Custom Electronic Sensing Solutions

67 Wolseley Road, Brighton, BN41 1SS Tel: +44(0)7976772841 tom@sensatech.com

Company Registration No. 10313103

Array Control

Software Development

Amplifier Design

Electrical Impedance Tomography

Remote Sensing

Electric Field Sensing

Look through/around Targets Technology

Technology

The principle of capacitive sensing is not a new one. The technique relies on the fact that any object in free space has an electrical capacitance to earth. The value of this capacitance depends on several factors, the principle ones being the object's surface area, the distance to earth and the permittivity of the intervening medium.

The range and sensitivity of an instrument depends on the ability of the electronics to accurately measure extremely small values of capacitance. It is in this area that much of Sensatech's research has been focused, resulting in techniques which maximise noise rejection and minimise the unwanted effects of temperature.

Sensatech has developed specific and unique skills focused around areas critical to the development and production of complex sensing solutions.

Array control

Arrays of multiple sensor heads are multiplexed to allow Sensatech to collect large sets of data and build images of a target object which can then be analysed with proprietary embedded software. Because through careful electrode design, parasitic capacitance remains very small, Sensatech are able to measure down to 3 femto farad total capacitance with 12 bit resolution and 3 atto farad accuracy. Such small change is valuable for example in gap measurement.

Software development

Data sets generated by sensor arrays can be large and complex. Some arrays contain 2000 odd electrodes all of which are scanned and the resulting data once processed provides knowledge of the target object.
Software can be taught the characteristics of the particular sensor in order to identify and reduce noise and interference. Often reference capacitors are included in the PCB design to further calibrate sensor elements.
Sensatech analytical software can vary from simple to very complex depending on the task requirements, neural nets can be used to predict what a sensor should see if detecting particular targets. Finite element analysis can split the target space into many sub spaces each of which can be separately solved to produce an overall result.

Amplifier design

Low noise with high input impedance and low capacitance guard amplifiers have been built with excellent temperature stability.

EIT Electrical impedance tomography

Uses array generated data, then using back propagation techniques compares and reshapes the permeability characteristics of the space until it meets the data found by the sensor. This is the basis of X-RAY type tomography that Sensatech carry out using electric fields. While EIT is normally carried out with a transmitter and receiver plate in contact with the target object, using the techniques outlined above, Sensatech do not require to contact or invade the target object and can non invasively detect through other materials.

Remote sensing

Sensor Head can be 15m away from the amplifier and signal electronics.

Basic types of electric field sensing

• Standard electric field sensing: Transmit and receive: In this format a transmitter produces a field and if the capacitance between the transmit and receive plates is large the sensor detects this.
• Standard using an array: A more complex variant of the standard electric field sensing model is to use an array of transmit and receive plates which generates many fields. By AC driving the plates at a frequency for example less than 1 Megahertz this provides a large data set. Using a swept frequency it is even possible to determine chemical parameters of the target material or object. This can be used for example for height independent soil water content.
• Potential sensing: Because Sensatech receiver plates have only a few femto farads of parasitic capacitance, if a voltage exists on an object, that voltage will be creating a field and this can be sensed at a range.

Look through/around Targets Technology

Because Sensatech uses field sensing techniques as opposed to beam sensing techniques, our sensor can work effectively where others fail.

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