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FIELD OF THE INVENTION The present invention relates to an electromechanical transducer, in
particular, in which a main mechanical motion is performed in a single direction, head mass and
compliant layers are alternately arranged, and one of the compliant layers. One relates to what is
known as a mass weighted vertical transducer transducer, which may be an active transducer
element. 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 piece of active
material, which is electrically driven to induce planar movement. For example, a flat disk or ring
formed of piezoelectric ceramic (e.g., based on lead zirconate titanate) having an electrode on its
flat surface and polarized in a direction perpendicular to the flat surface One acts as a vibrator.
This type of device is typically produced with its first longitudinal resonant frequency 1111 t 'fJI
to obtain high power. In order to obtain a compact, well-resonant device with a sufficiently low
resonant frequency, it is customary to apply a mass) to the two sides of the active material with a
piece of inert material. FIG. 1 (a) shows a conventional double vibrator doubled mass load (mass
1 oad) vibrator. Piezoelectric rings 1 are joined together to form a composite stack 2 and are
electrically wired in parallel so that all the rings are in harmony when the voltage is applied
between the leads, in the longitudinal direction of the device , Expand and contract. A single
vibrating head (head) mass element or head mass 3 has a front face 4 and acts as a radiation face
and as a load on the front end of the stack. The tail mass 5 is attached to the other end of the
stack and is usually larger in mass than the head mass 3 so that movement occurs mainly in the
direction of the head mass 3. A stress bar or pretensioned bolt 6 and its associated nut 7 are
used to connect the parts and to bias the stack 2 of active elements in a compressible manner.
The device of FIG. 1 (a) is used as a transmitter or receiver of mechanical or acoustic energy and
is operated at a frequency band centered on its secondary mechanical resonance frequency. At
its secondary resonance frequency, the head mass 3 and the tail mass 5 move in relatively
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 similar 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. The transformer represents
the electromechanical conversion characteristics of the piezoelectric material. The winding ratio
φ of this transformer is an electromechanical conversion ratio. The compliance of the ceramic
stack 2 is represented by a capacitor C, CO representing the actual electrical capacitance of the
stack. The electrical members on the right side of the transformer represent mechanical
members and the members on the left represent actual electrical members. The block at the right
end of the equivalent circuit represents the radiation impedance Z rad viewed at the radiation
plane of the transducer. The isostatic 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 prior art device can be calculated from the approximation by this equivalent circuit, where
TVR is proportional to the current U divided by the drive voltage E at the input of the transducer
circuit. In determining the responsiveness of the device, the radiation impedance can be ignored
as expressed by the following equation (1). TVRα □-□ (1) The transmission voltage response
has a single peak near the frequency when the denominator of the above equation (1) becomes
zero. This occurs at a resonant (angular) frequency ω r represented by the following equation
(2). Methods of the above analysis are well known in the transducer industry, for example
"Underwater, er Acoustics" by Leon Camp (Leon Cag + p) [Willie & Son 1 (1 filey & 5 OnS), New
York, published , 1970, pp. 142-150, and also under the heading of "Berlincourt", "Piezoelectric
and Piezoelectric materials and their functions in transducers (Pif3 ZOeleCtriC; ezoe + ectric),
lateral and Their Function in Transducers J". Physical Acoustics, Volume 1 A (vol, I A) J
[Academic Press (Aca) emic Press), New York, has announced the first 246-253 pages of 1964].
More accurate motion analysis can also be performed using a computer model. The method is,
for example, developed by Kae M. Farnham (K, H, Farnhai), and the state of Neuronton
Laboratories in Neuronton, Connecticut Navalton, Naval Underwater Systems Center,
Transducers and ff7L / Y Division (Transducer and Arrays Division, Naval tlnderwater Systems
Available at Nev London Laboratory). A graph of a typical response curve obtained by the abovedescribed transducer program of the transducer of FIG. 1 (a) is shown at 30 in FIG. The band of
this device has a width between 0.85 and 1.21 frequency units and 0,36 frequency units. A major
disadvantage of the prior art transducer of FIG. 1 is that the mechanical input impedance of the
emitting surface (hereinafter referred to as the head impedance) is very small in the operating
band at the vibration frequency. Low head impedance is a problem when transducers are used as
one element of the array structure. As a practical limitation, at any operating frequency, it is
often required that the head impedance of the elements of a high performance array be
sufficiently larger than the acoustic mutual impedance of the array. For this reason, it is often
necessary to forbid operation in a narrow frequency band near the peak of responsiveness. The
basic device shown in FIG. 1 (a) also has practical limitations on the achievable frequency band.
