| The high field sensitivity of SQUIDs, especially at low frequencies,
makes them ideally suitable for applications in nondestructive evaluation
(NDE). A SQUID can be employed in an eddy-current NDE system, in
which the SQUID measures the secondary magnetic field generated by eddy
currents in the material under test.
For research purposes, we developed an inexpensive SQUID-based non-destructive evaluation system using a sensitive niobium SQUID read-out by our 4-MHz flux-modulated readout electronics and our 250-kHz lock-in amplifier with integrated eddy current generator. The system has a field noise of about 50 fT in a bandwidth of 1 hertz, and can work unshielded in a normal laboratory environment. The system is ideal for scanning flat electrically conducting samples, such as metal sheets. It employs a fast-scanning translation stage with a scanning range of 30 cm by 30 cm and a maximum travel speed of 12 cm/s. The liquid helium consumption is about 1 liter per day. The system can be controlled manually, or by a standard personal computer via the serial port. For a very sophisticated SQUID-based NDE system developed for industrial use and employing our SQUIDs and controllers, please visit the webpages of WSK Mess- und Datentechnik GmbH, Hanau at www.wsk.de. |
| SQUID NDE System ESQ-NDE 1 |  |