Magneto-impedance sensor for marine magnetometry

One of the many applications for low field magnetometers, are magnetic anomaly detector (MAD)-devices which are used for archaeological survey and location of magnetic items i.e., pipelines, wellheads, etc. In recent years precision magnetometers of the optically pumped cesium and proton U magnetometers have been the preferred technology. These have the disadvantage of high cost and limited durability. We have developed and tested a new type of Magneto-Impedance Sensor for archaeological survey. It is not as sensitive as above-mentioned magnetometers, however large bandwidth, low cost, and portability makes it competitive with other magnetometers. We introduce a new resonant measurement technique involving tunnel diode oscillator (TDO) for fast and accurate measurements of frequency changes.' Field sensitivity for some of the measured samples appear to be as high as 40 MHz/Oe (400 Hz/nT) on the most sensitive part of the curve with a white noise of about 1 KHz. However, we found that the temperature instability of the tunnel diodes is very high and have to be taken into account when precise static measurements required. For temperature compensation we used dual channel system where second channel is field independent. Subtracted data is very accurate resulting with resolution down to 5 nT @ 1 Hz. Sensors have been successfully tested in the open sea alongside cesium magnetometers for comparison, showing good agreement with simulated results. Further work is required for optimum temperature compensation.