EP2741524B1 - Electroacoustic transducer - Google Patents

Description

The invention relates to an electroacoustic transducer comprising a transducer element, a passive electrode and an active electrode.

With the help of an electroacoustic transducer sound can be converted into an electrical measurement. The central element of such an electroacoustic transducer is a transducer element, also called a transducer, in which the pressure fluctuations of the sound are converted into an electrically evaluable received signal. A front side of the transducer element is facing the sound to be detected. A back side faces the front, i. the transducer element is located between the front and the back.

During the measurement, a passive electrode serves as a reference. It is usually at a ground or ground potential. The received signal is measured between the passive electrode and an active electrode. Since the sound signals to be detected are usually relatively weak, the received signal to be detected is also weak and susceptible to electromagnetic interference coming from, for example, other nearby electronic devices or machines.

To shield frontal electromagnetic interference, the passive electrode is located at the front of the transducer element. An electromagnetic shield to the side can be achieved by an electrically conductive housing in which the electro-acoustic transducer is located. However, to protect a user and to protect the electronics of the transducer, the external housing must not be electrically connected to the internal part, a non-conductive layer of non-conductive material must be necessarily present between the passive electrode and the housing, thereby providing a shielding gap is given, so that electromagnetic interference can penetrate into the interior of the housing. Furthermore, the transducer element is embedded in a damping material in order to quickly decay vibrations. This creates further gaps through which interference with sensitive electronics can penetrate. Such disturbances may continue to disturb the very weak signal on the active electrode despite the shielding measures.

Disturbances are indeed dampened in this previous design, however, it remains due to the system always an inevitable remnant of disturbances that penetrate into the interior and can lead to error signals.

The DE 42 15 271 A1 shows an ultrasonic transducer with a housing which is closed at the end by a membrane, on the inside of a piezoelectric transducer is firmly bonded, wherein the membrane is made of ceramic.

The WO 2008/127885 A1 shows an electroacoustic transducer element for ultrasound.

The DE 10 2008 044 351 A1 shows an ultrasonic sensor for a vehicle, which in a housing a contactable with at least one electrical lead transducer element for generating ultrasound, wherein at least the transducer element is shielded by one or more electrically conductive shield surfaces against electromagnetic radiation.

It is an object of the present invention to provide an electroacoustic transducer in which electromagnetic disturbances less affect the measurement result and consequently result in fewer error signals.

This object is achieved by an electroacoustic transducer according to claim 1.

Thus, the active electrode can also be shielded against interference from the rear in an advantageous manner. Such a rear shield may be located directly behind the active electrode. Parts of the rear shield could also be located obliquely behind or next to the active electrode. The rear shield may be at least partially or partially parallel to the active electrode. It may be at least partially or in sections parallel to the passive electrode, at least to a located at the front of the main body of the passive electrode. The active electrode, the passive electrode and the rear shield may each be flat. They can each lie directly next to each other in pairs.

In an advantageous embodiment, the active electrode is sandwiched between the passive electrode and a rear shield. Such a configuration is particularly compact.

With the inventive conductive connection of the passive electrode with the rear shield, the rear shield is also on a defined Potential. As a direct connection mechanism can serve in this case, for example, a solder joint or a short pin. The length of the electrical connection between the passive electrode and the rear shield may be on the order of the physical distance of the two parts. Compared to longer connections, where the passive electrode and the rear shield are each individually connected to a remote intermediate element, eg electronics, such a direct and / or short connection is less susceptible to interference. Furthermore, such a direct and / or short connection has better electrical properties, in particular a smaller impedance compared to an indirect and / or longer connection.

In particular, can be dispensed with a connection between the passive electrode and the rear shield on cable. Cables represent potential sources of error that can adversely affect the electrical properties of the connections. The connection may be insoluble, such as a solder joint.

Alternatively, the compound can also be detachable. It may be about a pressing or pressing connection.

In the embodiment according to the invention less interference signals can reach the active electrode. As a result, fewer error signals occur. Such an electroacoustic transducer is thus more reliable.

The invention can be further improved with the following, each for themselves advantageous and any other combinable developments and refinements.

The passive electrode may continue along a plurality of transverse sides of the transducer element located between the front and back surfaces. In particular, the passive electrode may continue along all the transverse sides of the transducer element situated between the front side and the rear side. In such an embodiment, the shielding effect is further increased, since a larger space area is covered.

