JPS61289799A - Electromechanical transducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to electromechanical transducers, and more particularly, to electromechanical transducers with predominant mechanical motion in a single direction and with alternating head masses and compliant layers. , known as a mass-weighted vertical oscillator transducer, in which one of the compliant layers can be an active transducer element.

BACKGROUND OF THE INVENTION Devices known as vertical transducers are simple and widely used electromechanical or electroacoustic transducers. Such a device, in its simplest form: consists of a thin strip of active material that is electrically driven to induce a planar movement. For example, piezoelectric ceramic (
For example, a flat disk or ring made of lead zirconium titanate (based on lead zirconium titanate), which has electrodes on its flat surface and is polarized in a direction perpendicular to the flat surface, is a vibrator. It acts as. This type of device usually uses its first longitudinal resonance frequency 1111 [t' f
JI will be made. In order to obtain a compact, well-controlled device with a sufficiently low resonant frequency, it is customary to weight the active material on two sides with a piece of inert material.

A prior art vertical vibrator with a double mass load (mass 1 load) is shown in FIG. 1(a). The piezoelectric material rings 1 are joined together to form a composite stack 2 and electrically wired in parallel so that when a voltage is applied between the leads, all the rings harmoniously move in the direction of the longitudinal axis of the device. , expand and contract. A single vibrating head mass element or head mass 3 has a front surface 4 and acts as a radiating surface and as a load for the front end of the stack. A tail mass 5 is attached to the other end of the stack and is typically larger in mass than the head mass 3, so that the movement is primarily in the head mass 3. Stress rods or pre-tensioned bolts 6 and associated nuts 7 are used to connect the parts and to compressively bias the stack 2 of active elements.

The device of FIG. 1(a) is used as a transmitter or receiver of mechanical or acoustic energy and is operated in a frequency band centered on its mechanical resonance frequency. At its secondary resonant frequency, the head mass 3 and the tail mass 5 move in relative opposite directions, while the stack of active material alternately expands and compresses along its length.

As is well known to those skilled in the art, the performance of the transducer of FIG. 1(a) can be approximated by analogous operation of the simplified electrical equivalent circuit shown in FIG. 1(b). In the same circuit, Mh and M represent head mass and tail mass.

A transformer represents the electromechanical transformation properties of piezoelectric materials.

The turns ratio of this transformer is φ is the electromechanical conversion ratio. The compliance of the ceramic stack 2 is represented by the capacitor C, CO representing the actual electrical capacitance of the stack. The electrical components to the right of the transformer represent the mechanical components, and the components to the left represent the actual electrical components. The rightmost block of the equivalent circuit represents the radiation impedance Z rad seen at the radiation surface of the transducer. The constant current U of the radiation impedance represents the velocity of the moving surface of the radiation surface.

The transfer voltage response (TVR) J of this conventional device can be calculated from this equivalent circuit approximation, and TVR is the current U,
It is proportional to the drive voltage E at the input of the transducer circuit. In determining the responsivity of the device, radiation impedance can be ignored, as expressed by equation (1) below.

TVRα□−□ (1) The transmission voltage response has a single peak near the frequency when the denominator of the above equation (1) becomes zero.

This is the resonance (angular) frequency ω expressed by the following equation (2)
It happens when r.

The methods of analysis described above are well known in the transducer industry, such as the LeonCag+p
"Underwater Acoustics" by the author
sticks)” [Willie and Son 1 (1fil)
ey & 5OnS), published New York, 1970, pages 142-150;
erlincourt) outside of ``Piezoelectricity and Piezoelectric Materials and Their Function in Transducers (Pif3ZOe
leCtriCand p;ezoe+etric
) lateral and Their Funct
ion in Transducers) Physical Acoustics under the title J.
, vol. IA J [Academic Press, New York, 1964], pages 246-253. Computer models can also be used for more accurate motion analysis.

The method is described, for example, by K.M. Farnham (K.H.
, Farnhai), Newton Research Institute, Newton, CT;
Naval Underwater Systems Center, Transducer and f
f7L/I part (Transducer and Arr.
aysDivision, Naval tlnder
Water Systems Center.