In order to increase the operating zone, it is sufficient to reduce the mass of the head and to
increase the mechanical compliance of the ceramic stack. This can be achieved by thinning the
head and stacking and / or lengthening the ceramic stack. However, such design techniques are
limited by practical design considerations as follows. As the emitting surface becomes thinner, its
first flexural resonance frequency penetrates into the operating band and significantly alters the
behavior to unit 1. The device becomes mechanically fragile if the active material is thin and
long, either of which is matahaso. If the active material is lengthened to obtain the desired
resonant frequency, this length corresponds to a substantial fraction of the mechanical
wavelength in the material, at which time the material becomes self-resonant and does not drive
the medium. Several techniques have been tried to extend the operating band of mass-loaded
vertical transducers. 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 responsiveness of the device. However, when such special
electrical termination is used, although the spread of the band can be obtained with a slight
amount, there is a problem that the size, amount and complexity increase and the entire device
becomes complicated.
Furthermore, in this method, there is a possibility that local high voltage may be generated at a
node of the circuit, and there is a problem that high voltage isolation and shielding measures
have to be taken. Curve 31 in FIG. 6 shows a typical response when the inductor is operated in
series with the electrical lead to operate the transducer. Tuned transducers operating in an array
structure, as well as untuned transducers, encounter practical problems in the frequency range
near each of the responsive peaks. However, this design broadens the peak-to-peak bandwidth
and relieves array problems due to low head impedance. The 3 dB band between the two peaks,
centered on the dip, extends to relative frequency units of 0.81 to 1.20 and has a width of 0.39
frequency units. Another known way of broadening the operating band of a transducer is to use
an external matching layer. In order to match the acoustic impedances of the transducer and the
medium, an external matching layer 8 is used as shown by the broken line in FIG. 1 (a). The
design using the extrinsic matching layer 8 results in a significantly wider band as shown by
curve 32 in FIG. However, this method also has disadvantages. With the external matching l1Ji8,
the shape of the response curve is a very sensitive function of the density and the speed of sound
of the matching layer material. Therefore, there is no guarantee that the material of the desired
material 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 increased. Furthermore, in
the design with the external matching layer 8, the head impedance becomes too small at two
frequencies making it unsuitable for operation in the array. For example, the responsive
transducer shown by curve 32 is one having an external matching layer of transparent synthetic
resin (lucite), but at a relative frequency of 0.80 and 1.78, the head impedance is Is down. Array
operation is inadequate at any of these two frequencies. Thus, for the responsiveness of curve 32
shown, a useful band is 0.88 frequency units wide, ranging from 0.85 to 1.73 frequency units. If
the drop in head impedance is acceptable, the 3 dB band extends from 0.78 to 1.90 frequency
units, ie, 1.12 frequency units. In a conventional transducer, another method for obtaining two
resonant frequencies is shown in FIG.
This device comprises a low frequency transducer 10, a head mass 11 and a high frequency nonlinear array 12 mounted in a nodal shape on the head mass 11. The transducer of FIG. 2 is not
only a very complex device requiring complex wiring and installation, but also provides high
power transfer in two frequency bands separated by more than two octaves. Each of the low
frequency oscillators 10 and the array 12 of the device operates as if the other were absent.
However, the transducer of FIG. 2 does not exhibit wide band responsivity between the two
resonant frequencies. This is because separate resonances are generated in the transducer by a
system in which the array 12 as a high frequency unit is mounted like a node on the head mass
11 of the vibrator 10 as a low frequency unit. In order to isolate the operation of the high
frequency unit from the structure of the low frequency unit, the nodal attachment must have a
resonant frequency of the system much lower than the high frequency operating resonance.
