New Absolute Null Method for the Measurement of Magnetic Susceptibilities in Weak Low-Frequency Fields

Abstract

Use is made of the magnetic equivalence of a uniformly polarized volume of paramagnetic material and a solenoid carrying electric current to design a very permanent variable standard of magnetic susceptibility. Such a standard is incorporated into a magnetic susceptibility bridge in a simple manner, surrounding the specimen; and the bridge is thereby transformed into an absolute null instrument of high accuracy and sensitivity, and of great ease and low cost of construction and operation. By this method numerous particular advantages of other methods are combined, and some of their notable limitations are overcome. A preliminary application was made showing that the bridge performs as expected. Important features in the design of this bridge are discussed. A detailed consideration of sources of error suggests that it may eventually be possible by this method to obtain greater absolute accuracy than by other known methods.