is typically from about 0 01 hz up to 10 khz it 39 s hard to measure at higher frequencies with this measuring system it 39 s possible to measure up to slightly higher frequencies for example 60 khz but this requires a specific designed measurement system to measure the susceptibility at yet higher frequencies for example up to 10 mhz a method based on detection of changes in inductance and resistance can be used for a toroide coil system with a soft magnetic material for example mu metal or some kind of ferrite material if high measuring frequencies shall be used the sample is then placed in a thin gap in the magnetic toroide and one measures the circuit parameters of the toroide when the gap is empty and after placing the sample in the gap respectively common for all these methods is that one can represent characteristics of a spiral wounded coil with a equivalent electric circuit consisting of an inductance l in series with a resistance r connected to a capacitance c in parallel with these the capacitance depends on the electrical isolation of the thread and can often be neglected at lower frequencies wherein the resistance and the inductance of the circuit can be changed when a magnetic sample is placed in the coil if a variable ac current i u03c9t in phase with the ac magnetic field is floating in the circuit it will induce a complex voltage which real part is in phase with the current while the imaginary part is out of phase in proportion to i u03c9t another often used way of characterizing brownian movement of a particle system is to study the response of the particles on a variable magnetic field in.