Moreover, nodal attachment requires that the resonant frequency of the system be above the low
frequency operating band. Otherwise, the low frequency radiator will be separated from the
radiation medium. The acoustic response of the transducer shows a sharp drop in the frequency
range of system resonances. As a result, the prior art device of FIG. 2 can not be used as a wide
band transducer in the entire frequency range between high and low frequency resonances. This
is because the resonant frequency of the nodal attachment is between the two operating bands of
the device. Thus, the device is not just a true broadband transducer, but with only two separate
frequency bands. Other features of typical transducers, such as insulating washers, wiring,
electrical contacts, etc., are well known to those skilled in the art and also can be found, for
example, in US Pat. No. 3,309,654 issued to Miller. It is described in 1I. It is an object of the
present invention to provide a vertical electromechanical transducer capable of operating in a
wider frequency range than before. 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 having a single wide operating
frequency band can be provided. According to one embodiment of the present invention, it is
possible to provide a transducer having high mechanical input impedance in the entire operating
band in the radiation plane, and thus can 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 having high transfer voltage response. Yet another object of the present invention is
to provide broadband frequency response without significantly reducing efficiency. According to
one embodiment of the present invention, a relatively flat response can be provided within the
transducer operating band. According to one embodiment of the present invention, a transducer
having approximately equal transmitted power levels can be provided at all frequencies within a
wide operating band. SUMMARY OF THE INVENTION The present invention provides a
transducer having a head portion including at least three layers to achieve the above-mentioned
object. The two layers of head mass are separated from one another by a heater element (having
compliance). The compliant member of the head may be an active transducer element or seven.
The head is attached to an active transducer element, which is attached to the tail mass. The
transducer with the new composite head has at least two resonant frequencies, which are the
transducer's resonant frequency and head when the compliant member of the head is removed.
Can be regarded as approximate to the resonance frequency of the head part when it is removed
from the part of. The frequencies of these two resonances can be adjusted independently of one
another depending on the particular application. (Means for Solving the Problems) According to
the present invention, in order to solve the problems of the above-mentioned conventional
transducers, in the first invention, N (N is an integer of 2 or more) head masses are used. And emechanical transducer means for securing to the head portion (N-1) compliant means fixed in a
stacked manner between the head masses and performing electromechanical conversion, and the
electromechanical transducer means. A means for fixing was provided. Then, at least N
resonances in the operating band are made to generate resonant oscillations. In a second aspect
of the invention, there is provided a vertical electromechanical transducer for emitting radiation
into a medium, comprising: a head mass in contact with the medium; a first electromechanical
transducer element in contact with the head mass; An intermediate mass abutting the first
electromechanical transducer element, a second electromechanical transducer element abutting
the intermediate mass, and a tail mass abutting the second electromechanical transducer element
The tail mass was then made to have sufficient mass to cause the main motion to occur in the
head and the intermediate mass, and the transducer structure was made to generate two
resonances in the operating band. EXAMPLE In order to obtain wide-band operating frequency
characteristics, the present invention has a mechanical structure having a laminated or laminated
structure in which mass elements and compliant members are alternately laminated in place of
the monolithic head mass 3 of FIG. 1 (a). A resonant head is used. The front of the head is in
contact with the radiation medium and the rear is connected to the rest of the transducer. This is
similar to the case of the conventional monolithic head mass. FIG. 3 shows an example of the
head portion 20 of the present invention having a three-layer structure, and the head mass 21 on
the front side and the head mass 23 on the rear side have sufficient materials to avoid bending
resonance, such as aluminum, steel, metal It is formed of 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, for example, Besbell (VESPEL), a
polyimide plastic sold by DuPont, or Torlon, a polyamide-imide plastic sold by Amoco Chemical,
or It may be an active transducer element or any other material which provides the desired
compliance. Although the compliant member 22 is illustrated to be the same size as the rear
head mass 23, it may be larger or smaller depending on necessity. A conventional epoxy adhesive
may be used to fix the head mass portions 20 to each other, or may be tensioned. FIG. 4 (a)
shows a transducer incorporating the three-layered head section 20 of FIG. The transducer 1
may be a piezoceramic material, for example a piezoceramic made of lead zirconate titanate, and
is available, for example, from VeritrOn Inc, Bedford, Ohio. The tail mass 5 may be tungsten, steel
or aluminium and should have a sufficient weight so that the main movement takes place at the
head 20. Each of the metal masses in the transducer must be sufficiently shorter than 1⁄4 of the
wavelength at the highest frequency of the operating band.
