GB2470225A

GB2470225A - Contactless microenvironment sensor

Info

Publication number: GB2470225A
Application number: GB0908363A
Authority: GB
Inventors: Matthew David Steinberg; Ivana Steinberg
Original assignee: ERASMUS TECHNOLOGY LLP
Current assignee: ERASMUS TECHNOLOGY LLP
Priority date: 2009-05-15
Filing date: 2009-05-15
Publication date: 2010-11-17
Also published as: GB0908363D0

Abstract

A wireless apparatus for contactless determination of physical and electrochemical microenvironment parameters in aggregate materials 103 such as cement, mortar, concrete (steel reinforced), sand and soil comprises at least one sensing device 101 and one reading device 102. The sensor is used to monitor corrosion of materials and includes a receiving antenna, electrode array, voltage source, adjustable current source and unique identification number such that plural sensors may be wirelessly interrogated. Typically, electrical resistance may be measured.

Description

Field of the Invention

The present invention relates to apparatus and methods for the contactless determination of physical and electrochemical microenvironment parameters in semi-permeable bulk materials such as cement, mortar, reinforced concrete (RC), sand and soil comprising at least one sensing device and one reading device.

Background to the Invention

Steel-reinforced concrete (RC) is the primary construction material for buildings, roads, bridges and other superstructures throughout North America, Europe and Asia thanks to its versatility, durability, strength and ease of manufacture into different shapes and finishes by moulding and casting (Broomfield, 2007).

Cracking, spalling and eventual collapse of concrete cover layers in superstructures may occur however when the embedded steel reinforcement bars (rebars) begin to rust from inside the concrete. The chemical processes leading to formation of rust in embedded rebars is well known, and arises most often as a result of the ingress of atmospheric carbon dioxide (C02) and chloride ions (Cl-) from sea salt and/or de-icing salts into the semi-permeable concrete cover layer.

The rate and status of the steel corrosion process is difficult to determine from the external appearance of the superstructure due to a lack of visible effects on the concrete cover until such time as cracking first appears. Maintaining steel-reinforced concrete infrastructure therefore against the effects of salt-induced and atmospheric corrosion is a significant and costly undertaking. The same difficulties equally apply to the early detection and status monitoring of corrosion processes in reinforced structures that may be buried underground or underwater, such as concrete and steel pipelines and storage tanks.

State of the Art Various measurement techniques have been developed and are currently in practical use for evaluating the condition and corrosion status of both RC and buried steel structures. Also, several different physical, chemical and electrochemical parameters are routinely measured and evaluated in order to estimate condition of RC structures and pipelines. The rusting of steel is an electrochemical reduction-oxidation (redox) reaction, in which iron is oxidised, i.e. it gives up electrons, to form the soluble ion Fe2. To maintain overall charge neutrality, a complimentary reduction reaction occurs elsewhere on the steel rebar where the free electrons recombine with water and oxygen to produce two hydroxyl ions, 20H. By determining the half-cell potential of the rebar created by this redox process against a standard reference electrode, it is possible to infer the extent of corrosion (Broomfield, 2007). Reference electrodes can be embedded during superstructure construction, or may be manually positioned upon the outside face of the concrete cover layer during routine preventative maintenance inspections. In either case, reference electrode systems usually require extensive wiring harnesses and cabling as well as an electrical connection to the rebar which makes their practical deployment rather complex. Significant time is required to map the rebar half cell potential over large areas of concrete cover because many tens to hundreds of separate measurements must be taken at regular spacings over the area to be mapped, which must then be analysed, interpreted and related to rebar status. Another approach often taken in determining the risk of corrosion to embedded steel rebars is to estimate the carbonation depth into the concrete cover layer (Raupach and Schiessl, 2001), (McCarter and Vennesland, 2004), (Raupach and Wolff, 2005), (Song, 2007).

The carbonation depth profile indicates the extent of penetration of atmospheric CO2 into the cover layer, and thus the likely rate of acidification of the concrete environment as gaseous C02 dissolves in the trapped pore water. Acidification is known to depassivate the protective surface layers of steel, and the material becomes significantly more susceptible to oxidative corrosion when its microenvironment pH drops below about 11 pH units. Also, chloride ion selective electrodes (lSEs) have been employed to determine the free chloride ion content of RC structures for the purpose of evaluating the penetration of sea and/or de-icing salts into the cover layer. The chloride ion concentration data is then related to corrosion status of the rebar, although this is often a non-trivial relationship since the corrosive effects of C1 on steel depends upon several other variables, such as temperature, humidity and the availability of water. The concrete cover layer resistivity is often measured, as it can provide an indirect indication of both the level of hydration and the free ion concentration within the material (McCarter

and Vennesland, 2004), (Broomfield, 2007).

