VIBRATION TRANSDUCER UNIT

Abstract: Vibration transducer unit for converting vibrations to electric signals, in which unit there is a transducer part (11) and a signal processing part (14), like a preamplifier part. The transducer part (11) and the signal processing part (14) are integrated to a single structure.

Description: VIBRATION TRANSDUCER UNIT This invention relates to a vibration transducer unit according to the preamble of claim 1. Vibration transducers can be used for example in saddle or bridge transducers for acoustic guitars, double bass and violin by means of which the vibrations of the strings are converted to electric signals. They are generally mounted under the saddle of the guitar or to the bridge of double bass and violin. They consist of a transducer part with electromechanical material such as elastic electret bubble film, piezoelectric crystals or polymers and electrically conductive electrode layers, as well as a connection cable, by means of which the signals are taken to a separate preamplifier. In US Patent publication 5,319,153 a piezoelectric transducer for instruments is presented. Therein a strip-formed polyvinylidene fluoride (PVDF) film is used as an active electromechanical material. A connection cable is connected to the transducer part by soldering. A drawback with vibration transducer units according to the prior art is their complicated structure and high price. When the preamplifier part and the transducer part are placed separately, a connection cable is needed between them. This causes extra costs and the connection cable often causes electrical interference especially if it has to be substantially long. If the electromechanical material used is film-like material, like PVDF rendered into piezoelectric, or elastic electret bubble film with permanent electric charge, the transducer must be very close the preamplifier. This is because this kind transducers have relatively low capacitance compared to standard cables capacitances. Additionally it is difficult to place a separate preamplifier in an electric guitar, double bass or violin. Furthermore, the transducer part and the preamplifier have to be protected by means of separate shields, in order to avoid mechanical damage and electrical interference. The aim of the present invention is to remove the drawbacks of the prior art technique and to achieve a vibration transducer unit, which is small and compact, and by means of which additional interference can be avoided, in the solution according to the present invention the preamplifier and the transducer part are, according to the attended claims, integrated into one unit. A connection cable between the transducer part and the preamplifier is not needed. As a result a very compact unit is achieved including both mechanical and electrical protection of said unit. In the following the invention is described in detail by the aid of examples, by referring to the attached set of drawings, wherein figure 1 presents an explosion picture of a vibration transducer unit according to the invention, figure 2a presents an explosion picture of one embodiment vibration transducer unit according to the invention, figure 2b presents an vibration transducer unit according to the invention placed in an electric guitar, figure 3 presents an explosion picture of one embodiment vibration transducer unit according to the invention, figure 4 presents an explosion picture of one embodiment vibration transducer unit according to the invention, figure 5a presents an explosion picture of one embodiment vibration transducer unit according to the invention, figure 5b presents a vibration transducer unit according to the invention with a heat-shrink tubing threaded on it, figure 6a presents an explosion picture of one embodiment vibration transducer unit according to the invention, figure 6b presents two vibration transducer units according to the invention placed on a double bass, and figure 7 presents a cross-section of an electret bubble film. Figure 1 presents a vibration transducer unit according to the present invention, with a strip-formed transducer part 11 , and a connector 12 connected to the end of it. A suitable method for manufacturing such transducer element is described in the WO 97/39602. Connector 12 attaches the transducer part 11 to the circuit board 13 consisting preamplifier control circuitry 14 as well as two output conductors 15 and a ground conductor 16. The transducer 11 , the connector 12 and the circuit board 13 have been protected with a metallic protection shield, said shield composed of both a bottom part 17 and top part 19 protecting the whole unit. The bottom part is composed of a plate 17, which is as wide as the transducer part 11 to which it is attached for example by gluing. It has side walls 18 substantially surrounding the connector 12. The shield consists of a plate 19, being as wide as the transducer part 11 , significantly surrounding the space of the circuit board, said top part having a form of a bottomless rectangular box 10, which protects and shields the circuit board and the components on it, and in- side which the walls 18 fit. The top and the bottom parts of the shield can be attached to each others for example by soldering. In this embodiment the output conductors 15 operate both as signal output conductors and power input conductors for the preamplifier. The ground conductor 16 is connected to either the top or the bottom part of the protection shield. It is to be noted that if one or both faces of the transducer are electrically conductive material and the glue in between it and the plate 19 and/or 17 is also electrically conductive, the ground conductor 16 is unnecessary. The transducer part 11 of the