An ultra-sensitive angular transducer using ferromagnetic film resonance

An instrument is described which is capable of measuring angles of rotation as small as 10⁻⁸ radians with respect to a reference plane. The high sensitivity is achieved by measuring the internal field of a thin Permalloy film as the film is rotated in relation to a reference static bias field. The internal field is measured by observing the low-frequency ferromagnetic resonance of the film. Brief descriptions of the instrumentation, consisting of a marginal oscillator, selective amplifier, phase detector, oscillator, and power amplifier, are included; sensitivity is determined by using the instrument as a readout mechanism for a seismometer.