Ultralow-power Circuit Techniques for Applications with Microscale Energy
あらゆるモノにセンサを取り付けインターネットに 接続することにより新たな価値を創出する IoT (Internet of things)社会の実現に向けて,様々な技術レ イヤーの研究開発が盛んに行われている.IoT技術の 今後の問題の一つに,モノをインターネットに接続す るための近距離無線センサ端末の電源問題がある.電 池駆動のセンサ端末は電池交換が必要となるからで ある.端末の電源問題を解決する一つの手法として, 我々の身の回りに微小ながら常に存在する熱,光,振 動といったアンビエントエネルギー源を活用するマイ クロ環境発電技術が注目されている [1]. 発電電力がミリワット級の環境発電応用としては, 照明用スイッチに電磁誘導型の発電素子を組込み,無 線で照明の ON/OFF制御を行う無線スイッチ [2]や, 列車の車軸に振動発電素子を組込み,無線で車軸のベ アリングを監視するモニタリングシステム [3] が,既 に実用化されている.我々は,人間の尿で発電する尿
Wireless self-powered plant health-monitoring sensor system
A self-powered plant-health-monitoring sensor powered by a battery that is activated by the sap of a vascular plant has been developed as an application for wireless biosensor networks. The battery consists of a galvanized iron nail inserted into a tree trunk and a stainless-steel electrode planted in the soil nearby. It outputs on the order of 1 μW of power. An intermittent power supply circuit with a divided-power-line structure, which separates the power line of a storage capacitor while it is discharging, makes it possible to charge the capacitor with an input power of around 1 μW and to supply power to a wireless transmitter. To verify the effectiveness of the circuit scheme, a prototype sensor was fabricated and tested on a potted pachira tree. The sap-activated battery acted as a current source (3 μA) with an open voltage of 1 V, and the sensor had a 10-mF storage capacitor. This setup enabled the sensor to transmit a signal about every 40 minutes over a distance of 5 m.
Urine-activated paper batteries for biosystems
The first urine-activated laminated paper batteries have been demonstrated and reported in this paper. A simple and cheap fabrication process for the paper batteries has been developed which is compatible with the existing plastic laminating technologies or plastic molding technologies. In this battery, a magnesium (Mg) layer and copper chloride (CuCl) in the filter paper are used as the anode and the cathode, respectively. A stack consisting of a Mg layer, CuCl-doped filter paper and a copper (Cu) layer sandwiched between two plastic layers is laminated into the paper batteries by passing through the heating roller at 120 °C. The paper battery is tested and it can deliver a power greater than 1.5 mW. In addition, these urine-activated laminated paper batteries could be integrated with bioMEMS devices such as home-based health test kits providing a power source for the electronic circuit.