Transducer assemblies

A transducer assembly includes a hollow support member disposed in a looped configuration and having an axial opening. A hollow transducer supported within the support member may be made from a piezoelectric material and may be provided with an axial opening corresponding to position to the axial opening in the support member. In one embodiment, the outer surface of the support member may be thinned at spaced positions as by sockets or spaced axial grooves extending partially through the support member. The support member may be thinned at strategic positions to control the vibrational frequency and the frequency bandwidth of the transducer assembly. The thinned portions of the support member may receive a compliant material such as urethane to smoothen the outer surface of the support member. In another embodiment, the hollow interior of the transducer assembly may be filled with a compliant material, such as urethane, which may be provided with air chambers. The compliant material causes the shape of the transducer assembly to be retained, particularly when end caps are disposed on the support member, and causes the vibrations to be damped and the bandwidth of the vibrations to be increased. The air chambers produce a mismatch between the impedances inside and outside the transducer assembly and facilitate the transmission of substantially all of the vibrational energy outside of the assembly. In still other embodiments, members are included for bracing the support member and the transducer to increase the amplitudes of the assembly vibrations without damaging the transducer.

This invention relates to transducer assemblies and more particularly 
relates to transducer assemblies for producing a vibration of a 
piezoelectric transducer when voltages are applied to the transducer. The 
invention is particularly concerned with transducer assemblies which can 
vibrate at controlled frequencies in an efficient manner to provide 
vibrations of high amplitudes without damaging any of the members in such 
assemblies. 
Transducer assemblies including piezoelectric transducers are known in the 
prior art. In one particular type of such transducer assembly, a hollow 
support member made from a suitable material such as a metal is disposed 
in a looped configuration and is provided with an axial opening. A hollow 
transducer made from a suitable material such as a piezoelectric material 
is supported within the support member and is provided with an axial 
opening corresponding substantially in position to the axial opening in 
the support member. When a voltage is applied to the transducer, the 
transducer vibrates and sends signals into the medium enveloping the 
transducer assembly. 
The transducer assemblies described in the previous paragraph have a number 
of different uses. For example, the transducer assemblies may be used in 
sonobuoys which are disposed in the ocean to detect underwater sounds. The 
transducer assemblies may be also included in oil well equipment to 
facilitate the recovery of oil from the earth. 
Regardless of the use which is made of the transducer assemblies described 
in the previous paragraph, the transducer assemblies have certain inherent 
limitations. For example, the frequencies of the vibrations cannot be 
controlled as precisely as might be desired for some applications. The 
bandwidth of the vibration frequencies cannot be made as wide as might be 
desired for some applications. Furthermore, the amplitudes of the 
vibrations cannot be made as large as might be desired for some 
applications, particularly since the transducer tends to crack when the 
amplitude of the vibrations becomes excessive and uncontrolled. These 
limitations become especially troublesome when the transducer assemblies 
are used in certain applications such as for sonobuoys. These limitations 
have existed for some time even though considerable efforts have been 
made, and significant amounts of money have been expended, to overcome 
these limitations. 
This invention provides transducer assemblies which overcome the 
limitations described in the previous paragraphs. The transducer 
assemblies include certain embodiments which control the operation of such 
assemblies to obtain a desired frequency and to increase the bandwidth of 
the vibrations in the assemblies. The transducer assemblies include second 
embodiments which also control the direction of the transmission of energy 
as a result of such vibrations so as to provide for the transmission of 
substantially all of such vibrational energy outwardly from the 
assemblies. The transducer assemblies also include third embodiments which 
include members for internally supporting the members in such assemblies 
so that the members can be vibrated at increased energies safely and 
reliably without cracking or otherwise damaging any of the members in such 
assemblies. In a further embodiment, the amplitudes of the vibrations in 
the transducer assemblies are singificantly enhanced. 
In this invention, a transducer assembly provides a transducing action 
between a voltage applied to the assembly and vibrations in the assembly. 
The assembly includes a hollow support member disposed in a looped 
configuration and having an axial opening and also includes a hollow 
transducer supported within the support member. The transducer may be made 
from a piezoelectric material and may be provided with an axial opening 
corresponding in position to the axial opening in the support member. 
In one embodiment, the outer surface of the support member may be thinned 
at spaced positions as by sockets extending at least partially through the 
support member or by the formation of spaced, axially extending grooves. 
The thinned portions of the support member may receive a compliant 
material such as urethane to smoothen the outer surface of the support 
member. The support member may be thinned at strategic positions to 
control the vibrational frequency and the frequency bandwidth of the 
transducer assembly. 
In another embodiment, the hollow interior of the transducer assembly may 
be filled with a compliant material such as urethane and the compliant 
material may be provided with air chambers. End caps may be disposed on 
the support member. The compliant material causes the shape of the 
transducer assembly to be retained, particularly when the end caps are 
disposed on the support member, and causes the vibrations to be damped and 
the bandwidth of the vibrations to be increased. The air chambers produce 
a mismatch between the impedances inside and outside the transducer 
assembly and facilitate the transmission of substantially all of the 
vibrational energy outside of the assembly. 
