GB2223377A

GB2223377A - Piezoelectric transducer

Info

Publication number: GB2223377A
Application number: GB8921990A
Authority: GB
Inventors: Wolfgang Kessler
Original assignee: Dornier GmbH
Current assignee: Dornier GmbH
Priority date: 1988-09-30
Filing date: 1989-09-29
Publication date: 1990-04-04
Anticipated expiration: 2009-09-29
Also published as: GB8921990D0; EP0438623B1; EP0438623A1; IT8967838A0; DE3833234A1; GB2223377B; DE3833234C2; IT1232453B

Description

7 7 1 PIEZOELECTRIC TRANSDUCER This invention relates to a piezoelectric

transducer which can be used as transmitter, receiver, hydrophone or sound measuring device.

It has long been known that electric charges are produced at the boundary surfaces of certain crystals when deformation occurs. The crystal undergoes deformation when a voltage is applied. Piezoceramic transducers make use of both these effects as sound receivers or sound transmitters.

Piezoelectric transducers are equipped with metallized electrodes which on the one hand tap the piezoelectricity in the form of electric charges of certain polycrystalline materials produced by mechanical deformation as a result of tension or pressure and on the other hand bring about the mechanical deformation in the form of tension or pressure due to the input of electrical energy.

The calibration of sound measuring devices operating with piezoelectric transducers has hitherto entailed difficulties due to the fact that piezoelectric transducers can only be operated when assembled. The evaluation of the receiving transfer factor, e.g. in underwater sound measurements by means of so-called hydrophones, can only be achieved by establishing a difference from measurement norms. Dimensioning and adapting a charge amplifier to the piezoceramic transducer is difficult by this method since the sensor cannot be replaced by any other laboratory source of signals.

Starting with piezoelectric transducers of the type indicated above, it is an object of the present invention to provide an arrangement which can be used to produce evidence of the possibility of testing the piezoelectric properties employed and make them available in the form of parameters for the specification, e.g. in the case of hydrophones. The

2 arrangement should enable the relevant characteristics to be determined by a simple and economical test method both during the development phase and during the manufacturing and finishing phase as well as the qualifying phase and the operational or use phase. It is also an object of the invention to improve the characteristic data of the charge amplifier and further develop the geometry of piezoceramic transducers.

According to a first aspect of this invention a hydrophone comprises a ceramic body, a receiving electrode, a common electrode, and at least a further electrode which is arranged on the side of the receiving electrode and galvanically separated from the receiving electrode, wherein the said further electrode is a transmitting electrode operable as a transmitter while the receiving electrode is operating as a receiver of mechanical vibration emitted by the transmitting electrode. Other aspects of the invention and features of preferred embodiment of the invention are set out in claim 2 and subsequent claims appended to this description.

In this way it is possible to integrate both a transmitter and a receiver in a single ceramic body. Piezoceramic transducers are suitable for carrying out absolute underwater sound pressure measurements. They convert the acoustic sound into a measurable electrical quantity (a charge/voltage signal) by mearis of the piezo effect of the ceramics used, the piezoceramic transducer in that case functioning as a sound receiver, i.e. as sensor. if, conversely, the ceramic body is subjected to an alternating voltage signal, then the same ceramic body has the property of converting the electrical energy into mechanical sound. The piezoceramic transducer then functions as a sound transmitter, i.e. as projector. These reversible or reciprocity properties of the piezoceramic transducer can be used in accordance with the invention to enable one and the 1 3 same piezoceramic body to function simultaneously as transmitter and as receiver.

The invention will now be described by way of example with reference to the drawings, in which:- Figure 1 is a schematic representation of the structure of a piezoceramic transducer in the form of a cylindrical disc; Figure 2 is a perspective view of a piezoceramic transducer in the form of a perforated cylindrical disc; Figures 3 to 8 are perspective views of further transducers having the geometric form of hollow hemispheres; Figure 9 is a circuit diagram of a measuring arrangement containing a piezoelectric transducer body; and Figure 10 is a circuit diagram of another measuring arrangement using piezoelectric transducers for determining the pairing (or matching) parameters of two hydrophones.

The piezoelectric transducer illustrated in Figure 1 comprises a piezoceramic body 1 in the form of a cylindrical disc having two end faces 2 and 3 with metallized electrically conductive layers 4 and 5 serving as electrodes.