Corrosion rate can alternatively be estimated more directly by measuring the changing electrical resistance of discrete sacrificial elements made from the same material as the rebar (Zivica, 1993), (Krajci and Janotka, 2004), (Legat, 2007). The disadvantage of the electrical resistance technique however is that the sacrificial elements should have the same, if not identical, material composition as the rebar, in order to be representative of rebar corrosion.

Furthermore, such sacrificial elements should ideally be distributed throughout the structure at suitable intervals during construction work, and are difficult to retrofit to pre-existing structures because of their physical size. More complex electrical analytical techniques that employ alternating current (AC) methods have been used to determine the electrical impedance of the rebar (Muralidharan et al., 2007), (Muralidharan et al., 2008). Electrochemical analytical methods have been used extensively in corrosion research studies, including electrochemical impedance spectroscopy (EIS) (Hu et al., 2003), (Davis et al., 2004), (Hong and Harichandran, 2005), estimation of linear polarisation resistance (LPR) (MATSUOKA et al., 2008), (Zhao, 2007, Scully, 2000), (Law et al., 2000b), (Song, 2000), (Law et al., 2000a), (Muralidharan et al., 2006), and measurement of galvanic current, (Short et al., 1991), (Yoo et al., 2003), (Park et al., 2005), (Choi and Kim, 2005). In the field however, simpler measurement methods are often more appropriate.

For example, in JP2006052960 a method is disclosed for measuring, amongst other parameters, the electrical resistance and the temperature of the concrete cover layer (YOKOZEKI et al., 2006).

Similarly JP2007240481 provides a prediction method for corrosion in a reinforcement and also a monitoring system for the corrosion in the reinforcement, capable of providing highly precise prediction, by installing all the time a sensor in an original position, and by using information monitored and collected in an optional period or interval. Sensor box is buried in concrete to store a collation electrode and a counter electrode, a concrete Ohmmeter, and a concrete thermometer (CHIKAMOTO and SUDA, 2007).

All of the above electrical, electrochemical and physical methods suffer from the disadvantage that they require the use of wiring cable harnesses, hard-wired embedded electrodes and sensors, and in some cases, an electrical connection to the rebar or steel structure to be monitored. Non-contact imaging techniques such as radar, impact-echo, and radiography (Broomfield, 2007) are therefore sometimes considered advantageous in condition monitoring of RC structures because of their non-invasive and non-destructive nature. However, all such non-invasive imaging techniques are time consuming and expensive to perform, require bulky and expensive equipment, and may only be performed on site by skilled technicians. Finally, experienced data analysts are then required to interpret the raw data that has been collected from the imaging survey, and in turn to relate this to the structural condition.

Condition monitoring systems that are permanently installed in situ and which may easily be retrofitted to existing superstructures and that are furthermore based on either remote wireless monitoring, or contactless interrogation methods can overcome these various limitations.

For example, in KR20000033818 a remote corrosion monitoring and corrosion-proof control system is provided to remotely monitor the corrosion state of buried metallic structures in electrolytes when underground or underwater by wireless communication (Bae et al., 2000). This system also remotely controls the current output from a corrosion-proof eliminator circuit thereby closing the loop between corrosion detection and providing galvanic protection.

In KR20020011004 a short range wireless system is described that provides communication between a pipeline corrosion monitor and a handheld device that is carried by inspection personnel (KIM, 2002). The monitored parameter is electrical potential.

Another device evaluates the condition of rebars using embedded ultrasonic transducers, and then wirelessly transmits this data to the outside world via a wideband microstrip antenna designed to operate at between 2.4 and 2.5 GHz in the microwave band (Hietpas et al., 2005). Similarly, in the development of a wireless embedded sensor system to monitor and assess corrosion damage in reinforced concrete, reinforced mortar specimens were manufactured with seeded defects to simulate corrosion damage. By taking advantage of waveguide effects of the reinforcing bars, these specimens were then tested using an ultrasonic approach. Using the same ultrasonic approach, specimens without seeded defects were also monitored during accelerated corrosion tests. Both the ultrasonic sending and the receiving transducers were mounted on the steel rebar. Advantage was taken of the lower frequency (<250 kHz) fundamental flexural propagation mode because of its relatively large displacements at the interface between the reinforcing steel and the surrounding mortar. Analysis of the waveform energy (indicative of attenuation) is interpreted in terms of corrosion damage and loss of bond strength between the reinforcing steel and the surrounding concrete has been detected and evaluated (Reis et al., 2005).

In US2005145018 a wireless sensor system is installed inside pipelines using sensors and wireless transceivers. The objective is monitoring the pipeline and recommending maintenance and repair at specific locations in the pipeline.

Maintenance includes detection of leaks and prevention of catastrophic failures as a result of internal corrosion or other damage, such as third party mechanical damage, using a multitude of sensors. After establishing the wireless sensor network the network is activated so the sensor can make measurements periodically or continuously using instructions transmitted via the base station.

