corresponding to the channel 25 but on the opposite side of the vibrating unit, as indicated clearly in Fig. 10. Each external electrode is connected to a vertical bus wire 23 and all of these, in the construction shown in Fig. 1, are joined and electrically connected to the bus bar 30' which is supported at either end to insulating brackets or supports 3| and 32 attached to the inside of the casing.

for instance, B, B, and, further, that the distance between the top of the vibrating unit 0 and the top edge of the crystal unit C is equal to the distance between the edge A and the external water surface ofthe plate 2. The vibrating unit by these means is made of a type which might be called a true harmonic vibrator inasmuch as the external water surface and the internal boundary of the vibrating unit with the air medium have substantially the same amplitude as the maximum amplitude between the points 13 and B neglecting, of course, the slight difference that occurs because of energy radiation or radiation resistance which, at the high frequencies here considered, hardly affects in any way the uniformity of the vibrating element. By making larger recesses for the crystals and consequently increasing the metal masses in the sections between crystals as compared to the inass of metal where the crystals are placed, the

vibrating element becomes loaded and this load- .ing may be so proportioned that maximum permissible vibrational amplitude is obtained. In using units such as just described for projecting sound beams is subaqueous media, it is essential .to maintain the working of the crystal units well within their operating capacity, since heating of the crystal elements soon brings about a loss of efficiency and, in fact, considerable danger from possibility of destruction or burning up of the crystals. This is particularly true. with the use of Rochelle-salt crystals.

In the arrangements indicated in Figs. 1 and 2 the vibrating units are of the type which may be called a whole wave-length vibrator. In this case the lower set of units and the upper set of units are always 180 degree out of phase with each other, one set contracting while the other set isexpanding. In this arrangement all the acoustic radiation is produced by the external surface of the plate 2 in contact with the liquidpropagating medium. The other free ends of the vibrating unit are sealed off from the liquid medium by means of the casing 5 and the cover plate 33. Where longer units are to be used as, for instance, in the arrangement indicated in Figs. 3 and 4, it is desirable to support both ends of the vibrating unit in the same manner. In

' the arrangement indicated in Fig. 3 the plate 40 has its external surface in contact with the radiating medium. On the plate 40 is nested a group of vibrators in a fashion similar to that indicated in Figs. 1 and 2. The plate 40 is bounded by a supporting thin flange 4| which merges into a heavy peripheral supporting member 42 formed as a shell about the vibrating units and radiating member. This shell 42 extends backwards into the wall 43 which has formed with it an outwardly extending flange 44. Attached to the other end of the vibrating units 46, in which the piezoelectric crystals 45 are placed similarly as H in Fig. 1, is a plate 4! which has the same thickness and is of the same general construction as the plate 49. The plate 40 is provided with separating ribs 48 andsimilarly the plate 41 is provided with the same kind of separating ribs 49. The plate 41 is also supported by the flange 50 of the same construction and thickness as the flange 4i, and this flange 50 merges into a supporting peripheral member 5| which extends backwards into the shell 52 meeting the outwardly extending flange 44 in the section 53 at the end of the shell 52. The flanges 53 and 44 come in face-to-face contact with each other and are bolted together to support the vibrators at a point midway between their ends. A cover or casing 55 may be placed on ithe back end of the unit Where it is desired that the unit shall radiate only from the forward end as, for instance, the plate member 49. To provide electrical connections for the electrodes the plate member 4? i perforated at spaced intervals with holes 56 to which the vertically extending bus wires 5'! connecting the external electrodes are projected. These bus wires 51 are electrically connected to a cross bus wire 58 to which all of the vertically extending bus wires 51 are joined. The insulating supporting member 59 is of the same type as described in Figs. 6 and 7, and supports the electrical connections free from the metal of the vibrating units.