invention can be composed of for example one or more dielectric films laminated together, the material of which can be for example polyester. Necessary signal and ground electrodes can be arranged to form suitable shape on the surface of the films for example by silk-screen printing or etching. Between the signal and ground electrodes there is an active electromechanical film, for example being composed of one or several permanently charged dielectric electret films 74 containing flat lens-like gas bubbles 75 or blisters (so called electret bubble film, fig. 7). Such film suitable as electromechanical material for a vibration transducer is presented in US Patent publication 4,654,546. In WO publication 96/06718 a method is presented, by means of which this kind of film can be swelled in order to form a swelled electret film with flat or teared gas blisters. Solid electret film or piezoelectric plastic film, such as PVDF, can also be used as the electrome- chanical material. Referring now to the figure 2a, the protection shield can also be made in such a manner that the top part 21 has a strip 22, which can be bent to form the bottom part of the protection shield for the preamplifier and control circuitry 23. In this case the separate bottom plate 17 can be omitted. Figure 2b shows a trans- ducer unit 24 according to the invention, placed in connection with a bridge 25 and saddles 26 of an electric guitar. One more transducer unit according to the invention is presented in figure 3. In this embodiment the transducer part 31 is integrated onto the same uniform, very thin (the thickness being for example 0,1 mm) circuit board 33 together with the preamplifier and control circuitry 34. In this embodiment the circuit board 33 is as long as the whole transducer unit. The connector 12 is not needed, and the structure becomes very thin, especially on the transducer part side. There is a metallized area 35 on the top side of the circuit board. This metallized area 35 operates as a signal contact for the transducer 31. The upper side of the transducer 31 is placed against protection shield 36, which is grounded. The protection shield 36 and the transducer 31 are glued together. The bottom side 37 of the circuit board 33 is metallized to provide the shield for the transducer. The bottom side 37 of the circuit board 33 is metallized at suit- able areas to be enable the protection shield to be grounded directly to the circuit board 33 for example by soldering. Output conductors 38 are soldered to the circuit board 33. In figure 4 one embodiment vibration transducer unit according to the invention is presented. In this embodiment a protection plate 41 is made of a strip-like metal plate. Said plate 41 is bent up as shown at one end of the structure, providing space for the preamplifier and control circuitry portion 42. The plate 41 connects to the electrical ground of the vibration transducer unit via suitable conductive, for example metallized, areas on the circuit board 43. The bent por- tion 45 of the plate 41 also forms the top part of the protective shield for the preamplifier and control circuitry portion 42. The bottom surface 44 of the circuit board 43 is metallized to provide the bottom part of the electrically protective shield for the preamplifier and control circuitry portion 42. In this embodiment, electrically protective shield for the preamplifier and control circuitry part 42 is solely formed by the bent portion 45 of the plate 41 and the metallized surface 44 of the circuit board 43, without any additional shield parts. A piece of heat shrink tubing or other suitable means can be placed over the end of the vibra- tion transducer unit to provide better mechanical and moisture protection. In this embodiment the protective shield does not need to have separate parts for providing walls or bottom for the shield. Between the protective plate 41 and circuit board 43 there is the transducer element 46 and they all are glued together. Figure 5a shows another embodiment of the invention. There the protection shield 51 for the preamplifier circuitry 52 and the circuit board 53 are made of one piece of flexible, very thin circuit board material, such as Kapton®. The signal electrode 54 for the transducer element 55 is arranged on top side of the circuit board 53 and the transducer element 55 is glued on top of it. The bottom side of the circuit board 53 is metallized and it provides the electrical shield for the signal electrode. On one end of the circuit board there are the components 56 of the circuitry and output conductors 57. The circuit board 53 has an extension 51 , with metallized outer surface, which extension is wrapped around the circuitry 52 to provide the electrical shield. Figure 5b shows how the extension 51 now completely wrapped around the circuitry 52, which can be covered with suitable heat-shrink tubing 58. In figure 6a one embodiment vibration transducer unit according to the invention is presented. In this embodiment the metallic protection plate 61 provides mainly mechanical reinforcement for the transducer part 62. However, it is recommended that the metal plate 61 connects to the electrical ground of the vibration transducer part 62 via suitable conductive outer layer, made from for example graphite. The plate 61 can also be made of non conductive dielectric material such as polyester. Transducer part 62 is preferably made according to WO 97/39602, containing a transducer element, electrically conductive layers and conductive contacts being attached by crimping or by other suitable means. Said conductive contacts are soldered onto a flexible circuit board 63. The circuit board 63 is made wider to provide extension 64 at the preamplifier and control