WO1986004477A1

WO1986004477A1 - Electro-mechanical transducer

Info

Publication number: WO1986004477A1
Application number: PCT/GB1986/000038
Authority: WO
Inventors: Thomas Griffith Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-01-21
Filing date: 1986-01-21
Publication date: 1986-07-31
Anticipated expiration: 1987-07-21
Also published as: AU5354886A; GB2181621A; GB8622675D0; EP0210214A1; GB8501475D0; GB2181621B

Abstract

An electro-mechanical transducer has two layers (20) of a polarised piezoelectric polymer coated on each face with a conductive coating (22). The two layers are arranged back to back and secured by a double-sided adhesive tape (24) with their positively charged conductive coatings facing each other. As the protective layers (26) of insulation and a protective sheath (28) are provided. The inner conductive coatings are interconnected by a pin (30) passing through the polymer layers with the outer conductive coating being omitted in the vicinity of the pin. The outer conductive coatings are likewise interconnected by a pin (32), connection to an external screened cable being made through these pins with pin (32) being connected to the outer screen of the cable and pin (30) to the inner signal wire. Because the device is piezo-electric no external power supply is required and interconnection of the two inner conductive coatings enhances the signal generated by the device while the two outer coatings act as an electro-magnetic and electro-static screen to reduce extraneous and unwanted spurious signals which would otherwise affect operation of the device.

Description

TITLE: ELECTRO-MECHANICAL TRANSDUCER

The present invention relates to an electro-mechanical transducer.

Electro-mechanical transducers, such as microphones, are often used with musical instruments to detect the audio frequency waves generated by the instrument and convert these to an electrical signal which can then be amplified to amplify the sound of the musical instrument. With some types of instruments such as a so-called electric guitar the microphone is in the form of a pick-up mounted on the body of the guitar.

The present invention seeks to provide an improved form of electro-mechanical transducer.

Accordingly, the present invention provides an electro-mechanical transducer comprising two layers of a polarised piezoelectric polymer coated on each face with a conductive layer, the said layers being arranged with conductive layers of one polarity facing one another, and wherein the outer conductive layers of the transducer are interconnected to form a screen and the inner conductive layers are interconnected to form a signal source.

The present invention is further described hereinafter. by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of an electro-mechanical transducer according to the present invention;

Figure 2 is a section along the line 2-2 of the transducer of Figure 1, and

Figure 3 is a section on the line 3-3 of Figure 1 showing a preferred form of electrical connection to the transducer.

Figure 1 is a diagrammatic view of a preferred form of, electro-mechanical transducer 10 according to the invention, in which a piezoelectric device 12 is. conveniently enclosed for protection in a plastics material sheath 14. The latter is conveniently moulded about the device and is formed of, for example, polyvinyl chloride. An external cable 16 is connected to the piezoelectric device 12, the junction being protected by an injection moulding 18 conveniently of ther o plastics material.

The piezoelectric device itself is shown in cross section in Figure 2 and comprises two layers 20 of a polarised piezoelectric polymer, each face of each layer being coated with a conductive material 22. The two layers 20 are arranged back to back, that is with their positively charged conductive coatings 22 adjacent, the two layers being secured together by means of a layer of double-sided adhesive tape 24 which may be ther oadhesive or self adhesive The outer, negatively charged conductive coatings 22 are protected by respective layers 26 of insulating material with the whole of the device conveniently enclosed in a protective sheath 28, conveniently of plastics material.

The two outer, negatively charged conductive coatings 22 are connected together and to earth conveniently through the earth. shield of conductor 16 while the two positively charged conductive coatings are connected to the signal output wire of the cable 16. The piezoelectric polymer which is used is conveniently polyvinylidene fluoride (PVdF) which is both piezoelectric and pyroelectric, conveniently in thin film form.

The outer conductive coatings when connected to earth form an electro-magnetic and electro-static screen around the two inner conductive coatings forming the signal source. The effect of this configuration is to increase the output signal provided by the piezoelectric device and also to provide a built-in conductive shield which considerably reduces extraneous and unwanted spurious signals which could otherwise be generated in the device due to external fluctuating electro-magnetic and electro-static fields. In addition, since the device is piezoelectric in operation no external power source is required.

Figure 3 shows a preferred way of connecting the piezoelectric device 12 to the external cable 16. As is shown in the drawing two electically conductive connecting pins 30, 32 pierce the two polymer layers 20 and tape 24 so that the ends of the pins project slightly above the adjacent conductive coating 22 and are secured to respective connectors 34. The pins 32 are located on respective sides of the device 12 in the end region adjacent the cable 16, the protective sheath 28 being omitted from the drawing for clarity.

The pin 30 as shown in the drawing connects the inner conductive coatings 22 to the inner wire of cable 16 while the pin 32 connects the outer conductive coatings 22 to the screen of cable 16. The two outer conductive coatings 22 are removed in the region of the connectors 34 of pin 30 while the two inner conductive coatings are removed in the region of pin 32 in order to ensure electrical isolation of the two pins.

Since pin 32 passes through the inner conductive coatings 22 at right-angles in order to ensure a good electrical connection with the coatings the latter are thickened at the locations where they are pierced by pin 30 by the addition of one or more layers of conductive ink. This is sufficient to ensure a sound connection of the inner coatings 22 with the pin 30.

The connectors 34 may be crimped, soldered or otherwise connected to the pins and, in the case of pin 32, to the outer conductive layers 22. A conductive adhesive may also be used.

If preferred, the outer conductive coating 22 may also be thickened by the addition of a conductive ink in like manner to that for pin 30 in order to provide an effective electrical connection between pin 32 and the outer conductive coatings.

In use, when used as for example, a pick up for a musical instrument such as a guitar, the device is attached to the body of the guitar and senses mechanical vibrations of the instrument which are transmitted both through the body of the instrument and through the air to the piezoelectric device.

With regard to the conductive coatings, these can be formed in any suitable manner such as metalising and can comprise any suitable metal such as aluminium.

Claims

CLAIMS :

1. An electro-mechanical transducer comprising two layers of a polarised piezoelectric polymer formed on each face with a conductive layer, the said layers being arranged with conductive layers of one polarity facing one another, and wherein the outer conductive layers of the transducer are interconnected to form a screen and the inner conductive layers are interconnected to form a signal source.

2. A transducer as claimed in claim 1 wherein said inner conductive layers are positively charged and said outer conductive layers are negatively charged.

3. A transducer as claimed in claim 1 or 2 wherein a further outer layer of insulating material is provided on each polymer layer.

4. A transducer as claimed in any of claims 1 to 3 wherein said two outer conductive layers are electrically interconnected by an electrically conductive pin passing through said polymer layers, said inner conductive layers being omitted in the region of said pin.

5. A transducer as claimed in any of claims 1 to 4 wherein said two inner conductive layers are electrically interconnected by an electrically conductive pin passing through said polymer layers, said outer conductive layers being omitted in the region of said pin.

6. A transducer as claimed in claim 4 or 5 wherein each said conductive layer is thickened in the region of the associated pin to provide an effective electrical connection with said pin.

7. A transducer as claimed in claim 6 wherein each said conductive coating is thickened by the addition of an electrically conductive ink.

8. An electro-mechanical transducer substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

9. An electro-mechanical transducer substantially as hereinbefore described with reference to Figurs 1, 2 and of the accompanying drawings.