The front side, the back side and / or the transverse side can each consist of a single surface or of several surfaces.

The passive electrode may extend to the backside. As a result, the shielding effect is further improved. The passive electrode may extend to a plane that at least partially contains the active electrode. If the passive If the electrode extends simultaneously along all transverse sides up to this plane, the passive electrode, viewed from the active electrode, covers a solid angle of two pi (2π), ie a half-space. By this configuration, interferences acting on the ultrasonic sensor are effectively shielded.

Parts of the passive electrode may be on the back. Parts of the passive electrode may be arranged or mounted, for example, on the back. The passive electrode may continue at least partially on the backside. In addition to improved shielding, such an embodiment can also have the advantage that the passive electrode can be contacted from the rear and not from the side. This allows a compact design to the sides.

The passive electrode forms, together with the rear shield, a shield surrounding the active electrode on all sides. As a result, the active electrode is shielded in all spatial directions. Interference can thus no longer influence the active electrode from any direction. The shield surrounding the active electrode on all sides may nevertheless have openings, holes or slots. These should be as small as possible. The dimensions and / or orientations of such openings may be adapted to the wavelengths or orientations of undesired disturbances, so that, for example, interferences with specific wavelengths, despite the openings, can not penetrate the active electrode or can only penetrate with great attenuation. For adequate shielding and perforated plates can apply.

The passive electrode forms, together with the rear shield, a shield completely enclosing the active electrode. Apart from smaller openings, which are necessary for making contacts for contacting the active electrode, the active electrode is thereby completely or almost completely shielded over the entire solid angle of four Pi (4π).

The electroacoustic transducer comprises electronics. The electronics can consist of different sub-electronics. Various subelectronics may be mounted at various locations in the electroacoustic transducer. Amplification electronics for amplifying a weak signal may, for example, be a sub-electronics of the electronics and be arranged in the vicinity of the active electrode. Other sub-electronics may be located near or even further away from the amplification electronics, even outside a housing. The Electronic may include part electronics such as signal processing and / or signal evaluation.

Electronic or electrical components of electronics or sub-electronics can be, for example, surface-mounted components, so-called SMD components (Surface Mounted Device).

The electronics or partial electronics can at least partially be designed as an integrated circuit. Such a configuration is particularly compact.

The electroacoustic transducer may comprise a substrate with electronics or sub-electronics disposed thereon. The substrate may in particular be a planar substrate or a flat body. In the case of a flat substrate or a flat body, an expansion in one dimension is substantially smaller than the extent in the other two dimensions. So there are essentially only two opposite sides available. For example, it may be a circuit board. Such a printed circuit board can be rigid or flexible.

The electronics or partial electronics can be arranged only on one side of the substrate. Alternatively, the electronics or partial electronics can also be arranged or attached to two or more sides of the substrate. In the case of a planar substrate, the electronics or partial electronics can be arranged or mounted on both sides. The entire electronics can be arranged on the substrate. Alternatively it can be arranged on the substrate only a partial electronics, such as an amplification electronics. Further sub-electronics may in this case be arranged, for example, on a further substrate or on other parts of the electroacoustic transducer.

In order to allow the most compact possible construction, in an advantageous embodiment, the active electrode is sandwiched between the passive electrode and the substrate. Such a configuration is particularly compact if the substrate is flat.

The electroacoustic transducer may comprise a substrate having a shielding layer on at least one side. Such a shielding layer can be made of electrically conductive material throughout. It can at least partially shield two areas from each other electromagnetically. For example, a sheet substrate such as a multi-layer printed circuit board, particularly a flexible printed circuit board, may be one Have shielding. On a substrate does not necessarily have to be arranged electronics or part electronics.

To shield the active electrode, the shielding layer together with the passive electrode forms a shield surrounding the active electrode on all sides. As a result, the active electrode is effectively shielded in all spatial directions. The shielding layer can thus serve in particular as the rear shield already mentioned above. Similarly as described above, a shield enclosing all sides can also have holes or free areas. Again, the size and / or orientation of such holes can be adapted to the wavelength to be shielded and / or the frequency to be measured. A shield formed by the passive electrode together with the shielding layer encloses the active electrode completely or almost completely. Only feedthroughs for contacts necessary to contact the active electrode may be present.

