Xiuhan Li

A wireless magnetic resonance energy transfer system for micro implantable medical sensors.

Based on the magnetic resonance coupling principle, in this paper a wireless energy transfer system is designed and implemented for the power supply of micro-implantable medical sensors. The entire system is composed of the in vitro part, including the energy transmitting circuit and resonant transmitter coils, and in vivo part, including the micro resonant receiver coils and signal shaping chip which includes the rectifier module and LDO voltage regulator module. Transmitter and receiver coils are wound by Litz wire, and the diameter of the receiver coils is just 1.9 cm. The energy transfer efficiency of the four-coil system is greatly improved compared to the conventional two-coil system. When the distance between the transmitter coils and the receiver coils is 1.5 cm, the transfer efficiency is 85% at the frequency of 742 kHz. The power transfer efficiency can be optimized by adding magnetic enhanced resonators. The receiving voltage signal is converted to a stable output voltage of 3.3 V and a current of 10 mA at the distance of 2 cm. In addition, the output current varies with changes in the distance. The whole implanted part is packaged with PDMS of excellent biocompatibility and the volume of it is about 1 cm3.

Effect of etch holes on the capacitance and pull-in voltage in MEMS tunable capacitors

Microelectromechanical systems (MEMS) tunable capacitors, switches or actuators are widely applied in wireless communication systems. In the fabrication process etch holes are used to release the sacrificial layer with relatively large structures, which obviously affects the performance of devices. However, most researchers neglect this effect during their designing of the capacitors, switches or actuators. This article presents the theoretical calculation of the capacitance of tunable capacitors with etch holes, and analyses the deviation of the capacitance and pull-in voltage with different parameters such as the length of the plates w, the length of the etch holes w h, the air gap between the two plates d, and the number of the etch holes. To validate the theory in this article, a tunable capacitor was fabricated by surface micromachined technology. The theoretical results compare well with the experimental results.

Electro-thermally actuated RF MEMS switch for wireless communication

This paper presents a lateral resistive-contact electrothermally actuated MEMS switch for wireless communication applications. It is manufactured on a standard low-resistivity substrate, and its RF performance was improved by suspending the structures 25μm from the substrate, which is good for future integration with active devices in the system-on-chip concept. The switch is driven by a metal electrothermal actuator, which can generate large displacements and contact forces at lower temperatures than polysilicon electrothermal actuators. Measurement results show that the RF MEMS switch have good performance under DC of 0.9 to 1.1A from 0–20GHz.

Stacked flexible parylene-based 3D inductors with Ni 80 Fe 20 core for wireless power transmission system

This paper presents a new high quality factor parylene-based stacked 3D spiral inductor with Ni80Fe20 core for wireless power transmission system. To achieve multilayers, planarization of parylene by oxygen plasma etching was realized. Ni80Fe20 was added as the magnetic core to enhance the performance. The maximum quality factor of the designed circular double-layer inductor reached 99.3 at 60MHz, which is much higher than the square coils with the same area. The double-layer inductor shows a 408% increment of maximum quality factor compared with single-layer coil. Furthermore, inductors with magnet arrays exhibited better performance than those with one magnet. Forming the power transmission system with these 3D inductors, the minimum attenuation was -26dB at 118MHz.

Design, Simulation, and Characterization of Variable Inductor With Electrostatic Actuation Fabricated by Using Surface Micromachining Technology

In this paper, a new variable inductor with electrostatic actuators was proposed and was fabricated using surface micromachining microelectromechancal systems (MEMS) technology. The variable inductor consists mainly of planar spiral inductor, the shielding metal plate above the spiral inductor, and the electrostatic-driven capacitive actuators. In order to enhance the tuning range of the variable inductor, the shielding metal plate has adopted electroplated Ni80Fe20 Permalloy as the “magnetic core” of the variable inductor. The fabricated variable microinductor was tested and characterized. The measured results indicated that the variable inductor had good performance at high frequency and the tuning range of the variable inductor was 77.8%. The effect of Ni80Fe20 Permalloy metal plate on the inductance of variable inductor was also discussed.

