Wireless sensor systems have been widely used for both industrial and civil applications. With the development of circuit design and fabrication technique, sensor nodes now can be implemented with small scale at low cost, which is promising for ubiquitous sensing. However, with more functions integrated, the conflict between power consumption and expected lifetime became critical. Sensor nodes powered with batteries are generally compromised by extra physical size and periodic battery replacement. Therefore, energy harvesting techniques are intensively involved in sensor design where environmental signal acts as auxiliary energy source.A typical energy harvesting sensor consists of four parts: energy harvester, energy storage, power management and sensor subsystem. Energy harvester scavenges power from environmental signal which is then transferred into energy storage. Since the output power is usually not in appropriate form, power management is used to provide a usable supply voltage/current for sensor subsystem. The limitation of energy harvesting sensor is determined by the power consumption of sensor subsystem, the efficiency of energy conversion and the available energy level from environment.In this dissertation, a novel solution referred as "self-powered sensor" is proposed to extend the limitation of energy harvesting sensor. The proposed sensor can directly harvest energy from input signal being sensed. Therefore the usage of energy storage and power management is eliminated, which achieves higher energy efficiency.To demonstrate proposed solution, the system and circuit design of a self-powered sensor are presented for long-term ambient vibration monitoring. Constrained by its application, the sensor can only scavenge energy from input strain signal itself, in which scenario all existing energy harvesting techniques fail. The greatest design challenge is to achieve both ultra-low power computation and non-volatile storage. In this dissertation, a novel technique based on floating-gate transistor is presented. By exploiting controllable hot electron injection procedure, specific computation can be performed according to the characteristic of input signal. In addition, floating-gates can also retain computation results with no power consumption.For autonomous sensing, a hybrid energy harvesting topology is proposed on system level. The sensor is designed with two different operation modes. In self-powered sensing mode, it can perform continuous monitoring, computation and data storage which is powered by input strain signal. In data interrogating mode, additional functions such as data sampling and wireless communication can be enabled once a certain reading device is provided.The dissertation is organized as follows. In chapter 1, the history of wireless sensor system is reviewed. The motivation of self-powered sensor and the contributions of this dissertation are presented. Existing energy harvesting techniques are evaluated in chapter 2. In chapter 3, the case of long-term ambient vibration monitoring is studied and the hybrid energy harvesting topology is proposed for self-powered sensor system. In chapter 4, the principle of ultra-low power computation and non-volatile storage is explored based on controllable injection procedure on floating-gate transistor. To verified proposed solution, a sensor prototype was fabricated in 0.5-um standard CMOS process. The details of circuit design and evaluation are presented in chapter 5, including analog signal processor, analog-to-digital converter, radio frequency front-end, digital baseband, etc. Chapter 6 shows an extension of ultrasonic powering and communication system based on preliminary work and chapter 7 draws final remarks.
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