The sensor data from the various sensors are transmitted inside the pipe and extracted to access points in the pipeline to a remote computer that stores the data within the computer memory. The sensed information can be used for monitoring as well as analysis using a recommendation engine to provide maintenance and repair alerts (SABATA and BROSSIA, 2005).

In JP2006337169 a corrosion sensor is disclosed for diagnosing the state of progress of corrosion of steel products buried in concrete structures, that is provided with both a corrosion detection part having a member for detection underlaid in an object to be measured or in the vicinity of the object to be measured for detecting corrosion of the member for detection made of metal, by measuring the electrical characteristics of the member for detection and a radio communication part for transmitting the detected results of corrosion to a reading device by radio. It is thereby possible to detect the corrosion of the member for detection, on the basis of the changes in the electrical characteristics and predict the occurrence of corrosion in steel products, such as reinforcing bars, PC steel wires, or sheath tube made of steel (OGAWA and KANEDA, 2006).

In W02006065770 a method of monitoring corrosion and a corrosion sensor are disclosed that includes a first element including a corrodible element to be exposed to a corrosive or corrosion-suspect environment, and a second element including a corrosion sensing circuit coupled with the corrodible element for generating a wireless signal based on the corrosion of the corrodible element (SUBRAMANIAN et al., 2006).

CN1900691 discloses an invention that is especially related to equipment for monitoring reinforcement corrosion in concrete through measuring parameters including the polarisation resistance of the corrosion system, and the Tafel slope.

The equipment includes a polarisation module for providing charge pulses, a monitoring probe, sensor, modem, software for monitoring corrosion, GSM communication module, CPU control module, and power supply module. Power supply module, polarisation module, and CPU control module constitute lower device. The PC and monitoring software constitute the upper device. The probe and sensor are connected via cable to the lower device. Data from the lower device is output to a data communications port, which is selectable between either wired or radio communication modes. The invention is applicable in sea area, underground and in buildings (Zhao, 2007).

The disadvantage of all such existing wireless systems is the requirement for an electrical power supply, such as a battery, with which to energise the embedded measurement system and the wireless transmission system. If the apparatus is energised from a primary power source, this necessitates a wiring harness with which to connect the power source, thereby diminishing some of the advantage gained by having wireless data communications. Conversely, if the embedded system is powered with an embedded battery pack, the batteries periodically need to be replaced or recharged. Thus the charge-discharge cycle of the battery pack becomes the dominant limiting factor in the practical operation, deployment, utility and lifetime of the measurement system. Although embedded batteries can be recharged wirelessly with inductive chargers, the duration of this task scales with battery capacity, cover layer depth, and the number of embedded batteries deployed across a structure, thus rendering the approach impractical for use with anything more than small-scale experimental systems. One approach to overcoming the limitations imposed by the availability and utility of embedded energy sources is to employ contactiess energy transfer methods.

In W02004010104 an embeddable corrosion rate meter (ECRM) for detecting and measuring corrosion in metal and concrete structures is provided. The system comprises an electrochemical cell with at least one working electrode evenly separated from a counter electrode, wherein a separation distance between electrodes determines an electrolyte medium resistance and the electrolyte medium resistance is less than or equal to a polarisation resistance.

The system further includes a signal generator connected to a plurality of resistances for creating a plurality of current amplitudes for generating a current source; a first selector for applying a current through each of the plurality of resistances to the working electrode and counter electrode; a second selector for selecting a duration of a current pulse; a voltmeter/A-D converter having an input impedance >1O Ohms for measuring polarisation of the working electrode; and an external reader-head with a data link and power link connected to a computing device for powering the system and collecting corrosion measurements data (SRINIVASAN etal., 2004).

In DE102006030519 an apparatus is disclosed that has an electronic device with transmitting and receiving devices and antenna for wireless transmission of corrosion condition of only one sensing unit of a sensor found by the electronic device to an external evaluation device and for controlling the electronic device by the external device. A power supply of the electronic device takes place over an electrical field produced outside a concrete part by the external device (Grommes, 2007).

In CN101246116 a concrete reinforcement corrosion wireless testing method and a sensor belong to the field of the concrete reinforcement corrosion detecting technique. The sensor comprises a sensing part and a reading part. The sensing part is mainly a resonance circuit which comprises at least one capacitance that is connected to the two ends of the inductance coil after series-connection to the switch of the steel wire, and the switching-off and switching-on of the steel wire switch is controlled by whether the steel wire is corroded and disconnected; the reading part works with the LC oscillating circuit, according to the principle of the resonance circuit the resonance frequency of the sensing part is measured through the phase frequency characteristic curve of the impedance in order to judge whether the steel wire is corroded and broken. The invention can more accurately confirm the degree of the reinforcement corrosion and the speed by embedding sensing part at the vicinity of the electric fie'd at the inner part of the concrete under the precondition that the concrete is not damaged, realises the wireless transmission of the corrosion signal inside and outside the concrete, and can be applied to the detecting and evaluating of the durability of the reinforced concrete structure in the structural engineering field (Jin et al., 2008).