In the illustrated embodiment, one of the electrically conductive layers is subdivided into segments 4a and 4b which are electrically (galvanically) separated from one another and yet are applied to the same homogeneous body 1 of piezoceramic material. The electrode segment 4a in this embodiment constitutes a transmitting electrode and the segment 4b a receiving electrode, the electrically 4 conductive layer 5 covering the second end face of the body 1 serving as a common counter-electrode.

When an alternating voltage signal is applied to the 5 transmitting electrode and the common electrode, an alternating electric field is produced which activates the piezoceramic transducer to undergo mechanical alternating deformation in its direction of polarization Z.

Mechanical tensions are then produced in all three axes. The electric charge thereby generated is tapped in the form of an alternating voltage output signal by way of the receiving and common electrode 5.

The following mathematical relationship then pertains:

Uin = Uout. K where K represents the reciprocity factor.

The term "segmentation" and "segment" are used hereinafter to denote the subdivision of the electrically conductive coating on the piezoelectric carrier body 1 into sections which are galvanically electrically separated from one another. The piezoelectric transducers are without exception covered with metallized layers, denoted here by the reference numerals 4 and 5.

Figure 2 shows the segmentation of a piezoceramic body la which has the form of a perforated cylindrical disc. In this case, the cylindrical surface of the bore carries two electrically separated conductive layers 8 and 9 as electrodes. The electrically conductive coating 10 on the outer circumferential surface of the cylindrical disc constitutes the common counter-electrode to the electrodes 8 and 9.

Z In the examples shown in Figures 3 to 8, the piezoelectric bodies are in the form of spherical half shells 13, 14, each of which constitutes a piezoelectric transducer.

The outer 15 and inner 16 surface of each half shell 13 and 14 is coated with electrically conductive metallic layers applied in known manner.

Figure 3 shows piezoelectric transducers outside the scope of the present invention, consisting of piezoceramic hemispherical bodies with unsegmented electrodes. Two ceramic piezohemispheres 13, 14 are joined together to form a piezoceramic sphere. When the internal surfaces (electrodes 11, 12) are connected together and, separately from these surfaces, the electrodes 15, 16 on the external surfaces are also connected together, the resulting spherical transducer can be operated by means of its electrodes either as transmitter (projector) or as receiver (hydrophone).

In the embodiment shown in Figure 4, which is in accordance with the present invention, the inner electrically conductive coating is subdivided into electrically separate segments. Each half shell 13 in this case forms a piezoelectric transducer. The half shell 14 forms the second transducer. In this embodiment, one of the half shells has a central bore 20 and an electrically conductive coating is applied to the internal surface 21 and 23. The electrically conductive coating on the internal surface of the shell is segmented into an inner region 23 concentric with the bore 20 and an outer region 21 concentric with the inner region.

According to the law of reciprocity, the transducer can in this case be operated either separately as transmitter or as a receiver (as a pressure microphone) or simultaneously as both transmitter and receiver.

6 Further exemplary embodiments of segmented-, electrically conductive coatings for the formation of electrodes which have transmitting and/or receiving properties and can be used simultaneously on one piezoceramic body are shown in Figures 5 to 8. The drawings shown segmentation into three, five, seven and nine parts but the segmentation is not limited to the number of segments shown in the drawings.

is Referring to Figure 9, a measuring arrangement for 10 determining the reciprocity behaviour of a piezoelectric transducer during the development or manufacturing phase has an amplifier 30 which is connected to a hydrophone (not shown) for underwater sound measurement, using a. transducer 31 operating on the basis of the piezoelectric effect and comprising a transmitting segment 32 and a receiving segment 33, for example in the form shown in Figure 4.

The transmitting segment 32 of the transducer 31 is connected to a transmitting signal line 34, and the receiving segment 33 is connected to a receiving signal line 35. While the transmitting signal line 34 is connected to a storage oscilloscope 38, the receiving signal line 35 is connected to the hydrophone amplifier 30 and at the same time to an analysis system 39. The transmitting signal line 34 is connected not only to thr; storage oscilloscope but also to a function generator 36 and to the analysis system 39.

The transmitting segment 32 of the transducer 31 is 30 subjected to a transmitting signal and converts this signal into mechanical vibration. The receiving segment receives a reception signal which has been converted or changed by the mechanical vibration.

The measuring arrangement of Figure 9 serves to determine the characteristic magnitudes during the development or manufacturing phase. The operating and testmethod 31 f, 7 illustrated is particularly suitable for determining certain hydrophone characteristics since it is possible to eliminate interfering transmission sound pressure influences such as are liable to occur when the atmospheric acoustic tube or 5 water tank or pistonphone method is used.