circuitry 65 end. In this embodiment, the circuit board 63 is made of very thin and flexible material such as Kapton®. The surface 66 of the circuit board 63 is metallized and it is wrapped around over the preamplifier and control circuitry portion 65 to provide protective shield for it. In this embodiment the electrically protective shield for the preamplifier and control circuitry portion 65 is solely formed by the circuit board 63, which enables very easy and cost- effective manufacturing and assembly processes. The flexible protective shield 64, 66 can also be made of a separate piece of flexible conductive material, which is connected to the electrical ground of the preamplifier and control circuitry part 65 by suitable means. In this case a separate insulator, made of non- conductive material, is first wrapped around or threaded over the preamplifier and control circuitry part, and the protective shield is then wrapped around or threaded over the insulator. Referring to figure 6b, a piece of heat shrink tubing 73 or other suitable means can be placed over the end of the vibration transducer unit to provide better mechanical protection and neater outlook . In figure 6b, a vibration transducer unit according to the invention has been placed on the bridge 67 of a double bass, in a slot formed by a curved body part 68 and an end of a wing part 69, close to the body part 68. The transducer is secured in the middle of the slot by wedge a 70 made from for example wood. Additionally, a second vibration transducer unit 71 according to the invention is placed under the bridge foot 72, between the bridge and the top plate (sound board) of the instrument. A similar transducer unit or set of multiple transducer units can also be placed on some other stringed instruments, for example cello or violin, by similar means. It is obvious for a skilled person in the art, that the embodiments of the invention are not solely restricted to the examples presented above, but they can be var- ied within the scope of the claims presented hereafter. Thus the vibration transducer unit according to the invention can also be used for example in other stringed instruments, as for example in pianos or grand pianos, in order to convert vibrations into electric signals. Embodiments of the transducer unit according to the invention can also be used in other than musical instrument applica- tions, actually in all applications in which mechanical vibrations are converted to electrical signals. Embodiments of the transducer unit according to the invention can be used for converting vibrations to electrical signals between any two or more separate vibrating objects, or inside any slot within any vibrating object, or even for measuring vibrations from any vibrating surface if an object having suitable mass is attached to the opposite surface of the transducer unit. Additionally, embodiments of said transducer unit can be used for converting vibrations below or above the audible range in frequency (infra-sonic and ultra-sonic, respectively) to electrical signals.

Claims: CLAIMS 1. Vibration transducer unit for converting vibrations to electric signals, in which unit there is a transducer part (11 ,31 ,46), and a signal processing part (14,23,34,52), like a preamplifier part, characterised in that the transducer part (11 ,31 ,46) and the signal processing part (14,23,34,52) are integrated to a single structure. 2. Vibration transducer unit according to claim 1 , characterised in that the protection shield of said transducer unit consists of a plate-like part shielding the transducer part and a box-like part protecting the signal processing part, which is attached to the end of the transducer part. 3. Protection shield according to claim 2, characterised in that it consists of top and bottom parts 4. Vibration transducer unit according to claim 1 , characterised in that the transducer part (31 ,55) and the signal processing part (34,52) have both been placed on the same flexible and thin circuit board (33). 5. Vibration transducer unit according to claim 4, characterised in that part of the circuit board (51) is wrapped around over the signal processing part (52) to provide protective shield. 6. Vibration transducer unit according to claim 1 , characterised in that the protection shield consists of one piece of strip-like plate (41). 7. Vibration transducer unit according to claim 6, characterised in that one face of the circuit board (43) has been metalled in order to form part of the protection shield. 8. Vibration transducer unit according to claim 1 , characterised in that the transducer part (62) is applied to the signal processing part (65), and the circuit board (63,64,66) is wrapped around over the signal processing part (65) to provide protective shield. 9. Vibration transducer unit according to claim 1 , characterised in that the transducer part consists of dielectric films, on the surfaces of which signal and ground electrodes have been applied, as well as one or several dielectric electret films having gas bubbles (so called electret bubble film) being set between the electrodes, said film(s) forming the active electromechanical element of the transducer part. 10. Vibration transducer unit according to claim 1 , characterised in that the transducer part consists of dielectric films, on the surfaces of which signal and ground electrodes have been applied, as well as one or several dielectric piezoelectric films forming the active electromechanical element of the transducer part.

Inventors: RAEISAENEN HEIKKI, RAEISAENEN, HEIKKI
Applicants: EMF ACOUSTICS OY LTD, RAEISAENEN HEIKKI, EMF ACOUSTICS OY LTD., RAEISAENEN, HEIKKI
Application year: 1999
Main classification: H04R1
IPC codes: G10H3