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The extensive use of metamaterials and metamaterial absorbers increases the demand for compact structures in various frequencies. Designing electrically small absorbers for lower frequencies, especially sub-gigahertz applications, is one of the open issues in this field. In this paper, a space filling curve is used to design an absorber operating on low frequencies. The unit cell design is based on a Sierpinski curve with the size of $$25\times 25\times 1.6\,{\text {mm}}^3$$ and air-gap of 10 mm. The structure shows 99.9% absorption at 900 MHz on the third step. The system also shows multiple resonances due to its structure. The proposed structure is fabricated and tested and shows a good agreement with simulation results.

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This paper develops a data-driven strategy for identification and voltage control for DC-DC power converters. The proposed strategy does not require a pre-defined standard model of the power converters and only relies on power converter measurement data, including sampled output voltage and the duty ratio to identify a valid dynamic model for them over their operating regime. To derive the power converter model from the measurements, a local model network (LMN) is used, which is able to describe converter dynamics through some locally active linear sub-models, individually responsible for representing a particular operating regime of the power converters. Later, a local linear controller is established considering the identified LMN to generate the control signal (i.e., duty ratio) for the power converters. Simulation results for a stand-alone boost converter as well as a bidirectional converter in a test DC microgrid demonstrate merit and satisfactory performance of the proposed data-driven identification and control strategy. Moreover, comparisons to a conventional proportional-integral (PI) controllers demonstrate the merits of the proposed approach.

© 2019 IEEE. This paper presents a new Multi-hop Device-to-Device (MD2D) routing protocol, referred to as SMDRP (SDN-based Multi-hop D2D Routing Protocol), for SDN-based wireless networks. Our proposed protocol can be considered as a semi-distributed routing protocol, where an SDN controller manages and controls part of the overall MD2D routing functionality to increase scalability while enabling network operators to control and maintain the out-of-band packet forwarding network. This paper also extends prior work on the Hybrid SDN Architecture for Wireless Distributed Networks (HSAW) [1] and is adapted to the framework presented in this paper. In HSAW, since all link state information is flooded by the controller to the nodes, the network will experience scalability problem. In our approach, this problem is overcome by only passing the next hop for each active route to the mobile nodes. To investigate this, we performed a theoretical and simulation studies comparing HSAW with SMDRP. From our result, it can be seen that for larger density populated networks, SMDRP shows better scalability than HSAW. In addition, mobile nodes need less memory and energy for their communications.

© 2004-2012 IEEE. Device-to-device (D2D) communications are set to form an integral part of future 5G wireless networks. D2D communications have a number of benefits such as improving energy efficiency and spectrum utilization. Until now much of the D2D research in LTE and 5G-type network scenarios have focused on direct (one-hop) communications between two adjacent mobile devices. In this paper, we propose a new routing framework called virtual ad hoc routing protocol (VARP). This framework introduces significant advantages such as better security, lower routing overheads, and higher scalability, when compared to conventional ad hoc routing protocols. It also reduces traffic overhead in LTE networks using multi-hop D2D communications under management of a software defined networking (SDN)-controller. Further, it enables the development of various types of routing protocols for different networking scenarios. To this end, a source-routing based protocol was developed on top of VARP, referred to as VARP-S. We present a detailed analytical study of routing overhead in the VARP-S protocol, as compared to overhead analysis of our previous proposed hybrid SDN architecture for wireless distributed networks (HSAW) Our results show that VARP-S, compared to HSAW, achieves higher network scalability and lower power consumption for mobile nodes.