The electronics or partial electronics mounted on only one side of the substrate can lie between the active electrode and the substrate. Other sides of the substrate may form a smooth outer surface, which may be advantageous in an assembly, for example, since the electronics are mechanically protected. In particular, the electronics or partial electronics alone or together with the active electrode as described above for the active electrode can be shielded on all sides or completely by a rear shield and / or a shielding layer. In a preferred embodiment, both the active electrode and the electronics or a sub-electronics, such as a reinforcing member, in the all-round or complete shield. Such a shield may again be formed by the passive electrode together with a rear shield or shielding layer.

Alternatively, the substrate, in particular the planar substrate, can be located between the active electrode and the electronics or partial electronics. A shielding layer can shield the active electrode from disturbances caused by electronic components. The active electrode may communicate with a component on another side through a hole in the substrate. Such a connection can be designed in particular in a flat substrate without cables. In particular, the length of the connection may be very small and / or the connection may be direct, thereby improving the electrical properties of such connection, such as impedance, as compared to a longer and / or indirect connection or connection via cable.

A substrate, in particular a planar substrate, with a shielding layer may be formed such that the shielding layer forms an outer shield for an electronics or part electronics located in an inner space formed by the shielding layer. Such a shield can shield the electronics or part electronics located in the interior to several sides. For example, a flat substrate may be folded so that the electronics or partial electronics are shielded in two or more directions. A flexible substrate may be bent. It may for example have a U-shape in cross section. Such a U-shape shields from several sides. The electronics or part electronics located in the interior can be shielded on all sides, in particular the electronics or part electronics can be completely or almost completely shielded by the shielding layer. Such an external shield is connected to the passive electrode or a ground. This connection can be short and / or direct, as described above for the rear shield. Furthermore, it may be solvable or insoluble.

The shielding layer of a substrate may simultaneously be a rear shield for the active electrode and an outer shield for an electronics located in an inner space formed by the shielding layer. For example, a part of the shielding layer may shield the active electrode to the rear, while the entire shielding layer forms an outer shield for an electronics located in an inner space formed by the shielding layer. The shielding layer thus fulfills a double function here. In a particularly advantageous embodiment, a part of the shielding layer together with the passive electrode forms an active electrode on all sides, in particular completely enclosing shielding, wherein at the same time the shielding layer is an external shield for an electronics or part electronics located in an interior space formed by the shielding layer.

The active electrode and the passive electrode may be separate regions of a previously bonded single layer. By way of example, a transducer element may have been completely coated and subsequently a part of the layer removed so that an active electrode and a passive electrode have been formed. Such a separation can be done for example by etching, scribing, grinding or by targeted evaporation by means of a laser.

In an easy-to-manufacture embodiment, the front side is flat or even. Also the back can be flat or even. Especially with a block-shaped Transducer element manufacturing can be simplified. Alternatively, for example, the front side be designed so that it receives a sound signal in its entire extent with the same phase. Such an embodiment could, for example, be adapted to a lobe or spherical shape of a sound signal to be detected. This would lead to minimal phase shifts.

The front can be parallel to the back. Such a configuration is easy to manufacture, especially if the transducer element is block-shaped. Furthermore, in such an embodiment, the occurrence of phase shifts in eventual echoes may be reduced.

In an advantageous embodiment, the transducer element may be block-shaped. A block-shaped transducer element is e.g. a block of material, such as a crystal. In such an embodiment, the passive electrode and / or the active electrode can be arranged on the block-shaped transducer element. For example, they may be attached to the block-shaped transducer element. In particular, they can be firmly connected to the block-shaped transducer element.

In a particularly advantageous embodiment of a transducer element, the passive electrode and / or the active electrode are mounted as a layer on the transducer element. Such a layer can be attached to the transducer element, for example, by coating methods such as physical vapor deposition, electroplating, or the like.

A transducer element may be cylindrical. In particular, the transducer element may be circular cylindrical. For example, it may be a disk, i. around a transducer element, wherein the expansion in one direction is substantially smaller than in the other two directions. Such a geometry is easy to produce and, due to the large area, allows a signal to be well detected while maintaining a compact design.

The sound to be detected may be ultrasound. When measuring with ultrasound, a user is not disturbed by the measurement. Conversely, such a measurement is not affected by conversations or ambient noise. Furthermore, measurements with ultrasound are usually more accurate than measurements with longer wavelengths.

