On the design of an energy-harvesting noise-sensing WSN mote
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On the design of an energy-harvesting noise-sensing WSN mote Wilson M Tan1,2* and Stephen A Jarvis1
Abstract Wireless sensor networks (WSNs) could potentially help in the measurement and monitoring of noise levels, an important step in mitigating and fighting noise pollution. Unfortunately, the high energy required by the noise measurement process and the reliance of sensor motes on batteries make the management of noise-sensing WSNs cumbersome. Giving motes energy harvesting (EH) capabilities could alleviate such a problem, and several EH-WSNs have already been demonstrated. Nevertheless, the high-frequency nature of the data required to measure noise places significant additional challenges to the design of EH-WSNs. In this paper, we present a design and prototype for a mote extension which enables the mote to detect noise levels while being powered by energy harvesting. The noise level detection carried out by the system relies primarily on the concept of peak detection. Results of performance testing are presented. Aside from the hardware design and prototype, we also discuss methods of assigning charge times for application scenarios where there are multiple pulse loads. We also propose a new opportunistic method for charge time determination. Experiments demonstrate that the new method could improve analytically-derived duty cycles by at least 350%. Keywords: Wireless sensor networks; Energy harvesting; Acoustics; Noise
Introduction Noise pollution is becoming an increasing concern in many urban regions all over the world (for example, [1]). An important step in fighting and mitigating noise pollution is its classification and quantification. Efforts being made towards this goal include cellphone applications that measure noise and noise-related legislations (such as the European Union’s Environmental Noise Directive [2] and the New York City Noise Code [3]). Wireless sensor networks (WSNs) could potentially help with these efforts, as they could enable the simultaneous and continuous gathering of data over wide geographic regions. Several WSNs for noise pollution monitoring have been demonstrated [4-6]. WSN nodes (‘motes’) however, are usually powered by batteries which have to be frequently replaced. The length of time between battery replacements depends on the energy demand of the application: for those nodes that have energy-intensive sensors, or do lots of routing, this could be days, while for nodes *Correspondence: [email protected] 1 Department of Computer Science, University of Warwick, Coventry, UK 2 Department of Computer Science, University of the Philippines, Quezon City, Philippines
that have simple sensors with very small duty cycles, this could be many months. The task of replacing these batteries on a regular basis makes the maintenance of such networks difficult. As an alternative to batteries, WSNs could also be powered through energy harvesting (EH). Several EH-WSNs have been demonstrated [7-9]; nevertheless, despite these past successes, creating an EH
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