CMOS Xylophone Bar Magnetometer with Automatic Resonance Control
There is an increasing need for miniature magnetometers for mapping magnetic fields in space and in industrial and environmental applications. The trend has been constantly toward smaller size, lower power consumption, and lower cost models having similar or better performance. Recent developments in piezoresistive cantilevers and micro magnetometers have produced devices that in some stages require intricate processing. Sensitivities, defined as the minimum detectable field change are in the range of 1 milli Tesla to 1 micro Tesla.
The Johns Hopkins University Applied Physics Laboratory has developed and is in the process of patenting a technology utilizing a Lorentz force magnetometer with an automatic resonator control. This invention is a simple, small, lightweight, low-cost and low-power consumption sensor. The magnetometer is based on the classical xylophone resonator, which is intrinsically linear and has a wide dynamic range that can measure magnetic fields over ranges from nanotesla and tesla. The magnetometer comprises a resonator such as a bar supported by 2 wires placed at the nodal points of the fundamental resonance frequency. The wires also supply the current of this frequency to the resonator. In the presence of a magnetic field, the Lorentz forces cause the resonator to vibrate. The amplitude of this vibration is proportional to a vector component of the magnetic field. The motion of the resonator is detected using a number of possible methods including optical beam deflection. The automatic resonance control is determined by switching the positive and negative drive voltage and a voltage control oscillator (VCO) for controlling the voltage input switch, and adding a feedback loop connected between the sensor output and the input of the VCO.
US 7,064,541 [MORE INFO
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