Development of a Broad Bandwidth Helmholtz Coil for Biomagnetic Application

The alternating uniform magnetic field is useful for the biomagnetic study with magnetic nanoparticles. However, for the coil system driven by the magnetic field generator with a conventional low-voltage power source, it is challenging to achieve the desired field strength with a large coil due to the large impedance at higher frequencies. This article proposed a Helmholtz coil system that can generate the dc and ac magnetic field up to 1.3 kHz with low distortion. In order to overcome the inductive load, a computer-controlled parallel capacitor array was designed and built to tune the series coil-capacitor circuit to the resonant frequency. Experimental results show that the coil system has a bandwidth over 1 kHz with a 1% uniform region covering the 10 × 10 mm sample area. The proposed system is promising for the application in biomagnetic assay using the tunnel magnetoresistance sensors.