Nev London Laboratory). A graph of a typical response curve of the transducer of FIG. 1(a) obtained by the transducer program described above is shown at 30 in FIG.

The band of this device ranges between 0.85 and 1.21 frequency units and 0.36
It has a width in frequency units.

A major drawback of the conventional transducer of FIG. 1 is that the mechanical input impedance of the radiation surface (hereinafter referred to as head impedance) is extremely small in the operating band at the resonant frequency. If the head impedance is low,
A problem arises when the transducer is used as one element in an array structure. Practical constraints often require that the head impedance of the elements of a high performance array be significantly larger than the acoustic mutual impedance of the array at any operating frequency.

For this reason, it is often necessary to prohibit operation in a narrow frequency band near the peak of responsiveness.

The basic arrangement shown in FIG. 1(a) also has practical limitations as to the achievable frequency band.

The operating band can be increased by reducing the mass of the head and increasing the mechanical compliance of the ceramic stack. This can be achieved by making the head thinner and the ceramic stack tapered and/or longer. However, such design techniques are limited by practical design considerations such as: As the radiation surface becomes thinner, its first flexural resonance frequency (flexural
resonance frequency) invades the operating band and significantly changes the behavior of unit 1. If the active material is thin and long, either on one side or the other, the device will be mechanically fragile. To obtain the desired resonant frequency, the active material is lengthened such that this length corresponds to a significant fraction of the mechanical wavelength in the material, and the material then becomes self-resonant and no longer drives the medium.

In order to widen the operating band of a mass-loaded vertical resonator,
Several techniques have been tried. One technique is to connect an electrical component, such as an inductor or capacitor, between the electrical terminals of the transducer and the amplifier circuit associated with the transducer to tune the response of the device. However, such special electrical termination methods (Termina
tion), the band can be slightly broadened, but the problem is that the size, quantity, and complexity increase, making the entire device more complicated. In addition, 1) this method has the problem that localized high voltages may occur at nodes of the circuit, and high voltage isolation and shielding measures must be taken. Curve 31 in FIG. 6 shows a typical response characteristic when the transducer is operated with an inductor connected in series with the electrical lead. Like untuned transducers, tuned transducers operating in array structures encounter practical problems in the frequency range near each of their responsivity peaks. but,
With this design, the peak-to-peak band is widened, and problems with arrays due to small head impedance are avoided. The 3 dB band between the two peaks, centered on the depression, extends from 0.81 to 1.20 relative frequency units and has a width of 0.39 frequency units.

Another well-known method of extending the operating band of a transducer is to use an external matching layer. An external matching layer 8 is used to match the acoustic impedance of the transducer and the medium, as shown in dashed lines in FIG. 1(a). A design using external matching layer 8 results in a significantly wider bandwidth, as shown by curve 32 in FIG. However, this method also has drawbacks. With external matching l1Ji8, the shape of the response curve is a very sensitive function of the density of the matching layer material and the speed of sound. Therefore, there is no guarantee that a material of desired quality can be obtained for a particular application. Moreover, there is the problem that in some cases the required thickness of the matching layer may be undesirably large. Furthermore, the design with the external matching layer 8 causes the head impedance to be too small at two frequencies to be suitable for operation in an array. For example, a transducer with the responsivity shown by curve 32 has an external matching layer of transparent synthetic resin (lucite).
The head impedance decreases at relative frequencies of 0.80 and 1.78. At either of these two frequencies, array operation is inadequate. Therefore, for the responsivity of curve 32 shown, the useful band is 0.8
It is 0.88 frequency units wide, ranging from 5 to 1.73 frequency units. If the drop in head impedance is acceptable, the 3dB band is 0.78 to 1
．． It spans a band of up to 90 frequency units, or 1.12 frequency units.

