GB2385135A - Portable device for electrical impedance measurements - Google Patents

Abstract

A portable test device for measuring properties of a non-medical or non-dental system comprises; an electrical signal generator, electrode means for applying the signal to the system under test, signal receiving means and signal processing means to provide data indicative of the system. Typically, the device is used for electrochemical impedance spectroscopy (EIS) measurements, also known as AC impedance spectroscopy. The device may be used in NDT applications such as corrosion or wear measurement and material characterisation.

Description

METHOD AND APPARATUS FOR APPLYING ELECTRICAL STIMULUS TO

A SYSTEM AND ACQUIRING A SYSTEM RESPONSE

FIELD OF INVENTION

The present invention relates to a device and apparatus for applying electrical stimuli to a system and acquiring a system response, particularly in non- clinical environments. 5 BACKGROUND TO INVENTION

Many physical or chemical phenomena give rise to a specific electrical response on application of an electrical stimulus. Consequently, such electrical or electrochemical measurements are widely used in a variety 10 of laboratory and industrial environments.

The application of these measurements may use AC or DC based methods such as potential steps, voltammetry and electrochemical impedance spectroscopy (EIS), also known as the AC impedance spectroscopy Technique (RACISTS. EIS has 15 become particularly useful in the investigations of charge transfer, ion transport and adsorption processes, among others. In addition, impedance measurements have little or no effect on the sample under investigation making it applicable where changes in the measured system due to the 20 effect of electrical polarization are undesirable and thus particularly suitable for non-destructive testing and material characterization in general.

Measurements of impedance spectra can be made using one of two methods, that is the frequency domain or the P12195GB

time domain. In the frequency domain impedance measurements made using, for example, the EIS technique can be performed using a single sine method. With this a small amplitude fixed frequency sinusoidal signal is applied to 5 the system under study, and the response signal is measured. In this frequency domain the in-phase (real) and out-of-phase (imaginary) components of the total impedance are determined. From this information, the phase shift between source and response waveforms is calculated which 10 leads to the magnitude of the impedance. To construct an impedance spectrum, the single sine technique requires a number of measurements to be performed at discrete frequencies in a sequential manner.

The EIS technique can alternatively be performed using 15 a multi sine signal wherein the output waveform is constructed by the summation of sinusoids, each a multiple of the lowest frequency, and in this case measurements are performed in the time domain. In this case a test signal constructed from a plurality of frequencies is applied in 20 the time domain and this is used to generate the corresponding frequency domain representation by Fourier transform. A computer acquires the resultant response signal emitted by a system, to which a test signal has been applied, and performs the calculations, typically using the 25 Fast Fourier Transform (FFT) algorithm, necessary to produce AC impedance spectra from such signals.

In some studies in which the measurements are P12 1 95GB

performed in the frequency domain the impedance spectra are achieved by analysis of the response of a test system to an applied signal of single frequency and then repeating the process at different frequencies to achieve the desired 5 frequency range. This technique has become colloquially known as the swept sine technique whereby a single frequency signal is applied to the test system and the response analyzed and recorded, the process then being repeated for signals of different frequency and by this 10 means an impedance spectrum is built up.

The equipment which is used to perform such measurements in the frequency domain, as described above, is typically a computer controlled frequency response analyser attached to an electrochemical interface to 15 measure current or voltage response. An example of such an arrangement is shown in Figure 1. This equipment, which is used to measure ac impedance in the frequency domain comprises a frequency response analyser (FRA), in this in,-) case, a Solartron 1255, an electrochemical interface (ECI) mrm) 20 in this case a Solartron 1286, a PC with general-purpose interface bus (GPIB) and controller software which links all of these devices. In such an arrangement of equipment, the FRA generates and measures AC signals and the ECI operates as a potentiostat/galvanostat, however, it may 25 simply be used as a current measuring resistor and amplifier. Both applied signals and response signals would be returned to input channels of the FRA and subsequently acquired by the PC via the interface board for further data P12 1 95GB

manipulation. Similar equipment exists for measurements in the time domain such as Stanford Research Systems SR780. However, for these measurements the equipment typically comprises a 5 spectrum/network analyzer, a PC with GPIB and controller software linking each of these devices.

As can been seen, such equipment is usually heavy, expensive, and complex. Additionally, complex software is required to be installed in each equipment arrangement to 10 link the component devices and perform the required processing functions. Further, due to its cumbersome nature the usefulness of known conventional apparatus is limited in some circumstances. In particular, known apparatus is unable to be easily used in small or awkward 15 spaces, nor is known apparatus convenient for performing measurements in environments outside of the laboratory as this would require the disassembly and moving of the components of the testing apparatus and the reassembly in the testing environment.

20 An object of at least one aspect of the present invention is to obviate or mitigate at least one of the aforementioned problems.

SUMMARY OF INVENTION

According to a first aspect of the present invention 25 there is provided use of a portable test device for measuring at least one property of a system, other than a dental or medical system, by generating an electrical signal to be applied to a system and acquiring a response P12195GB

signal generated by the system, the device comprising: signal generation means; signal receiving means; and signal processing means; 5 wherein, in use, the device generates a signal to be applied to a system to be tested and receives a response signal of the system which was tested whereby the applied and received signals undergo processing by the signal processing means, providing data indicative of a 10 characteristic of the system.

Preferably the provided data is transferred to data storage means for storage.

Preferably the device may be hand held.

Preferably the device includes means for visually 15 displaying data.

Preferably the device measures an impedance of the system. Preferably the device is battery operated.

Conveniently the device may be connected to a mains 20 power supply to allow charging of the battery to take place. Preferably the portable device may include means for associating the device with electrode means comprising at least a first electrode and a second electrode wherein the 25 first electrode applies the generated signal to the system to be tested and the second electrode collates response signals from the system response.

Preferably the device is configured or arranged such P12 1 95GB

-6 that connection to an external power supply and electrode means cannot occur simultaneously.

Alternatively the device is configured or arranged such that connection to an external power supply and 5electrode means can occur simultaneously.

Conveniently the device is provided with safety features conforming to an appropriate standard requirements for medical electrical equipment.

Preferably the device may be provided with only one 10input/output port wherein the device cannot be connected to an external power supply and a system to be tested simultaneously. Alternatively the device may be provided with two or more input/output ports wherein the power to the device and 15the signals transferring to and from the device are assigned to individual input/output ports.

Preferably the signal applied to the system comprises at least one period of a periodic signal such as an AC signal. 20Preferably the applied signal is formed of a plurality of sine waves.

Conveniently each of the sine waves is of a different frequency and random phase.

Alternatively the applied signal is of a single 25frequency. Alternatively the applied signal is a square waveform or other waveform (e.g. triangle, saw tooth or arbitrary).

Preferably the applied signal is a sine wave.

