Single-shot dual frequency excitation for magnetic induction tomography (MIT) at frequencies above 1 MHz

In order to make MIT fast it is recommendable to excite several transmit coils in parallel and to acquire all receive channels simultaneously. The separation between the transmit channels can be achieved e.g. by slightly separating the excitation frequencies, so that it is possible to separate their contributions in the receivers by synchronous demodulation. One major problem is the low output impedance of the driver amplifiers so that each transmit coil acts as short circuited when seen from the other transceivers and hence perturbs the primary field. This causes a number of complications both in the reconstruction software as well as from the viewpoint of SNR optimization. Therefore we propose a special passive coupling network which transforms the low driver impedance into a high termination impedance for the coils at two frequencies (1 MHz and 10 MHz). We designed a dual-frequency transformation networks which operates at 1 and 10 MHz and which provides a termination impedance >5kΩ. The feeding current is typically 10mA per Volt driving voltage.