Another method for obtaining two resonant frequencies in a conventional transducer is shown in FIG. The device consists of a low frequency transducer 10, a head mass 11 and a high frequency nonlinear array 12 attached nodularly to the head mass 11. The transducer of FIG. 2 is not only a very complex device requiring complex wiring and installation, but also transmits high power in two frequency bands more than two octaves apart. Low frequency transducer 10 and array 12 of this device
Each operates as if the other did not exist. However, the transducer of FIG. 2 does not exhibit broadband responsivity between the two resonant frequencies.

This is because a separate resonance is generated in the transducer by the system in which the array 12 as a high frequency unit is mounted in a nodal manner on the head mass 11 of the transducer 10 as a low frequency unit. In order to separate the operation of the high frequency unit from the structure of the low frequency unit, the nodal mounting requires that the system's resonant frequency be much lower than the high frequency operating resonance. Moreover, the nodal mounting requires that the resonant frequency of the system be above the low frequency operating band. Otherwise, the low frequency radiator would be separated from the radiating medium. The acoustic response of the transducer exhibits a sharp drop in mounting in the frequency range of system resonance.

As a result, the prior art device of FIG. 2 cannot be used as a broadband transducer in the entire frequency range between the high frequency resonance and the low frequency resonance. This is because the resonant frequency of the nodal mounting lies between the two operating bands of the device. Thus, the device is not a true broadband transducer but only has two separate frequency ranges.

Other features of typical transducers, such as insulating washers, wiring, electrical contacts, etc., are well known to those skilled in the art and are described, for example, in U.S. Pat. No. 3,309,654 to Miller. 1I.

It is an object of the present invention to provide a vertical electromechanical transducer capable of operating over a wider frequency range than previously available.

According to one embodiment of the present invention, a wide operating frequency band can be provided without special electrical termination.

According to one embodiment of the present invention, a transducer with a single wide operating frequency band can be provided.

According to one embodiment of the invention, it is possible to provide a transducer that has a high mechanical input impedance in the radiation plane over the entire operating band and can therefore be used in an array structure.

According to one embodiment of the present invention, a transducer that does not require a matching layer can be provided.

Still another object of the present invention is to provide a transducer with high transmission voltage responsiveness.

Yet another object of the present invention is to provide broadband frequency response without significantly reducing efficiency.

One embodiment of the invention can provide a relatively flat response within the transducer operating band.

According to one embodiment of the present invention, a transducer can be provided that has substantially equal transmitted power levels at all frequencies within a wide operating band.

SUMMARY OF THE INVENTION To achieve the above objects, the present invention provides a transducer having a head that includes at least three layers.

The two head mass layers are separated from each other by a compliant member.

The compliant member of the head portion may be an active transducer element 7. The head portion is attached to an active transducer element, and the active transducer element is attached to the tail mass. Transducers containing new composite heads have at least two resonant frequencies, one of which is the resonant frequency of the transducer if the compliant member of the head were removed, and the other if the head was other than the transducer. It can be seen as an approximation to the resonant frequency of the head section when it is removed from the section.

The frequencies of these two resonances can be adjusted independently of each other depending on the particular application.

(Means for Solving the Problems) According to the present invention, in order to solve the problems of the conventional transducer described above, in the first invention, N (
(N is an integer of 2 or more) head masses and (N-1) compliant means fixed in a laminated manner between the head masses; electromechanical transducer means fixed to the head part and performing electromechanical conversion; and a till mass fixed to the electromechanical transducer means. Resonant vibrations are caused by at least N resonances within the operating band.

In a second aspect of the invention, a vertical electromechanical transducer that emits radiation into a medium includes a head mass in contact with the medium, a first electromechanical transducer element in contact with the head mass, and a first electromechanical transducer element in contact with the medium. an intermediate mass that abuts one electromechanical transducer element, a second electromechanical transducer element that abuts the intermediate mass, and a tail mass that abuts the second electromechanical transducer element. has been established. The tail mass was then of sufficient mass to cause the principal motion to the head and intermediate masses, causing the transducer structure to exhibit two resonances within its operating band.