P12195GB

Alternatively the signal applied to the system may be a DC signal.

Preferably the means for analysing the applied signal and received signal performs Fast Fourier Transform S spectrum analysis upon the applied signal and received signal. Preferably the device is customised for specific end use by embedded PC-based control software.

Conveniently the device may be programmed to perform 10 a range of measurements with subsequent analysis, presentation, data storage and retrieval.

Preferably the device further comprises means for performing variable amplification on the received signal.

Preferably the signal receiving means includes data 15 acquisition means.

According to a second aspect of the present invention there is provided a portable apparatus for use measuring at least at least one property of a system, other than a dental or medical system, by applying electrical stimulus 20 to a system and acquiring a system response, the apparatus comprising: signal generation means; signal receiving means) signal processing means; and 25 electrode means which, in use, are applied to the system, wherein a generated signal is applied to the system by said electrode means, a response signal of the system is P12195GB

-8- detected by said electrode means and received by the signal receiving means, the applied and received signals undergo processing by the signal processing means.

Preferably data generated by the signal processing 5 means is transferred to data storage means for storage.

Preferably the signal processing means performs signal analysis on the generated signal and received signal.

Conveniently the electrode means comprises one or more electrodes and may comprise an array of electrodes.

10 According to a third aspect of the present invention there is provided a method of electrochemical impedance measurement on a system, other than a dental or medical system, using a portable device, the method comprising the steps of: 15 generating a signal; applying the generated signal to the system by electrode means; detecting a response signal generated by the said system using said electrode means; 20 processing said applied signal and detected signal and generating data representative of a feature or property of the system from said signal processing.

Preferably the method further comprises the step of transferring the said generated data to and storing the 25 said generated data in a storage means.

Preferably tests carried out using the device generating a signal having a frequency in the range of DC lOOkHz provides accurate results for measurements made P12195GB

- 9 - involving systems characterized by low frequency response such as polymers, dielectrics and electrode processes or other high impedance media.

Preferably tests performed using the device generating 5 a signal in a range above lOOkHz provides accurate results for measurements made involving systems characterized by high frequency response such as highly conducting electrolytes or other low impedance media.

BRIEF DESCRIPTION OF DRAWINGS

10 These and other aspects of the invention will become apparent from the following description when taken in

combination with accompanying drawings in which: Figure 1 shows a prior art arrangement for performing

the measurement of impedance spectra; 15 Figures 2 shows a first embodiment of the front casing a portable device of the present invention; Figure 3a shows a first embodiment of the end view of a portable device according to the present invention; Figure 3b shows a second embodiment of the end view of 20 a portable device according to the present invention; Figure 4 shows a block diagram of the internal components of the portable device; Figure 5 shows a simplified block diagram of the input and output channels according to the present invention; 25 Figure 6 shows a simplified block diagram representative of the interconnection of the digital signal processor and the analogue circuitry of a portable device according to the present invention; P12195GB

-10 Figure 7a shows a schematic representation of the analogue input and output channels of the portable device of Figure 3a; Figure 7b shows a schematic representation of the 5 analogue input and output channels of the portable device of Figure 3b; Figure 8a shows a schematic representation of the interface panel of the portable device of Figure 3a; Figure 8b shows a schematic representation of the 10 interface panel of the portable device of Figure 3bi Figures 9a, b and c show the schematic view of cable configurations required for operating the device in different function modes in accordance with the present invention; 15 Figure lea, b, c and d shows a schematic representation of the component waveforms and the resultant constructed pseudo-random noise wave form suitable for use with the present invention; Figure 11 shows a flow diagram of the initialization 20 routine for the hardware of the device of the present invention; Figure 12 shows a flow diagram representative of the /Xrm) measurement routine called the ACIST Engine_ of the portable device of the present invention; 25 Figure 13 shows a block diagram of an EIS operation (bred achieved when an ACIST application is embedded within the device in accordance with an embodiment of the present invention; P12195GB

-11 Figures 14a, 14b and 14c show output display screens according to an embodiment of the present invention; Figure 15 shows a two electrode cell configuration measured using the present invention; 5 Figures 16a, 16b and 16c show graphical representation of measurements performed on a polymer electrolyte film by the device of the present invention; Figure 17a shows a known equivalent circuit used in the below comparison) 10 Figure 17b shows a graphical comparison of measurements made using the known prior art apparatus and

the present invention using the equivalent circuit of Figure 17ai Figure 18 shows a dental instrument incorporating the 15 device in a manner outwith the scope of the present invention; Figure 19 shows a flow diagram of an example program embedded within the device in a manner outwith the scope of the present invention for use in clinical application; 20 Figures 20a, 20b, 20c and 20d show selected screen displays which may be shown on screen of the device while operating in a manner outwith the present invention; Figures 21a, 21b and 21c show the electrode arrangement for use with the device operating in a manner 25 outwits the scope of the present invention when performing in vitro measurements) Figures 22a and 22b show graphical representations of typical AC impedance spectra for whole human teeth measured P12 1 95GB

-12 using the device operating in a manner outwith the scope of the present invention; Figures 23a and 23b show receiver operating characteristic (ROC) curves for measurements made on whole 5 teeth using the device in a manner outwith the scope of the present invention.

Figure 24 shows an electrode arrangement associated with the device when used in performing analysis of skin tissue in a manner falling outwith the scope of the present 10 invention.

DETAILED DESCRIPTION OF DRAWINGS

With reference to Figure 2 there is shown the front face of a hand held portable device 10. The device 10 comprises a housing 19, upon the surface of which is 15 disposed an 'OK' button 12, a cancel button 14, cursor keys 20, an alpha-numeric keypad 22, programmable soft keys 18, and a graphical LCD screen 16 and LEDs 15a, b and c which are red, amber and green respectively. The LED's 15a, b and c provide a visual indication of the state of operation 20 of the device 10. At the top end of the housing 19 is provided a panel 17 on which is provided appropriate signal transfer interfaces, depending on the proposed use of the device 10. The device 10 is a data acquisition device which is battery powered, in this case by a rechargeable 25 Li-ion unit.

In Figure 3a there is shown an end view of a first embodiment of the device 10 in which can be seen interface panel 17a on which is provided input/output (I/O) ports P12 1 95GB

-13- 25a, 25b and 25c, infrared data association (iRda) port 26 and RS232 port 27. I/O ports 25b and 25c provides connection to means, such as electrodes, for performing measurements. I/O port 25a provides connection to a power 5 supply for either directly powering the device or for recharging the device battery. RS-232 port 27 provides connection means for hardwire transfer between the memory of the device 10 and a remote PC (not shown). The information transferred by a cable attached to this port 10 can be used in conjunction with information transferred using the iRda port 26.

