1-D probe array for ACFM inspection of large metal plates

The theory and experiments behind the development of a novel one-dimensional ACFM probe array system for nondestructive evaluation of ferromagnetic and nonferromagnetic metal plates are explained. In this linear array, each element consists of a linear pick-up coil and a rhombic inducer arranged specifically for high detection sensitivity. The special sequential switching arrangement of the array allows the fabrication of the array, theoretically, to any required length on flexible or ordinary printed circuit boards. The switching circuit, the signal acquisition system, and the signal processing method, are presented, and the limitations that the switch imposes on the array length are addressed. Example signals from the array as applied to crack and saw-cut notch samples in different rectangular metal blocks (cut from metal plates) are shown, and methods for the inversion of the crack signal to the crack depth are discussed.