〔Example〕

In order to obtain a wide band operating frequency characteristic, the present invention is shown in FIG. 1 (a).
Instead of the monolithic head mass 3 of ), a mechanically resonant head portion having a laminar structure in which mass elements and compliant members are alternately laminated is used. The frontmost part of the head is in contact with the radiation medium and the rearmost part is connected to other parts of the transducer. This is similar to the case with conventional monolithic head masses.

FIG. 3 shows an example of the head section 20 of the present invention having a three-layer structure, in which the front head mass 21 and the rear head mass 23 are made of a material sufficient to avoid bending resonance, such as aluminum, steel, metal, etc. It is formed from a matrix composite or a graphite-epoxy composite. A compliant member 22 is inserted between the front and rear head masses 21 and 23. The compliant member 22 may be, for example, a plastic, such as VESPEL, a polyimide plastic sold by DuPont, or TORLON, a polyamide-imide plastic sold by Amoco Chemical; It may be an active transducer element or any other material that provides the desired compliance. Although the compliant member 22 is shown to be the same size as the rear head mass 23, it may be made larger or smaller as needed. The head masses 20 may be secured together using conventional epoxy adhesives or by tension bonding.

FIG. 4(a) shows a transducer incorporating the three-layer head section 20 of FIG. The transducer element 1 may be a piezoelectric element made from a piezoceramic material, such as one based on lead zirconate titanate, available for example from veritrOn Inc., Bedford, Ohio, USA. The tail mass 5 may be tungsten, steel or aluminum and should have sufficient mass so that the main movement occurs in the head section 20. Each of the metal masses within the transducer has one wavelength at the highest frequency of the operating band.
It must be sufficiently shorter than /4.

The stress rod 6 is artificially aged (aged coin processing) after machining, and is made into a Rockwel
l) 1/4 hardness A to obtain C57-42
It may also be beryllium copper designated alloy number 172 according to STM S-196. The nut 7 may be made of aluminum or steel, but the dilmas 5 should be flat and in contact with each other,
Natsuto's locking must not occur. The entire assembly of the transducer can be done using epoxy and then tensioning the stress rods 6, or by loosely assembling and securing with the stress rods 6. Adjustment of the compression bias using the stress rod 6 is easy for those skilled in the art.

An approximate equivalent electrical circuit for the transducer of FIG. 4(a) is shown in FIG. 4(b). In this equivalent circuit,
Mh is the front head mass 21 of the head section 20 that is in contact with the medium. M is the mass of the rear head mass 23 in contact with the ceramic stack 2. Mt represents the tail mass 5 of the transducer. The electromechanical conversion ratio of the piezoceramic stack 2 is φ. CO represents the actual electrical capacitance of the piezoceramic material, C represents the compliance of the ceramic stack 2, and C1 represents the front and rear head masses 21 and 23.
represents the compliance of the compliant member 22 that separates each other from each other. The transmission voltage response of this 1-transducer is obtained by the following equation (3).

The equation (3) of U TVRa represents the response of a doubly resonant system, and the approximate resonant frequency can be obtained by solving the denominator equation. The method is similar to that done for equation (1) to obtain equation (2).

Equation (3) is based on the front and rear head masses 21 and 23.
By selecting the mass of the compliant member 22 and the compliance of the compliant member 22, it is possible to tune the frequency and the coupling between the two resonant modes.

The two resonant frequencies in this example are the transducer resonance, assuming the compliant member of the head is removed, and the head-only resonance, assuming the head is removed from the ceramic stack. It can be more easily approximated as a frequency. However, the above is only an approximation, and a little experimentation is required to obtain a complete configuration for actual application.

The transmitted voltage response of this example was calculated using the computer program described above. The results are shown in Figure 6, curve 3.
Indicated by 3. Song 1133 of FIG. 6 illustrates the response obtained from the transducer of FIG. 4(a) without the addition of electrical termination or tuning elements. Transmitted voltage response is ANS I transducer standard 31.20
-1972. As can be seen by comparing the conventional response curves (30, 31, 32) and the response curve 33 of the embodiment of the present invention shown in FIG. ) has a much wider frequency band. Figure 1 (
Curve 30 of the conventional transducer in a) has a 3 dB bandwidth of approximately 0.36 frequency units, while a conventional transducer tuned using electrical elements has a bandwidth of 0, as shown by curve 31.゜39 frequency units. However, the signal level is high.