A similar passive radio frequency device is disclosed in US2008204275. A passive sensor is located on or adjacent to a structure that can be used to monitor the affect of environment on a structure or coating that is used to protect the structure. The sensor includes a parasitic element that interacts with the environment and influences the intensity of the electromagnetic response between the inductive element of the sensor and the antenna of the interrogation reader device. The condition of the parasitic element is determined by the radio frequency interaction of the reader antenna and the inductive element of the sensor. The parasitic element condition correlates to the environmental severity, or corrosivity of the environment and damage to metallic structures or protective coatings. An integrated circuit within the sensor is capable of storing identification, time, material, and measurement information. The sensor and system of the invention is useful for tracking and monitoring cumulate environmental damage to a structure (WAVERING et al., 2008).

JP2008256596 provides a sensor for non-contact and precise measurement of corrosion speed in a structure. The corrosion speed measuring sensor includes a corrosion speed measuring circuit comprising a pair of to-be-measured electrodes, an electrochemical resistance measuring circuit, a communication circuit, and a transmitting/receiving antenna. The measuring circuit includes: an impedance measuring circuit for applying a voltage between the electrodes, measuring an electrical resistance, calculating a polarisation resistance, and obtaining the corrosion speed; and a dual frequency applying circuit for applying two types of frequencies to the measuring circuit. The antenna includes an induction coil for converting electromagnetic waves transmitted from an external activator into an induction current, and converting corrosion speed calculation data transmitted from the communication circuit into the electromagnetic waves.

The communication circuit transmits the induction current converted by the antenna to the measuring circuit, receives the corrosion speed calculation data from the measuring circuit, and transmits it to the antenna (MATSUOKA et al., 2008).

In US2009039864 a wireless corrosion detector includes a surface acoustic wave (SAW) sensor tag. The SAW sensor tag has an output port and at least one electro-resistive (ER) corrosion sensor is coupled to the output port (GORDON, 2009).

The existing contactiess corrosion detectors, monitors and sensors mentioned above, and the methods of energising and querying such passive or semi-passive devices suffer from the disadvantage that the various modes of operation are such that only a single embedded sensor may be interrogated at any one time, If two or more sensors coincidentally appear in the interrogating (vicinity) field of the reader simultaneously, their responses combine and it is difficult or even impossible to deconvolve individual sensor responses at the reader. Furthermore, devices that depend upon changes in tuned electrical circuit parameters to infer corrosion status, such as those disclosed in both CN101246116 and US2008204275, are sensitive to many other environmental factors that affect such properties of tuned electrical circuits, including temperature, device orientation relative to the reader, the dielectric constant of nearby or surrounding materials and bodies, and the presence of liquids and humidity.

Hence, there is a need for an apparatus and method to address the limitations of the existing systems. Such an apparatus would include at least one passive or semi-passive contactless microenvironment sensor that may be embedded in RC during construction work, or buried in soil or any other aggregate material, or which may alternatively be retrofitted to existing RC structures or buried around pipelines during routine maintenance operations without the requirement for wiring harnesses, cables, external electrodes or electrical connections to the steel or to external power sources. Furthermore each such sensor measures temperature and at least one additional physical or electrochemical parameter from its immediate surrounding microenvironment, such as electrical resistance, and many such sensors may be distributed throughout a structure or material at different spatial locations in order to gather microenvironment data throughout the complete structure or material over a large area or volume. The additional advantages of the disclosed apparatus are that data from any one or many microenvironment sensors may be gathered by non-contact interrogation or wireless methods with a remote reading device or devices that energise and query for data, and furthermore that multiple sensors falling simultaneously within the vicinity field of any one reading device may be queried sequentially. This facilitates, for example, accurate microenvironment depth profiling where a group or array of sensors may be embedded together at slightly different locations through the cover layer, for example at staged intervals along a single bore hole, or down through the soil cover or similar aggregate material. By collecting and analysing microenvironment data from one or many such embedded sensors in this manner, the environment in the structure or material can be determined, and furthermore, if this data is logged, stored and compared to historical data, then the rate of change and direction of change in the microenvironment parameters can be determined and this information allows estimates of the time needed to reach certain threshold or limiting conditions to be calculated.

According to the present invention therefore, there is provided a receiving antenna, reference voltage source, adjustable current source, electrode array, voltage difference amplifier, analogue to digital converter, data and clock extracter, and a serial data output port.

Preferably, the reference voltage source, adjustable current source, voltage difference amplifier, analogue to digital converter, data and clock extracter, and serial data output port are integrated in a monolithic integrated circuit together with a voltage rectIfier, voltage regulator, temperature sensor and a microprocessor or digital logic state machine and which furthermore collectively have a unique digital identification number.

