Ultra-wide band energy harvesting for ultra-low power electronics applications

International Journal of Electrical and Computer Engineering (IJECE) Vol. 11, No. 2, April 2021, pp. 1158~1165 ISSN: 2088-8708, DOI: 10.11591/ijece.v11i2.pp1158-1165  1158 Ultra-wide band energy harvesting for ultra-low power electronics applications 1Department Nasr Rashid1, Mohamed Shehata2 of Electrical Engineering, College of Engineering, Jouf University, Sakaka, Saudi Arabia 1Department of Electrical Engineering, Faculty of Engineering, Al-Azhar University, Cairo, Egypt 2SOURCE, Department of Research Training, Giza, Egypt Article Info ABSTRACT Article history: In this work, the feasibility of energy harvesting in the useful UWB band (i.e., 3.1-10.6 GHz) is analytically investigated. A typical UWB communications/EH chain in this band is modeled and analyzed, considering the spectral constraints imposed by the federal communications commission (FCC) to UWB signaling. Based on the developed model, accurate analytical expressions are derived for the average received powers of two common types of impulse radio UWB (IR-UWB) signaling waveforms. Numerical simulations on the system-level show excellent agreement with the obtained analytical expressions. Moreover, the DC power levels expected from spectrally constrained IR-UWB waveforms are extremely low (less than 0.3 microwatt) and, accordingly, provide useful guidelines for the design and development of ULP electronics applications in the sub-microwatt range. Received Jul 19, 2020 Revised Sep 9, 2020 Accepted Oct 1, 2020 Keywords: Energy harvesting Impulse radio Low-power electronics Ultrawide band This is an open access article under the CC BY-SA license. Corresponding Author: Nasr Rashid Department of Electrical Engineering College of Engineering, Jouf University Sakaka, Saudi Arabia Email: 1. INTRODUCTION The interests in energy harvesting (EH) techniques have increased to enable wirelessly chargeable and self-powered electronic devices such as the internet of things (IoT) modules, radio frequency (RF) identification (RFID) tags and wireless sensor networks (WSN) [1]. Numerous efforts have been reported to demonstrate the feasibility of RF energy as a promising resource for EH applications, either on the system level (e.g., [2]), the device level (e.g., [3]), and/or the materials (e.g., [4]) of which these devices are fabricated. Most often, the harvested RF energy is collected either from single tone [5] or multi-tone communication signals [1], located at discrete parts of the spectrum. Since the emission frequencies of RF wireless communication systems are distributed over a sufficiently wide spectrum, the corresponding EH systems are expected to cover high bandwidths to collect the maximum possible RF energy [6]. Moreover, the frequencies of the RF signals incident to the input of an energy harvester are usually not predictable. Motivated by these technical requirements, there has been increasing interests in the design and development of ultra-wide band (UWB) devices/systems for EH. In [6], for instance, two rectifier designs have been reported and fabricated to operate from 0.6 to 3 GHz. In [7], two rectifier designs for UWB EH have been presented. The designed rectifiers focus on EH in the frequency bands from 470 to 860 MHz, and between 250 MHz and 3 GHz. More examples for the design of UWB energy harvesters are reported in [8, 9], where printed UWB microstrip antenna, based organic substrates, for RF EH applications from 2.4 GHz, up to more Journal homepage: http://ijece.iaescore.com Int J Elec & Comp Eng ISSN: 2088-8708  1159 than 10 GHz. Such designs are very favorable for EH from different signals occupying different frequency bands of the spectrum, including UWB signals. From the afore-mentioned overview, it is clear that, the majority of the studies reported on the design and development of wide/narrow band energy harvesting rectennas have competed to demonstrate their individual capabilities in terms of the RF-to-DC conversion efficiency. However, according to [10], the RF-to-DC conversion efficiency of a rectenna is, in general, not only a function of the rectenna design, but also of its input waveform. Therefore, in another category of studies reported on RF EH, the signaling waveforms carrying this RF energy have been considered. For different RF waveforms having the same power level, the harvested DC power levels are strongly dependent on the particular RF signaling waveform and some of its time domain characteristics such as the highly desirable peak-to-average-power-ratio (PAPR) [11]. Fortunately, the interests in developing broad band energy harvesters to collect RF energy from high PAPR signals perfectly matches the temporal as well as the spectral characteristics of impulse radio-UWB (IR-UWB) waveforms. Despite the severe spectral constraints imposed by the Federal Communications Commission (FCC) to their spectra (less than -41.3 dBm/MHz), IR-UWB signals are allowed to occupy a bandwidth as large as 7.5 GHz (i.e., 3.1 GHz - 10.6 GHz) [12], commonly called the useful UWB band. Moreover, in IR-UWB signaling, the energies of IR-UWB signals are emitted in the form of transient bursts of very short duration (typically, ns or ps) and large voltage amplitudes (compared to the DC levels of IRUWB waveforms). Meanwhile, due to the poor radiation efficiency of UWB antennas at low frequencies (below 1 GHz), the radiated IR-UWB signals often possess DC-null components [13]. This results in IRUWB signals with high PAPR levels. To the best of the authors' knowledge, no study has yet been reported to assess the maximum DC power levels that can be extracted from these signals. In this paper, a systemlevel abstraction approach is adopted to evaluate the maximum DC power levels expected from IR-UWB signals under the FCC spectral constraints, regardless of the specific realization of the EH circuit/system. Under this assumption, the calculated DC power levels are guaranteed to be the maximum achievable levels, regardless of the detailed architecture of the EH circuit and/or its RF-to-DC conversion efficiency. The rest of this paper is organized as follows. A UWB communications/EH chain is described and is modeled in Section 2, considering typical IR-UWB signaling waveforms. In section 3, analytical expressions for the average DC powers harvested from the considered waveform types are developed. The developed expressions are then numerically evaluated and are analyzed in section 4. Based on the obtained results, the whole work provided in this paper is finally concluded in section 5. 2. UWB SIGNALLING/ENERGY HARVESTING MODEL Figure 1 illustrates the block diagram of a typical IR-UWB signaling/EH chain, inspired from the models provided in [4]. Generally, it consists of an IR-UWB transmitter and an UWB energy harvester at the receiver side, each equipped with a broadband UWB antenna. At the transmitter side, an information source emits a stream of M−ary encoded symbols. Moreover, it is assu (...truncated)