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VIDEO DOI: https://doi.org/10.48448/mhe9-4x97

technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Low Power High Precision MI Sensor Driven by Low Frequency Wiegand Pulse

We present a magneto-impedance (MI) sensor having a low power consumption of 2.44 μW per pulse and driven by Wiegand pulses at 10 Hz. The oscillator circuit conventionally used for a MI sensor is replaced by a Wiegand sensor to generate a pulse voltage. The MI sensor exhibited a good output linearity of 0.04 mV/μ0T for detecting magnetic field in the range of ±150 μT when Wiegand pulses of amplitude 1 V were supplied. This method reduces the power consumption of MI sensor down to μT level, enabling its use as battery-less sensors and Internet of Things (IoT) devices in Intelligent Transport Systems (ITS) and bio-sensing fields 1, 2. The Wiegand sensor consisted of a twisted FeCoV wire (Wiegand wire) and a 3000-turn pick-up coil. The length and diameter of the wire were 11 mm and 0.25 mm, respectively. A 10 Hz AC magnetic field of 5 mT/μ0 was applied to the Wiegand sensor. A fast magnetization reversal of the wire induced a pulse voltage 3. Alternating Wiegand pulses of 12 V (±2 V) and 20 μs width were induced in the pick-up coil. The impedance of an amorphous wire changes sensitively with the external magnetic field with an applied AC current. This is called the MI effect 4. The pulse parameters affecting the MI effect have been explored. For pulse frequency below 500 kHz, the rise time and the excitation current control the MI effect. The MI effect driven by pulses with rise times in microseconds is too small to be observed and is greatly affected by fluctuations in the voltage. A fast rise time pulse shaping circuit was designed to shape the Wiegand pulse with a fixed amplitude and a rise time less than 100 ns, as shown in Fig. 1. The shaping IC input voltage VCC can be adjusted and supplied by a coin cell. The low power consumption was achieved under the conditions of the 100 ns rise time and 0.3 mA excitation current. The characteristic of the output voltage of the MI sensor Ew with respect to the applied magnetic field Hex is shown in Fig. 2. A DC power supply using the Wiegand pulses was designed 5, which could make the MI sensor completely battery-less.


1) T. Uchiyama, J. Ma, Journal of Magnetism and Magnetic Materials, Vol.514, 2020, 167148
2) Y. Takemura, N. Fujinaga, A. Takebuchi, etc., IEEE Trans. Magn., 53, 4002706, 2017.
3) J. R. Wiegand and M. Velinsky, U.S. Patent 3,820,090, (25 June 1974).
4) K. Mohri, T. Uchiyama, L.P Shen, etc., Journal of Magnetism and Magnetic Materials, Vol.249, p.351-356,
5) Sun, X.; Iijima, H.; Saggini, etc. Energies 2021, 14, 5373.


Transcript English (automatic)

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