In the assembly of the system the units 46 are cemented to the radiating plate members 40 and boltedin place by means of screws 60 which may be properly adjusted through the hollow channel 6! in each unit. At the top of the vibrating unit there is provided near diagonal corners two threaded taps 62 and 63 and the screws 64 and 65 screwed into these holes through the plate 41. The unit should also be cemented in these joints to the plate 41 as well as in the joint to the plate 4!). In order to establish the units as balanced harmonic vibrators the distance from the outer surface of the back plate 41 to the edge of the nearest crystal is half the distance between successive crystals and is equal to the distance between the water surface and the end of the nearest crystal.

The vibrating unit, when operating as a harmonic vibrator, has the crystals positioned successively along the vibrator operating in opposite phases so that when one crysta1 is experiencing an expansion node, the crystal next in line F is experiencing a contracting node. In order that the crystals should cooperate in this arrangernent they must be correctly poled. This may be accomplished either by the arrangement indicated in Fig. 8 or that indicated in Fig. 9. i

In the arrangement of Fig. 8, which may be applied to the vibratory unit of Fig. 1, in which there are two pairs of crystals in line, the one pair of crystals 6! and 62 may have their external electrodes 53 and 64 energized from one terminal 66 of the oscillating source 55, the inner electrodes 61 and 68 being connected to ground which is the vibratory body itself. The inner electrodes 69 and. 10 of the other pair of crystals H and 12 are likewise grounded to the vibratory unit while the external electrodes 13 and 14 are connected to the other terminal 16 of the oscillator 65'. In efiect this may be called a series parallel connection with the crystals BI and. 62 being connected in parallel as wel1 also as the crystals H and l2,v the two pairs being connected in series with the oscillating source. In this arrangement in Fig. 8 it will be noted that when the potentials on. the electrodes 63' and 64 are positive that the potentials on the electrodes 13 and M are negative, and that this condition in the next half cycle of the oscillator 65 is reversed. This arrangement, however, will permit one group to operate under a contraction node while the next group is operating under an expansion node, and vice versa. Where eight crystals are used, two alternate pairs will have the external electrodes connected to one terminal of the oscillator and the two other pairs will have the external electrodes connected to the other terminal of the oscillator.

In the arrangement indicated in Fig. 9 the crystals are all excited in a similar fashion. In this case the oscillator'B5 has one terminal connected to the external electrodes of each crystal iii, 82, 83 and 34 while the internal electrodes are all grounded, the ground being the other terminal of the oscillator 85. Since in the arrangement of Fig. 9 the potentials will all be simultaneously impressed in the same phase on all the exter nal electrodes, the same result may be accomplished of operating the crystals with expansion and contracting nodes in successive crystals along the vibrator by orienting the crystals 8| and 82 opposite from that of 83 and 84. In other words, the crystal 8| will be so oriented as regards 83 that when the external electrodes of 81 and 83 are positive, the crystal 8| will be under an expansion node and 83 under a contraction node, or vice versa, and when the potentials change, the reverse effect will obtain. The orientation is simply accomplished by using as the external electrodes alternately opposite crystal faces of the crystal, or, in other words, simply reversing the crystal.

The arrangement of the circuit of Fig. 9 may at times be preferable to that of Fig. 8 since it will be evident from the circuit that the arrangement of Fig. 8 has four times the impedance of that of Fig. 9.

Having now described my invention, I claim:

1. A piezoelectric oscillator for the production and reception of compressional Waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate. said longitudinal vibrating elements each having mounted in recesses in the sides thereof a plurality of piezoelectric crystals. said elements together with the crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase and all crystals nearest the plate, for piston operation of the plate, are vibrating in the same instantaneous phase. and electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration.

2. A piezoelectric oscillator for the production and reception of compressional waves comprising a longitudinal vibrating element having mounted in the sides thereof a plurality of piezoelectric crystals, said element together with said crystals forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, and electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration.