Preferably, the integrated circuit and discrete components are assembled onto an insulating substrate made from ceramic, polyimide, glass fibre, or other suitable insulator and where furthermore preferably the electrical connections between such components are made with conducting tracks formed across and through the substrate.

Preferably, the receiving antenna is arranged in a planar configuration as a strip or spiral or other appropriate shape of conducting track suited to the reception of electromagnetic radiation and is further preferably formed on the insulating substrate but which may alternatively be formed directly on the monolithic integrated circuit or on the insulating packaging of the monolithic integrated circuit.

Preferably, the electrode array consists of at least four separate conductors arranged geometrically in parallel to one another with a spacing between any two adjacent conductors of not less than 1 centimetre and where the width of each individual conductor is not less than 1 millimetre.

Preferably, the parallel conductors of the electrode array are formed from rods or annular rings but which may equally be any other convenient size and shape of conductive material such as printed or etched conductive tracks formed on the same insulating substrate together with the receiving antenna and where furthermore each electrode in the array may be made from the same or dissimilar materia Is.

Preferably, the adjustable current source is arranged to pass a known current between the outer two electrodes of the electrode array and where furthermore said known current may include the zero or null current condition.

Preferably, the known current through the electrode array is generated by the adjustable current source by means of selecting one of a plurality of fixed resistances of known value and applying the reference voltage source to said resistance.

Preferably, the data and clock extracter is arranged so that the current in the electrode array may be switched on and off at a sub-frequency of the extracted clock frequency and preferably with any favourable ratio of on-time to off-time such that any desired pulsatile current waveform may be produced in the electrode array.

Preferably, a potential difference between the inner two electrodes of the electrode array is accurately determined by applying said potential difference to the inputs of the voltage difference amplifier.

Preferably, the output of the voltage difference amplifier is connected to the analogue to digital converter such that the potential difference arising between the inner electrodes of the electrode array may be digitised and may further preferably be stored in digital form in a memory element of the microprocessor or digital logic state machine.

Preferably, the output of the temperature sensor is connected to the analogue to digital converter such that temperature data may be digitised and may further preferably be stored in digital form in a memory element of the microprocessor or digital logic state machine.

Preferably, the unique digital identification number, digitised potential difference data and digitised temperature data are sent via the serial output port to the receiving antenna for the purpose of wireless transmission.

Preferably, the resonant frequency of the receiving antenna is tuned to match the frequency of an externally generated alternating electromagnetic field by means of a tuning capacitor and furthermore preferably the tuning capacitor is integrated in the monolithic integrated circuit.

Preferably, the externally generated alternating electromagnetic field induces a voltage in the receiving antenna which is further preferably rectified by the voltage rectifier and regulated by the voltage regulator for the purpose of providing electrical energy to the integrated circuit and discrete components but where such energy may additionally be provided from any other suitable electrical energy source such as, by way of non-limiting example, a battery or solar cell.

Preferably, the microprocessor or digital state machine is arranged such that electrical energy to the reference voltage source, adjustable current source, electrode array, voltage difference amplifier, analogue to digital converter, serial data output port, and temperature sensor can be switched on and off at periodic intervals or on demand for the purpose of conserving energy.

Preferably, the analogue to digital converter has a resolution of ten digital bits but which may equally be any number of bits that is greater than two bits.

Preferably, the electrical resistance, linear polarisation resistance, open circuit polarisation potential and other parameters of a material in uniform contact with the electrode array may be computed from the relationships of the potential difference arising between the inner electrodes to the magnitude of the current flowing between the outer electrodes of the electrode array, and where furthermore preferably the electrical resistivity and conductivity of said material may be computed from knowledge of the geometry of the electrode array.

Preferably, a sensor according to all of the above for measuring temperature and at least one other microenvironment parameter such as, by way of non-limiting example, electrical resistance.

Preferably, there is furthermore provided at least one reader for contactless transfer of electrical energy to one or more such sensors by means of electromagnetic induction as herein described and which furthermore preferably provides means for individual interrogation of sensors according to their unique identification number and the reception of transmitted digitised serial data from said sensors.

Preferably, a method of storing and processing digital data from sensors according to their unique identification number.

Description of the Invention

A preferred embodiment of the invention is now described with reference to the accompanying drawings in which: FIGURE 1 is an arrangement of the apparatus of the invention, showing a bulk material or structure to be monitored with microenvironment sensors distrbuted throughout the bulk material or structure, a remote contactiess reader for interrogating the distributed sensors, and a computing device for detailed data analysis and long term data storage.

FIGURE 2 is an illustration of the functional blocks of a microenvironment sensor.

FIGURE 3 is one embodiment of a microenvironment sensor equipped with annular ring electrodes.

FIGURE 4 is an alternative embodiment of a microenvironment sensor equipped with planar electrodes.

FIGURE 5 is an alternative embodiment of a microenvironment sensor equipped with rod electrodes.