In Figure 3b is shown an end view of a second embodiment of the device lO having interface panel 17b on which is a disposed a 12 way I/O port 24 and an iRda port 15 26 which can allow wireless data transfer to and from the non-volatile memory of the device 10 and an associated PC system (not shown), for example, a desktop system.

In the arrangement shown in Figure 3b, the device lob is arranged for use, in particular but not exclusively, 20 performing in viva measurements such as medical or dental measurements, which are outwith the scope of the present invention, as only one I/O port 24 has been provided on interface panel 17b. I/O port 24 can provide connection to electrodes thus allowing measurements to be performed, or 2 5 can provide connection to a power supply thus allowing the device battery to be recharged. The provision of only one I/O port 24 means these functions can only be performed exclusively and therefore the device is suited to in vivo P12195GB

-14 use as at no time would a patient be in direct contact with a mains power source or other external power supply including a mains powered device.

In Figure 4 there is shown a simplified block diagram 5 of the hardware of the device 10 which is integrated within the device housing 19. The hardware comprises analogue circuitry 11, rechargeable battery 45, digital board 42 including digital signal processor (DSP) 13 and data storage means.

10 The data storage means are, in this case, Flash memory where data acquired by the device is stored after processing. With reference to Figure 5 there is shown a simplified block diagram representative of the analogue circuitry of 15 the device 10 and illustrates signal source, output channel 31, analogue input channels 29 and 30 and the respective operations which are performed on each of these channels.

Also illustrated is a digital trigger 28 which, for example is a remote switch, fire button or some other appropriately 20 connected digital stimulus.

In figure 6 there is shown a simplified block diagram which illustrates the interconnection between the digital signal processor (DSP) 13 and the analogue circuitry 11 of the device 10. A software application embedded within the 25 device 10 creates an output signal which is generated by DSP 13 and is carried as serial data on output channel 31 where it is converted to an analogue signal by a digital to analogue convertor and passed to analogue circuitry 11 from P12195GB

-15 where it is applied to a system to be tested and also redirected in order to return to the DSP 13 for use in data analysis. The redirected output signal and detected response signal from the test system are carried from 5 analogue circuitry 11 by channels 29 and 30 respectively, through the ADC 46 and back to the DSP 13 where they undergo signal analysis, such as transfer function and FFT, for EIS measurements performed over a wide range of impedance and/or frequency.

10 In Figure 7a there is shown the analogue circuitry lla corresponding to the device 10 being provided with interface panel 17a. In this arrangement, the analogue circuitry lla of the device 10 has a signal source output channel 31 which provides the generated signal to DAC 32, 15 the analogue signal output from which is either applied to the system to be tested, for example a battery via output 38a or is directed by AS1 switch 37a to input/ output channel 29. The response signal generated by the tested system is carried on input channel 30 where it can be 20 directed through, or allowed to bypass programmable variable gain amplifier 40 by means of AS2 switch 41a.

Switch AS3 36a is included in input channel 30 to prevent back drive of high voltage from the amplifier 40 through switch 41a to the system being tested and the operation of 25 this switch is coupled to switch AS2 41a for this reason.

This circuitry lla further shows that by wiring CH.Z 31a to CH.X 29, external noise is incorporated back from IN1 29 (or COUNTER 34 in circuitry lib). This "common mode noise" P12 1 95GB

-16 is thus removed on execution of transfer function (CH.X/CH.Y) required for an impedance measurement. Such an analogue circuit arrangement is suitable for use performing tests in systems such as batteries, coatings, stress 5 detection in civil engineering fields eta wherein the

device can perform measurements whilst battery powered.

However, tests may also be performed whilst the device is connected to a mains power supply or mains powered device.

In Figure 7b there is shown the analogue circuitry llb 10 corresponding to the device 10 being provided with interface panel 17b. In this arrangement the analogue circuitry llb is provided with a signal source output channel 31 which provides the generated analogue output signal to be applied to the system being tested. The 15 circuitry llb further comprises analogue input channels 29 and 30 into which are input the generated signal and detected response signal respectively. The output channel 31 implements the output provided by a digital signal source and includes digital to analogue converter (DAC) 32.

20 The generated analogue output signal, which in this case is a multisine wave, is passed from output channel 31 to, in this case counter electrode 34 which is connected to the system being tested, for example a battery. A response signal from the probe or working electrode 33, which is 25 connected to another site on the test system, is directed through a programmable variable gain amplifier 40 which may amplify the signal by a factor from the range of for example xl to xlO9, before reading the amplified signal to P12 1 95GB

-17 input channel 30. The output signal carried on output channel 31 is also directed back into the input channel 29 thus allowing use of the source wave in data analysis. As can be seen medical safety features conforming to British, 5 European and IEC standard requirements for medical electrical equipment that allow safe use of the device 10 in viva are incorporated into the analogue circuitry lib.

However the in vivo use of the device 10 falls outwith the scope of this invention. On the end of the output channel 10 31 which connects to counter electrode 34, there is placed a 36KQ resistor 35 which limits the current transmitted to the counter electrode 34 to below 20pA. Furthermore, a 1,uF DC blocking capacitor 36 and voltage clipping diodes 39a and 39b are placed in series with resistor 35 which starts 15 to clip the maximum voltage amplitude passing to counter electrode 34 at 500mV. Similarly, 1pF DC blocking capacitors 42a and 42b are provided on signal input channels 29 and 30 respectively at the test system side of circuit lib. In order for the device to meet the voltage 20 limits under single fault conditions, high voltage sources, such as the battery charger input and RS-232 port are isolated from the test system whilst system measurements are being made. This is achieved by the provision of only one 12-way I/O port 24 being constructed as shown in figure 25 3b to overcome medical safety issues regarding clinical measurements by ensuring that any person on which measurements are being made is safely isolated from a mains AC power supply. Additionally, any power source dedicated P12195GB

-18 to generating a backlight in the display of the device is disabled within the hardware.

A schematic diagram of the interface panel 17a having I/O ports 25a, 25b and 25c, RS232 port 27 and iRda port 26 5 which is used when the device 10 is provided with the analogue circuitry lla is shown in Figure 8a. Each of the pins of the I/O ports and RS232 port are enumerated with pin number 1-7, 1-6, 1-6 and 1-9 respectively. The detailed pin configurations are examples only and all the 10 connections can be customized for specific end uses.