In still another embodiment, members are included for bracing the support 
member and the transducer to increase the amplitudes of the assembly 
vibrations without damaging the transducer. The members include a second 
support member disposed within the transducer in substantially concentric 
relationship with the first support member and also include rods extending 
between the first and second members to brace the members. A second 
transducer may be disposed on the second support member to form a second 
transducer assembly. Preferably the first and second transducer assemblies 
vibrate at substantially the same frequency so that the vibrations from 
the second assembly reinforce the vibrations from the first assembly.

In the embodiment of the invention shown in FIGS. 1 and 2, a transducer 
assembly generally indicated at 10 is provided. The transducer assembly 10 
includes a hollow support member 12 made from a suitable material such as 
a metal. The metal may preferably be aluminum or steel. The support member 
is provided in a looped configuration, preferably annular, and is provided 
with an opening 14 which extends in an axial direction. The support member 
12 may have a suitable thickness such as approximately one eighth of an 
inch (1/8") to one fourth of an inch (1/4"). 
Sockets 16 are provided in the outer periphery of the support member 12. 
The sockets 16 preferably extend only partially through the thickness of 
the support member 12. In this way, the sockets 16 tend to make the 
support member 12 thinner at the positions of the sockets. The sockets 16 
are shown in FIG. 2 as being disposed at spaced positions on the complete 
periphery of the support member 12. However, the sockets 16 can be 
disposed only at positions adjacent the opening 14 or only at positions 
diametrically opposite the opening 14 or at any other portion of the 
periphery surface of the support member 12. 
The sockets 16 may be filled or partially filled with a suitable material 
18. Preferably the material 18 is compliant and has a weight per unit of 
area less than that of the material of the support member 12. For example, 
the material 18 may be a urethane or a polyurethane. As will be 
appreciated, some, but not necessarily all, of the sockets 16 may be 
filled with the material 18. 
A hollow transducer 20 is disposed within the support member 12 in an 
adhered relationship to the support member. The transducer 20 may be made 
from a suitable material such as a material having piezoelectric 
properties. For example, the g transducer 20 may be made from a suitable 
ceramic such as lead zirconium titanate. The transducer 20 may be bonded 
to the inner periphery of the support member by a suitable bonding agent. 
An axial opening 22 is provided in the transducer 20 at a position 
corresponding to the opening 14. 
When the electrical signals are introduced to the transducer 20, the 
transducer vibrates. The maximum vibration occurs at the natural resonant 
frequency of the transducer 20. The amplitude of the vibrations increases 
progressively with progressive distances from the openings 14 and 22. 
Thus, the minimum amplitude of vibration occurs at a position 24 
diametrically opposite the opening 14. However, the position 24 is where 
the maximum stress occurs in the piezoelectric transducer 20 because this 
is where the support member experiences the maximum amount of bending. 
When the vibrations become excessive, the transducer 20 may crack at the 
position 24. One of the functions of the support member 12 is to limit the 
amplitude of the vibrations of the transducer 20 so that the transducer 
does not become cracked. 
The sockets 16 provide certain advantages when included on the periphery of 
the support member 12. They decrease the weight of the transducer 
assembly. They also tend to provide a controlled frequency for the 
transducer assembly 10. For example, when the sockets 16 are disposed in 
the area around the position 24 but not in the area adjacent the openings 
14 and 22, the vibrational frequency of the transducer assembly 10 is 
decreased. This results from the fact that the decreased weight of the 
support member 12 at the position 24 relative to the weight of the support 
member at the positions adjacent the opening 14 increases the difficulty 
of the support member in vibrating. This reduction can be from a value of 
approximately five hundred hertz (500 Hz) to a value as low as 
approximately three hundred and fifty hertz (350 Hg). 
Similarly, when the sockets 16 are provided in the support member 12 at the 
positions adjacent the opening 14 but not in the area adjacent the 
position 24, the vibrational frequency of the transducer assembly is 
increased. As will be appreciated, the vibrational frequency of the 
transducer assembly 10 is affected by the number of sockets 16 provided in 
the support member 12 and by the spacing between the sockets. The 
mechanical Q of the transducer assembly 10 can also be reduced by 
providing the sockets 16. When the mechanical Q is reduced, the bandwidth 
of the vibrational frequencies of the transducer assembly 10 is increased. 
The inclusion of the material 18 in the sockets 16 provides certain 
additional advantages. For example, particularly when the material 18 is 
compliant, the vibrations of the transducer assembly 10 tend to become 
damped. This results in part from the fact that the mechanical Q tends to 
become reduced such as from a value of twenty (20) to a value as low as 
fourteen (14). The bandwidth of the vibrational frequency of the 
transducer assembly 10 also becomes increased. 
The embodiment shown in FIGS. 3 and 4 has a construction corresponding in a 
number of respects to the g embodiment shown in FIGS. 1 and 2 and 
described above. However, instead of providing the sockets 16 in the 
support member, a support member 30 is provided with grooves 32 extending 
axially along the length of the support member. The grooves 32 may be 
filled with a material 34 such as urethane. The grooves 32 and the 
material 34 provide the same advantages as described above for the 
embodiment shown in FIGS. 1 and 2. This is even true with respect to the 
control of frequency since the relative disposition of the grooves 32 
controls the vibrational frequency of the transducer assembly 10 in a 
manner similar to that described above. 
