Tomoaki Kageyama

An ohmic contact type RF-MEMS switch having Au-Au/CNTs contacts

In this paper, we report the fabrication results of an ohmic contact type RF-MEMS switch having Au-Au/CNTs contacts. The Au-Au/CNTs contacts have been proposed to improve the reliability and the high power handling capability of the ohmic contact type RF-MEMS switches. In the fabrication, we applied Au/CNTs composite electroplated film to the contact area in the signal line whereas the Au electroplating was used to form contacts under the cantilever of the switch. As a result, we achieved low insertion loss less than 0.7 dB up to 40 GHz and 2.7 times longer life time than that of Au-Au contacts switch.

A wireless sensor network platform for water quality monitoring

We have developing a wireless sensor network system for water quality monitoring. It consists of various sensors for the sensing of physical and chemical properties of water, and systems including wireless communication module, power module and interface between sensors and wireless communication module. In this paper, we report the development results of a novel wireless sensor network platform for water quality monitoring, which is proposed for rapid prototyping of wireless sensor network system. In order to demonstrate our novel wireless sensor network platform, we fabricated the platform as a sensor node and field-tested it with several sensors in the lake. As a result, we could confirm that our proposed novel platform was operated successfully in real environment.

A microfluidic device fully integrated with three pH sensing electrodes and passive mixer for nanoparticle synthesis

We have proposed a novel microfluidic device for nanoparticle synthesis which is integrated with a pH sensing electrode array for in situ real time pH monitoring and a passive mixer for effective reaction of two chemical fluids within a small scaled microfluidic device. The passive mixer is fabricated with three glass substrates and the mixing channel is designed 3 dimensionally to maximize the mixing efficiency. Moreover, our pH sensing is achieved with three electrodes measurement method. The three electrodes are working electrode of IrO2, counter electrode of Pt and reference electrode of Ag/AgCl, which are fabricated by lift-off process on a silicon substrate. By the anodic bonding of the Si substrate having pH sensing electrode array to the glass substrates having passive mixer, we have accomplished the microfluidic device fabrication. The liquid junction between the flow channel and KCl solution chamber for reference electrode is realized by pores created at both sides of dummy metal layer of Pt during the anodic bonding process. We have performed pH measurement and mixing experiment as well. As a result, we have verified the performance of our microfluidic device.

Flexible and stackable terahertz metamaterials via silver-nanoparticle inkjet printing

There is presently much interest in tunable, flexible, or reconfigurable metamaterial structures that work in the terahertz frequency range. They can be useful for a range of applications, including spectroscopy, sensing, imaging, and communications. Various methods based on microelectromechanical systems have been used for fabricating terahertz metamaterials, but they typically require high-cost facilities and involve a number of time-consuming and intricate processes. Here, we demonstrate a simple, robust, and cost-effective method for fabricating flexible and stackable multiresonant terahertz metamaterials, using silver nanoparticle inkjet printing. Using this method, we designed and fabricated two arrays of split-ring resonators (SRRs) having different resonant frequencies on separate sheets of paper and then combined the two arrays by stacking. Through terahertz time-domain spectroscopy, we observed resonances at the frequencies expected for the individual SRR arrays as well as at a new frequency due...

A Feasibility Study on the Simultaneous Sensing of Turbidity and Chlorophyll a Concentration Using a Simple Optical Measurement Method

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.

Turbidity monitoring of lake water by transmittance measuresment with a simple optical setup

We are developing a wireless sensor network system for the lake water quality monitoring, which consists of sensor module, wireless transceiver module, control ICs and power module. In the sensor module, sensors to monitor the water quality such as pH sensor, turbidity sensor, chlorophyll concentration sensor and dissolved oxygen concentration sensor, will be integrated as a microfluidic device. The power module of a sensor node of the wireless sensor network system will be implemented with solar cells and thermoelectric effect based energy harvesting devices utilizing temperature difference between the surface and the bottom water layer. In this paper, we report the feasibility study results of a turbidity sensor that will be integrated into the sensor module for the lake water quality monitoring. Our turbidity sensor has been achieved by a simple optical setup, which consists of LED and photodiode. The turbidity is determined by measuring the transmittance of scattered LED light by the particles in the water sample. As a result of experiments with the lake water sample, we could verify that our simple optical measurement setup can be a useful tool in turbidity sensing.