Operational Gradientmeter

This paper presents a gradient magnetometer meant to measure the variation rate of the first-order gradient of a magnetic field, with applications in magnetic defectoscopy or detection of small ferromagnetic inclusions. The operational gradientmeter presented here is named like this because it executes the time derivation of the gradient of the measured magnetic field. The operation principle of the gradientmeter, the transfer characteristics, and resulted performances are described. At the same time, an electronic procedure is presented for the separation of the wanted signal from the signal produced by a disturbing external field. The advantage of the operational gradientmeter as compared to the classical gradient meters is rendered evident by its higher signal/noise ratio. The main causes of the errors in gradient measurements are analyzed, as well as the solutions to reduce them. The experimental results are also presented with regard to the dynamic detection of some small ferromagnetic inclusions embedded in dielectric materials-wood or textile-and metallic nonferromagnetic materials-aluminium and copper.