The electroacoustic transducer may comprise at least one piezoelectric transducer element. The piezoelectric transducer element converts sound into an electrical voltage.

An inventive electro-acoustic transducer can not only serve as a receiver, which converts sound into an electrical measurement, but at the same time also serve as a transmitter for generating sound. In order to switch between the function as a receiver and the function as a transmitter, a switching mechanism and / or a switching element may be present. This allows the electroacoustic transducer to be connected to various electronics or sub-electronics for transmission and reception, depending on the function.

In order to be able to connect as well as possible to a sound transmitting medium, a matching layer may be present in the electroacoustic transducer. Such a matching layer is arranged on the front side of the transducer element.

Sensitive parts of the electroacoustic transducer, namely the active electrode and electronics, are all sides shielded by the measures mentioned, in particular completely electromagnetic. The entire electronics and / or the entire electroacoustic transducer can be shielded on all sides, in particular completely electromagnetic. In such a case, a shield by an outer housing may no longer be necessary. An outer housing may then consist of an insulating material.

The shielding solutions described above can also be used independently of each other. For example, a rear shield could also be present in an electroacoustic transducer in which the passive electrode does not continue on a transverse side. The same applies to the shielding of electronics by an outer shielding layer of a substrate.

In the following, the invention will be explained in more detail by way of example with reference to advantageous embodiments with reference to the drawings. The described embodiments represent only possible embodiments in which, however, the individual features, as described above, used independently and combined with each other and / or can be omitted. The same reference numerals stand in the various drawings in each case for the same objects.

Fig. 1

einen schematischen Querschnitt eines aus dem Stand der Technik bekannten elektroakustischen Ultraschallsensor;

Fig. 2

einen schematischen Querschnitt eines Teils eines nicht beanspruchten elektroakustischen Wandlers;

Fig. 3

einen schematischen Querschnitt eines nicht beanspruchten elektroakustischen Wandlers;

Fig. 4

einen schematischen Querschnitt einer Ausführungsform eines erfindungsgemäßen elektroakustischen Wandlers.

Show it:

Fig. 1

a schematic cross section of a known from the prior art electroacoustic ultrasonic sensor;

Fig. 2

a schematic cross section of a portion of an unclaimed electroacoustic transducer;

Fig. 3

a schematic cross section of an unclaimed electroacoustic transducer;

Fig. 4

a schematic cross section of an embodiment of an electroacoustic transducer according to the invention.

In Fig. 1 an embodiment of an ultrasonic sensor known from the prior art is shown in a cross section. With this sound 2 can be converted into an electrical measurement. An electroacoustic ultrasonic transducer 1 has a matching layer 4 in order to couple the sound 2 as well as possible to a transducer element 3. The transducer element 3 then converts the sound 2 into a received signal. The transducer element 3 is connected via cables 5a, 5b to an electronics 6. This electronics 6 comprises an amplification electronics 7, in which the usually weak received signal is amplified. After amplification, the signal can be further processed, for example, it can be filtered or evaluated. Subsequently, the signal can be output via an output (not shown) located on a connection side 8.

The electroacoustic ultrasonic transducer 1 comprises a housing 9. The housing 9 may for example consist of an electrically conductive material to shield from the side acting noise.

The ultrasonic sensor shown here can not only work as a receiver, but also as a transmitter. In this case, the transducer element 3 emits sound at intervals and, between the transmission intervals, measures the sound 2 reflected by an object to be measured.

In order to damp the oscillations that occur in the transmission interval as effectively as possible, the transducer element 3 is embedded together with the matching layer 4 in a damping material 10. As a result, the cooldown is reduced, which allows, for example, a measurement even at short distances to the object to be measured. The Transducer element 3, the matching layer 4 and the damping material 10 are arranged in a cup 11, which in turn is held by the housing 9.

