Reducing the Noise Level in a Gaussmeter with a Hall Probe for Reliable Magnetic Impedance Tomography

The paper presents the results obtained from a Gaussmeter noise optimization procedure. The device facilitates to perform 3D magnetic field mapping and is applicable in magnetic impedance tomography. The relevant measurement was performed in a specialized magnetic field mapping laboratory. To define the impact of electromagnetic disturbance suppression, we performed repeated measuring cycles in both an environment with strong electromagnetic disturbance and an environment lacking such an effect, namely, a Faraday chamber. In order to suppress the given problem, we exploit synchronous detection in a lock-in amplifier; the amplifier facilitates the suppression of spurious signals, enabling us to select the desired ones. In the designed 3D magnetic field meter, Hall probes are used to measure magnetic induction. The Hall probe is applicable for the discussed purpose mainly thanks to its small active area and high dynamic range of the measured magnetic field. Pink noise is suppressible via alternating current excitation. For the selected Hall probe (Advanced Sensor Technology), spectral density measurement of the input noise voltage was performed. This input noise voltage was converted to the input magnetic induction noise. The measurement involved several excitation currents and is instrumental for determining the relevant optimization rate. The used input amplifier is a modulation device enabling pink noise suppression. The applied optimization approach satisfies the requirement for the maximum frequency bandwidth. The achieved parameters markedly surpass the frequency bandwidth of conventional commercial meters. The designed apparatus was calibrated with Helmholtz coils.