A conventional transducer with an external matching layer has curve 3
As shown by 2, it has a bandwidth of approximately 1.12 frequency units, but the signal level is low. In contrast, in this embodiment, the 3 dB bandwidth is approximately 1.28 frequency units.

This embodiment also has a relatively high signal level and a flat response curve. Another advantage of the present invention is its superior performance in array structures.

In the present invention, high head impedance can be obtained in a bandwidth of 1.18 frequency units. In the prior art, the widest bandwidth without drop in head impedance is obtained with a device having a matching layer, the bandwidth being approximately 0.88 frequency units wide. According to the present invention, there is also no need for a matching layer. This is because the head portion of the transducer has the function of a matching layer.

Another embodiment of the invention is shown in FIG.

In this embodiment, the plastic compliant member 22 of the embodiment of FIG. 4(a) is replaced by an active element 24 forming a second active stack 25. As a result, the till mass 23 is a mass ζ constituting the head portion.
Rather than that, it's more of an intermediate mass. These active transducer elements 24 may be of the same material as the transducer elements 1.

However, different transducer materials, such as barium titanate or piezoelectric crystals, such as lithium 5ulfa
Different response characteristics can also be obtained by using te).

In general, the dimensions of the piezoelectric materials of the two stacks 2 and 25 can be adjusted separately to meet specific requirements. In the drawings, the thicknesses of elements 24 and 1 are made different to illustrate this. In this example, the tail mass 5 is the head mass 2.
1 and the intermediate mass 23. The head mass 21 is equal to or less than the quality ω of the intermediate mass 23,
Preferably, the front part (21 and 25) resonates at the highest frequency. However, it is also possible to reverse the mass balance. In this case, the performance of the transducer will be lower than . The resonant frequency and response of this embodiment can be calculated in the same manner as in the case of FIG. 4(a). As a design approximation, the low frequency resonance is mass 21.25 and 2
An approximate value can be obtained by considering 3 as a single mass and considering the compliance of stack 2 together with tail mass 5. The high frequency resonance can be approximated by the resonance of members 21, 23 and 25 if they were isolated from the rest of the transducer.

In reality, the true low frequency resonance is somewhat lower than the above approximation, and the high frequency resonance is somewhat higher.

When operating as an oscillator, the two active stacks 2 and 25 are driven by separate amplifier circuits depending on the application. However, in a preferred embodiment, which allows a simpler drive circuit to be used, two active stacks 2
The electrical leads from and 25 are connected in parallel so that a positive applied voltage will cause one of the stacks to expand and the other to contract. In such a configuration, the sensitivity is slightly decreased at low frequency resonance (approximately 0.1 dB), and the sensitivity is significantly improved (3 dB or more) at high frequency resonance. This is particularly advantageous in applications where the transmitted power level needs to be approximately equal across all frequencies over a wide operating band. On the other hand, in the device shown in FIG. 4(a), the sound pressure levels in the transmission axis direction are approximately equal, as shown by the curve 33 in FIG. 6, but in this device, the transmitted power level is low at high frequencies. This is because the device is more directional so that the energy is radiated over a smaller angular area.

The electrical leads can also be connected in parallel when the transducer is operating as a receiver to simplify the electrical circuitry required.

FIG. 7 shows the transmitted power at constant drive voltage as a function of frequency for several transducer configurations according to the invention. Curve 34 shows the power response of the prior art device of FIG. 1(a). Curve 35 is the fourth
As shown in Figure (a), the power response of the device of the present invention using an inert compliance member in the head section is shown. However, the same design parameters as those used when calculating the transmitted voltage response of song 11133 in FIG. 6 are used. This device has somewhat higher bandwidth in terms of power response. However, the response at high frequency peaks is extremely low. Curve 36 represents a transducer using an inactive transducer element in the head shown in FIG. The device has a relatively flat power response at constant drive voltages over a bandwidth that includes two resonances.