The electronics 6 shown in this example is located on two sides 100, 101 of a printed circuit board 14. Electronic components 15 are mounted on both sides 100, 101. Laterally to a preferred direction of sound 2r, ie in the Fig. 1 up, down, out of the plane of the drawing and into the plane of the electronics 6 is electromagnetically shielded by the housing 9, since this consists of an electrically conductive material. To the rear, such a shield may be present on the connection side 8. To the front, the electronics 6 may be electromagnetically shielded by an inner coating 11 b of the cup 11. However, such a coating must have a certain minimum distance from the housing 9 in order to prevent internal parts, which are connected to the coating 11b, such as the electronics 6, are conductively connected to the housing 9, since this could endanger a user. Also, to protect the internal electronics 6 from external influences such a connection must not exist. In order to protect especially a sensitive amplifying electronics 7 from penetrating electromagnetic interference, the electroacoustic transducer 1 therefore has a shield 7a for the amplification electronics 7. To shield the 11 of the cup 11b of the cup 11 only partially shielded, sensitive active electrode 13 better, is the passive electrode 12, which is arranged on the front side 120 of the transducer element 3, which is opposite to the back side 130, specially designed.

In Fig. 2 a part of the electroacoustic transducer 1 is shown enlarged. In Fig. 2 a passive electrode 12 is shown. The passive electrode 12 not only extends on the front side 120 of the transducer element 3, but also continues on a transverse side 140 that lies between the front side 120 and the rear side 130. As a result, the active electrode 13 is effectively protected not only from front-side noise 16a, but also from front-end noise 16b. In addition to a portion 12v located on a front side 120 of the transducer element 3, the passive electrode 12 also has lateral parts 12s which are located on transverse sides 140 of the transducer element 3. The front part 12v is in particular made in one piece with the side parts 12s. The side parts 12s extend laterally around the entire transducer element 3 around, which has a particularly far-reaching protection result. In other embodiments, such side parts 12s may also extend only partially around the transducer element 3.

The passive electrode 12 is connected via a cable 5a to an electronic system. The passive electrode 12 is connected to a ground potential of the electronics in order to achieve the best possible shielding.

An active electrode 13 is located on a rear side 130 of the transducer element 3. It is connected to the electronics via a cable 5b.

Between the active electrode 13 and the passive electrode 12, a received signal generated by the sound 2 in the transducer element 3 is measured. For example, the transducer element 3 may be a piezoelectric transducer element. If such a piezoelectric transducer element is exposed to the pressure fluctuations of the sound 2, a voltage difference arises between the passive electrode 12 and the active electrode 13 which can be measured. This received signal can be further processed in an electronic system. It can be reinforced, for example.

By means of the matching layer 4, the sound 2 is coupled to the transducer element 3 in a particularly efficient manner. Depending on the field of application and the frequencies to be measured, the matching layer 4, in particular the material of the matching layer 4, can be suitably chosen. The matching layer 4 can be bonded to the transducer element 3, that is to say in particular to the passive electrode 12 which is located on the transducer element 3.

The active electrode 13 and / or the passive electrode 12 may each be a layer on the transducer element 3. This can be applied there by coating methods such as physical vapor deposition or electroplating. In particular, the active electrode 13 and the passive electrode 12 may be separated regions 25a, 25b of a previously connected layer 25. For example, the transducer element 3 can have been completely coated and the layer has been divided into different, mutually independent regions 25a, 25b. The separation can be effected for example by etching or by laser irradiation.

The transducer element 3 shown here is block-shaped and in particular cylindrical. A front side 120 is executed parallel to a rear side 130.

In order to obtain the strongest possible signal, the transducer element 3 should have a large width 3w and / or a large cross-sectional area 3f. Of course, sound from other directions can also hit the electroacoustic transducer 1. In the embodiment shown, only the component of the sound 2 that lies along the preferred sound direction 2r is measured. The along the preferred sound direction 2r measured thickness 3d of the transducer element 3 can be relatively small compared to the width 3w. The transducer element 3 may thus be disk-shaped.

In Fig. 3 a cross section of an electroacoustic transducer 1 is shown. In addition to the components shown here, other elements may be present. For example, an electronics can still be connected.

The transducer element 3 is designed block-shaped. At the front side 120, a front part 12v of the passive electrode 12 is mounted. The passive electrode 12 continues on the transverse sides 140 of the transducer element 3. Side portions 12s of the passive electrode 12 are thus located on these transverse sides 140. The passive electrode 12 also continues on the rear side 130 of the transducer element 3. On this rear side 130 there is a rear part 12h of the passive electrode 12.

The passive electrode 12 extends to a plane 13e containing the active electrode 13, thereby shielding the entire front half space for the active electrode 13.

Via connecting elements 20, the passive electrode 12 is connected at its rear part 12h directly to a rear shield 17 in the form of a shielding layer 18. The shielding layer 18 is disposed on a side 105 of a substrate 19. The substrate 19 is planar and has two sides 104, 105. The first shielding layer 18 is opposite to a second shielding layer 18 'on the other side 104 of the planar substrate 19.