The embodiment shown in FIGS. 5 and 6 includes a support member 40 and a 
transducer 42 corresponding in construction to the support member 12 and 
the transducer 20. Although the embodiment shown in FIGS. 5 and 6 does not 
specifically include the sockets 16 or the grooves 32, it will be 
appreciated that one or both of these features may be included in the 
embodiment shown in FIGS. 5 and 6. 
The embodiment shown in FIGS. 5 and 6 includes a compliant material 44 such 
as urethane within the hollow interior of the transducer 42. The material 
44 may be suitably bonded to the interior surface of the transducer 42. 
Air chambers or cavities 46 may be provided in the material 44 at spaced 
positions. The air chambers 46 preferably extend axially through the 
compliant material 44. End caps 48 made from a suitable material such as 
urethane plug the ends of the hollow interior of the transducer 42. 
The apparatus described above and shown in the drawings has certain 
important advantages. It has an enhanced strength because the interior of 
the transducer 42 is filled by the material 44 and because the ends of the 
transducer are plugged by the end caps 48. The air chambers 46 are 
advantageous because they cause the transducer assembly to operate as if 
it is entirely filled with air. Furthermore, the air chambers 46 cause an 
impedance mismatch to be produced between the interior of the transducer 
42 and the exterior of the support member 40. Because of such mismatch, 
substantially all of the energy produced by the vibrations of the 
transducer assembly is directed outwardly from the transducer assembly. 
This enhances the efficiency of operation of the transducer assembly. The 
compliant material 44 and the air chambers 46 also cause the mechanical Q 
of the transducer assembly to be reduced to a value as low as nine (9), 
thereby causing the bandwidth of the vibrational frequencies to be 
increased. Since the interior of the transducer 42 is sealed by the 
material 44 and the end caps 48, the transducer assembly can be exposed to 
sea water without any leakage of sea water into the transducer assembly. 
The embodiment of FIGS. 7 and 8 shows a transducer assembly, generally 
indicated at 50, which includes the support member 12 and the transducer 
20. The transducer assembly 50 also includes a second support member 52 
which is disposed in concentric relationship with the support member 12 
and the transducer 20. The support member 52 may be made from a suitable 
material such as a metal, steel or aluminum being illustrative. 
The support member 52 has an opening 54 corresponding radially in position 
to the opening 12 in the support member 14 and the opening 22 in the 
transducer 20. Bracing members such as rods 56 are disposed at one end at 
positions adjacent the openings 14 and 22 and at the other end at a 
position adjacent the opening 54 and are attached to the support members 
12 and 52 at the opposite ends. 
The embodiment shown in FIGS. 7 and 8 has certain 
important advantages. As will be seen, the support member 52 reinforces the 
support member 12, particularly in view of the bracing action provided by 
the rods 56. This prevent the transducer 20 from cracking at its weak 
points. Because of this, the amplitudes of vibration in the transducer 
assembly 50 can be increased without damaging the transducer 20. 
The embodiment shown in FIGS. 9 and 10 is substantially similar to the 
embodiment shown in FIGS. 7 and 8 except that it includes a second 
transducer 60 on the support member 52. The transducer 60 may be made from 
the same material as the transducer 20. The support member 52 and the 
transducer 60 accordingly act as a second transducer assembly. 
Preferably the second transducer assembly vibrates at substantially the 
same frequency as the transducer assembly formed by the support member 12 
and the transducer 20. This can be accomplished by carefully selecting the 
parameters of the support member 52 and the transducer 60. Since the two 
transducers vibrate at substantially the same frequency, the vibrations 
from one reinforce the vibrations from the other. As a result, the 
amplitudes of the vibrations from the transducer assembly formed by the 
support member 12 and the transducer 20 are significantly enhanced. 
FIG. 11 illustrates a sixth embodiment of the invention. This embodiment is 
similar to the embodiment shown in FIGS. 1 and 2. However, openings 70 and 
72 respectively provided in a support member 74 and a transducer 76 are 
disposed at an angle having components in the circumferential and axial 
directions. Preferably this angle is approximately 45.degree. relative to 
the axial direction. The opening extends to the opposite axial ends of the 
support member 74 in a substantially linear direction displaced at one end 
circumferentially from the other axial end. Providing the openings 70 and 
72 in a diagonal direction is advantageous because it tends to distribute 
the stress on the transducer 76 while maintaining the vibrations of the 
transducer assembly at substantially the same frequency as that produced 
by an axial opening. Furthermore, the diagonally disposed openings 70 and 
72 allow the transducer 76 to be driven at an increased voltage, thereby 
providing for increased amplitudes in the vibrations in the transducer 
assembly. 
Although this invention has been disclosed and illustrated with reference 
to particular embodiments, the principles involved are susceptible for use 
in numerous other embodiments which will be apparent to persons skilled in 
the art. The invention is, therefore, to be limited only as indicated by 
the scope of the appended claims.