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A Novel GMR-Based Eddy Current Sensing Probe With Extended Sensing Range

A common approach to detect a metal's proximity or analyze some characteristic of it in applications, such as proximity sensing, non-destructive evaluation, and so on, is to generate eddy currents in it and then extract the desired information from the features of these eddy currents using eddy current sensors (ECSs). Some of the common ECS are Hall-effect sensors and inductive coils. Lately, giant magnetoresistive (GMR) sensors are also used for ECS due to their higher sensitivity and better low-frequency response. Due to these features, a new application has been identified for GMR-based ECS probes, which is real-time detection of metal shrapnel in human body during surgery. Since metal shrapnel cause grievous injuries to victims of bomb blasts, land mines, and so on, and the imaging modalities that doctors use presently to locate them do not provide any real-time information of their location during surgery, this probe will provide immense help to the doctors for tracing these shrapnel during surgery. However, existing GMR-based probes have limited sensing range, and therefore, they are not suitable for this application. Hence, a new probe topology is presented here, which has much longer sensing range than existing probes. The design of this probe, its performance, and the details of a new circuit that minimizes the temperature drift and hysteresis effects of the GMR sensor in the probe simultaneously are presented in this paper.