Patent ID: 6946835

Claim:
A method for determining electrical impedance associated with a material sample, the method comprising: providing an excitation signal, having an excitation electromagnetic field with a selected excitation electromagnetic field direction in a sample, the excitation signal having at least one of a substantially static amplitude and a time varying amplitude with a selected frequency component f exc ; allowing the excitation field to interact with a selected portion of the sample, and to produce an impedance signal arising from the sample portion; using an evanescent wave probe, located adjacent to the sample, to perform at least one of (i) excitation and (ii) sensing of the impedance signal for the sample portion; providing a sensing mechanism having a detection port to detect the impedance signal for the sample portion; providing a signal cancellation mechanism that suppresses presence of the excitation signal at the frequency f exc at the detection port when the impedance signal is sensed; providing low noise amplification of the signal sensed after suppression of the presence of the excitation signal at the detection port; and detecting the amplified signal of the impedance as an output signal.