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JPS60261293

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DESCRIPTION JPS60261293
[0001]
Industrial Application] The present invention relates to a hydrophone provided with a flat
piezoelectric substrate. [Prior Art] A plurality of wave receiving elements having a piezoelectric
active area are arranged in a straight line in a flat piezoelectric substrate, and on the circular top
side of the substrate, patterns of metal electrodes and electrical connection leads are respectively
formed by these piezoelectric elements The electrically active area of the substrate is polarized in
the direction of the thickness of the film and has a slight extension on the surface on the other
side of the substrate. Small hydrophones are known and are used for the measurement of the
ultrasound field in a sound propagation medium. As a substrate, a membrane comprising
polyvinylidene fluoride P V, D F or a copolymer of vinylidene fluoride and tetrafluoroethylene or
trifluoroethylene, for example, having a thickness of about 25 p, m is used, and this membrane is
It can be tensioned and fixed between two metal rings as a diaphragm. At its center point there is
a piezo-active area, which comprises the electrodes and forms the wave-receiving element. The
film can also be tensioned and fixed on the end of the coaxial cable, whose piezoelectric active
area having a size of about 1 mm is arranged approximately on the tip of the needle. This needle
structure provides a sensitivity of about 6.3 x 10-I'V / Pa ("Illtrasonics J, June 1981, pages 213
to 216). However, it takes a relatively long time to scan a relatively wide ultrasonic field using
such a sonde that incorporates only one wave receiving element. The film of polyvinylidene
fluoride PVDF used as a substrate is already provided with a linear arrangement of a large
number of piezoelectric active areas, which are generally associated with metal electrode and
lead patterns. This pattern is fixed by vapor deposition on the ladder surface of the film. The
receiving element has a diameter of about 2 mm and a capacitance of about 8 pF. The amplifier
is connected to a cable approximately 30 cm long. With this apparatus, a sensitivity of about 3.2
× 10 -6 V / Pa can be obtained ([Journal of the Acoustical Society of America (J, Accoust, Soc, A,
m,) J, Volume 61, Supplement No. 1, Spring 1977 , Pages 17 and 18). Due to the poor adhesion
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of the metal electrode to the polymer film, the size of the wave receiving element can not be set
arbitrarily. Furthermore, the sensitivity can only be increased when each receiving element is
associated with an electronic amplifying element, in particular a field effect transistor, which has
to be arranged in the immediate vicinity of the receiving element.
The connection of the amplifier placed relatively far is loaded by the conductor capacitance CL of
the wave receiving element, and when the capacitance of the wave receiving element is Ct and
the receiver output voltage is UE, it drops to the voltage U by the following equation Be done.
The coaxial cable has a capacitance of, for example, about 1 pF / cm, so that for a 30 cm
conductor, for example, the drop in receiver voltage is C [/ 30 PF times. At the output of the
amplifier, on the other hand, the impedance has already changed and leads can be led to other
parts of the amplifier. Thus, when multiple receiver elements are placed in close proximity to one
another, the dependent amplifiers must also be placed with approximately the same grid
dimensions. [Problem to be solved by the invention] The present invention is to improve such
known small hydrophones, and in particular to provide a hydrophone which can measure a wide
range of unknown ultrasonic fields in a short time and easily. With the goal. It is a further object
of the invention to enhance the usefulness and sensitivity. A known ultrasound transducer with a
plurality of transducer elements for recording ultrasound vibrations from a sound propagation
medium has a film of polyvinylidene fluoride PVDF as a substrate. This substrate comprises on its
two planar sides electrodes of respectively conductive material in a predetermined
piezoelectrically active area forming each transducer element. The film is polarized only in this
area in the direction of its thickness, and this area is arranged on the substrate together with its
electrodes on one side. This monolithic structure of the ultrasound transducer forms a broad
band receive array with high sensitivity (DE-A 31 49 732). The thickness of the electrode, which
may be fixed, for example deposited, on the L-face of the support generally does not significantly
exceed several gm and is advantageously much smaller than Igm. Accordingly, the dependent
electrical connection leads are also not allowed to significantly exceed this thickness. The
connecting wires are produced in a relatively simple manner together with the electrodes in the
same work step, for example in a photolithographic process. However, when trying to connect
the lead to an electrical element disposed on the surface portion of the support, and when the
surface portion forms a ridge with the upper surface, it is difficult to guide the connecting lead
around the ridge of the support is there. In this case, it is possible to provide a groove 5
extending perpendicularly to the ridge on the surface portion adjacent to the ridge on the top
and side.