In Figure 8b a schematic diagram of I/O port 24 which is used when the device 10 includes the safety features of analogue circuitry lib. Each of the pins has been enumerated with pin numbers 1 to 12. The function assigned 15 to each of these pins is as follows: Pin 1 is assigned the RS232 DTR function, which connects Pin 1 to Pin 6. The DTR function is Data Terminal Ready and is driven by the Data Terminal Equipment (DTE) i. e. the PC when it is ready for action; 20 Pin 2 is assigned to analogue input channel 30; Pin 3 is assigned to analogue output channel 31; Pin 4 is assigned to external (EXT) TTL trigger 28 with the trigger operating between O to 5 V.; Pin 5 is assigned to a AGND function, analogue ground; 25 Pin 6 is assigned to a RS232 DCD\DSR function. The DCD function is Data Carrier Detect and is driven by the Data Circuit terminating Equipment (DCE) i.e. a modem or other peripheral. For a modem, this indicates that the P12195GB

-19 line signal is being received, for other peripherals it means that they are ready to transmit. A DSR signal indicates the device 10 is powered up and ready to transmit; 5 Pin 7 is assigned to a RS232 TxD OUT function, where TxD is "Transmit Data" and this carries data to and from the RxD pin; Pin 8 is assigned to a RS232 RxD IN function, where RxD is "Receive Data" and this carries data to and from the 10 TxD pin; Pin 9 is assigned to a RS232 CTS IN function where CTS is "clear to send" and a signal on this pin indicates the device is ready to accept data; Pin 10 is assigned to a RS232 RTS OUT function where 15 RTS is "ready to send" and indicated the device is wanting to send data. The modem, or other peripheral, responds by switching its CTS line on when ready to accept; Pin 11 is assigned to a EXT DC IN function which is a 12V DC input; and 20 Pin 12 is assigned to a DGND function which is a Digital ground. By combining all I/O connections into a single port and constructing an individual cable for each I/O operation, the device is physically prohibited to simultaneously connect to a mains AC powered device or 25 supply while also connected to a patient for in viva measurement. As the device 10 is capable of performing several operations, for example taking measurements, performing P12195GB

-20 analysis, database storage, transfer of data by various means such as RS232, and charging/monitoring of battery, depending on the software application embedded into the ROM of the device there are at least three cables required to 5 perform all operations.

In Figures 9a, 9b and 9c there are shown three embodiments of cable construction, each one capable of performing a different operational function when connected to device 10 having circuitry llb via I/O port 24. In this 10 case, the cable illustrated is a 12-way port commercial socket from Fischer.

With reference to Figure 9a, there is shown the cable construction of the signal cable which is used when connecting device 10 to a system to be tested and in this 15 case is constructed in a manner that provides BNC connection for channels 29 and 30 respectively. Trigger 28, is in this case, a switch provided remotely, as a fire' button, upon operation ofwhich an output signal is generated by the DSP 13, and is connected to pin 4 and pin 20 5 as well as to the BNC connections for channels 29 and 30.

The signal cable construction shown in Figure 9b allows hardware transfer between the flash memory of device 10 and a remote PC. In this case the cable shown for this operation is wired for connection to a modified DCA26, 25 which is a standard 9 pin serial plug modified to overcome standard wiring configurations, with pins 1, 6, 7, 8, 9, 10 and 12 of I/O port 24 being assigned as detailed with reference to figure 8b. The information transferred by P12195GB

-21 this cable can be used in conjunction with information transferred, for example, using the IRDA port 26.

The cable shown in Figure 9c allows the charging of battery when connecting the I/O port 24 to an external 5 power supply unit 43. This operation involves pins 11 and 12 providing DC input and digital ground functions respectively. In order to allow device 10 to be used for a specific application in a given environment, custom software is 10 embedded into the memory system of the device 10 thus allowing the user to be provided with a specialist measurement without any need to modify the hardware characteristics of the device 10. Alternative software is embedded within the memory system of the device if it is to 15 be used in alternative specialist uses.

Typically the device operates in an Electrochemical Impedance Spectroscopy (EIS) mode with, for example, the EIS operations performed using a multi-sine method.

The construction of a pseudo-random noise output 20 waveform which can be used in the EIS measurement to be carried out by the device 10 is shown in Figures lea to lOd. The waveform is constructed using sinusoids based on a fundamental sine wave of 15mV amplitude and having fundamental frequency fo Of lOOHz which is shown in Figure 25 lOa.

The pseudo-random noise source waveform, is constructed by a summation of n sinusoids based on the user defined fundamental lower frequency fo and an upper P12195GB

-22 frequency fn (= n. fo) and amplitude aO, each with random phase. In practice, each point k of the voltage waveform is generated according to the function 5 n Ek=aO (20ifotk+0i) i=1 where Ek is the voltage at any given time tk, and Hi is the phase randomised for each sinusoid. The peakto-peak 10 amplitude of the voltage perturbation signal could be adjusted by multiplying Ek with appropriate coefficients applied by multiplying the resulting waveform by an appropriate value in the software.

The waveforms generated by the summation of three 15 sines representing lOOHz to 300Hz is shown in Figure lob, and the waveforms generated by the summation of ten sines representing lOOHz to lKHz are shown in Figure lOc. As can be seen these already resemble random patterns.

In Figure ad the waveform generated for a frequency 20 range of lOOHz to 20KHz is the result of 200 overlapping sines and this provides a waveform resembling white noise.

The time period for each of the waveforms shown in Figures lOa to lOd is ten milliseconds. Typically, in the performance of a measurement made using the device the 25 entire signal measurement is completed in a full cycle period of the lowest frequency, that is the applied duration of the source waveform on output channel 31 is (l/fo) seconds, which in the case of Figure lOd, is 10 ms.

This means the entire experiment time, including analysis, 30 can be completed in approximately 3 seconds. The use of P12 1 95GB

-23 the multi-sine signal, which has a root mean square voltage of 35% of the selected peak amplitude, means that measurements taken by the system are exposed to less severe perturbations than measurements taken using a series of 5 discrete sine waves as these typically have a root mean square voltage of 70% of the selected peak amplitude. This advantage is of particular importance at lower frequencies where measurement periods are longer and the possibility of corrupting the system during measurement is high.

10 In order for a measurement to be taken using the device 10, the I/O channels 29,30 and 31 and the digital signal processor 13 must be initialized. The software application embedded within the device, regardless of the functionality it imposes upon the device, runs an 15 initialization routine, typically when an instance of the program is first executed. Upon being switched on, device 10 will power up with the software application instance already running and therefore already present.

A flow diagram of the initialization routine common to 20 each software application is shown in Figure 11. Upon initialization, the DSP driver file, which is stored in the flash memory of the device 10, is opened and the relevant software code, which is a data file stored in Flash that has controlling software functions, is read into a buffer, 25 stored within a software array, where it is manipulated before being sent to DSP as serial data in the correct format for receiving. This process is represented by Step 71 of the flow diagram. Similarly, as can be seen in step P12195GB

l -24 73, an analogue driver file is also loaded from Flash memory into the application of embedded software which is currently running. Each of the analogue input channels 29 and 30 has a corresponding calibration file which is a data 5 file storing calibration data which is loaded from the Flash memory. Information from each data file is read by the software application and sets up the appropriate tolerances of coarse offset, fine offset and factor values.

