GB2462643A

GB2462643A - Piezoelectric pressure-sensitive tiles for surveillance and monitoring of large areas

Info

Publication number: GB2462643A
Application number: GB0814916A
Authority: GB
Inventors: Jack Michael Hale; Robin Stephenson
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-08-15
Filing date: 2008-08-15
Publication date: 2010-02-17
Also published as: GB0814916D0

Abstract

The piezoelectric pressure-sensitive the comprises a sandwich of materials containing the pressure-sensitive piezoelectric coating between two conductive coatings 4, 5. The lower coating 5 is protected by resilient plastic film 3, typically 1mm thick. The upper conductive coating 4 is protected by a layer of conventional flooring material 2, typically a 5mm layer of a rubbery or foamy material such as vinyl, or carpeting. Connections to a charge amplifier (11, fig 3) are by way of tabs 6, 7. A large number of individual tiles may be laid together to monitor large areas for intruders or the like (fig 1). The sensor device does not require a power source.

Description

PIEZOELECTRIC PRESSURE SENSITIVE TILES FOR SURVEILLANCE &

MONTTORLNG LARGE AREAS

Background

This invention relates generally to identifying where any object or animal or person is on a large surface by detecting the pressure that is exerted on a defined section of that surface by that presence. It uses the piezoelectric effect to produce an electrical charge when a force is exerted on a piezoelectric material.

When a large area needs to be under surveillance for any reason then earlier methods may resort typically to cameras, ultra-sound or infra-red monitoring to record the area above the ground. Alternatively there has been the use of sensors on or under the surface in the form typically of strain gauges, inductive gauges or capacitance gauges to detect pressure or proximity of objects, animals or people. These devices and others of a similar nature have a number of limitations. They require a separate power supply at the sensor and are therefore vulnerable to loss of electrical power and have a limited operating life if dependent upon batteries. Additional problems arise with cameras which may be set up to cover large areas but many situations and locations do not warrant the expense which needs to be incorporated in the means of data capture, recording and analysis. Cameras are not typically effective for fast dynamic events in poor light. Also the infra-red or ultra-sound monitors have not the facility to identify the particular properties of the interference in the area under surveillance.

Surface or below-surface sensors may be adequate when activated despite needing separate power supplies but are typically used in small areas or are distributed in such a way (referred to as mine-field disposition') as to leave parts of the area exposed to objects, animals or people being undetected.

There is a need for a new and improved type of monitoring of large areas such as provided by the present invention. A general description of these circumstances would include the need to monitor small to large areas typically up to a hectare in size on which objects may fall onto the ground at any time of the day or night throughout the year. Another instance would be a large compartment or confined area where it may be necessary to identify the presence exactly of where a person or animal may be but use a very discrete and sensitive means to establish that fact. The continuous recording of traffic on a thoroughfare can be impracticable by conventional means whereas it is possible with a continuous recording and automatic analysis of a very fast response sensor that had the ability to define the two-dimensional co-ordinates of any particular activity in contact with that surface.

All of the above methods and devices lack the usual advantages in construction, operation and results for detailed surveillance, inspection or monitoring of the present invention. They may be easily disabled and are also limited to temperature of operation lower than generally accepted for the piezoelectric sensors that are the basis for this invention in which internal electronics are absent. For this invention the upper temperature limit is defined by the properties of the materials employed in the design and by the Curie temperature of the Piezoelectric ceramic. Also the charge amplifier characteristics allow the gain to be independent of input capacitance so that the varying lengths of connecting leads do not effect the system sensitivity.

To overcome the problems associated with current monitors the present invention proposes the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas. This device comprises a special piezoelectric layer sandwiched between layers of thin films. The piezoelectric layer can be in the form of paint similar to that developed by Hale & Stephenson and described in previously published papers: Stephenson R, Hale J.M, White J.R, de Poumeyrol B & Gniedi I, Manufacture and Application of Piezoelectric Paint Sensors; Proc 9th Annual International Conference on Composites Engineering (ICCE/9), San Diego, USA, July 2002.

Hale J.M, Stephenson R, de Pounieyrol B & White J.R, Field Trial of Paint Based Thick-film Piezoelectric Strain Sensors on the Gateshead Millennium Bridge. Sensors and their Applications XI/ ISMCR 2001, City University, September 2001.