In this groove at least a part of the surface is provided with a metallized layer, by means of which
a lead connection between the electrode and the above-mentioned electrical element is made, for
example, by soldering (German Patent Application DE 324 fli 681). SUMMARY OF THE
INVENTION The present invention uses this known constructional feature of an ultrasound
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transducer and is constructed on the basis of the features of claim 1. The size of the wave
receiving element on the plane side L of the substrate is generally smaller than 1 mm, and the
distance is limited to a value not significantly exceeding 0.1 mm. Since the size of the dependent
amplifiers, preferably the hybrid amplifier, also does not significantly exceed this size, these
results in grid sizes of a linear configuration smaller than 1 mm. This hydrophone has a
sensitivity of at least 10-5 V / Pa. For measurement of the ultrasonic sound field, it is sufficient to
move only once in the direction perpendicular to the linear arrangement of the wave receiving
elements. In a special embodiment of the hydrophone, the distances from the beginning or end of
the support to the first and last receiving elements are respectively only approximately half the
distance between the receiving elements. Therefore, it is possible to arrange a large number of
modules one after another so as to form a common structural unit having the same grid size in
the linear arrangement direction of the receiving elements, and using this unit, a wider range of
Sound field can be measured in a short time. Further embodiments of this hydrophone are
described in the subclaims. The invention will now be described in more detail with reference to
the drawings showing embodiments of the invention according to the invention. In the
embodiment shown in FIG. 1, the wave receiving element 10 is formed from the piezoelectric
active area 3 indicated by a broken line in the drawing of the base 2, and in this area 3, the
electrode 4 is disposed on the other side of the base Further, an electrode 5 is attached to the
lower flat side, and the electrode 5 is fixed on a support 16. The electrode 5 is capacitively
coupled to the piezoelectric active area 3 of the substrate 2 via a non-conductive adhesive layer 6
having a high dielectric constant. The lower electrode 5 comprises an electrical connection lead
11. For the adjacent wave receiving elements in the linear arrangement of the wave receiving
elements 10, the connecting conductor 12 is shown in the figure. The -L surface 15 of the
support 16 is laterally defined by two inclined side surfaces 17 and 18 which together with the
upper surface 15 form the ridges 22 and 23, respectively. These weirs 22 and 23 are provided
with grooves 24 and 25 respectively in the area of the connecting wires 11 and 12 and which
extend perpendicularly to the weirs 22 and 23 and the internal surfaces thereof are respectively
at least partially shown. The metallized layer is not shown in tlj.
The metallization layer in the groove 24 is, for example, as an electrical connection, preferably a
solder pot, of the connecting conductor 26 for the amplifier 32 which is subordinate to the
receiving element 1o and arranged on the substrate 33. Play the role of For adjacent receiver
elements not shown in the figure, the dependent connection conductor 27 and the amplifier 36
likewise arranged on the substrate 37, -L: are shown in the figure. The substrate 2 of the wave
receiving element 10 comprises a sheet of a polymer, preferably polyvinylidene fluoride PVDF or
a copolymer of vinylidene fluoride and tetrafluoroethylene or trifluoroethylene, and its thickness
is, for example, about 25/7. At m, the sheet is polarized in the direction of its thickness in its
piezoelectric active area 3. B) The electrodes 4 and 5 provided are made of metal and their
thickness preferably does not exceed several kilometers, and in particular can be significantly
smaller than lpm. Suitable as electrodes are chromium / silver or chromium / gold bilayers, in
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which, for example, a chromium layer of about 20 nm thickness serves as an adhesion medium
and on top of this chromium layer eg 0.2 pLm A silver layer is deposited. The electrodes 5 can be
provided, in particular, by vapor deposition or sputtering on the support 16 together with the
subordinate connection leads 11 in one common working port. The electrode 5 is fixed to the
substrate 2 in a face-to-face manner by the adhesive layer 6, and the adhesive layer 6 is made of
an electrically insulating material having a high dielectric constant, preferably an adhesive layer
or a putty layer. The support 16 (so-called backrest) can preferably be made of a material having
a high acoustic impedance. For example, a ceramic, preferably alumina Al2O3, is suitable for this
embodiment as a so-called rigid backing, the acoustic impedance of which is about 40 × 10 L kg
/ m 2 s. Also suitable are glasses or quartz having an acoustic impedance of 14 × 106 kg / m 2
s. As the support 16 it is also possible to use a soft backing which absorbs the ultrasound itself
and which is, for example, made of rubber. The received ultrasound signal is capacitively
transmitted from the lower side of the active area 3 to the electrode 5 in the conversion element
10 in the frequency band of about I MHz to at least 10 MHz, and the connecting wires 11 and 26
The signal is then supplied to the dependent amplifier 32. A suitable amplifier 32 is a hybrid
amplifier arranged on a substrate 33, preferably a thin film substrate. This hybrid amplifier has a
hetero structure. The resistor can preferably be formed by thin film technology-4, while the
attached transistor is glued as a transistor chip and its conductive connection is pounded.
