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Signal Conditioning System With a 4–20 mA Output for a Resonant Magnetic Field Sensor Based on MEMS Technology

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4 Author(s)
Saúl M. Dominguez-Nicolas ; Centro de Investigación en Micro y Nanotecnología, Universidad Veracruzana, Boca del Río, Mexico ; Raúl Juarez-Aguirre ; Pedro J. Garcia-Ramirez ; Agustin L. Herrera-May

Several resonant magnetic field sensors based on microelectromechanical systems (MEMS) technology use piezoresistive detection techniques to convert the magnetic field signal into an electrical signal. We present a signal conditioning system implemented in a printed circuit board (PCB) for a resonant magnetic field sensor based on MEMS technology. This sensor is formed by a resonant structure of thin silicon beams (5 μm thick), an aluminum loop (1 μm thick), and a Wheatstone bridge with four p-type piezoresistors. The Wheatstone bridge is biased with an alternating voltage of 2 Vpp at 1 kHz and the aluminum loop is supplied using an alternating current with a root-mean-square (RMS) value of 20 mA. This current is applied to the resonant frequency of the sensor (14.38 kHz) through an oscillator that has a frequency stability of ± 100 ppm at atmospheric temperature and a resolution of 1 Hz. The proposed system obtains the sensor's electrical response in voltage or current mode, which presents an approximately linear behavior for a range of magnetic field density from -150 to +150 μT. This system minimizes the offset of the sensor's electrical response and allows the detection of the polarity and magnitude of the magnetic field density. A virtual instrument is designed using Lab VIEW software to visualize the 4-20 mA output of the sensor. The designed system can help the development of portable measurement equipment to detect (at pressure atmospheric) low magnetic field densities with a sensitivity and resolution of 4 V · T-1 and 1 μT, respectively.

Published in:

IEEE Sensors Journal  (Volume:12 ,  Issue: 5 )