Multi-frequency electrical conductivity imaging via contactless measurements

Özkan, Koray Özdal
A multi-frequency data acquisition system is realized for subsurface conductivity imaging of biological tissues. The measurement procedures of the system at different frequencies are same. The only difference between the single frequency experiments and the multi-frequency experiments is the hardware, i.e. the sensor and the power amplifier used in the single frequency experiments was different than that were used in the multi-frequency experiments. To avoid confusion the measurement system with which the single frequency experiments were performed is named as prototype system and the measurement system with which the multi-frequency experiments were performed is named as multi-frequency system. This system uses magnetic excitation (primary field) to induce eddy currents inside the conductive object and measures the resulting magnetic field due to eddy currents (secondary field). For this purpose, two differential-coil sensors are constructed; one is for the single frequency measurements and the other is for the multi-frequency measurements. Geometrically the coils are same, the only difference between them is the radius of the wires wound on them. The sensor consists of two differentially connected identical receiver coils employed to measure secondary field and in between the receiver coils is placed a transmitter coil, which creates the primary field. The coils are coaxial. In the prototype system the transmitter coil is driven by a sinusoidal current of 300 mA (peak) at 50 kHz. In the multi-frequency system the transmitter coil is driven by a sinusoidal current of 217 mA (peak), 318 mA (peak), 219 mA (peak) and 211 mA (peak) at 30 kHz, 50 kHz, 60 kHz and 90 kHz, respectively. A data acquisition card (DAcC) is designed and constructed on a printed circuit board (PCB) for phase sensitive detection (PSD). The equivalent input noise voltage of the card was found as


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Citation Formats
K. Ö. Özkan, “Multi-frequency electrical conductivity imaging via contactless measurements,” M.S. - Master of Science, Middle East Technical University, 2006.