Harmonic Coil Method

The harmonic coil method is used to make precise measurements of the direction and magnitude of the magnetic field. A loop of wire is rotated through a magnetic field and measures the intercepted flux. The voltage generated due to electromagnetic induction is measured using a voltmeter or an integrator, and the harmonics of the magnetic field are determined using the known geometry of the coil. Two sides of the coil are always parallel to the magnet axis, and the coil is usually mounted tangentially or radially. 

A typical radial coil setup                  

For a simple radial coil in a dipole field, such as shown above, the amount of flux enclosed by the coil as a function of the coil angle is given by:

 where B_ref is the amplitude of the magnetic field, and S is the coil’s effective surface given by:

             with:

                        N = number of turns of the coil

                        L_eff = effective length of the coil

                        R_ext, R_int = the radii of rotation of the wires

The use of a voltage integrator makes the measurement independent of time.

Slip Ring       

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