A cryocooled SQUID-based metal detector with improved noise reduction and signal extraction

Due to their high sensitivity to magnetic fields, superconducting quantum interference devices (SQUIDs) can be used for measuring weak magnetic fields produced by stainless steel particles [1]. The detection of these particles is important in the food industry and in security applications. Hypodermic needles, for example, can break off in cattle during vaccination. The practicability of a SQUID-based metal detection system depends on both high detection reliability and low maintenance costs. To avoid periodic refilling with liquid nitrogen, we have used a Joule-Thomson cryocooler operating at about 70 K. The complete system consists of a mu-metal shield, a detection head and a conveying mechanism. To reduce the influence of environmental noise and to reduce false responses, two magnetometers are mounted in planar configuration on a macor holder which is connected to the cold head of the cryocooler. Digital signal processing of the time series of the two magnetometer channels allow advanced noise reduction and detection algorithms to be applied. We will show how these techniques can adaptively reduce external interferences and how the signal can be extracted from the noise even though the signal-to-noise-ratio of the unprocessed time series is smaller than 1. The combination of these techniques produces a system with high robustness with respect to false responses. We will present measurements on contaminants of different shapes and sizes. Acknowledgements: We would like to thank Graham Daniels, CSIRO ICT centre, for valuable discussions and many helpful comments. [1] see, for example, S.Tanaka, H.Fujita, Y.Hatsukade, T.Nagaishi, K.Nishi, H.Ota, T.Otani, and S.Suzuki, submitted to Supercond.Sci.Technol., 2006.

Keywords

Squid devices, Noise pollution control, Signals, Extraction, Magnetic fields, Steels, Food industry, Nitrogen

Citation

Oppolzer, F., Yeoh, L., Heng, H.-S., Sullivan, P., Cusack, P., Tilbook, D., Bick, M. A cryocooled SQUID-based metal detector with improved noise reduction and signal extraction. Paper presented at the Australian Instute of Physics 17th National Congress 2006, Brisbane Convention and Exhibition Centre, Brisbane Australia, Sunday 3 - Friday 8 December 2006. Retrieved from: https://www.aip.org.au/resources/Documents/Congress/AIPCongress-2006-Program.pdf

URI

https://www.aip.org.au/resources/Documents/Congress/AIPCongress-2006-Program.pdf
https://apo.ansto.gov.au/dspace/handle/10238/13645

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