Selective drive of electrostatic actuators using remote inductive powering

doi:10.1016/S0924-4247(01)00738-5

Sensors and Actuators A: Physical

Volume 95, Issues 2–3, 1 January 2002, Pages 269-273

https://doi.org/10.1016/S0924-4247(01)00738-5 Get rights and content

Abstract

A remote inductive powering system for driving electrostatic actuators is proposed. The actuators can be controlled selectively by matching transmitter’s frequency to the resonance frequency of the receiver LC-circuits. An 8 mm² square and 20 turns square- planar coil are used as a receiver coil. The operational frequency of the transmitter is set from 4 to 7 MHz. The output voltage of the receiver was obtained maximally about 45 V with a load resistance of more than 100 kΩ. A conventional electrostatic comb drive microactuator was used for a prototype of a receiver. The coil and the actuator were fabricated on the same surface of a commercially available silicon on insulator (SOI) wafer. The displacement of the actuator was selectively controlled by changing the transmitter’s frequency.

Introduction

Many types of remote inductive powering systems have been reported. They have been mostly used for radio frequency identification (RFID) system or electrical powering of biomedical implantable sensor devices [1], [2]. The main advantage of such remote powering method is that the energy can be transferred to the receiver without connecting wires.

For such kind of the inductive powering, the received energy can be of the order of milliwatts [3]. This is enough to drive not only a sensor circuit but also a microactuator such as an electrostatic actuator. Since the receiver circuit can be fabricated in the size of a microactuator, this method will be useful for driving a microactuator which is expected to work in a closed small space, for example an implantable actuator [4] or a drive actuator of a micro mobile unit [5].

The concept of wireless selective driving using differences of the mechanical resonance frequencies was already proposed by Yasuda et al. [6]. In this paper, we propose a driving method using the differences of the electrical resonance frequencies, which will be very compatible to other electrically driven devices. Also, in the applications where an array of microactuators is needed, this approach can be utilized for selective control of each actuator without any wiring problems.

Section snippets

Principle

Fig. 1 shows a principle of the remote inductive powering system. An actuator is connected to a parallel LC resonant circuit. The resonance frequency of the receiver, f_r, is given by $f_{r} = 1 2π L_{r} C_{r},$ where L_r is the coil inductance and C_r the capacitance of the receiver circuit. A diode is used for supplying dc voltage to the actuator.

In this paper, a planar square coil is used as the receiver because the fabrication process is compatible to other MEMS technologies. The self inductance of a planar

Experimental results and discussion

As receiver coils, three types of planar coils, which is type A, B and C, as shown in Fig. 2, have been investigated. Type A is a coreless coil fabricated on a silicon wafer. Type B and C have a NiFe core under copper windings. The core of type B was fabricated by a sputtered NiFe thin film, the thickness is 10 μm. Type C core was fabricated by electroplating NiFe on the sputtered NiFe thin film. All the coil windings are fabricated by copper sputtering and patterned by wet etching (HNO₃:CH₃

Conclusions

A remote inductive powering system for driving electrostatic actuators is proposed. A 8 mm² and 20 turns square-planar coreless coil of 3.5–4 μH was used for the receiver coil. The Q-factor of this coil showed about 2 at 4 MHz which was higher than that of the coil with NiFe core. The maximum output voltage of 45 V can be obtained approximately when a load resistance is more than 100 kΩ. A conventional electrostatic comb drive actuator was designed and fabricated inside the planar coil for a

Acknowledgements

Photolithography masks were fabricated using EB lithography apparatus of VLSI Design and Education Center (VDEC), the University of Tokyo. Shoji Takeuchi received the Research Fellowships of the Japan Society for the Promotion of Science (JSPS) for Young Scientists in 2000.

Shoji Takeuchi was born in Japan in 1972. He received the BE, ME and PhD degrees in mechanical engineering from the University of Tokyo in 1995, 1997 and 2000, respectively. He is currently a Lucturer of the Institute of Industrial Science, The University of Tokyo, Japan.

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Isao Shimoyama was born in Japan in 1955. He received the BE, ME, and PhD degrees in mechanical engineering from the University of Tokyo in 1977, 1979, and 1982, respectively. He joined the University of Tokyo in 1982 and is currently a Professor in the Department of Mechano-Informatics, The University of Tokyo. His research interest is in micro robotics.

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