The testing and measurement method illustrated in Figure 9 is based mainly on the known physical principles that in the low voltage signal range and in certain frequency ranges the reciprocity relationship is linear, i.e. the electric field strength and the deformation are proportional to one another.

A second measuring arrangement shown in Figure 10, serves to 15 determine the pairing (synchronicity) of two hydrophones by the method of synchronous reciprocity. The two hydrophones are in this case indicated by the references A and B. In accordance with the invention, each of the hydrophones A and B contains two piezoelectric transducers Al and Bl, each having a receiving segment B2 and A2, respectively and a transmitting segment B3 and A3, respectively. The two hydrophones A and B are connected together by way of receiving signal lines 501 and 50 and transmitting signal lines 511 and 51 by way of a function generator 54 by means of transmission lines 521 and 52. The receiving signal lines 50 lead to an analysis system 53 which is connected to a graph plotter. The receiving signal lines 501 and 50 lead to the receiving segments B2 and A2, respectively while the transmitting signal lines 51' and 51 lead to the transmitting segments B3 and A3 of the piezoelectric convertor A! or Bl, respectively.

8

Claims

A hydrophone comprising a ceramic body, a receiving electrode, a common electrode, and at least a further electrode which is arranged on the side of the receiving electrode and galvanically separated from the receiving electrode, wherein the said further electrode is a transmitting electrode operable as a transmitter while the receiving electrode is operating as a receiver of mechanical vibration emitted by the transmitting electrode.
2. A hydrophone according to claim 1, wherein the ceramic body is discshaped, and wherein the transmitting electrode and the receiving electrode are on one face 15 of the body and the common electrode is on an opposite face.
3. A hydrophone according to claim 2, wherein the transmitting electrode and the receiving electrode are 20 semi-circular and placed together, while the common electrode is circular.
4.

A hydrophone according to claim 1, wherein the ceramic body is in the form of a cylinder having a longitudinal bore, the transmitting electrode and the receiving electrode being on the surface of the bore and the common electrode in the form of a counter-electrode is on the outer circumferential surface.
5. A hydrophone according to claim 1, wherein the ceramic body is formed of part-spherical shell-shaped ceramic parts, and wherein the electrodes are also at least part-spherical, those on the internal surfaces of the body being in the form of part-spherical zones or biangular (twocornered) portions of spheres.
9 A hydrophone according to claim 5, wherein one electrode comprises a part- spherical zone and is surrounded by a plurality of bi-angular (twocornered) spherical sections.
A piezoelectric hydrophone transducer comprising a ceramic body with at least a pair of oppositely directed surfaces bearing electrodes, the electrodes including a receiving electrode and a transmitting electrode located on one of the said surfaces and galvanically separated from each other, and a common electrode located on the other of the said surfaces, the transmitting electrode being operable as a transmitter while the receiving electrode is operating as a receiver for receiving mechanical vibrations emitted by the transmitting electrode.
8. A transducer according to claim 7, wherein the ceramic body is in the form of a drum, and wherein the 20 transmitting and receiving electrodes are on one end face of the body, while the common electrode is formed on the other end face.
9. A transducer according to claim 7, wherein the ceramic 25 body is in the f orm of a drum with an axial bore, the transmitting and receiving electrodes being located on the bore surf ace, and the common electrode being located on the outer curved surface of the drum.
10. A transducer according to claim 7, wherein the ceramic body is substantially in the form of a hollow sphere which is subdivided into two part-spherical shell parts, and wherein the receiving and transmitting electrodes are located on the inner surf ace of the body and the common electrode is located on the outer surface of the body.
11. A transducer according to claim 10, wherein the innersurface of the ceramic body bears a first part-spherical electrode surrounded by at least one other partspherical electrode.
12. A transducer according to claim 11, wherein the first part-spherical electrode is surrounded by a plurality of part-spherical electrodes divided from each other along meridians.
13. A piezoelectric transducer operable as a pressure or sound transmitter and receiver, wherein the transducer has metallised electrodes which are subdivided into at least two segments or sections and are electrically 15 separated from each other (segmented).
14. A piezoelectric transducer according to claim 13, wherein the electrodes are situated opposite each other, and on one electrode side are segmented in a transmitter 20 and a receiver.
15. A hydrophone constructed and arranged substantially as herein described and shown in Figures 1, 2, and 4 to 8 of the drawings.

Published 1990 atThe Patent Office. State House. 6671 High Holborn, LondonWCIR4TP. Further copies maybe obtained from The Patent Office Sales Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd. SL Mary Cray. Kent. Con. 187