Design of a digitally based ΔE measurement system

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Abstract
The magnetic field dependence of Young's modulus is a useful technique for probing the magnetic moment configuration and the anisotropy energy density of magnetostrictive soft magnetic materials. More recently, a high resolution vibrating reed system, based on the closed loop operation of an analogue lock in amplifier (LIA), coupled with an analogue voltage controlled oscillator (VCO) has been used. This system has shown that such measurements are capable of providing new information about subtle domain rearrangements during magnetisation of as-cast amorphous wires. The performance of this system is limited by the use of the analogue components, especially the VCO, to a resolution of a few parts in 10/sup 5/. To overcome this limitation a digital LIA and a function generator which employs digital frequency synthesis methods have been used in a new system. This offers an order of magnitude reduction in noise, with a frequency stability of better than 10/sup -6/ HZ, which can provide a resolution better than 2 parts in 10/sup 6/ for Young's modulus. Example of data obtained are included.