Zero-power sensors with near-zero-power wakeup switches for reliable sensor platforms

The near zero-power sensor node solution is presented with piezoelectric sensors and DC tunable threshold electrostatic switches. A sensor suite measuring acceleration, rotation, and magnetic field based on PZT lateral bimorphs is used with NEMS switches for the detection of a desired signal pattern and generating a wake up trigger. The sensors are capable of detecting physical signals from 5 Hz to 1.5 kHz, with sourcing load capacitances as high as 200 pF. The sensor sensitivities achieved are: 0.1 V/g for the accelerometer, 31 mV/Gauss for the magnetic field, and 0.31 mV/(°/s) for rotation. NEMS switches, with threshold voltages in the mV to 15V range, can combine multiple sensor outputs through multi-gate actuation to detect desired event specific features. Using the sensors, we demonstrate the detection of a portable electrical generator in its different operational modes (On/Off state and the Eco mode).

Introduction

Sensor node reliability is limited by the longevity of the energy sources used to power them [1]. In order to have sensor nodes operational for extended periods of time, power consumption has to be minimized. The power consumed by the sensors of the sensor node is especially critical because the sensors must operate all the time, and generate wakeup trigger for the digital and communication components. MEMS sensors made of piezoelectric materials hold the promise of sensing signals without any power consumption, owing to charge being generated as a result of strain in the materials [2]. At the same time, the zero power sensors can trigger near-zero power consuming electrostatic switches that in turn generate a digital trigger as shown in Fig. 1 [3].