The apparatus and methods of the invention can be used to provide information concerning the microenvironment in bulk aggregate materials such as cement, mortar, reinforced concrete, sand and soil and may provide early indication of changes in the material microenvironment that could cause a threshold condition to be approached or reached in a structure, and which may furthermore provide input to planned preventative maintenance schedules, monitor the effect of repairs and protective measures, and provide data for deterioration and cost models of the structures.

Detailed description of the Invention

As shown in FIGURE 1, the apparatus of the invention comprises at least one sensing device 101 and one reading device 102 which communicate with one another via a non-contact radio-frequency wireless data link. As shown in FIGURE 2, a preferred sensing device 101 of the apparatus comprises a receiving antenna 201, reference voltage source 202, adjustable current source 203, electrode array 204, voltage difference amplifier 205, analogue to digital converter 206, data and clock extracter 207, and a serial data output port 208.

In the preferred embodiment, the reference voltage source 202, adjustable current source 203, voltage difference amplifier 205, analogue to digital converter 206, data and clock extracter 207, and serial data output port 208 are integrated in a monolithic integrated circuit 100 together with a voltage rectifier 209, voltage regulator 210, temperature sensor 211 and a microprocessor or digital logic state machine 212, and the integrated circuit 100 is assigned a unique digital identification number. To those versed in the art of integrated circuit (IC) design, it is apparent that any of these component parts of the sensing device could be discrete or integrated as deemed appropriate to available IC technologies. In the embodiment shown in FIGURE 3, the integrated circuit 100 and discrete components are assembled onto a substrate 301 patterned with the necessary conductive interconnections 302 needed to make electrical connections between the various parts. The substrate could be, by way of non-limiting examples, a glass fibre printed circuit board, a ceramic hybrid board, or a flexible polyimide circuit substrate. In an alternative embodiment shown in FIGURE 4, to facilitate ease of manufacture of the sensing device, the receiving antenna 201 is also fabricated on the insulating substrate as a strip, spiral or other appropriate shape of conducting track suitable for the reception of radio-frequency electromagnetic radiation together with planar conductors 303 to make the electrode array 204.

The electrode array 204 of the sensing device consists of four separate conductors 303, arranged geometrically in parallel to one another with a spacing between any two adjacent conductors of ideally not less than 1 (one) centimetre and where the width of each individual conductor is ideally not less than 1 (one) millimetre. As shown in FIGURE 3 the conductors 303 of the electrode array 204 are formed from annular rings, but might alternatively be any other convenient size or shape of conductive material, including, but not limited to, printed or etched conductive tracks made on the same insulating substrate together with the receiving antenna 201 and the interconnects for the IC and discrete components 302, an example of which is shown in FIGURE 4, or rod electrodes an example of which is shown in FIGURE 5, which facilitates simple attachment of a sensing device 101 to a wall or facing or cover layer. To those versed in the art, it is apparent that in order to cater for different types of electrical or electrochemical measurement, each individual electrode 303 in the array 204 can be made from a different material, as required. In the embodiments shown in FIGURE 3 and FIGURE 5, by way of non-limiting example all four electrodes of the array 204 are made from the same material, but any individual electrode 303 in the array could equally be made from gold, platinum, carbon, silver or any other useful electrode metal or material, including composite materials commonly used in the fabrication of electrode systems, such as, by way of non-limiting example, silver/silver-chloride (Ag/AgCl), an example of which is shown in FIGURE 4 where the inner electrodes are fabricated from one material and the outer electrodes from a second material.

During operation of the sensing device 101, the adjustable current source 203 passes a known current between the outer two electrodes of the electrode array 204. The current range covered by the current source includes zero current (the null current condition). The adjustable current is derived under control of the IC by selecting one of a plurality of fixed resistances of known value and referencing this to the reference voltage 202. Also, the clock extractor 207 is arranged in such a way that the current into the electrodes may be switched on and off at a sub-frequency of the extracted clock frequency under control of the IC 100 and with various ratios of on-time to off-time so that different pulsatile current waveforms can be produced in the electrode array 204. The potential difference between the inner two electrodes of the electrode array 204 is determined with the voltage difference amplifier 205, and the output of the voltage difference amplifier is connected to the analogue to digital converter 206 so that the reading may be digitised. Once the analogue voltage data has been digitised, it is stored in digital form in a memory element of the microprocessor or digital logic state machine 212. Similarly, the output of the temperature sensor 211 is also connected to the analogue to digital converter 206, which allows temperature data to be digitised and stored in memory. When queried by a reading device 102, the unique digital identification number, digitised potential difference data and digitised temperature data are sent together with appropriate start, stop, error, and cyclic redundancy check (CRC) frames via the serial output port 208 to the receiving antenna 201 for the purpose of wireless transmission of said data back to the reading device 102.

