Division of Electrical and Computer Engineering, Yokohama National University, Japan
Yasushi TAKEMURA received the B.S., M.S. and Ph.D. degrees in Electrical and Electronic Engineering from Tokyo Institute of Technology, Japan, in 1988, 1990 and 1993, respectively. He is currently Professor at Division of Electrical and Computer Engineering, Yokohama National University, Japan. His research interests are magnetic sensors, and bio-medical application of magnetic nanoparticles. He has been an author of 150 papers published in international journals, and an invited speaker for 40 international conferences.
Battery-less device operation and wireless power transfer for sensor networks and IoT
One of the key issues to realize the Internet of Things (IoT) is how to feed electrical power to “things”. Using power cables from commercial power supply is reliable, but the cables for a number of things are complicated. A battery is also practical, but maintenance including replacing the battery is necessary. These conditions may be similar to develop sensor networks.
Battery-less device operation and wireless power transfer are promising technical methods for developing sensor networks and IoT. In this talk, requirements and several examples for battery-less device operation and wireless power transfer are reviewed, followed by presentation of our recent achievements using Wiegand wire.
A magnetization reversal in magnetic materials, especially magnetic wires, with bistable magnetization states induces pulse voltage in a pick-up coil. A twisted FeCoV wire exhibits a fast magnetization reversal and is one of the optimum material generating the pulse voltage. This phenomenon is known as Wiegand effect . The amplitude of the output pulse voltage does not depend on the changing rate of an externally applied excitation magnetic field. Due to this unique feature, Wiegand wire is useful in power generation as energy harvester and in coil-core material for wireless power transmission.
Fe0.4Co0.5V0.1 wires of 10−15 nm length were used as the core material in the pick-up coil. A NdFeB magnet of 3×3×5 mm3 was used to switch the magnetization of the wire. The typical pulse voltage induced during a magnetization reversal of the wire is approximately 0.35 mV per one turn of a pick-up coil. The voltage induced in the pick-up coil was applied to a Hall sensor by way of connected rectifying diodes, capacitor and resistor. We could operate the Hall sensor using a single pulse voltage generated from the wire .
When an alternating magnetic applied field is applied to the wire, the positive and negative pulse voltages corresponding to the magnetization reversal of the wire are induced in the pick-up coil. The voltages were rectified and regulated to DC voltage. We achieved the wireless power transmission of 20 mW . The experimental details and other possible applications  are also discussed in the presentation.
 J. R. Wiegand and M. Velinsky, U.S. Patent #3,820,090, 1974.
 Takemura et al., IEEE Trans. Magn., 53, 4002706, 2017. doi: 10.1109/TMAG.2017.2713837.
 Takahashi et al., J. Mag. Soc. Jpn, 42, 49, 2018. doi: 10.3379/msjmag.1803R008.
 Takebuchi et al., J. Mag. Soc. Jpn, 41, 34, 2017. doi: 10.3379/msjmag.1701R004.
Battery-less sensor, wireless power transmission, energy harvesting, Wiegand sensor