3. A piezoelectric oscillator for the production and reception of compressional waves comprising a radiating plate having mounted in rows thereon a. plurality of longitudinal vibrating elements,

said plate having on the inner side thereof a plurality of small projecting ribs spacing said rows of vibrators from each other, said longitudinal vibrating elements having mounted in recesses in the sides thereof a plurality of piezoelectric crystals, said elements together with said crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, and electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to th crystals according to its instantaneous phase of vibration. g

4. A piezoelectric oscillator for the production and reception of compressional waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate, said longitudinal vibrating elements each having mounted in recesses in the sides thereof a plurality of piezoelectric crystals, said elements together with the crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, and electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration, the spacing between the radiating surface of said radiating plate and the end of the nearest crystal being equal to one-half the distance along the longitudinal vibrating element between successive crystals.

5. A piezoelectric oscillator for the production and reception of compressional Waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate, said Ion gitudinal vibrating elements each having mounted in recesses in the sides thereof a plurality of piezoelectric crystals, said elements together with the crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, and electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration, the spacing between the radiating surface of said radiating plate and the end of the nearest crystal being equal to one half the distance along the longitudinal vibrating element between successive crystals and the distance between the end of any vibrating element and the nearest crystal is also equal to one-half the distance between successive crystals along the longitudinal vibrating element.-

6. A piezoelectric oscillator for the production and reception of compressional waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate, said longitudinal vibrating elements each having mounted in recesses in the sides thereof a plurality of piezoelectric, crystals, said elements together with the crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration, the external electrodes having conductive elements extending in channels to the sides of said longitudinal vibrating elements and conductive bus elements positioned in channels at the' along the'vibrator at any instant of operation are vibrating in opposite phase, electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals-according to its instantaneous phase of vibration, and a non-radiating plate element to which the other ends of said longitudinal vibrating elements are attached, said plate element being of the same thickness as said radiating plate and means for supporting the same in a plane mid way between the ends of the vibrator.

8. Apiezoelectric oscillator for. the production and reception of compressional waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate, said longitudinal vibrating elements each having mounted in recesses in the sidesthereof a plurality of piezoelectriccrystals, said elements together with the crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration, and a non-radiating plate element to which the other ends of said longitudinal vibrating elements are attached, said plate element being of the same thickness as said radiating plate and means for supporting said plate.

9. A piezoelectric oscillator for the production and reception of compressional waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate, said longitudinal vibrating elements each having mounted in recesses in the sides thereof a plurality of piezoelectric crystals, said elements together with the crystals and the radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according t its instantaneous phase of vibration, a non-radiating plate element to which the other ends of said longitudinal vibrating elements are attached, said plate element being of the same thickness as said radiating plate, means for supporting said plate, and a cover spaced away from and. covering said plate element and separating said plate element from the compressional wave propagating medium.

10. A piezoelectric oscillator for the production and reception of compressional waves comprising a radiating plate having mounted thereon a plurality of longitudinal vibrating elements substantially covering said radiating plate, said 1ongitudinal vibrating elements having mounted in recesses formed in two opposite sides only of said vibrator piezoelectric crystals, said .elements together with said crystals and said radiating plate forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, electrodes attached to said piezoelectric crystals, one group of said electrodes being in face-to-face contact with said longitudinal vibrating element and making electrical contact therewith, the other external electrodes of said crystals having means connecting the same to a bus conductor, said bus conductor being mounted in a channel in the side of said longitudinal vibrating element adjacent the side in which said crystals are mounted.

11. A piezoelectric oscillator for the production and reception of compressional waves comprising a longitudinal vibrating element having a radiat- 10 ing face at one end, said longitudinal vibrating element having uniformly spaced recesses formed in the sides thereof, piezoelectric crystals mounted in said recesses and having electrodes on opposite faces thereof, one of which substantially abuts the inner longitudinal wall of said recess and the other being external thereto, said longitudinal vibrating element together with the crystals forming a harmonic vibrator in which successive crystals along the vibrator at any instant of operation are vibrating in opposite phase, and electrodes attached to said piezoelectric crystals providing the desired instantaneous polarity to the crystals according to its instantaneous phase of vibration.

HUGO BENIOFF.