Apparatus and method for determining a characteristic of a material

An apparatus for determining a characteristic of a material within a region, the apparatus comprising:

• a first plurality of electrodes disposed within or about the region;
• an energisation source arranged to apply an applied stimulation signal to at least one of said first plurality of electrodes;
• a stimulation monitor arranged to monitor an electrical parameter at a second plurality of said first plurality of electrodes in response to said applied stimulation signal, the stimulation monitor being configured to generate a received stimulation signal for each of said second plurality of electrodes;
• a monitor configured to generate a series of data values, each data value being indicative of a phase difference and/or an amplitude relationship between the applied stimulation signal and a received stimulation signal associated with one of the second plurality of electrodes, said series of data values defining an electromagnetic fingerprint;
• a controller configured to:
• receive the electromagnetic fingerprint;
• identify an interrelationship between at least some of the data values of the electromagnetic fingerprint;
• determine the characteristic based on the interrelationship.

A method of determining a stability of a material within a region, the method comprising:

• receiving a first electromagnetic fingerprint, the first electromagnetic fingerprint being defined by data indicative of a phase difference and/or amplitude relationship between an applied stimulation signal applied to at least one of a first plurality of electrodes disposed within or about the region and a received stimulation signal received at a second plurality of said first plurality of electrodes in response to said applied stimulation within a first time period;
• receiving a second electromagnetic fingerprint, the second electromagnetic fingerprint being defined by data indicative of a phase difference and/or amplitude relationship between an applied stimulation signal applied to at least one of a first plurality of electrodes disposed within or about the region and a received stimulation signal received at a second plurality of said first plurality of electrodes in response to said applied stimulation within a second time period, the second time period being later than the first time period;
• comparing the first and second electromagnetic fingerprints;
• determining a stability of the material between the first time period and the second time period based on the comparison.