The Design of a Wireless Power Transmission Mechanism for Locomotion in Active Medical Inspection MEMS

Abstract

The minimally invasive inspection based on medical MEMS has been in clinical use since the Israel invention of a passive capsule endoscope, M2A, followed by similar capsule endoscopes made in Japan and Korea. Due to the need of external control, active medical MEMS containing autonomous locomotion started to appear with power cable connections to replace in sufficient batteries. Unfortunately, power cables cannot be used in medical practice. As such, wireless power transmission for active MEMS is a must for interests of both researchers and doctors. In this paper, we present a design of a wireless power transmission mechanism to drive a micro brushless DC motor whose small size fits MEMS. Though the power transmission is done at a working frequency of RFID, the power supply system in this paper to drive a motor witha much larger current is different from the one in RFID tags. The power transmission system consists of an antenna, an impedance matching network circuit, a rectifier circuit cum voltage multiplier, and a LDO (low drop out voltage regulator). Both mathematical analysis and simulations based EDA tools are carried out to verify the system design. The RF part of the system is simulated with Agilent ADS tools, while the DC part, i.e. the LDO based on MOSFETs, is simulated by Cadence Spectre with a TSMC 0.18um technology library. Both simulation results and mathematical analysis show that the micro motor is able to receive sufficient power to work in vivo in real time.