Design of a sensor coil and measurement electronics for magnetic induction tomography

Magnetic induction tomography (MIT) is a tomographic imaging technique that is able to map the electromagnetic properties within an object or vessel from magnetic field measurements. Excitation coils are used to induce eddy currents in the medium, and the magnetic field produced by the induced eddy current is then sensed by receiver coils. Because of its noncontact nature, MIT is particularly attractive for biomedical and some industrial applications, such as pipe-flow monitoring, when compared with traditional contact electrode-based electrical impedance tomography. This paper describes the design and performance of an MIT transceiver circuit that can operate from 400 kHz to 12 MHz. The in-phase and quadrature (I/Q) demodulation technique is used to measure the signal perturbation due to the induced conduction eddy currents. The transceiver circuit design employs a single integrated circuit, containing a variable-gain amplifier and an I/Q demodulator. This paper contains characterizations of the transceiver's measurement noise, system stability, and sensitivity for detecting saline solutions and metal plates. A novel balanced coaxial screened coil structure with integrated current sensing was also developed to minimize capacitive coupling between coils and to allow measurement of the current in the driving coils. Experiments were carried out at 3 and 10 MHz using bottles of saline solutions (1%–5% concentration) and metal sheets (aluminum and steel) to verify the sensitivity for conductivity imaging.