Spin-Dependent-Tunneling Sensors for Non-Destructive Evaluation

The proposed innovation is a two-axis spin-dependent-tunneling (SDT) sensor which detects small magnetic signals for use in non-destructive evaluation (NDE) of defects in metallic materials and structures. The proposed SDT sensor offers several advantages for NDE eddy current detection methods: (1) High sensitivity. The ability to resolve fields of 10 nOe/root Hz or better, yet operate at room temperature, and have a broad band frequency response. (2) Two-axis magnetic field sensing. This allows vector determination of the magnetic signal in the plane of the detector. (3) Sensor arrays. Fabrication of the sensors uses silicon-based techniques, and therefore the sensors are small--roughly 2 mm on a side. Compact sensor arrays are possible and offer advantages for defect recognition and spacial determination without requiring the sensor to be scanned. Phase I will develop an innovative approach for fabricating a two-axis sensor on a single chip. The proposed sensor is suitable for many types of eddy current detection methods as well as suitable for position sensing. Phase II will use the sensor in the development of a sensing array for an eddy current NDE system.