This study aims to propose a new fabrication method for an ohmic contact type RF-MEMS switch with Au–Au/carbon nanotube (CNT)-composite contacts. These contacts are proposed to improve the reliability and the high-power handling capability of the ohmic contact type RF-MEMS switch. During the fabrication, we applied Au/CNT-composite electroplated film to the contact area in the signal line, whereas Au electroplating was used to form contacts under the cantilever of the switch. We investigated the influence of the Ar ion beam etching angle on metal layers formation and optimized the Ar ion beam etching conditions to achieve a more reliable RF-MEMS switch. We designed, fabricated, and evaluated an RF-MEMS switch to demonstrate the feasibility of our new fabrication method. We successfully fabricated an Au–Au/CNT-composite contact RF-MEMS switch; it exhibited a low insertion loss of less than 0.7 dB at frequency up to 40 GHz and a cycle life 2.7 times longer than that of an Au–Au contact switch.

We have been developing a wireless sensor network system to monitor the quality of lake water in real time. It consists of a sensor module and a system module, which includes communication and power modules. We have focused on pH, turbidity and chlorophyll a concentration as the criteria for qualifying lake water quality. These parameters will be detected by a microfluidic device based sensor module embedded in the wireless sensor network system. In order to detect the turbidity and the chlorophyll a concentration simultaneously, we propose a simple optical measurement method using LED and photodiode in this paper. Before integrating a turbidity and chlorophyll a concentration sensor into the microfluidic device based pH sensor, we performed feasibility studies such as confirmation of the working principle and experiments using environmental water samples. As a result, we successfully verified our simultaneous sensing method by using a simple optical setup of the turbidity and the chlorophyll a concentration.

In this article, a supercapacitor is developed as a power supply for wireless sensor network (WSN) systems. The proposed supercapacitor is an electric double-layer capacitor (EDLC) that employs an environment-friendly electrolyte comprising potassium hydroxide (KOH) solution along with charcoal and a steel plate. The EDLC does not contain heavy metals and toxic substances and does not adversely affect the environment. Furthermore, the use of aqueous KOH as an electrolyte eliminated the possibility of ignition, ensuring the safety of the capacitor. The charcoal EDLC was fabricated and experimentally demonstrated. The supercapacitor was used as power supply for a WSN system, and a 10-W photovoltaic module was coupled with the charcoal EDLC for a 25-Wh power storage. The WSN system was continuously operated outdoors for 24 h with a power consumption of approximately 0.7 W. These results proved that the WSN system can be successfully operated in a continuous manner for 24 h by employing the charcoal EDLC as the power supply. At night, the WSN system consumed 35% (8.4 Wh) of the power that was stored in the charcoal EDLC. From these results, we can conclude that the proposed environment-friendly charcoal EDLC may be a solution to serve as a reliable and safe power supply for WSN systems.