Electrical energy to power the sensing device or devices 101 may be provided with a dedicated battery, typically one per sensing device, but in different embodiments the battery can be supplemented or even replaced by energy from the radio-frequency vicinity field 105 generated by the reading device 102. To those versed in the art, the principle of near field electromagnetic induction is well known. The resonant frequency of the receiving antenna 201 is tuned to match the frequency of the externally generated alternating electromagnetic vicinity field by means of a tuning capacitor. The tuning capacitor is either integrated in the monolithic integrated circuit 100 or can be a discrete component mounted on the printed circuit substrate 301, or a combination of both, which allows for simple manual tuning. The alternating electromagnetic vicinity field 105 produced by the reading device 102 induces a voltage in the receiving antenna 201 of the sensing device 101, and this is rectified by the voltage rectifier 209 and regulated by the voltage regulator 210 in order to provide a stable electrical energy supply to the integrated circuit 100 and discrete components of the sensing device 101. As herein described, inductively-coupled energy for the sensing device 101 can supplement or replace that of alternative primary energy sources such as, by way of non-limiting example, a battery or solar cell. But in any case, in order to ensure that the sensing device 101 operates at ultra-low power levels, the microprocessor or digital state machine 212 is arranged such that electrical energy to the adjustable current source 208, electrode array 204, voltage difference amplifier 205, analogue to digital converter 206, serial data output port 208, and temperature sensor 211 can be switched on and off at periodic intervals or on demand.

In the preferred embodiment, the analogue to digital converter 206 has a reso'ution of ten digital bits, but it will be apparent to those versed in the art of sensor and measurement science that useful banding and threshold data can also be acquired from sensing devices with any resolution greater than two bits.

With a sensing device 101 arranged as herein described, the electrical resistance, linear polarisation resistance, open circuit polarisation potential of any material 103 in uniform contact with the electrode array 204 can be directly measured or computed from an analysis of the various relationships between potential difference and current. Furthermore, it will be apparent to those versed in the art that the electrical resistivity, p, and its reciprocal, the electrical conductivity, o, of the material 103 can be computed using well known formulae that relate the measured resistance to the specific geometry of the electrode array 204,303.

Hence a sensor is provided for that can determine temperature and at least one other microenvironment parameter. Additionally, the apparatus of the invention also provides for at least one reading device 102 for the contactless transfer of electrical energy to one or more such sensors by means of near field electromagnetic induction, as herein described, and which also provides the means for individual interrogation of sensors according to their unique identification number and the reception of transmitted digitised serial data from these sensors. The reading device 102 also stores and processes digital data from sensors according to their unique identification number, and can also transfer this data to a separate, more powerful computing device 104 or memory store as required as shown in FIGURE 1.

The methods of the invention provide for contactiess measurement of microenvironment parameters by means of remote interrogation of at least one sensing device 101 that is attached to, embedded in, or placed within the body of a bulk material or structure 103 or a vessel containing the material, and which may be interrogated with a reading device 102 that is positioned externally to the body or vessel under investigation. The sensing device or devices 101 are capable of determining at least two parameters from the immediate surroundings on or within the body or vessel 103, including for example, temperature and electrical resistance, and multiple sensing devices 101 may be distributed in two or three dimensions throughout the body or vessel 103 in order to provide information on the spatial distribution of the measured parameters on or within the body or vessel. The parameters are measured and supplied by the sensing device or devices 101 on demand from the reading device 102 and may be shown on a data display 106 within the reading device. Alternatively the data may be stored in the memory of the reading device 102 and may further be processed and analysed by the reading device or transferred to a separate computing device 104 for subsequent storage, processing and analysis. The microenvironment parameters obtained from the body or vessel 103 under investigation may be evaluated and compared with previously logged measurement data so as to further provide information on the temporal course of the measured parameters. Estimates of how the measured microenvironment parameters might change in the near future may be computed by applying known numerical extrapolation techniques to the logged temporal and spatial data from which the probable time needed to reach particular threshold values in any one or more of the measured microenvironment parameters at a particular location on or within the body or vessel 103 can be derived.