High performance MEMS spiral inductors

In this paper, fabrication and performance of RF MEMS planar spiral inductors is presented. The fabrication process is simple, using surface micromachined technology with three masks. Two types of spiral inductor were fabricated and the measured results showed that the spiral inductors had high performance at high frequency. The maximum quality of the spiral inductor-Type A is 15.8 at 1.4GHz with inductance of 4.61nH. The maximum quality of the spiral inductor-Type B is 19.7 at 4.1 GHz with inductance of 1.40nH.

Design and fabrication of flexible parylene-based inductors with electroplated NiFe magnetic core for wireless power transmission system

Integrated flexible parylene-based MEMS inductors were successfully designed, fabricated and analyzed. By elctrodeposition technique, Ni80Fe20 Permalloy with high permeability was acquired as the magnetic core to increase the inductance and quality factor of inductors. Using parylene as substrates, these inductors became more flexible and biocompatible. For small scale inductors, by HFSS simulation, a maximum quality factor of 51.52 was achieved at 3.10 GHz. The inductance of inductors with magnetic core was enhanced by 3.3% than those with air core. As the width of the core increased from 25 μm to 100 μm, the inductance was also increased by 11.3% maximally. For large scale inductors fabricated, the tested maximum quality factor was 110 at 6 MHz. Based on the IC compatible fabrication process, these inductors could be used in wireless power transmission system for implantable medical devices.

Wireless energy transfer system based on high Q flexible planar-Litz MEMS coils

Wireless energy transfer system tends to replace the battery for the power supply of implantable prosthetic devices. Coils are the key point of the wireless transfer system and affect the transfer efficiency. In this paper, high Q flexible planar-Litz coil is designed and implemented for the wireless energy transfer system. Theoretical model of planar-Litz coil is given and the measurement result matches the theoretical analysis. The efficiency of wireless transfer system is improved by using the high Q planar-Litz coils. The experiment results show the coupling efficiency can be improved by about 40% as the transfer distance is 0.5cm. At last, resonant coils are added into transfer system to enhance the magnetic resonance, which makes the energy transfer efficiency improved greatly.

A tunable metamaterial absorber employing MEMS actuators in THz regime

As Micro-electromechanical Systems (MEMS) fabrication and actuation methods are very suitable to realize the tunability of metamaterials in terahertz regime, a kind of tunable metamaterial absorber based on MEMS techniques is proposed in this paper. Firstly, an improved electric ring resonator (ERR) absorber model is put forward and the geometrical parameters are optimized to improve the absorption characteristics. Then the feasible fabrication method of the movable ERR structure is discussed. By employing MEMS actuators the frequency of absorption peak is tunable. A simulated full width at half maximum (FWHM) absorbance of 4% is achieved and the simulation results demonstrate a peak absorbance greater than 98% at the whole tunable frequency range from 1.08 THz to 1.20THz.

Magnetic energy coupling system based on micro-electro-mechanical system coils

In this paper, a high efficiency wireless energy transfer system based on MEMS coils is first developed. The permanent magnetic core used in the transmitting coil can not only enhance the magnetic flux but also applies a strong and uniform magnetic field distribution around the core. Ansoft hfss is then used to analyze the performance of two coupling coils designed to be resonated at the same frequency. The distribution of magnetic field strength and coupling efficiency is modeled and characterized. High-performance bio-compatible MEMS coils were fabricated on a glass wafer by thick glue photolithography and electroplating technique. We measured a peak value of energy transfer at the resonant frequency of 23 MHz, and the coupling efficiency is higher than 10% within the distance of 10–20 cm by sweeping frequencies from 1 MHz to 200 MHz. Experiments also show that the resonant coupling efficiency is not much affected by the relative position of the two coils in a large range.