Composite electro-acoustic transducer configuration

Aug. 29, 1961 d. _R church etal

COMPOSITE ELECTRO-ACOUSTIC TRANSDUCER

Filed April 29, 195S

2,998,535

CONFIGURATION

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Patented Aug. 29, 1961

Oiiited States Patent Office

993 S35 Τ'®¹™ imnsducer ^c‘*^M wf, ?’.^Ν·^Υ·&gt; ^a corporation of New York Fded Apr. 29,1958, Ser. No. 731,768

Claims. (Cl. 310—8.3) “vention relates to electro-acoustic transducers mel^^0ΓΊΈ^η^^Γ1Υ ‘ΐ.^{transducers us}®^d with isolation _f ' ,, . Pⁿmary object of the present invention is to generally improve such transducers.

_ Jⁿ “e design of electro-acoustic transducers of the maefrea_liemlv^Ve’ ^{piezoelectric and} ferroceramic types, it fs £ nt ‘° ⁱ⁸⁰¹T ^a ^”8 framer el“ ment from the load or, m the reciprocal case to isolate b’^ λρ ^m minimum of attenuation energy with a strac^urSy“«“'ta”?'™ “°” “ =€Ξ=“5£== S£®S=:;S=-: B®· bon on soiled parts lowered into the t£k ±Γ^δ ducer Assembly,” whereim'a Sing cySe^of' fef”⁵' ceramic material is used to sense tJ nr« “ of ferroS,^A ee™.“Li 2” “ *· differential is set un an excessive temperature iisiPsBs simple manner. Our invention eliminates the difference in thermal expansion between the transducer and a coupling or isolation section, and provides a high degree of thermal isolation, which is valuable when the load is ?^{Ot an&lt;}? ^{above the safe} °Pe^ra'mg temperature of the heat sensitive transducer material itself. For this E^S^^We P^rov!^de a composite transducer assembly in which the vibrating element itself, and the coupling or isolation slug, are of one and the same material.

। To accomplish the foregoing general objects, and other more specific objects which will hereinafter appear, our ton _Pi°^{n re}_t^SldeS u^{he combine}d transducer and isolation elements, and their relation one to another as are SficaSn”⁰^ ^{particalariy describ}ed in the following ing whfch: ^{specificatl0n 1S} accompanied by a draw. ^^IG' ^{1 18 a} P^ersI’^ective view, drawn to reduced scale »^ilh ™ bodying features of our invention;

FIG. 3 is a perspective view showing a modified form of our invention in which the entire assembly “Z ^f p_r%^ngl^{e J}?^{tegraI bod}Y ^of transducer material;

?’ u S°^{WS a further} modification of the invention mounting flange;^ranSdUCer “ ^{With an integral}FIG. 5 is a perspective view showing the same feature .» . ^Sh0™⁸ °^l “» ”'«·“« ·ΡΡ1Μ nitoJ?’ ^{8 1S a scbem}atic view showing the invention anphed .o a magnetostrictive transducer assembly

Referring to the drawing FIG 1 X ,. nlanm^⁶¹” ^{pUrposes of} comparison with^amTexplanation of the invention Τη εγω i block of transducer material 12, to the ends of wl/ n° ^lddeposited fired silvered electrodes 14 and 16 wlih ^3Γ6

24. The transducer material 12 is suitably polarized ^the “^factore of the tansducer and C ^al‘“^g voltage isZS he eUed i ipSfe ita*,¹?’ ?^Ψ““¹ '’““X Preferably’core/ SI b 1“ ™&gt; ftwenoy _{of lhe} ,„_n!.