The first shielding layer 18 together with the passive electrode 12 surrounds the active electrode 13 on all sides and thereby forms an all-round shielding for the active electrode 13. The all-round shield has only small gaps. For example, it is interrupted to allow the contacting of the active electrode 13 by means of a contacting element 22. In particular, the active electrode 13 is completely shielded by the all-round shielding. As a result, the active electrode 13 is shielded not only against disturbances 16a coming from the front and interferences 16b acting obliquely from the side, but also against disturbances 16c acting from the rear.

The signal measured at the active electrode 13 is relayed via the contacting element 22 and an electrical connection 5c. For example, it can be connected to a Electronics be forwarded. In this case, the electrical connection 5c is shielded between the first shielding layer 18 and the second shielding layer 18 '.

The active electrode 13 is crossed by the passive electrode 12 over a solid angle of two pi (2π), i. Shielded over a half-space. By the rear shield 17 in the form of the first shielding layer 18, the active electrode 13 is additionally over the other half space, i. again shielded over two Pi (2π). Overall, the all-round shielding by the rear shield 17 and the passive electrode 12 is a shield over the entire solid angle of four Pi (4π). The passive electrode 12 is thereby conductively connected to the rear shield 17. This conductive connection is made via the connecting elements 20, which bridge only a short distance. The connecting elements 20 may be, for example, solder or pin-shaped connecting elements. The length of the connecting elements 20 is of the order of the physical distance between the passive electrode 12 and the rear shield 17. The connection may be detachable or insoluble.

The transducer element 3 is accommodated together with a matching layer 4 and the planar substrate 19 in a damping material 10.

The in Fig. 3 shown electroacoustic transducer 1 can be similar to in Fig. 1 be installed in a housing. Alternatively, however, it can also be installed differently, in particular no additional shielding must be present if the shielding of the active electrode is sufficient for reliable functioning.

In Fig. 4 an advantageous embodiment of an electroacoustic transducer 1 according to the invention with an embodiment of a transducer element 3 is shown in a cross section. Similar to the in Fig. 3 shown transducer 1 is also in the in Fig. 4 illustrated embodiment of an electro-acoustic transducer 1, the passive electrode 12 pulled to the back 130 of the transducer element 3 to the rear. The passive electrode 12 comprises a front part 12v arranged on the front side 120, which constitutes the main part of the passive electrode 12, side parts 12s arranged on the transverse sides 140 and rear parts 12h arranged on the rear side 130.

The passive electrode 12 is connected at its rear parts 12 h via connecting elements 20 with a shielding layer 18. The shielding layer 18 is located again on a substrate 19, which is also formed here flat. However, the substrate 19 has in this case only on one side 102 via a shielding layer 18. On the other side 103, an electronics 6 is attached.

The substrate 19 is folded so that the shielding layer 18 forms an outer shield 23 for the electronics 6 located in an inner space 24 formed by the shielding layer 18. The outer shield 23 could also shield only a part of electronics, such as a boost electronics 7, shield. Other sub-electronics could be connected via an electrical connection 26 with the located in the interior 24 sub-electronics. A shielding of further sub-electronics may be unnecessary if the signals relayed by the sub-electronics located in the interior 24 are already adequately evaluable.

The electronics 6 is composed of individual electronic components 15. The components 15 are mounted only on one side 103 of the substrate 19. The components 15 may in particular be surface-mounted components. The electronics 6 or a sub-electronics can, even only partially, be designed as integrated circuits.

The electronics 6 are shielded by the shielding layer 18, which is mounted on the other side 102 of the substrate 19 to a plurality of sides. At the same time, the shielding layer 18, at least a front part of the shielding layer 18, is part of an all-round shielding for the active electrode 13. Only in the region of a contacting element 22 in which the active electrode is directly connected to the electronics 6, the all-round shield for the active electrode 13 is interrupted.

The contacting element 22 establishes a direct connection between the active electrode 13 and the electronics 6. Such a contact element 22 may be, for example, a solder joint or a pin-shaped element. It passes through an opening of the substrate 19 to the electronics 6. Since the distance between the electronics 6 and the active electrode 13 is comparatively short, can hardly interfere with interference in the compound. In the example shown, the connection is only slightly longer than the distance between the active electrode 13 and the substrate 19. The connection can again be detachable or insoluble.

