Rowland ring
Rowland's ring (aka Rowland ring) is an experimental arrangement for the measurement of the hysteresis curve of a sample of magnetic material. It was developed by Henry Augustus Rowland.
The geometry of a Rowland's ring is usually a toroid of magnetic material around which is closely wound a magnetization coil consisting of a large number of windings to magnetize the material, and a sampling coil consisting of a smaller number of windings to sample the induced magnetic flux. The electric current flowing in the magnetization coil dictates the magnetic field intensity ![\mathbf{H}](/Images/godic/202502/08/da3623c683c463e210845c6d757af4dd2324.png")
in the material. The sampling coil produces a voltage proportional to the rate of change of the magnetic field ![\mathbf{B}](/Images/godic/202502/08/41968d7938b8145f26e1d196abc771442324.png")
in the material. By measuring the time integral of the voltage in the sampling coil versus the current in the magnetization coil, one obtains the hysteresis curve.