In yet another embodiment of the invention, in addition to the rigid connection of the stress rod 6 to the front head mass 21 and the tail mass 5, a connection is provided between the stress rod 6 and the rear head mass 23 of the compliant member 22. I can think about things.

By adjusting the mass and compliance of the transducer elements using equation (3), a single transducer with two different operating bands can be obtained. There are no fundamental constraints on the frequency separation of the two bands. However, the length of the ceramic stack is 1/1/2 of the wavelength of sound in the ceramic material at the highest resonant frequency.
When the length is longer than 4, a practical limit is reached.

Multiple layers of masses and compliant members may also be provided. In such an embodiment with N mass layers:
If there are N resonant frequencies and the peaks of the response curves are close enough to each other, a very flat response curve will be obtained.

The prior art electrical termination and external matching layer methods are:
Compatible with the present invention, the performance of the device of the present invention can be further improved by combination with electrical elements and matching layers. This will be understood by those skilled in the art.

(Effects of the Invention) According to the present invention, without using a special electrical termination,
A wide operating frequency band can be provided and a transducer with a single wide operating frequency band can be provided. Further, according to the present invention, it is possible to provide a transducer having high transmission voltage responsiveness.

[Brief explanation of the drawing]

FIG. 1(a) is a diagram showing the elements and structure of a conventional transducer, FIG. 1(b) is a diagram showing an equivalent electric circuit of the transducer of FIG. 1(a), and FIG. 3 shows the main elements of the head section 20 of the transducer of the present invention, and FIG. 4(a) shows the head section of FIG. 3. 4(b) is a diagram showing an equivalent electric circuit of the transducer of FIG. 4(a), and FIG. 5 shows a structure in which the compliant member 22 is an active element. 24
FIG. 6 is a graph showing a comparison of the responsiveness of the transducer of the prior art and the transducer of the invention shown in FIG. 4(a). The figure shows the transmitted power in a general transducer configuration of the present invention in comparison with the prior art. DESCRIPTION OF SYMBOLS 1... Transducer element, 2... Ceramic stack, 4... Head mass, 5... Tail mass,
6... Stress rod, 7... Nut, 20... Head portion, 21... Front head mass, 22... Compliant member, 23... Rear head mass, 24...
Active transducer element, 25...active stack. F/to, /(0) na z. FIG, 4(0) 41tIf, -$

Claims (1)

[Claims] 1. A head portion having N head masses (N is an integer of 2 or more) and (N-1) compliant means fixed in a stacked manner between the head masses; and the head portion. an electromechanical transducer means fixed to said electromechanical transducer means for effecting electromechanical conversion; and a tail mass fixed to said electromechanical transducer means, said vertical transducer means producing resonant oscillations with at least N resonances within a band of operation. Electromechanical transducer. 2. The transducer according to claim 1, wherein the head section is a three-layer head section. 3. A transducer according to claim 1, wherein the compliant means has a compliance significantly greater than that of metals and piezoelectric ceramics. 4. A vertical electromechanical transducer for radiating into a medium, comprising: a head mass in contact with the medium; a first electromechanical transducer element in contact with the head mass; and an intermediate in contact with the first electromechanical transducer element. a second electromechanical transducer element that abuts the intermediate mass; and a tail mass that abuts the second electromechanical transducer element, the tail mass producing a primary motion in the head and the intermediate mass. 1. A transducer having a mass sufficient to cause the transducer structure to produce two resonances within its operating band. 5. The transducer according to claim 4, wherein the first and second electromechanical transducer elements are electrically connected in parallel. 6. The transducer according to claim 5, wherein the electrical connection is made such that one of the first and second electromechanical transducer elements expands and the other contracts. . 7. The transducer according to claim 4, wherein the first electromechanical transducer element is made of a first transducer material, and the second electromechanical transducer element is made of a first transducer material. A transducer comprising a different second transducer material. 8. The transducer of claim 4, wherein the first electromechanical transducer element has a first thickness and the second electromechanical transducer element differs from the first thickness. A transducer having a second thickness.