The wave receiving element 10 is coupled to the cover film 39 via the ultrasonic coupling
medium 38, which can be made of, for example, a polymer and also serves as a closing wall on
the front side of the chamber, in this chamber The illustrated constituent units are arranged. As
shown in the perspective view of FIG. 2, because of the large number of wave receiving elements
10 indicated by broken lines in the figure, all the wave receiving elements lO1 are placed on the
side of the common substrate 2L-i's plane iI'41. A common electrode 4 is provided. The substrate
2 with the adhesive layer 6 is shown at a distance from the lower electrode 5 for the sake of
clarity, the electrode 5 having for example 16 receiving elements 10 not shown in detail in the
figure. The modules are arranged in tandem in the linear extension direction of the module. For
example, assuming that the length l = 0, 8 mm, the width b = 0.7 mm, the distance a-0, 1 mm
between the electrodes 5 and the lattice size of the receiving element flO be 0.8 mm, the total
length L of the module is about It will be 12 mm. Thus, for example, at a frequency of 2 MHz, the
capacitance Cf of the wave receiving element 10 is approximately 1.6 pF. In a particularly
advantageous embodiment of the hydrophone, the amplifiers 32 or 36 dependent on the wavereceiving element 10 are respectively arranged on the side 17 or 18 of the support 16 at the
intersection 1. The electrical lead connections between the electrodes 5 and the dependent
amplifiers 32 which are made up of the connecting leads 11 and 26 and which are
interconnected with the aid of the metallization layer in the groove 22 are very short, for
example It may be about 1 mm and may be the same for all the receiving elements io. The
sensitivity of this system of receiver / -10 and amplifier 32 or 36 is therefore uniform and very
high. For example, a small intrinsic capacitance of about 2 pF and a high input impedance of
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about 100 Ω, and a small channel width of about 20 times amplification and a small channel
width of about 1.6 mm, and a wide bandwidth of about 15 MHz and a low about 8 nV / rHz Due
to the noise, a sensitivity of about 10 -5 v / Pa is obtained in an idrophone having 16 wave
receiving elements 10 and a substrate 2 with a thickness of 257 pm. The amplifier 32 comprises
a signal lead 43 with the aid of a metallization area 42 on the surface of the substrate 33, which
signal lead can be routed to another component of the amplifier 32. In the embodiment shown in
FIG. 3, a module with a large number of wave receiving elements 10 is arranged in a chamber 40,
which is closed on its front side by a cover film 39, which is An ultrasonic coupling medium 38 is
coupled to the wave receiving element 10 disposed on the support 16.
The support 16 consists of a hard backing and is provided with an absorber 46 at the end
opposite to the wave receiving element 10, which absorber may consist of an epoxy resin
incorporating a filler made of alumina powder, for example. it can. The end of the support 16 is
sharpened such that the portion of the ultrasound that has penetrated into the support 16 is
reflected off the interface between the absorber 46 and the support 16. The walls of the chamber
40 generally consist of metal. The cover film 39 is made of a high strength, water impermeable
material. The cover film can be made of, for example, polyethylene / one or polyurethane or
polyimide having a thickness of about 254 m. In a particularly advantageous embodiment of the
hydrophone, the cover film 39 is provided with a metallized protective layer 41 which serves for
shielding. In addition to the receive elements lO and their subordinate amplifiers 32 and 36 and
their electrical connection lines which are not shown for the sake of simplicity, the chamber 40
has these amplifiers 32 and 36 for each series of amplifiers 32 and 36. Attached components
such as ti Ws, resistors and capacitors can be incorporated, these components are shown as
common components in the figure for the sake of simplicity and are labeled 52.56. These
components 52 and 56 are each arranged on an unsigned printed circuit board with a
multiplexer 44.45 common to all the amplifiers 32.36, the output signals of the multiplexers
being common to each other. Signal leads 48 can be used. The signal line 48 can preferably be
configured as a multiplex cable, which contains not only the current supply for all parts of the
hydrophone but also an addressing. The ultrasonic coupling medium 38 only has the function of
preventing the formation of an air layer between the wave receiving element 10 and the cover
film 39. A layer of, for example, a water-containing gel or silicone grease is suitable as the
ultrasonic coupling medium 38, the thickness of this layer generally not exceeding Ggm and can
be for example 5 gm. In the embodiment of the hydrophone shown in FIG. 4, the substrate 2 of
the wave receiving element 10 is used as a force / heat film for the chamber 40. The adhesive
layer 6 simultaneously constitutes the electrical coupling medium for the electrodes 5 fixed on
the support 16. In this embodiment, the metal cover 4 simultaneously serves as the ground
electrode for the wave receiving element 10.
[0002]
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Brief description of the drawings
[0003]
1 is a partial cross-sectional view of a first embodiment of the hydrophone according to the
present invention, FIG. 2 is a partial perspective view of the hydrophone shown in FIG. 1, FIG. 3 is
a cross-sectional view of the second embodiment, and FIG. FIG. 10 is a partial cross-sectional
view of Example 3;
2 ... basic body, 3 ... piezoelectric active area, 4.5 ... electrode, 6-... adhesive layer, lO ...-wave
receiving element, 11.12-... electrical connection lead (lead wire · · · · · · · 1-1 face, 16 · · · support ·
17. 18 · · · side face, 22 · · · · fistula, 24, 25 · · · groove, 26 27 , 32.36 ... amplifier, 33.37 ...
substrate, 38 ... ultrasonic coupling medium, 39 · IIII force / <-7 (lum, 40--chamber, 41-protective
layer, 42 ... Absorber, 44.46 @ .. Multiplexer. FIG17′FIG340FIG4
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