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
A wireless self-powered urinary incontinence sensor system
A self-powered urinary incontinence sensor system consisting of a disposable urine-activated coin battery and a wireless transmitter has been developed as an application for wireless sensor networks. The urine-activated battery makes possible both the sensing of urine leakage and self-powered operation. An intermittent power-supply circuit that uses an electrical double-layer capacitor (EDLC) with a small internal resistance suppresses the supply voltage drop due to the large internal resistance of the battery. This circuit and a 1-V SAW oscillator reduce the power dissipation of a wireless transmitter. The SAW oscillator quickly responds to the on-off control of the power supply, which makes it suitable for intermittent operation. To verify the effectiveness of the circuit scheme, we fabricated a prototype sensor system. When the volume of urine is 0.2 ml, the battery outputs a voltage of over 1.3 V; and the sensor system can transmit signals over a distance of 50 cm.
A 150pW program-and-hold timer for ultra-low-power sensor platforms
Lifetime and form factor are two critical concerns for emerging sensor platforms, particularly for applications such as implantable medical devices. The limited energy from power sources, typically either microfabricated batteries or scavenged energy, remains one of the biggest challenges for such platforms. Reducing power consumption can lower system volume and extend lifetime. To achieve very low power consumption aggressive voltage scaling has been applied in recent microsystems [1, 2]. The average power consumption of sensor platforms, which are often low duty cycle, can be greatly reduced by applying strong power gating while idling [3]. A key component in power gating is the timekeeping device while the system is in the idle mode. Since the timer is always active, it is often the dominant source for energy loss and must oscillate at a low frequency (e.g., from sub-Hz to 10Hz).