Fluorescent Troffer-powered Internet of Things: An Experimental Study of Electric-field Energy Harvesting

Things: An Experimental Study of Electric-field Energy Harvesting O. Cetinkaya and Ozgur B. Akan A totally new energy harvesting architecture that exploits ambient electric-field (E-field) emitting from fluorescent light fixtures is presented. A copper plate, 50x50cm in size, is placed in between the ambient field to extract energy by capacitive coupling. A low voltage prototype is designed, structured and tested on a conventional ceilingtype 4-light fluorescent troffer operating in 50Hz 220V AC power grid. It is examined that the harvester is able to collect roughly 1.25J of energy in 25min when a 0.1F of super-capacitor is employed. The equivalent circuit and the physical model of the proposed harvesting paradigm are provided, and the attainable power is evaluated in both theoretical and experimental manner. The scavenged energy is planned to be utilized for building battery-less Internet of Things (IoT) networks that are obliged to sense environmental parameters, analyze the gathered data, and remotely inform a higher authority within predefined periods. Introduction: Thanks to the advances in ultra-low power transceiver technology, plenty of source such as light, heat, motion and electromagnetic waves/fields have become more viable to build wireless sensor networks (WSNs) which are free from battery constraints [1]. Although the conducted researches theoretically and experimentally revealed the capabilities of these techniques in providing adequate and stable power, rising and diversified needs of today’s communication architectures such as IoT, require more enhanced, robust and durable power provision systems. In this regard, electric field energy harvesting stands as the most promising candidate with the characteristics of ambient variable in-dependency, sufficient power rating, low complexity, and excellent energy continuity [2–7]. When an office-like commercial environment is envisioned, illumination can be referred as one of the most crucial systems that needs to be operated perpetually, mostly due to security issues. Regarding this fact, and the strong E-field gradient in the vicinity of fluorescent light fixtures a reference procedure has been represented in [6] as the very first approach. This model is able to provide 200μW of DC power with respect to the designated configuration; however, the setup is bulk, hard to employ, and affects light propagation. Regarding these issues we propose a new architecture that enables ease of implementation, less complex circuitry, and highly increased efficiency as allowing self sufficient IoT networks to be built for online condition monitoring. E-field Energy Harvesting: According to the basics of electrostatics, any conductive material energized at some voltage level emits a radial electric field. In AC, this time varying field results in a displacement current ID which dispatches the E-Field induced electric charges to be collected in a storing element Cs. Since the stored energy is harnessed from the surrounding field, this method can be referred as Electric Field Energy Harvesting (EFEH) [2–8]. EFEH is first proposed for high and middle voltage overhead power lines by regarding the E-Field in abundance. It is then applied to low voltage systems as mounting single-phase AC power cords with metallic sheaths [2–4]. These efforts revealed that, it is also possible to constitute an applicable EFEH methodology for applications in which E-Field intensity is considerably low. As an alternative to the previous studies, Linear Technology (LT) has brought a new perspective to the area with their parallel plates model [6]. This work includes placing copper plates under the fluorescent troffers to exploit the surrounding field. The plates act as a capacitive voltage divider, block the outward field flow, and utilize the leakage electric charges to provide stable voltage. The idea presented by LT is taken as the basis of this paper, and modified to build a more flexible and efficient EFEH model. Principle: Fig. 1 roughly depicts the basics of our proposed E-field energy harvesting concept. As shown in Fig. 1(b), a copper plate, i.e., capacitive voltage divider, is situated between ceiling and the field emitting fluorescent light bulbs. Splitting up the field by a conductive material not only results in a voltage difference, but also formation of stray in-plane capacitances as in Fig. 2(a). In this figure, capacities from bulbs to harvester are stated as Cf while the residual ones, between the harvester and ground planes, are titled as Ch. It is also required to Reflector Fluorescent