The stress bars 6 are artificially aged (ageed coin treatment) after machining to obtain Alloy 1
with ASTM No. 172 according to ASTM S-196 with a hardness of 1/4 so as to obtain Rock 1 C.
C57-42. It may be beryllium copper. The nut 7 may be aluminum or steel, but it should be flat so
that the rocking of the nut does not occur. The entire assembly of the transducer can be done by
using epoxy and then tensioning the stress rods 6 or by loosely securing them with the assembly
stress rods 6. Adjustment of the compression bias using the stress rod 6 is easy for those skilled
in the art. The approximate equivalent electrical circuit of 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 unit 20 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
piezoelectric ceramic stack 2 is φ. CO represents the actual electrical capacitance of the
piezoelectric ceramic material, C represents the compliance of the ceramic stack 2 and C1
represents the compliance of the compliant members 22 separating the front and rear head
masses 21 and 23 from each other. The transfer voltage response of this 1-transducer is
obtained by the following equation (3). The UTVRα-set (3) 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 made to obtain equation (2) for equation (1).
Equation (3) shows that the selection of the mass of the front and rear head masses 21 and 23
and the compliance of the compliant member 22 allows tuning of the frequency and coupling
between the two resonant modes. The two resonant frequencies in this example are the
resonance of the transducer assuming that the compliant member of the head has been removed
and the resonance of the head only assuming that the head has been removed from the ceramic
stack. It can be approximated more easily as a frequency. However, the above is only an
approximation, and in actual application, some experiments are required to obtain a completed
configuration. The transfer voltage response of this example was calculated using the computer
program described above.
The results are shown by curve 33 in FIG. Curve 1133 of FIG. 6 shows the response obtained
from the transducer of FIG. 4 (a) without the addition of electrical termination or tuning
elements. Transfer voltage response is measured as defined by ANS I Transducer Standard 31.201972. As can be seen by comparing the conventional response curve (30, 31, 32) with the
response curve 33 of the embodiment of FIG. 4 (a) of the present invention, in this embodiment
3d3 (1/2 power) compared to the prior art. ) The frequency band is much wider. The curve 30 of
the conventional transducer of FIG. 1 (a) has a 3 dB bandwidth of approximately 0.36 frequency
units, and a conventional transducer tuned using electrical elements has a curve 31, as shown by
curve 31. The bandwidth is 0 ° 39 frequency units. However, the signal level is high. A
conventional transducer with an external matching layer has a bandwidth of approximately 1.12
frequency units as shown by curve 32, but has a low signal level. On the other hand, in the
present embodiment, the 3 dB bandwidth is approximately 1.28 frequency units. Also in this
embodiment, the signal level is relatively high and the response curve is flat. Another advantage
of the present invention is its superior performance in array structures. The present invention
provides high head impedance in a bandwidth of 1.18 frequency units. In the prior art, the widest
bandwidth without head impedance dip is obtained with a device having a matching layer, the
bandwidth of which is about 0.88 frequency units. According to the invention, there is also no
need for a matching layer. This is because the function of the matching layer is given to the head
portion of the transformer. Another embodiment of the invention is shown in FIG. In this
embodiment, instead of the plastic compliant member 22 of the embodiment of FIG. 4 (a), an
active element 24 forming a second active stack 25 is used. As a result, the till mass 23 is an
intermediate mass rather than the mass that constitutes the head portion. These active
transducer elements 24 may be the same material as the transducer element 1. However,
different response characteristics can also be obtained by using different transducer materials,
such as barium titanate or piezoelectric crystals, such as lithium sulfate. On the other hand, the
dimensions of the piezoelectric material of the two stacks 2 and 25 can be adjusted separately to
meet specific requirements.
In order to illustrate this in the drawing, the thicknesses of the elements 24 and 1 are different.