“^ech,“·^{1 m}»“ “ οώώ

For purposes of example, and for future reference and comparison, we may mention that a block of coin arium titanate material, measuring about 2 inches htoh

33098,688 solid block of ferroceramic material has the pair of electrodes 46 and 48. Electrode 46 is silvered in conventional fashion. Electrode 48 is a thin band silvered around the four sides of the block, preferably midway between the ends. The electrodes are applied by means of conventional high temperature silver deposition techniques. Thereafter the block is polarized by the application of a high direct current voltage between the electrodes 46 and 48, which aligns the molecules and makes only the lower half of the block piezoelectric. In order to prevent polarization of the upper half, the top face may be held in contact with a metal plate which is held at the same potential as the center band during the polarization period. Thereafter, in use, the application of an alternating voltage to terminals 46 and 48 will provide performance identical to that achieved with the assembly shown in FIG. 2. However, the bond between blocks 30 and 32 required in FIG. 2 has been entirely eliminated, at a saving in labor, and with a great increase in reliability.

Referring now to FIG. 4, the transducer assembly there shown is like that shown in FIG. 3 except for the provision of a peripheral ledge or collar 60.. This is made of transducer material, barium titanate in the specific case here shown, and is preferably cast integrally with the transducer portion 62 and isolation portion 64 of the assembly. In other words, the transducer 62, isolation slug 64, and collar 60, are all molded or cast integrally as a single body of transducer material. An electrode 66 is provided at one end of transducer 62, and a peripheral electrode 68 is provided at the other end. Conductors 70 and 72 are connected to the electrodes. The assembly is part polarized, and part short-circuited to prevent polarization, all as described above in connection with FIG. 3.

The main difference is in the mounting of the assembly, as may be explained in connection with FIG. 6. We there show a cleaning apparatus comprising a tank 74 in a supporting housing 76. The bottom of the tank is vibrated by means of a transducer 78, the upper end of which is cemented or otherwise secured to the bottom of the tank. Heretofore the weight of the transducer was supported by the bond to the tank, that is, the transducer was suspended from the tank. The increasing use of barium titanate, and the ever increasing power 45 and size the transducer blocks used, creates a problem in that the bond between the transducer and the tank must withstand both the force of vibration and the added gravitational load of the large transducer blocks.

In the apparatus shown in FIG. 6, however, the weight

FIG. 1, although the latter is drawn to half the scale of the former. Accordingly, the transducer material .30, 32 is dimensioned for vibration at the same desired frequency. It comprises both a transducer, which is the lower portion 30, and an isolation means or slug, which is the upper portion 32. There are means 34, 36 to electrically energize the transducer portion 30, while the isolation portion 32 is not energized. Preferably it is only the energized portion 30 which is polarized whereas the isolation portion 32 is left unpolarized. In the specific case here shown the means to electrically energize the part 30 consists of a metal electrode 34 at the lower end, and another metal electrode 36 at the upper end. The electrical conductors 38 and 40 are connected to the electrodes. The parts 30 and 32 are separate blocks of ferroceramic material which are secured together, as by means of a cement bond, preferably an epoxy cement, at their interface. The parts 30 and 32 preferably are made of identical material, so that they have the same coefficient of expansion, and the same resonance frequency.

For purposes of illustration, the overall vertical height of the two blocks 30 and 32 may be maintained at two inches, in which case the natural fundamental resonant frequency of the lower block 30 in free space would be twice that of the two inch block shown in FIG. 1, or 80,000 cycles per second (c.p.s). When solidly joined to block 32, however, a composite tranducer is formed wherein the overall length resonance of the structure is reduced to 40,000 c.p.s. The surface with the arrow will oscillate, and forms part of an isolation slug which can be affixed to a load by more positive means than heretofore found possible. Section 32 is inert and does not vibrate of its own accord. Therefore, it need not be polarized to provide a piezoelectric effect, and thus may be handled as an ordinary ceramic at temperatures well above those allowable to affix with high temperature cement the surface 14 (FIG. 1) to a load. Non-polarization has the further advantage of avoiding possible electric shock by reverse piezo effect. Furthermore, and most important, interface 36 in FIG. 2 is not subjected to stress set up by differential expansion, and remains reliable despite wide sudden temperature change. The use of the inert block 32 also provides a considerable measure of heat isolation which is of great value in cases where very hot liquids are in near proximity to the surface to be attached, in this case the top end. Thus a low temperature epoxy cement may be used at interface 36.

