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Based on NIST’s miniature atomic clock (see EW, 08/09/04), the magnetic sensor is built on the chip-scale – at least 100 times smaller than existing devices with similar sensitivities, according to NIST.
Powered by batteries, the device could form the basis of sensors in handheld equipment for unexploded ordnance, navigation, geophysical mapping and medical sensors.
A resolution of 50microtesla is enough to sense a 150mm steel pipe buried 35m underground.
The sensor relies on MEMS and standard semiconductor processing, using the changing energy levels of electrons in a magnetic field.
Light from a semiconductor laser (a VCSEL) passes through a rubidium vapour held within the sensor. A PIN photodiode detects changes in the received light due to varying absorption by the rubidium atoms.
Because the sensor is not directional it measures the complete magnetic field, irrespective of its orientation, claimed NIST. The existing ‘fluxgate’ designs can only detect the field in the direction of the sensor.
A complete packaged instrument would measure around 1cm³, claimed NIST.
While the GMR heads in hard disk drives are smaller and cheaper, they are less sensitive. Squids – superconducting quantum interference devices – are more sensitive, but need expensive cryogenic cooling and are larger.
The NIST magnetometer was described in Applied Physics Letters. The same technology was used to create an atomic clock with a long term frequency drift of around -2×10-8 per day.
Rotational speed estimation utilizing a magnetoresistive (MR) sensor is accomplished by tallying ferromagnetic imprints, for example, teeth of a detached apparatus wheel or the quantity of attractive components of a charged ring. provide a magenitic Sensors http://www.candoosys.com makes a custom data acquisition system to mate with their sensors, and software to display, analyze, and store the sensor data.