Claims

CLAI MS1. A contactless microenvironment sensor comprising a receiving antenna, reference voltage source, adjustable current source, electrode array, voltage difference amplifier, analogue to digital converter, data and clock extracter, and a serial data output port.
2. A contactless microenvironment sensor according to claim 1, in which the reference voltage source, adjustable current source, voltage difference amplifier, analogue to digital converter, data and clock extracter, and serial data output port are integrated in a monolithic integrated circuit together with a voltage rectifier, voltage regulator, temperature sensor and a microprocessor or digital logic state machine and which furthermore collectively have a unique digital identification number.
3. A contactless microenvironment sensor according to claims 1 and 2, in which the integrated circuit and discrete components are assembled onto an insulating substrate made from ceramic, polyimide, glass fibre, or other suitable insulator and where furthermore preferably the electrical connections between such components are made with conducting tracks formed across and through the substrate.
4. A contactless microenvironment sensor according to claims 1, 2 and 3, in which the receiving antenna is arranged in a planar configuration as a strip or spiral or other appropriate shape of conducting track suited to the reception of electromagnetic radiation and is further preferably formed on the insulating substrate but which may alternatively be formed directly on the monolithic integrated circuit or on the insulating packaging of the monolithic integrated circuit.
5. A contactless microenvironment sensor according to claim 1, in which the electrode array consists of at least four separate conductors arranged geometrically in parallel to one another with a spacing between any two adjacent conductors of not less than 1 centimetre and where the width of each individual conductor is not less than 1 millimetre.
6. A contactless microenvironment sensor according to claim 5, in which the parallel conductors of the electrode array are formed from rods or annular rings but which may equally be any other convenient size and shape of conductive material such as printed or etched conductive tracks formed on the same insulating substrate together with the receiving antenna and where furthermore each electrode in the array may be made from the same or dissimilar materials.
7. A contactless microenvironment sensor according to any of the preceding claims, in which the adjustable current source is arranged to pass a known current between the outer two electrodes of the electrode array and where furthermore said known current may include the zero or null current condition.
8. A contactless microenvironment sensor according to any of the preceding claims, in which the known current through the electrode array is generated by the adjustable current source by means of selecting one of a plurality of fixed resistances of known value and applying the reference voltage source to said resistance.
9. A contactless microenvironment sensor according to any of the preceding claims, in which the data and clock extracter is arranged so that the current in the electrode array may be switched on and off at a sub-frequency of the extracted clock frequency and preferably with any favourable ratio of on-time to off-time such that any desired pulsatile current waveform may be produced in the electrode array.
10. A contactless microenvironment sensor according to any of the preceding claims, in which a potential difference between the inner two electrodes of the electrode array is accurately determined by applying said potential difference to the inputs of the voltage difference amplifier.
11. A contactless microenvironment sensor according to any of the preceding claims, in which the output of the voltage difference amplifier is connected to the analogue to digital converter such that the potential difference arising between the inner electrodes of the electrode array may be digitised and may further preferably be stored in digital form in a memory element of the microprocessor or digital logic state machine.
12. A contactless microenvironment sensor according to any of the preceding claims, in which the output of the temperature sensor is connected to the analogue to digital converter such that temperature data may be digitised and may further preferably be stored in digital form in a memory element of the microprocessor or digital logic state machine.
13. A contactless microenvironment sensor according to any of the preceding claims, in which the unique digital identification number, digitised potential difference data and digitised temperature data are sent via the serial output port to the receiving antenna for the purpose of wireless transmission.
14. A contactless microenvironment sensor according to any of the preceding claims, in which the resonant frequency of the receiving antenna is tuned to match the frequency of an externally generated alternating electromagnetic field by means of a tuning capacitor and furthermore preferably the tuning capacitor is integrated in the monolithic integrated circuit.
15. A contactless microenvironment sensor according to any of the preceding claims, in which the externally generated alternating electromagnetic field induces a voltage in the receiving antenna which is further preferably rectified by the voltage rectifier and regulated by the voltage regulator for the purpose of providing electrical energy to the integrated circuit and discrete components but where such energy may additionally be provided from any other suitable electrical energy source such as, by way of non-limiting example, a battery or solar cell.
16. A contactless microenvironment sensor according to any of the preceding claims, in which the microprocessor or digital state machine is arranged such that electrical energy to the reference voltage source, adjustable current source, electrode array, voltage difference amplifier, analogue to digital converter, serial data output port, and temperature sensor can be switched on and off at periodic intervals or on demand for the purpose of conserving energy.
17. A contactless microenvironment sensor according to any of the preceding claims, in which the analogue to digital converter has a resolution of ten digital bits but which may equally be any number of bits that is greater than two bits.
18. A contactless microenvironment sensor according to any of the preceding claims, in which the electrical resistance, linear polarisation resistance, open circuit polarisation potential and other parameters of a material in uniform contact with the electrode array may be computed from the relationships of the potential difference arising between the inner electrodes to the magnitude of the current flowing between the outer electrodes of the electrode array, and where furthermore preferably the electrical resistivity and conductivity of said material may be computed from knowledge of the geometry of the electrode array.
19. A contactless microenvironment sensor according to any of the preceding claims for measuring temperature and at least one other microenvironment parameter such as, by way of non-limiting example, electrical resistance.
20. A contactless microenvironment sensor according to any of the preceding claims, in which there is furthermore provided at least one reader for contactless transfer of electrical energy to one or more such sensors by means of electromagnetic induction as herein described and which furthermore preferably provides means for individual interrogation of sensors according to their unique identification number and the reception of transmitted digitised serial data from said sensors.
21. A contactiess microenvironment sensor according to any of the preceding claims, in which is provided a method of storing and processing digital data from sensors according to their unique identification number.