Planar array

Quantum mechanics

Magnetic field

Phase (matter)

Engineering

Materials science

Planar

Computer graphics (images)

Excitation

Computer science

Acoustics

Current (fluid)

Image resolution

Physics

Magnetoresistance

Optics

Electronic engineering

Eddy-current testing

Sensitivity (control systems)

Eddy current

Inductive sensor

Optoelectronics

Nondestructive testing

Electrical engineering

IEEE Transactions on Industrial Electronics

Detecting defects in metal structures quickly and robustly is critical to maintaining safe operation in industry. This work discloses an eddy current (EC) testing probe with coils carrying three-phase currents as excitation and integrated array tunnel magnetoresistance (TMR) sensors measuring the magnetic field as receiver. The three-phase currents in the planar layout coils induce EC that migrates electrically in the material under test. This excitation method does not require multiplexing of the coils and is sensitive to defects of any orientations. The TMR array contains 64 sensors, which are microfabricated and packaged in a line. Within single probe pass, the sensors generate magnetic field image with high sensitivity (1.99 nT/√Hz@30 kHz) and fine spatial resolution (0.5 mm pitch). By analyzing the output image, defects are identified and localized. The operating principle of the probe was investigated based on a finite-element method model. A prototype probe was developed and tested, with which machined defects in aluminum samples were inspected. Experimental results show that the probe has comparable sensitivity for horizontal and vertical defects, and it can recognize a small defect with length × width × depth = 1 × 0.2 × 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The defects are located within 1 mm with an artificial neural network.

Eddy Current Probe With Three-Phase Excitation and Integrated Array Tunnel Magnetoresistance Sensors