This is an idea. A loop antenna responds to the derivative of the magnetic flux and, up to it's first resonance, can be modeled as a second order circuit. By using an I-V converter as signal conditioner the equivalent capacitance gets bypassed by the low input impedance of the converter and the equivalent inductance and resistance forms a lossy integrator (with a current proportional to the integral of induced emf). The ac source amplitude is the concatenated flux of the loop (in Webber, which is a huge unit, usually flux is in the nWb to mWb range). The loop should be wound with many turns and have a big area for good sensibility. This circuit should operate at low frequencies up to the VLF or low-LF band (30kHz to 100kHz) if implemented with operational amplifiers. The output is differential and requires further amplification.