The active electrode 13 is sandwiched between the passive electrode 12 and the substrate 19. The front part 12v of the passive electrode 12, the active electrode 13 and the substrate 19 are each flat and parallel to each other. They are spaced from each other by the block-shaped piezoelectric transducer element 3 and the contacting element 22.

The substrate 19 is a flat body, it may for example be a printed circuit board, in particular a flexible printed circuit board.

The transducer element 3 is embedded again in a damping material 10 together with the matching layer 4 and the substrate 19.

When in the Fig. 4 shown embodiment of an electro-acoustic transducer 1, the active electrode 13 and the electronics 6 are electromagnetically shielded. On another shield, such as a housing made of an electrically conductive material, has been omitted in this case. Such a housing may therefore consist of an insulating material.

Claims (14)

1. Electroacoustic transducer (1) through which sound can be converted into an electrical signal, comprising a transducer element (3), a passive electrode (12) which is located on the front side (120) of the transducer element (3) and which can be used as an electromagnetic shield, and an active electrode (13) located on the rear side (130) of the transducer element (3), whereby the active electrode (13) is located between the passive electrode (12) and a rear shield (17, 18) and the passive electrode (12) is conductively connected to the rear shield (17, 18), whereby the passive electrode (12) together with the rear shield (17, 18) forms a shield enclosing the active electrode (13) on all sides and the electroacoustic transducer (1) comprises an electronic unit (6) and the electronic unit (6) is also located in the all-round shield and no additional shield is provided for.
2. Electroacoustic transducer (1) in accordance with Claim 1, characterized in that the passive electrode (12) continues along at least one transverse side (140) located between the front side (120) and the rear side (130) of the transducer element (3).
3. Electro-acoustic transducer (1) in accordance with Claim 1 or 2, characterized in that the passive electrode (12) extends to the rear side (130).
4. Electroacoustic transducer (1) in accordance with any one of the preceding Claims, characterized in that a part (12h) of the passive electrode (12) is located on the rear side (130).
5. Electroacoustic transducer (1) in accordance with any one of the preceding Claims, characterized in that with the electro-acoustic transducer (1) as a receiver, sound can be converted into an electrical signal, and as a transmitter sound can be generated, and the electroacoustic transducer (1) can be switched between its functions as a receiver and as a transmitter by means of a switching mechanism and/or a switching element.
6. Electroacoustic transducer (1) in accordance with any one of the preceding Claims, characterized in that the electroacoustic transducer (1) comprises a substrate (19) with an electronics unit (6) located on it, and the active electrode (13) is located like a sandwich between the passive electrode (12) and the substrate (19).
7. Electroacoustic transducer (1) in accordance with any one of the preceding Claims, characterized in that the electroacoustic transducer (1) comprises a substrate (19) which has a shielding layer (18) on at least one side (102, 104, 105), whereby the rear shield (17) is designed in the form of the shielding layer (18).
8. Electroacoustic transducer (1) in accordance with Claim 7, characterized in that the passive electrode (12) together with the shielding layer (18) forms the shield enclosing the active electrode (13) on all sides.
9. Electroacoustic transducer (1) in accordance with any one of Claims 6 to 8, characterized in that the substrate (19) has an electronic unit (6) on only one of its sides (103).
10. Electroacoustic transducer (1) in accordance with any one of Claims 6 to 9, characterized in that the shielding layer (18) forms an external shield (23) for an electronic unit (6) located in an interior space (24) formed by the shielding layer (18).
11. Electroacoustic transducer (1) in accordance with any one of Claims 1 to 10, characterized in that the active electrode (13) and the passive electrode (12) are two separate areas (25a, 25b) of a previously connected, single layer (25).
12. Electroacoustic transducer (1) in accordance with any one of Claims 1 to 11, characterized in that the passive electrode (12) and/or the active electrode (13) is/are mounted as a layer on the transducer element (3).
13. Electroacoustic transducer (1) in accordance with any one of Claims 1 to 12, characterized in that the passive electrode (12) is conductively connected to the rear shield (17) by means of connecting elements (20).
14. Electroacoustic transducer (1) in accordance with Claim 13, characterized in that the connecting elements (20) are solder joints or pin-shaped connecting elements.

Images