In this paper, we present the development of two piezoelectric MEMS generators, {3-1} mode and {3-3} mode, which have the ability to scavenge mechanical energy of ambient vibrations and transform it into useful electrical power. These two piezoelectric MEMS generators are of cantilever type made by a silicon process and which can transform mechanical energy into electrical energy through its piezoelectric PZT layers. We developed a PZT deposition machine which uses an aerosol deposition method to fabricate the high-quality PZT thin film efficiently. Our experimental results show that our {3-1} mode device possesses a maximum open circuit output voltage of 2.675 V P-P and a maximum output power of 2.765 μW with 1.792 V P-P output voltage excited at a resonant frequency of 255.9 Hz under a 2.5 g acceleration level. The {3-3} mode device possessed a maximum open circuit output voltage of 4.127 V P-P and a maximum output power of 1.288 μW with 2.292 V P-P output voltage at its resonant frequency of 214 Hz at a 2g acceleration. We also compared the output characteristics of both the {3-1} mode and the {3-3} mode piezoelectric MEMS generators which were both excited at a 2g acceleration level.

Electrostatic-driven microelectromechanical systems devices, in most cases, consist of couplings of such energy domains as electromechanics, optical electricity, thermoelectricity, and electromagnetism. Their nonlinear working state makes their analysis complex and complicated. This article introduces the physical model of pull-in voltage, dynamic characteristic analysis, air damping effect, reliability, numerical modeling method, and application of electrostatic-driven MEMS devices.

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Bone tissue engineering provides many advantages for repairing skeletal defects. Although many different kinds of biomaterials have been used for bone tissue engineering, safety issues must be considered when using them in a clinical setting. In this study, we examined the effects of using a common clinical item, a hemostatic gelatin sponge, as a scaffold for bone tissue engineering. The use of such a clinically acceptable item may hasten the translational lag from laboratory to clinical studies. We performed both degradation and biocompatibility studies on the hemostatic gelatin sponge, and cultured preosteoblasts within the sponge scaffold to demonstrate its osteogenic differentiation potential. In degradation assays, the gelatin sponge demonstrated good stability after being immersed in PBS for 8 weeks (losing only about 10% of its net weight and about 54% decrease of mechanical strength), but pepsin and collagenases readily biodegraded it. The gelatin sponge demonstrated good biocompatibility to preosteoblasts as demonstrated by MTT assay, confocal microscopy, and scanning electron microscopy. Furthermore, osteogenic differentiation and the migration of preosteoblasts, elevated alkaline phosphatase activity, and in vitro mineralization were observed within the scaffold structure. Each of these results indicates that the hemostatic gelatin sponge is a suitable scaffold for bone tissue engineering.

This paper presents the design, fabrication and characterization of an RF MEMS switch. Low actuation voltage and high isolation of the switch were achieved by exploiting buckling and bending effects induced by well-controlled residual stress. The effects of residual stress on improving the switch performance have been investigated using both analytical and numerical methods. The proposed RF switch has been fabricated by surface micromachining. The minimum actuation voltage of the fabricated switch was measured to be 10.2 V. At a 5 GHz signal frequency, the measured insertion loss and isolation are 0.21 dB and −44 dB, respectively. These results demonstrate that low voltage and high isolation of RF MEMS switches can be achieved with proper utilization of residual stresses.