Alternating current sensor with second-harmonic detection

Abstract

We describe a novel optical sensor based on the Faraday effect for measuring ac. The sensing element is a piece of material of high Verdet constant placed between polarizers. When the angle between the polarizers differs by 45 degrees, a signal of twice the frequency of the ac is generated--in addition to the usual signal with the same frequency as the current. The quotient of these two signals allows a normalized output to be obtained that is proportional to the amplitude of the current. Experimental results demonstrating the practicality of the procedure are presented.

Optical current sensor using a self-induced light source

“…The light passes a spatial filter and a collimator positioned directly in front of a cylindrical 3-mm-diam hole in an iron core used to concentrate the magnetic field, as described in Ref. 10. The magneto-optical material was an 11-mm-long rod of terbium gallium garnet ͑TGG͒ with a Verdet constant of 6.68ϫ10 3 deg/T m for ϭ633 nm.…”