A conformable, highly directional eddy current sensor, the Meandering Winding Magnetometer (MWM®), and eddy current array (MWM-Array) are described along with inverse methods that use precomputed databases to rapidly convert sensor responses to material properties of interest. An arrangement of four stacked MWM sensors, oriented at 0°, 90°, +45° and −45°, forms the quadri-directional magnetic stress gage (QD-MSG™). The QD-MSG is described and an example of noncontact torque measurement in a rotating helicopter main rotor shaft is presented. Dynamic torque measurement has previously relied upon shaft mounted hardware, such as strain gages, that must receive power and transmit signal through slip rings or rotary transformers, directionally magnetized areas of the shaft or rotational position sensors separated by some distance and sensing shaft rotational deflection. The QD-MSG has the advantages of being noncontact, requiring no modifications to a steel shaft and requiring access to a small area of the shaft.

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