A modified form of the invention is shown in FIG. 3.

™ tas the advantage that the lower or tranter for- „ W J'S tion 42, and the upper or isolation portion 44, are parts of a single integral block of transducer material. Thus, for a frequency of 40,000 c.p.s. the block shown in FIG.

may be about two inches high, and may be identical with that shown in FIG. 1, except that the upper electrode is entirely different.

In FIG. 3 the lower electrode is a coating of metal at 46. The upper electrode 48 is a peripheral strip of metal around the body between its ends. In preferred form it has a coating of metal located about halfway between the ends. A conductor 50 is connected to a tab 52 at one end of the electrode 46, while another conductor 54 is connected to the band 48.

It may be mentioned that in manufacture of the transducer assembly the electrodes 46 and 48 are used when polarizing the transducer portion 42. At this time the assembly may be inserted in a holder which provides a third electrode at the end 56 of the isolation portion 44. A short circuiting connection is preferably provided between the third electrode at 56 and the electrode 48 during the polarizing step. This short circuit effectively prevents polarization of the isolation portion 44, with advantages pointed out above.

In. this form of the invention, the interface between two similar blocks is completely eliminated. A single ease the assembly is cylindrical, and may be quite small, on the bottom 82 of the apparatus. The support 80 receives the collar 84, and the dimensioning of the parts is such that the support 80 takes the dead weight load.

The transducer may be and preferably is a half-wave long, with the collar 84 located midway between the ends, and therefore at a nodal point which is stationary. The ends are free for vibration. With a block of different length the collar should nevertheless be located at a nodal point.

With the arrangement shown in FIG. 6 the presence of high temperature liquid in the tank does no harm. The possibility of destroying polarization is of no consequence because the upper half of the transducer block is unpolarized, while the lower half is insulated from 65 the high temperature by the upper half. The high temperature will not open the cement bond to the block because a high temperature epoxy cement may be used, and that in turn is possible because there is no concern over loss of polarization when using the high tempera70 ture cement. A similar remark would apply to the use of a soldered connection to a fired metal coating, which also is possible.

FIG. 5 shows a different form of transducer assembly which may be used for a very different purpose. In this g 2,098,53«

Say a fraction of an inch in diameter and length It may be used as a sensor element to determine the pres^ce&gt; ^absence&gt; ^or level of a liquid material, as disclosed in the copending application Serial No. 656,372 mentioned above. The sensor is normally used with the t ? ^{at and the} transducer portion 92 at the top. The collar 94 may be formed integrally with the parts 90 and 92, all being made for example, out of barium titanate ceramic. ^S The unner electrode 96 is a coating of fired silver at the end of the .transducer portion 92, while the lower electrode 98 end ^r₊f^hei^{ral b}f^d °^{f fired silver} located at the lower ini ?! ?! ^transdu,^cer P⁰^⁰¹¹ »2. Conductors 100 and 102 iead to the electrodes, and all of these parts may ^b k°^Ur^ed ,Y^{lthln a} cylindrical housing, suggested by the broken lines 104, the said housing preferably being secured to the annular collar 94. The collar is^referably located at a vibration nodal point. ^P

Polarizing voltage is applied across leads 100 and 102 during manufacture, and part 90 is short circuited to prevent polarization, as described above. Alternating voltage is applied during operation, or in a reciprocal auVStom^nS^^lta8eJi ^developed· ^The lc^ad end is to vffirateXy. ^S“^{PPOrt all}°^{WS the two ends}