The software handles, which are variables in software 10 representing the input and output channels, are then assigned to the physical channels 29, 30 and 31 on the analogue circuit board 11. The initialization process is checked for errors at steps 72,74 and 76 and any errors are processed by the software application and retries are made 15 at each step if not successful on the previous attempt. A suspended worker thread is started 77 for the external digital trigger 28 and operates in the background upon

completion of the calibration data concluding successfully.

Once resumed from the suspended mode in which it was 20 started, at a point in the application where triggering is required, for example, if a measurement is to be taken, the external trigger thread will execute. This happens when an event occurs that is triggered by the external digital trigger 28, which is for example a fire button or some 25 other appropriately connected digital stimulus. The return to calling routine step 78 occurs when the software function ends.

With reference to Figure 12 there is shown a flow P12195GB

-25 diagram of the routine which is performed by the device 10 when taking an EIS measurement, also known as an ACIST( -,4 measurement. The software for performing such a measurement is termed ACIST Engine_. The flow diagram 5 represents the core operation which allows the device 10 to acquire EIS data. The analogue source channel 31 is assigned a software handle then set up with a high pass filter enabled. The sample rate is sufficiently high to accurately represent the appropriate output waveform such 10 as the one shown in Figure lOd without aliasing at its highest frequency component. The response channel 30 is assigned a unique software handle and the programmable gain stages of the variable gain amplifier 40 are set before all the setup information data is flushed to the DSP 13. The 15 DSP process is first set up by software in a manner similar to the setup operation of the analogue hardware channels, by specifying the average number of measurements to be taken during an experiment, that is any single measurement of a sample or system. Following this, the measurement 20 type is specified as a transfer function by the embedded software application, and the number of points is given Windowing is then selected if required, however, in the case of the present EIS experiment none are chosen.

The DSP process is started upon the generation of a 25 waveform, such as that shown in Figure lOd, which is then sent to the output channel 31 as a serial data block. The routine, sets up a software timer and waits for data to be received from the analogue input channel 30 at the DSP 13, P12 1 95GB

-26 that is it waits for the response data from the tests carried out. If no response data is received within the specified timeout period determined by the software timer, the user receives an indication of the problem, typically 5 via the display screen 16. However, if response data is successfully received and read by the DSP 13, the real and imaginary parts of impedance, as well as coherence information, are read into a buffer array in the software from the data block, in this case as a fixed length of 10 serial response data from the DSP 13. The DSP process is then terminated and the measurement data is passed to an appropriate fitting routine defined in the software application and which can call appropriate models from Flash memory for use to provide a target function, that is 15 a mathematical model representing the physical properties of the system under test, from those of a chosen equivalent circuit model. The received response data and fitted parameters are then stored by a persistent data storage routine which saves data to the Flash memory for later 20 retrieval to be used throughout the software application.

The program implemented within the device during the {' N use of the ACIST Engine_ is represented by a flow diagram in Figure 13. This flow diagram shows the EIS graph for the application process which was performed by the device 25 10. Having the ACIST Engine_ embedded within the device 10 means that it operates as an EIS measurement instrument, termed ACIST-hpc, and displays graphs resulting from tests performed as well as offering data storage options to allow P12195GB

-27 storage of information gleaned from the measurements made.

64TM) When the ACIST Engine_ application is first executed, it calls on the initialization routine to set up the DSP driver and assign hardware channels as described 5 previously. The programmable softkeys 18a, b, c and d are then assigned their respective operations by the application, or by the user and the appropriate display chart is constructed for display on the default display page on the LCD screen 16. Virtual buttons 91, 92, 93 and 10 94 are added at the bottom of the main display corresponding to a function which each softkey can execute.

Each virtual button works on an event driven basis such that each softkey performs a designated operation before returning to the default, or main, display page. On 15 pressing the SETUP button, in this case virtual button, 92, a dialogue window is displayed that allows the user to modify the amplitude, fo and En of the generated waveform.

The SAVE button, in this case virtual button 93, displays a dialogue window that gives the user an option to save the 20 acquired impedance data to a designated filename. By pressing the left cursor 20a or right cursor 20b on the handset 19 of the device 10 the graph view is changed to a different type such as Nyquist ( Zimaginary vs Zreal) or Bode plots, that include Zimaginary vs f and Zreal vs f. The MEASURE 25 button, in this case, virtual button 94 executes the ACIST() Engined thus performing a measurement as described earlier in the text. During the measurement, amber LED 15b is lit indicating that the device 10 is waiting to collect data.

P12 1 95GB

-28 The amber LED 15b is switched off and a green LED 15c is switched on for a period of, for example, 2 seconds when the acquisition is complete. At this point a fitting routine is called if required and the graph view on the 5 main display of screen 16 is updated.

In Figures 14a,b and c some screen displays from the EIS application presenting the result of measuring the impedance response of a parallel RC dummy test circuit constructed from a 1MQ resistor and a 15pF capacitor. The 10 source waveform was generated from the summation of 200 sinusoids, each of 15mV amplitude and random phase, representing the frequency range lOOHz to 20kHz, such as that shown in Figure led. The display is provided by a graphical user interface such as Figure 14.

15 In Figure 14a there is shown a graphical representation of -Zimaginary US Zreal' Figure 14b illustrates Area VS f and in Figure 14c there is shown -Zimaginary VS. f.

Some examples will now be described in order to illustrate applications of the device 10 operating as an 20 ACIST-hpc in selected fields of research & development,

non-destructive testing and medical diagnosis. The first and second examples use the EIS program described above and relate to R & D experiments, while the third example describes a more complex system that incorporates the ACIST 25 Engined being used in a dental environment in a manner outwith the scope of the present invention.

The first example concerns polymer electrolytes which are tonically conducting phases formed by the dissolution P12 1 95GB

-29 of salts into suitable coordinating polymers, such as polyethylene oxide (PEO). Extensive research into the development of rechargeable lithium batteries using solid polymer electrolytes is ongoing due to the advantages they 5 offer in comparison with conventional liquid systems, for example, polymer electrolytes can be manufactured into thin films with large surface areas giving high power levels (>100 W dm 3). Construction of all solid-state batteries can proceed in a variety of configurations, and be 10 incorporated into devices such as notebook PC's, cellular telephones, and thin smart credit cards.

In this case the polymer electrolytes were formed by mixing and processing LiCF3SO3 salt and dry PEO. In this case the LiCF3SO3 salt was formed by 15 trifluoromethanesulphonic acid (0.667 mol dm 3) being slowly added to a suspension of lithium carbonate (Li2CO3, Aldrich) in distilled water. The solution was then stirred for 3 hours, filtered through a fine sinter and the majority of water removed on a rotary evaporator, leaving the hydrated 20 lithium trifluoromethanesulphonate (LiCF3SO3) salt. The anhydrous salt is obtained after heating the hydrated salt sample under vacuum for 24h at 150 C.

