Experiments Validating the Effectiveness of Multi-Point Wireless Energy Transmission with Carrier Shift Diversity

Abstract

SUMMARYThis paper presents a method to seamlessly extend the coverage of energy supply field for wireless sensor networks in order to free sensors from wires and batteries, where the multi-point scheme is employed to overcome path-loss attenuation, while the carrier shift diversity is introduced to mitigate the effect of interference between multiple wave sources. As we focus on the energy transmission part, sensor or communication schemes are out of scope of this paper. To verify the effectiveness of the proposed wireless energy transmission, this paper conducts indoor experiments in which we compare the power distribution and the coverage performance of different energy transmission schemes including conventional single-point, simple multi-point and our proposed multi-point scheme. To easily observe the effect of the standing-wave caused by multipath and interference between multiple wave sources, 3D measurements are performed in an empty room. The results of our experiments together with those of a simulation that assumes a similar antenna setting in free space environment show that the coverage of single-point and multi-point wireless energy transmission without carrier shift diversity are limited by pathloss, standing-wave created by multipath and interference between multiple wave sources. On the other hand, the proposed scheme can overcome power attenuation due to the path-loss as well as the effect of standing-wave created by multipath and interference between multiple wave sources. key words: wireless sensor networks, multi-point wireless energy transmission, carrier shift diversity, indoor environment, experimental validation

Efficient Wireless Charger Deployment for Wireless Rechargeable Sensor Networks

“…In this section, we review the research results [3][4][5][6][7][8][13][14][15][16][17] most related to our work. Kim et al [3] investigated various ambient energy-harvesting technologies using different power sources, such Energies 2016, 9, 696 3 of 22 as solar power, thermal power, piezoelectric power, and wireless RF power, in the aspect of their applicability for self-sustainable wireless sensor platforms.…”

“…Maehara et al [14] proposed a WPT scheme called multi-point carrier shift diversity (MPCSD), in which the center frequency of the carrier of each power transmitting point (or transmitter) is slightly shifted with a predefined amount to create artificial fading. Suppose there are N different transmitters, the carrier frequency f n of the nth transmitter is defined in Equation (3), shown below:…”

“…Many recent studies [4][5][6][7][8][9][10][11][12][13] focus on the WRSNs due to their sustainability. Some other studies [14][15][16][17][18][19][20] investigate battery-less or battery-free wireless sensor networks (WSNs) in which sensor nodes are powered by capacitors storing energy harvested through wireless power transmission (WPT), especially microwave power transmission (MPT). Without loss of generality, such WSNs are regarded as WRSNs in this paper.…”

Experimental Study on Battery-Less Sensor Network Activated by Multi-Point Wireless Energy Transmission

“…Once multiple Txs simultaneously transmit radio wave, destructive interference occurs and creates deadspots where sensor nodes cannot be charged and activated. To deal with this problem, we proposed to introduce Carrier Shift Diversity (CSD) to the multi-point system [6] [7]. Since the CSD creates artificial fading and the instantaneous received power fluctuates against the required power for activating sensor node, capacitor playing the role of rechargeable battery is introduced to average the received power over the period of artificial fading.…”

“…In our previous works [6][7], we conducted indoor experiments performed in a three dimensional space of an empty room by measuring only the propagation characteristics using a receiving antenna of IC tag and spectrum analyzer. The experimental results showed that the multi-point wireless energy transmission with CSD can mitigate power attenuation due to the path-loss as well as the effect of standing-wave created by multipath and interference between multiple wave sources.…”