2D simulation studies and initial experimental results for hall effect imaging /

Gözü, Mehmet Soner
In this thesis, 2D simulation studies of Hall Effect Imaging (HEI) technique using linear phased array transducer are performed and initial experimental results are obtained. The goal of HEI is to image the conductivity distribution in biological bodies. For this purpose, HEI uses the interaction of ultrasound with a static magnetic field to generate velocity current density distribution inside the body. Due to the velocity current density, a resultant voltage is sensed by electrodes attached on the surface of the body and used for reconstructing the conductivity distribution. The theory of HEI is reviewed for numerical studies. A specific 16-element ultrasound array is modeled to obtain optimum beam directivity and steerability of acoustic wave. Thereafter, a numerical model of breast and tumor body is formed to analyze the multiphysics solution which couples acoustics and electromagnetic fields. Pressure and velocity current density distributions in these numerical models are calculated for different ultrasound excitations. To sense the resultant voltage due to the velocity current density, two electrodes are attached on the surface of the body. For image reconstruction, truncated singular value decomposition method is used with different signal-to-noise ratio values. Furthermore, the linear phased array transducer is located on two different edges of the body to obtain better lateral and axial resolution in the reconstructed images. To verify the numerical results, an initial experimental setup is prepared. A chamber is filled with oil and saline water to prepare a conductivity interface. A static magnetic field of 0.243 Tesla is generated with ferrite and neodymium permanent magnets. In addition, a single element ultrasonic transducer having a central resonance frequency of 1 MHz is used to generate acoustic waves inside the chamber. In the measurement part, copper electrodes are attached to the internal surface of the chamber and connected to an amplifier which has gain of 62.7 dB. A Hall voltage signal is obtained due to oil-saline interface that has a magnitude on the order of mV. The order of the signal is verified numerically.


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Citation Formats
M. S. Gözü, “2D simulation studies and initial experimental results for hall effect imaging /,” M.S. - Master of Science, Middle East Technical University, 2014.