This paper presents a novel fabrication method of scalloping-free and footing-free vertical electrodes for micromachined capacitive inclinometers with a high sensing resolution. The proposed fabrication method is based on additional crystalline wet etching of a (1 1 0) silicon that is bonded to a silicon substrate with a patterned insulator layer. The sensing electrodes, which are aligned to the (1 1 1) plane, have very smooth sidewalls because the morphological defects formed by the silicon deep reactive ion etching (DRIE) process are drastically reduced in the crystalline wet etching. The fabricated capacitive inclinometer with smooth sensing electrodes was evaluated in terms of capacitance change and resolution. The capacitance of the fabricated inclinometer is changed from −0.246 to 0.258 pF for the inclination angle (−90° to 90°). The temporal deviation of the capacitance is as small as 0.2 fF, which leads to a high resolution of 0.1° or less for ±45°.
In this paper, we present the ultrasonic wireless power transmission system as part of a brain-machine interface (BMI) system in development to supply the required electric power. Making a small-size implantable BMI, it is essential to design a low power unit with a rechargeable battery. The ultrasonic power transmission system has two piezoelectric transducers, facing each other between skin tissues converting electrical energy to mechanical vibrational energy or vice versa. Ultrasound is free from the electromagnetic coupling effect and medical frequency band limitations which making it a promising candidate for implantable purposes. In this paper, we present the design of piezoelectric composite transducer, the rectifier circuit, and rechargeable battery that all packaged in biocompatible titanium can. An initial prototype device was built for demonstration purpose. The early experimental results demonstrate the prototype device can reach 50% of energy transmission efficiency in a water medium at 20mm distance and 18% in animal skin tissue at 18mm distance, respectively.
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