Self-Powered Height Sensor With ZigBee Networks for Intelligent Systems

Introduction

Modern vehicles are intelligentized with various sensors in different systems. These sensing systems will monitor driving conditions, detect the abnormal problems, and alert the driver through the vehicle computer. At the same time, more and more automobile manufactures start to equip their vehicles with automated driving system or develop the autonomous car like the Google Self-Driving Car or Tesla Autopilot. Thanks to utilization of a great variety of sensors in those cars, it can easily obtain real-time surrounding environment information and make proper timely responses. One can assert that more sensors will be applied in vehicles in the near future. In comparison with the current wired sensing system, wireless sensor networks (WSN) can bring more convenience for the layout design of a vehicle. With the development of this burgeoning technology, it shows a great advantage in distributed, automatic detection.

With the development of wireless sensor networks (WSN), this burgeoning technology for distributed, automatic detection can be applied in many parts of a vehicle, and these small computing devices are increasingly embedded in different sensors to work as monitoring devices or for emergency response (Hersent, Boswarthick, & Elloumi, 2011). Thus, it is profitable to research the possibility of replacing a wired sensor with a wireless sensor node in some appropriate parts. Typically, a wireless sensor node has four main parts: a power supply unit, a processing unit, a physical sensor and a RF transceiver (Labiod, Afifi, & Santis, 2007). One of main limitations for a WSN is the power consumption of each node. Normally, one solution is to focus on energy saving techniques by establishing a low-cost, low-power wireless network to extend the functional life with limited battery (Hersent, Boswarthick, & Elloumi, 2011). Another employs the environmental energy harvesting devices as the power supply (Bibo & Daqaq, 2013). The height sensors in truck suspension air spring provide a good way to research these two problems. Originally, the height sensor is powered by an external wire. But considering the inside vibration environment of the truck suspension air spring, an energy scavenger may supply the power for the whole wireless sensor nodes by converting the vibration kinetic energy into available electrical energy.

As a direct method of converting kinetic energy to electrical energy, piezoelectric materials have been the research focus of power supply for small devices (Bibo & Daqaq, 2013). Experiments show that the produced polarized charge is proportional to the applied stress. This feature of the stress-dependent charge output has typically been applied to many different devices, including physical sensors, actuators, microphones, etc. (Galchev & Najafi, 2009). A huge amount of research has been done in the field of power harvesting to enable power up wireless sensor nodes (Bibo & Daqaq, 2013; Galchev & Najafi, 2009; Choi, Jeon, Jeong, Sood, & Kim, 2006; Kim, Kim, & Kim, 2011).

ZigBee is a specification for low-cost, low-power and wireless mesh network based on the IEEE 802.15.4 standard (Hersent, Boswarthick, & Elloumi, 2011). With the development of this specification more and more companies begin to develop their own products (Baronti et al., 2007). ZigBee technology is gradually applied in the field of smart home, industrial control, intelligent transportation, etc. As a basic application of wireless sensor networks, the remote sensor is also one of the research hotspots (Guo, Healy, & Zhou, 2010; Xu et al., 2010).