To form the polymer electrolyte, a stoichiometric mixture of LiCF3SO3 and dry PEO (MW=5x106), in 40EO:lLi 25 ratio, was transferred to a stainlesssteel tube for cryogrinding and a small sample of the intimate cryoground mixture was then pressed to 5 tons for 30 seconds between two stainlesssteel discs in a 13mm pellet press. This was P12195GB

-30 heated for at least 3 hours at 120 C under no applied pressure using a band heater. Upon cooling to 65 C, a pressure of 3 tons was applied and the sample allowed to cool to room temperature overnight under the applied 5 pressure. In this case the film produced using this process was 0.36 mm thick.

To perform the measurements using device 10 in this example a twoelectrode cell configuration 60 such as that shown in Figure 15 was used with blocking stainless-steel 10 electrodes which, when assembled, was placed in a Buchi(,T-) oven and the temperature was monitored by a K-type thermocouple running through the cell. The geometric constant of the assembled cell was 4.734 x 10-2 car. Contact between the cell 60 and the device 10 was made by BNC 15 electrical breakthroughs from the glove box. The BNC interface 23 provides connection of the cell 60 to the ACIST-hpc, that is device 10, via the associated cables.

The cell 60 was allowed to thermally equilibrate at each temperature for at least lh before measurements were made.

20 All operations and measurements were performed in an argon filled mBraun glove box. AC measurements were made using the ACIST-hpc and there were compared to measurements performed by a sweeping single-sine system operating in the frequency domain. The swept-sine instrumentation in this intro) > 25 case comprised a Solartron FRA coupled to a Solartron 1286 potentiostat, driven by a PC under custom software control.

In both cases measurements were made in the frequency range 20 kHz Hz.

P12195GB

-31 An idealised lithium ion conducting polymer sandwiched between symmetric blocking electrodes can be modelled by a parallel (RB CB) equivalent circuit. The resistor RB represents the migration of lithium ions moving back and 5 forth in phase with the voltage. At the same time, a dielectric polarization of the polymer chains occurs in the alternating field which is represented by the capacitor CB.

Figure 16a shows the Nyquist plot comparison of each measurement of the polymer electrolyte film at 30 C, that {'roan 10 is the measurements achieved using the Solartron FRA arrangement which are represented using an open circle and fir, -) measurements achieved using the ACIST-hpc device which are shown in closed circles. As can be seen from this graph At, A) the results achieved using the ACIST-hpc are consistent 15 with those achieved using conventional prior art

arrangements. In Figure 16b the EIS measurements achieved using the ACISThpc are shown for selected temperatures, in this case 30.0 C, 46.4 C and 56.0 C.

20 The fitted values for RB and CB at each temperature are listed in Table 1 below along with the calculated specific conductivity values.

PI 2 1 9 5GB

-32- Tabl e 1 Fitted values to temperature dependent EIS.

O T / C RB / kQ / Scm l C / pi 23. O 3021. 568X10-7 439

5 30. O 1622. 922X10-7 467

46.4 59.27.997X10-7 437

56. O 22.62. O95X1O-6 411

A plot of logy vs. T-1 is shown in Figure 1 6C indicating that Arrhenius behaviour is observed over the 10 chosen temperature range with an activation energy for conduction of Ea = 60.86 kJ mold.

The second example concerns corrosion protection of engineering structures using selected coatings which are commonly used worldwide. However, degradation of such 15 coatings does occur leading to an underlying metallic corrosion problem. In order to allow more informed decisions on which structures require attention, quantitative inspection methods have been introduced. Some DC electrochemical techniques have already been applied in 20 the evaluation process with only limited success. EIS measurements, however, can provide a fast, non-destructive and quantitative method of assessing coating properties and identify the early onset of steel corrosion. An apparatus, incorporating device 10 using the EIS application as a 25 basis, can operate as a field portable inspection unit to

provide the user with quantitative information on coating degradation. The BNC interface 23 allows connection of the an equivalent circuit, shown in Figure 17a by crocodile clips P12195GB

(A a) -33 61 to the ACIST-hpc, that is device 10, via associated cables and using this arrangement measurements of the capacitance and/or impedance of the coating can be made to assess the thinning of the coating due to wear or, in the 5 case of the coating being applied to provide protection the growth of the coating layer. The equivalent circuit model, proposed by Zdunek et al, representing the physical characteristics of a corrosion system, such as coated steel, is shown in Figure 17a. R5 represents the ohmic 10 resistance of the electrolyte, while the resistance and capacitance of the coating are RC and Cc, respectively. The corrosion reaction is modelled by the polarization elements RP and Cp. At very low frequencies an impedance response attributed to diffusion ED may be observed. In Figure 17b 15 there is shown a Nyquist plot of a measurement of the equivalent circuit using the present invention in the form of ACIST-hpc, represented on the graph using a closed circle, compared with data collected from a standard swept sine system. The swept-sine system used with the circuit -) 20 of Figure 17a comprised a Solartron FRA coupled with a bare) Solartron 1286 potentiostat and PC, controlled by custom data acquisition software. As can be seen from the Nyquist plot of Figure 17b both resultant measurements are very similar, however, the time to complete the measurement run (ATE 25 with the ACIST-hpc 10 was only 3 seconds compared with the 7 minutes measurement time of the large FRA-based system.

The device 10 can be setup in a manner outwith the scope of the present invention as a dental diagnostic P12195GB

-34 instrument, having the analogue circuitry llb for in-vivo clinical examination, by the addition of custom peripherals as are shown in Figure 18. A dental probe 33 is placed in contact with a site on the tooth to be tested and a counter 5 electrode 34, in the form of a hand-held grip is held by the patient. A BNC interface box 23, the wiring of which is described in Figure 7a, connects the probe 33 to the response channel 30 and the counter electrode to the signal source channel 31, via cables 2a and 2b respectively. The 10 signal cable 3 leads from the interface box to the device 19. In Figure 19 there is shown a flow diagram of an IT*) example program that demonstrates use of the ACIST Engine_ in a device for use in the clinical field 10. This

15 application, when embedded into the device 10, transforms the unit into a dental caries diagnostic tool that offers HIS measurement capability and a database of patient records. Each of the records stores personal details of the patient and results of measured teeth for each visit.