In the aforesaid application Serial No. 656 372 the 1?^™^°?'°“ ⁹°λ ^^{neath tbe c}y^lindrical housing 104 is a metal slug, and this must be cemented to the transducer material. In the present arrangement, even if a 90^m_anⁿd^teo9^UnCtI?? u^{ere employed}’ ^{38 in} FIG· 2, the parts “^{d 92 W}°^{U d be made out o£} identically the same ' transducer material, which eliminates the problem of differential expansion or contraction when changing to ^b'^gh °^r n^W ‘^PerariH-e. Even better, the parts 90 92 quency by a transducer 110. Such soldering irons are already known, but there is a problem in attempting to secure the transducer 110 to the hot soldering tip 112 ment 114. In accordance with the present invention an and^ath^Ont^S1U8^^{116 1S disposed} between the soldering tip w^transducer I!»- and the isolation means 116, is part Ho⁷ Tvl⁶ °h ί?^{6 S}T^{e transducer} “atenal as the part 110. Even better, they preferably are parts of a trod_e^em^dy °^{f transducer} material with the upper efecthp niJ¹⁸ °!^{Π one},^{end of} the transducer portion 110, and the other electrode 120 formed as a peripheral strip c~ ^ba?^d c^fT^o^ta ’ ^{a11 as} Previously described. ^P ,^£GS· ² through 7 the transducer body may be each^hA^{f Wave}J°^ng’ ^{With the u}PP^er and lower portions each one-quarter wave long. This is not essential howfulTwX l^{6 b}°^{dy might}&gt; ^for instance, be a ₅₅ full wave long, m which case the energized and isolation ⁵⁵portions would each be one-half wave long. However in such case, if a mounting collar be provided it preferably would not be located at the same point as the electrode. Instead, such a collar is preferably located at a «η nodal pomt, and therefore with a composite body which ® is a full wave long, the collar is preferably located onequarter wave from the end. one

It is not essential that the transducer be piezoelectric and^fesnch^eramlC· ^Π “^{ay b}® °^{f the} magnetostrictive type’ and such an arrangement is schematically illustrated in POrtioi’122tor^Chd^th?i^aSSen^{bIy comprise}s a transducer

V^{22 f} k^d J^ntegrally with an isolation portion 124. These are both made of laminations of magnetoDuroole T ’^{tyPiCaHy a n}'^{Ckel all}°^{y designed for the}purpose. The lower part 122 is energized by a suitable Md 128 ^ah h Τ'⁰”^{1 CaSe there arc tWO coiis 126}source n ^{may 6}_f^{COnnected t0 a} power ⁷¹¹⁶ J^e®^ona,^nce frequency of the assembly will rmmed by the overall dimension, but only the _{Λβ assemb}iy nZoEed” “ ^^larized’^{6whiIe the u}PPer portion is More specifically, the lower or transducer half of the core is magnetized, and usually this is done by applying a direct current to the coils shown. The upper or isolation portion is preferably not magnetized, and this desirable result is obtained automatically because the flux path when magnetizing the lower half forms a closed circuit without entering the upper half. The resulting isolation spX’h’T* ^{the Useful} P^urPose as previously described, because high temperature tends to destroy the necessary D.C. magnetization of the core. However, the interposed isolation portion is non-energized and nonmagnetized.

The invention may be used with such common piezodS'rnn¹” T^S u^{S qUartz}’ ^RocheIle salts, ammonium ‘hydrogen phosphate, and potassium dihydrogen phosphate, in addition to the commonly encountered ferroceramic materials. Magnetostrictive transducers fabried from nickel or nickel alloy laminations surrounded by coils carrying alternating current may also be made in the composite form shown, thereby eliminating the need for a difficult bonding operation hitherto found necessary.

In all the cases mentioned, the transducer may be used ktiu^eratOr °^{r r}f^c“^ve.^{r of} vibratory energy because, as istics^{Π kn}°^Wn’ ^{SUcb devlces} display reciprocal characterIt is believed that the construction and method of use of our improved transducer assemblies, as well as the advantages thereof, will be apparent from the foregoing detailed description.

Our transducer configuration will withstand wide temperature gradients, and will effectively isolate the vibratory element itself from extremes of temperature. Furof^esuch^edSs.^{qUe appreciably} Amplifies the construction

It will be apparent that while we have shown and described our invention m several preferred forms, denartinJT^{7 be} ™^{ade In the st}™ctures shown without , ^p, 1^{e £ron}? ^tbe scope of the invention as sought to be defined in the following claims.