GB2466184A

GB2466184A - An efficient and low-cost means of connecting a signal wire to a piezoelectric layer

Info

Publication number: GB2466184A
Application number: GB0822384A
Authority: GB
Inventors: Jack Michael Hale; Robin Stephenson
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-12-09
Filing date: 2008-12-09
Publication date: 2010-06-16
Also published as: GB0822384D0

Abstract

This invention describes a method of attaching an electrical signal lead 4 to a piezoelectric layer 1 by way of a paint or ink electrode 2. The paint or ink uses a low-cost coating with metallised mica flakes as the pigment acting as a conducting electrode. To this electrode a small piece of metal shim 5 typically metal foil is attached incorporating on one side a special contact adhesive 6. On the other side of the metal shim is a soldered wire connection 7 that constitutes the electrical signal lead 4. The contact adhesive allows the metal foil to adhere to the conductive coating which is typically applied to the surface of the piezoelectric material. The result is a reliable, easily applied and robust low impedance transmission connection for a charge to or from a piezoelectric material.

Description

AN EFFICIENT AND LOW-COST MEANS OF CONNECTING A SIGNAL

WIRE TO A PIEZOELECTRIC LAYER

Background

Piezoelectric material can be used as a sensor or an actuator. In either condition it requires electrically conducting leads to be attached to a conductive layer in order to transmit an electrical charge. The conductive layer covers the surface of the piezoelectric material to maximise the piezoelectric effect. The charge is produced as a result of distortion to the material in the case of a piezoelectric sensor while an electrical charge is applied to a piezoelectric actuator to cause displacement.

Piezoelectric material operating as a sensor can be in the form of paint or ink. In order for piezoelectric sensors to work as charge generators they must be poled in a high electrostatic field. The poling requirement means that the electrode must be in direct contact with the piezoelectric layer so that there is no dielectric layer such as air between them. In practice this means that an electrode has to be deposited as a liquid paint or ink to achieve the intimacy necessary. By the nature of the piezoelectric operation there is no continuous flow of current in the circuit because the sensor is generating a charge to be measured by a charge amplifier. As a result it is possible to use an electrode material of moderate conductivity but of sufficient low resistance to ensure fast response.

Current practice is to make electrodes using flakes of noble metals such as gold or silver as the pigment suspension in the liquid coating. These are expensive whereas this invention uses metallised mica flakes which are commercially available and are far cheaper. Also they can be readily mixed into a liquid vehicle to provide a thin electrode layer for easy application onto piezoelectric sensors. This invention relates generally to ensuring an effective and reliable electrical connection to a piezoelectric ink or paint typically of a thickness in the order of l0.im up to 100tm.

The piezoelectric layer can be applied to a surface that is either electrically conducting or electrically non-conducting. When applied to an electrically conducting surface then that surface acts as return electrode for any electrical charge induced in the piezoelectric layer. Another electrode is applied to the exposed surface of the piezoelectric layer with the addition of a conducting lead. This second electrode completes the electrical circuit to transmit the electrical charge to a measuring or monitoring device.

If the piezoelectric layer is to be applied to a non-conductive surface then a conducting electrode coating is introduced to reside between the non-conductive surface and the piezoelectric layer. A return circuit typically in the form of an electrically conducting lead needs to be attached to this conductive electrode coating in a way similar to the attachment of the conducting lead on the exposed face of the piezoelectric layer.

With these conducting leads in place the piezoelectric layer can then be electrically prepared by poling for use as a sensor or an actuator. See for example Pat App UK 0814916.3. The current practice of attaching wires to piezoelectric sensors use forms of attachment that can be effective for solid or rigid materials but are unsuitable for a flexible material such as paint or ink. This invention overcomes these disadvantages in that it provides an effective and durable connection between the conducting lead via a metal strip using a mechanical joint that is typically soldered but could be mechanically fixed in other traditional ways. The metal strip is of a size and shape to provide a sufficiently large contact area with the conductive electrode coating on the piezoelectric layer. This coating is in turn an extremely effective and inexpensive collector for the charge produced by the piezoelectric layer. The attachment of the metal strip to the conductive coating is by a contact adhesive which provides minimal electrical impedance to the electrical charge passing from the piezoelectric layer. It is essentially a robust and effective method of electrical connection for the application of piezoelectric paint and ink.

Drawing Description

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows the assembled view of a means of connecting a signal wire to a piezoelectric layer via a conductive electrode coating Figure 2 details the construction of the means of connecting a signal wire to a piezoelectric layer via a conductive electrode coating

Detailed Description

Figure 1 shows the piezoelectric layer I that is coated with a conductive coating material 2 incorporating metallised mica as the conductive pigment. This conductive coating covers the whole surface of the piezoelectric layer. This coating acts as one of the electrodes to be charged either positive or negative by a piezoelectric effect. The other electrode 3 is either negative or positive to complete the electrical circuit and is on the other opposite face of the piezoelectric layer. Typically this could be the conductive surface of a metal structure 3 or a thin conductive coating 8 as in 2.

In Figure 2 the view shows the section elevation. A piezoelectric charge can be induced by a deformation of the piezoelectric layer and this charge appears at the conductive electrodes. In order to measure the value of the charge an electrical conducting lead 4 is required so that the effect can be monitored should the piezoelectric layer be acting as a sensor to detect movement or dynamic strain. To attach the lead in this invention there needs to be a thin metal strip or shim 5 joined to the conductive coating using an adhesive interface 6. The lead is attached to the thin metal strip or shim with a soldered joint 7. Additionally a similar arrangement of an adhesive metal strip or shim with lead attached would be joined to the electrically conductive surface 3 or the sub-deposited conductive coating 8.

Claims

AN EFFICIENT AND LOW-COST MEANS OF CONNECTING A SIGNALWIRE TO A PIEZOELECTRIC LAYERClaims 1. A means of connecting a signal wire to a piezoelectric layer comprising a means for applying a thin metal strip or shim with an adhesive coating to make an electrical bond between the metal shim and a conductive electrode consisting of a mica-loaded coating applied to the piezoelectric layer.
2. A means of connecting a signal wire to a piezoelectric layer according to claim 1 in which the thin metal strip and the attached wire serve as an electrical conductor to the piezoelectric layer.
3. A means of connecting a signal wire to a piezoelectric layer according to claim 1 in which the piezoelectric layer can be prepared with an electric voltage of a magnitude that would produce the characteristic piezoelectric properties up to a maximum effect.
4. A means of connecting a signal wire to a piezoelectric layer according to claim I in which the charge produced in the piezoelectric layer can be measured using the electrical circuit provided by the connected signal wire.
5. A means of connecting a signal wire to a piezoelectric layer according to claim 1, 2, 3 & 4 in which the means for completing the construction of the piezoelectric layer sensor will allow for the measurement or monitoring of impact, dynamic pressure or strain.
6. A means of connecting a signal wire to a piezoelectric layer as claimed in 1, 2, 3, 4 & 5 whereby the piezoelectric layer may be attached to metal, plastics, wood, ceramic or a combination of all of these materials as described herein and illustrated with accompanying drawings.