20 The actual functionality of the measurement, including an impedance plot, is not shown to the user.

When the application is first executed, it calls the INITIALISE routine to setup the DSP driver and assign hardware channels. The programmable softkeys are then 25 assigned their respective operations and the patient database if it already exists is loaded, or otherwise a new record is created. The main screen display is updateable to show a list of each patient with summary details, an

P12195GB

-35 example of which is shown in Figure 20a. Virtual buttons 91, 92, 93 and 94 are added at the bottom of the main screen corresponding to each softkey function and these work on an event driven basis, as detailed previously, 5 performing a designated operation before returning to the main screen. On pressing the FILE button 91 a popup menu is presented that offers the user a selection of options that may include battery status, file uploading or downloading to a PC and erase record. The NEW button 92 10 displays an empty patient details page for the new record, which is shown in Figure 20b and that prompts the user to complete the form including a unique identifier code. The softkey functions are modified in the patient details page to allow the user to access additional pages within the 15 same patient record. These other pages include visit dates, tooth selection which is shown in Figure 20c, and table of results. The visits and results pages are only accessible from within an existing record that contains a measurement. Once the new record details have been 20 entered, the OK button 12 is pressed to add the record to the database, or CANCEL button 14 to reject changes. The UPDATE button 93 opens the patient details page and displays the contents of the currently selected patient record. The results recorded at previous visits can be 25 viewed in a table. By pressing the up cursor 20c or down cursor 20d the selection on the main screen, is moved through the patient list. The MEASURE button 94 displays the measurement screen for the currently selected patient, P12195GB

-36 as shown in Figure 2Od. Within this page, the user can select any surface of any tooth and move backwards and forwards through the selections as required. The softkeys were again reprogrammed to offer appropriate functionality.

5 The GO button 94 on the measure screen executes the ACIST r) Engined and performs the measurement upon the tooth.

During the measurement, the amber LED 15b is lit indicating that the instrument is waiting to collect data. The amber LED 15b is switched off and green LED 15C is switched on 10 for 2 seconds when the acquisition is complete. A fitting routine is then called and the measurement screen of Figure 20d is updated with the result code before moving the selection to the next tooth or surface in the sequence. At any time the user can press the OK button 12 to accept the 15 data or CANCEL button 14 to reject the measurements. On returning to the main screen of Figure 20a, the patient list is updated to reflect the visit. The patient database can as has been described be uploaded to a desktop PC by serial cable, wireless iRda or by transferral of Flash data 20 storage.

For in-vi pro measurements, a cell comprising ten spring-loaded compartments made of stainless-steel for holding whole teeth is shown in Figures 21a, 21b and 21c.

Each compartment has a common contact acting as a counter 25 electrode 34. Above each tooth is a fixed stainless-steel probe that acted as a working electrode 33. To this is An) attached a Perspex lid 53 with electrical breakthroughs to BNC connections 49. After loading the teeth or as shown in P12195GB

-37 Figure 21a, a tooth 50 on which measurements are to be performed, the assembled unit 54 is placed inside a stainless-steel can 51 filled with approximately 250ml of 0.lmol dm 3 saline + thymol mixture. An O-ring 56 maintains 5 the seal when the unit is screwed into place via the holes care) 52 provided on Perspex lid 53. A 'K'-type thermocouple allows accurate monitoring of the solution temperature within the can 51. The complete can is placed into an oil bath (not shown) that is thermostatically controlled by a 10 Haake DC5 controller and cooler to within +0.1 C. The cell is left to equilibrate at each temperature for approximately 40 minutes before measurements are made. AC measurements are made using the ACIST-hpc application detailed previously.

15 The graphs shown in Figures 22a and 22b present typical AC impedance spectra obtained from the occlusal surface of whole human teeth in-vitro while controlled for hydration and temperature at 30 C. The effect of caries on these measurements is clearly demonstrated with the 20 measurements having been performed on sound teeth, teeth showing advanced caries and teeth showing early caries.

The impedance values for each group differ significantly from the other two groups. Impedance of a sound tooth surface approaches 2MQ while the presence of early caries 25 reduces the impedance to approximately 400kQ. More advanced caries lowers the impedance to around 100kQ.

Figures 23a and 23b show receiver operating characteristic (ROC) curves for measurements made on whole P12195GB

-38 teeth. In Figure 23a the in vivo values for sensitivity and specificity were 91.7% and 84.2%, respectively, and in Figure 23b the in vitro valves for sensitivity and specificity were 92.9% and 95.8%, respectively. In all 5 cases, measurements were validated by histology. These high values of sensitivity and specificity demonstrate the potential of the device for the detection of dental caries by EIS, or ACIST{)-By using in-vivo probes engineered specifically for the oral environment, the successful 10 execution of the technique in the clinic and examiner reproducibility could be improved further.

An alternative arrangement, falling outwith the scope of the present invention, involves the device 10 being set up for performing in-vivo clinical examinations in a 15 medical environment.

As is shown in Figure 24, the device 10, is provided with an array of flat pad electrodes, with in this case, one of these electrodes being employed as the counter electrode. However, the array design can be configured in 20 any desired custom manner. Each electrode is held against a patients skin by adhesive. The counter electrode may alternatively take the form of a hand held stick to be gripped by the patient. In the arrangement shown, the device 10 is configured for use performing measurements in 25 the chest area carrying out, for example, skin scans in order to detect the presence of tumours, lesions, cysts or the like.

During the examination, the patient, has the flat pad P12195GB -39 electrodes attached to their skin by temporary adhesive means, in this

case sticking plaster. The medic performing the examination places the electrodes on the skin of the patient and performs big-impedance measurements using the 5 device 10. Living tissues have differing, often unique, electrical properties so structural and chemical alterations may be reflected in impedance changes. Of importance to medicine would be the determination of pathology via the use of such non-destructive electrical 10 methods.

For example, the device may be used to determine changes in tissues or cells that may be physiological, pathological or pharmacologically induced. Therefore changes such as inflammatory, infective, ischaemic, 15 neoplastic, metabolic, fibrotic, necrotic, hypertrophic, hyperplastic or degenerative, eta may be measured. Such measurements are also useful in the evaluation of cardiovascular, pulmonary and renal function, body fat estimation, hydration, etc. All of the above may be 20 visualised using imaging techniques such as electrical impedance tomography (EIT). The device may also be used to distinguish normal tissue/biological material from that with any changes adverse or otherwise that may be acquired, developmental or age related, where such changes may be 25 determined by the means of applying an electrical stimulus and measuring its response.