In this embodiment, the tail mass 5 should have a mass equal to or greater than the sum of the
head mass 21 and the intermediate mass 23. It is preferable that the head mass 21 is equal to or
less than the quality ω of the intermediate mass 23, and the front portions (21 and 25) resonate
at the highest frequency. However, mass balance can be reversed. In this case, it is lower than the
performance of the transformer. The resonant frequency and responsiveness of this embodiment
can be calculated in the same manner as in FIG. 4 (a). As a design approximation, the low
frequency resonance can be known by considering the masses 21.25 and 23 as a single mass
and considering the compliance of the stack 2 together with the tail mass 5. The high frequency
resonances can be approximated by their resonances when the members 21.23 and 25 are
separated from the other parts of the transducer. In practice, the true low frequency resonance is
somewhat lower than the above approximation, and the high frequency resonance is somewhat
high. When operating as a transmitter, the two active stacks 2 and 25 are driven by separate
amplification circuits in some applications. However, in the preferred embodiment which allows
the use of simpler drive circuits, the electrical leads from the two active stacks 2 and 25 have
positive applied voltages such that one of the stacks expands and the other contracts. , Connected
in parallel. In such a configuration, at low frequency resonances, the sensitivity is slightly
reduced to about 0.1 dB), and at high frequency resonances, the sensitivity is significantly
improved (3 dB or more). This is particularly advantageous in applications where the transmitted
power levels need to be approximately equal at all frequencies in a wide operating band. On the
other hand, in the device shown in FIG. 4 (a), the sound pressure level in the transmission axial
direction is substantially equal as shown by curve 33 in FIG. 6, but in this device the transmission
power level is low at high frequencies. This is because the device is more directional so that the
energy is emitted into smaller angular regions. Electrical leads can be connected in parallel to
simplify the necessary electrical circuitry also when the transducer is operating as a receiver. FIG.
7 shows the transmitted power at constant drive voltage as a function of frequency for several
transducer configurations according to the present invention. Curve 34 illustrates the power
response of the prior art device of FIG. 1 (a). Curve 35, as shown in FIG. 4 (a), shows the power
response of the device of the present invention using an inactive compliance member in the
However, the same design parameters as those used when calculating the transfer voltage
response of the song 11133 of FIG. 6 are used. In terms of power response, this device has a
somewhat wider bandwidth. However, the response at high frequency peaks is very low. Curve
36 shows a transducer using an inactive transducer element in the head portion shown in FIG.
This device has relatively flat power response at constant drive voltage throughout the
bandwidth including the two resonances. As yet another embodiment of the present invention, in
addition to the rigid connection of the stress rods 6 to the front head mass 21 and the tail mass
5, a connection is provided between the stress rods 6 and the rear mass 23 of the compliant
member 22. I can think of 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 restrictions on the frequency separation of the two bands.
However, the practical limit is reached when the length of the ceramic stack is longer than 1⁄4 of
the wavelength of the sound in the ceramic material at the highest resonance frequency. Multiple
mass and compliant member layers can also be provided. In such an embodiment having N mass
layers, there are N resonant frequencies, and if the peaks of the response curve are sufficiently
close to one another, a very flat response curve is obtained. The prior art methods of electrical
termination and external matching layer are compatible with the present invention, and the
performance of the device of the present invention can be further improved by the combination
with the electrical elements and the matching layer. This would be ml to the person skilled in the
art. According to the present invention, it is possible to provide a wide operating frequency band
without specially using an electrical termination, and to provide a transducer having a single
wide operating frequency band. it can. Further, according to the present invention, it is possible
to provide a transformer user having high transmission voltage response.
Brief description of the drawings
1 (a) shows the elements and structure of a prior art transducer, and FIG. 1 (b) shows the
equivalent electrical circuit of the transducer of FIG. 1 (a), FIG. FIG. 4 shows a prior art device
having two resonant frequencies, FIG. 3 shows the main elements of the head portion 20 of the
transducer according to the invention, FIG. 4 (a) shows the head portion of FIG. FIG. 4 (b) shows
the equivalent electric circuit of the transducer of FIG. 4 (a), and FIG. 5 shows an element in
which the compliant member 22 is active. FIG. 6 is a graph showing another embodiment of the
present invention having 24. FIG. 6 is a graph showing the response of the transducer of the
present invention shown in FIG. 4 (a) in comparison with the transducer of the prior art. FIG. 7
shows the general transducer configuration of the present invention in comparison to the prior
art. It illustrates a transfer power.
DESCRIPTION OF SYMBOLS 1 ... Transducer element, 2 ... Stack of ceramics, 4 ... Head mass, 5 ...
Tail mass, 6 ... Stress bar, 7 ... Nat, 20 ... Head part, 21 ... Front head mass, 22 ... Compliant
member, 23 ... Rear head mass, 24 ... Active transducer element, 25 ... Active stack. F/に、
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