Hale J.M, White J.R, Stephenson R, Liu F. Development of Piezoelectric Paint Thick-film Vibration Sensors; Proc. IMechE Vol. 219 Part C: I Mechanical Engineering Science, 2005 The upper and lower surfaces of the piezoelectric layer are in contact with electrically conductive coatings to take the charge away and the total construction is protected by a conventional flexible flooring material. The device comprises a tile of a size and shape which may be rectangular hexagonal or triangular or some other shape to suit the location for which it is intended. It has at least two electrical connections on the lower conductive coating to enable any number of these tiles to be joined in one electrically conductive sheet referred to as the common return. It has another electrical connection on the upper conductive coating to attach to a thin insulated film conductor that leads to an amplifier beyond the boundary of the area to be monitored.

The amplifiers are also wired into the common return. These charge amplifiers are equal in number to the number of tiles and are of a special design for this application being necessarily small and inexpensive. The wiring could in certain circumstances be reversed with common attached to the upper coating and the lower conductive coating individually attached to the independent amplifiers

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 number of the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas Figure 2 details the construction of the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas Figure 3 shows the schematic view of the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas

Detailed Description

Figure 1 shows the assembled arrangement of the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas in a rectangular array. Each of the tiles 15 needs to be connected to its respective charge amplifier 11. One conductor 9 is a common return and is only linked to the charge amplifiers from one tile on the boundary of the assembly. Each tile is then electrically connected to its adjoining tiles 8 so that there is a common electrical path from every tile to the common on all of the charge amplifiers. In addition each tile is separately connected electrically to the signal input 10 of a single charge amplifier uniquely associated to each tile The overall sensitivity of a tiled area is in part defmed by the size of the tile. If the tiled area under surveillance is to detect small objects in close proximity impacting onto the surface and that these impacts need to be identified separately then the unit tile area must be small enough to accommodate. However if the small objects are expected to be widely dispersed then the tiles may be appropriately large.

In Figure 2 the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas comprises of a sandwich of materials containing the pressure-sensitive piezoelectric coating between two conductive coatings 4 & 5. The lower conductive coating 5 is protected underneath by a thin but resilient plastic film 3 typically 1mm thick. The upper conductive coating 4 is protected above by a layer of conventional flooring material 2 typically a 5mm layer of rubbery or foamy solid such as vinyl material or carpeting.

Connections to the charge amplifier are by extended tabs to the coatings 6 & 7. On a rectangular tile the lower coating has four tabs 6 to provide the electrical link to adjoining tiles. The lower conductive coating on each tile is used to attach to a common conductor and therefore that part of the tile is physically joined to as many tiles that surround it. The signal conductors from the charge amplifiers are each connected singly to the upper conductive coating on each tile so that there is a charge amplifier associated independently to each tile. The upper coating has one tab 7 to allow an electrical link to the charge amplifier. The upper conductive coating of each tile and the piezoelectric layer is electrically insulated from its neighbouring tiles with typically a lacquer sprayed onto the exposed surfaces.

The means by which the tiles sense the impact or contact of object animal or person on the surface is by the piezoelectric effect. The piezoelectric coating is in the form of a paint but could also be in the form of an ink or resin. These types of coating are particular developments of the inventors and have been used successfully to show that pressure or otherwise distortion on the tile will produce an electrical charge at the conductive coatings. This charge is related to the strain and hence the force of impact to the piezoelectric coating and is capable of high-frequency response.

Figure 3 shows schematic view of the Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas with the charge amplifier 11. The charge amplifier transforms the charge from the tile transmitted via the connecting lines 12 into a signal that can be transferred to a device for recording and analysis that identifies the event at a precise location in the area under surveillance. No other electrical supply is required within the tiled area and the electrical supply to the charge amplifiers and micro-computer are local and outside the area and of low electrical power.

Claims

Claims 1. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas comprising means for applying prepared and processed piezoelectric coating to monitor large areas for identifying the presence of anyone or anything contacting the ground.
2. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas according to claim 1 in which the means for monitoring an area can be achieved with separately connected tiles of any shape and size.
3. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas according to claim 1 in which the means for collecting information for an area under surveillance is by conductive leads attached to charge amplifiers.
4. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas according to claim 1 in which the means for constructing the tile is by sandwiching the piezoelectric coating between two thin film conductive coatings.
5. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas according to claim 1, 2, 3 & 4 in which the means for completing the construction of the tile is protective film coating or layers that will allow for the transmission of impact or pressure
6. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas as claimed in 1, 2, 3, 4 & 5 which is made from paint, ink, metal, plastics material, wood, ceramic or a combination of any or all of these materials or others yet to be defined.
7. A Piezoelectric Pressure Sensitive Tile for Surveillance & Monitoring Large Areas as described herein and illustrated with accompanying drawings.