Various modifications may be made to the arrangements as hereinbefore described without departing from the scope P12195GB

-40 of the invention. For example, the signal generated by the device 10 has been described as being a simple square wave or a plurality of sine waves however, a single DC voltage step, or a square wave over one period may alternatively be 5 generated. Also, in the description, the iRda port 26 has

been detailed as providing a link between the device 10 and a PC for data transfer, however, the iRda port 26 can alternatively be used as a link to other devices to allow wireless data transfer or printing. Similarly, recharging 10 of the battery may be performed wirelessly if an inductive charging unit is incorporated into the device. While the panel 17 of the device has been shown in two configurations 17a and 17b, the I/O configurations of the device can be configured in any desired custom manner, with the 15 associated analogue circuitry 11 being correspondingly customized. For example the amplifier gain stage with current-to-voltage conversion on response input channel 30 may be by- passed and connection of output channel 31 to input channel 29 can be switched off, this allows an 20 additional interface, such as a potentiostat, to be coupled to the device and allow other ranges of experiments to be performed. P 1 2 1 9 5GB

Claims (1)

1. -41- CLAINS

   1. Use of a portable test device for measuring at least one property of a system, other than a dental or medical system, by generating an electrical signal to be applied to 5 a system and acquiring a response signal generated by the system, the device comprising: signal generation means; signal receiving means) and signal processing means; 10 wherein, in use, the device generates a signal to be applied to a system to be tested and receives a response signal of the system which was tested whereby the applied and received signals undergo processing by the signal processing means, providing data indicative of a 15 characteristic of the system.

   2. Use of a portable test device as claimed in claim 1 wherein the provided data is transferred to data storage means for storage.

   3. Use of a portable test device as claimed in claim 1 or 20 claim 2 wherein the device is hand held.

   4. Use of a portable test device as claimed in any preceding claim wherein the device includes means for visually displaying data.

   25 5. Use of a portable test device as claimed in any preceding claim wherein the device measures an impedance of P121 95GB

   -42 the system.

   6. Use of a portable test device as claimed in any preceding claim wherein the device is battery operated.

   7. Use of a portable test device as claimed in claim 6 5 wherein the device is removably connectable to a mains power supply to allow charging of the battery to take place. 8. Use of a portable test device as claimed in any preceding claim wherein the portable device includes means 10 for associating the device with electrode means comprising at least a first electrode and a second electrode wherein the first electrode applies the generated signal to the system to be tested and the second electrode collates response signals from the system response.

   IS 9. Use of a portable test device as claimed in any preceding claim wherein the device is configured or arranged such that connection to an external power supply and electrode means cannot occur simultaneously.

   10. Use of a portable test device as claimed in any of 20 claims 1 to 8 wherein the device is configured such that connection to an external power supply and electrode means can occur simultaneously.

   P12 1 95GB

   -43 11. Use of a portable test device as claimed in any preceding claim wherein the device is provided with safety features conforming to an appropriate standard requirements for medical electrical equipment.

   5 12. Use of a portable test device as claimed in any of claims 1 to 9 or 11 wherein the device may be provided with only one input/output port wherein the device cannot be connected to an external power supply and a system to be tested simultaneously.

   10 13. Use of a portable test device as claimed in any of claims 1 to 8, 10 or 11 wherein the device is provided with two or more input/output ports wherein the power to the device and the signals transferring to and from the device are assigned to individual input/output ports.

   15 14. Use of a portable test device as claimed in any preceding claim wherein the signal applied to the system comprises at least one period of a periodic signal such as an AC signal.

   15. Use of a portable test device as claimed in any of 20 claims of 1 to 14 wherein the applied signal is a sine wave. 16. Use of a portable test device as claimed in any P12195GB

   -44 preceding claim wherein the applied signal is formed of a plurality of sine waves.

   17. Use of a portable test device as claimed in claim 16 5 wherein each of the sine waves is of a different frequency and random phase.

   18. Use of a portable test device as claimed in any of claims 1 to 14 wherein the applied signal is of a single 10 frequency.

   19. Use of a portable test device as claimed in any of claims 1 to 14 wherein the applied signal is a square waveform or other waveform (e.g. triangle, saw tooth or 15 arbitrary).

   20. Use of a portable test device as claimed in any of claims 1 to 13 wherein the signal applied to the system may be a DC signal.

   20 21. Use of a portable test device as claimed in any preceding claim wherein the means for analysing the applied signal and received signal performs Fast Fourier Transform spectrum analysis upon the applied signal and received signal. 25 22. Use of a portable test device as claimed in any preceding claim wherein the device is customised for P12 1 95GB

   -45 specific end-use by embedded PC-based control software.

   23. Use of a portable test device as claimed in any preceding claim wherein the device may be programmed to perform a range of measurements with subsequent analysis, 5 presentation, data storage and retrieval.

   24. Use of a portable test device as claimed in any preceding claim wherein the device further comprises means for performing variable amplification on the received signal. 10 25. Use of a portable test device as claimed in any preceding claim wherein the signal receiving means includes data acquisition means.

   26. A portable apparatus for use measuring at least at least one property of a system, other than a dental or 15 medical system, by applying electrical stimulus to a system and acquiring a system response, the apparatus comprising: signal generation means; signal receiving means; signal processing means) and 20 electrode means which, in use, are applied to the system, wherein a generated signal is applied to the system by said electrode means' a response signal of the system is detected by said electrode means and received by the signal P12195GB

   -46 receiving means, the applied and received signals undergo processing by the signal processing means.

   27. A portable apparatus as claimed in claim 26 wherein 5 data generated by the signal processing means is transferred to data storage means for storage.

   28. A portable apparatus as claimed in claims 26 or 27 wherein tests carried out using the device generating a signal having a frequency in the range of DC - lOOkHz 10 provides accurate results for measurements made involving systems characterized by low frequency response such as polymers, dielectrics and electrode processes or other high impedance media.

   29. A portable apparatus, as claimed in any of claim 26 to 15 27 wherein tests performed using the device generating a signal in a range above lOOkHz provides accurate results for measurements made involving systems characterized by high frequency response such as highly conducting electrolytes or other low impedance media.

   20 30. A portable apparatus as claimed in any of claims 26 to 29 wherein the signal processing means performs signal analysis on the generated signal and received signal.

   31. A portable apparatus as claimed in any of claim 26 to 30 wherein the electrode means comprises one or more P12 1 95GB

   -47 electrodes and may comprise an array of electrodes.

   32. A method of performing electrochemical impedance measurement on a system, other than a dental or medical system, using a portable device, the method comprising the 5 steps of: generating a signal; applying the generated signal to the system by electrode means; detecting a response signal generated by the said 10 system using electrode means; processing said applied signal and detected signal and generating data representative of a feature or property of the system from said signal processing.

   15 33. A method as claimed in claim 32 further comprising the step of transferring the said generated data to and storing the said generated data in a storage means.

   34. Use of a portable device as hereinbefore described 20 with reference to figures 2 to 16c, 17b, 22a and 22b.

   35. A portable apparatus as hereinbefore described with reference to figures 2 to 16c, 17b, 22a and 22b.

   36. A method of performing electrochemical impedance measurements as hereinbefore described with reference to 25 figures 2 to 16c, 17b and 22b.

   P12 1 95GB