© 2018 IEEE. The effect of multitone excitation on the dc response of a voltage-doubler radio frequency energy harvester is analyzed. Theoretical analysis as well as frequency and time domain (TD) simulations were conducted to clarify the findings. Measurements were also carried out to validate the results. The measured, simulations and theoretical results are in good agreement. This paper focuses on evaluating the performance of a voltage doubler rectifier under multitone excitation (input power is the same in the single-tone and multitone case). Based on TD and harmonic balance simulations, theoretical and measurement analyses, it is evident that the application of multiple tones simultaneously within the matched frequency band and with the same average available power results in a lower average output dc power when compared with the single-tone case with the same input power. This trend is evident over a broad low input power range of −50 to −10 dBm (0.01–100 µW). ispartof: IEEE INTERNET OF THINGS JOURNAL vol:5 issue:4 pages:2804-2816 status: published

© 2017 University of Western Australia. Wireless Sensor Networks (WSNs) are the key part of Internet of Things, as they provide the physical interface between on-field information and backbone analytic engines. An important role of WSNs-when collecting vital information-is to provide a consistent and reliable coverage. To Achieve this, WSNs must implement a highly reliable and efficient coverage recovery algorithm. In this paper, we take a fresh new approach to coverage recovery based on evolutionary algorithms. We propose EMACB-SA, which introduces a new evolutionary algorithm that selects coverage sets using a fitness function that balances energy efficiency and redundancy. The proposed algorithm improves network's coverage and lifetime in areas with heterogeneous event rate in comparison to previous works and hence, it is suitable for using in disaster management.

© 2015 EuMA. Due to the abundance of ambient RF (Radio Frequency) energy, considerable research effort has been invested in RF energy scavenging. In this paper, we propose a rectifier which can be embedded into the building materials to provide a sustainable energy source in urban environments. The power will be available through DC sockets with different voltage settings. A highly sensitive and efficient rectifier operating at the FM frequency band is proposed which exhibits favorable impedance matching over a broad low input power range of-50 to-20 dBm (0.01 to 10 μW). Measurement results of input reflection coefficient and rectified output power are provided. An output DC power of around 11 μW is achieved from concurrently rectifying six tones of-20 dBm, providing a viable perpetual energy source for low power applications.

Due to the growing implications of energy costs and carbon footprints, the need to adopt inexpensive, green energy harvesting strategies are of paramount importance for the long-term conservation of the environment and the global economy. To address this, the feasibility of harvesting low power density ambient RF energy simultaneously from multiple sources is examined. A high efficiency multi-resonant rectifier is proposed, which operates at two frequency bands (478–496 and 852–869 MHz) and exhibits favorable impedance matching over a broad input power range (−40 to −10 dBm). Simulation and experimental results of input reflection coefficient and rectified output power are in excellent agreement, demonstrating the usefulness of this innovative low-power rectification technique. Measurement results indicate an effective efficiency of 54.3% and an output DC voltage of 772.8 mV is achieved for a multi-tone input power of −10 dBm. Furthermore, the measured output DC power from harvesting RF energy from multiple services concurrently exhibits a 3.14 and 7.24 fold increase over single frequency rectification at 490 and 860 MHz respectively. Therefore, the proposed multi-service highly sensitive rectifier is a promising technique for providing a sustainable energy source for low power applications in urban environments.

© 2014 European Microwave Association. RF (Radio Frequency) energy harvesting is a promising technique to provide a sustainable energy source for the long-term conservation of the environment and the global economy. To address this, we proposed an efficient rectifier over a wide low input RF power range (-40 to -10 dBm) for broadcasting band (520- 590 MHz) to determine the usefulness of exploiting freely available RF energy sources in this band. The input reflection coefficient and rectified output power demonstrate the practical feasibility of this low-power rectification technique. Power conversion efficiency (PCE) of 53% and 1.5% are achieved for a single-tone input power of -10 dBm and -40 dBm respectively. Therefore, this innovative technique has the potential to generate a viable perpetual energy source for low power applications in urban environments.

The investigations of an end-launcher transition in Carbon Fibre Reinforced Plastic (CFRP) WR90 waveguides is presented. The applicability of the feed for CFRP slotted waveguide antenna is addressed. Some of the aspects pertaining to the efficiency of CFRP slotted waveguide antenna and its use for radar applications are discussed. The results are presented in comparison with those obtained from the same concepts implemented in aluminium waveguides. A recently implemented anisotropic model for CFRP laminates, which describes the electrical anisotropy of the composite material, was used. The data obtained provide promising indicators for the potential use of slotted waveguide antennas made of CFRP for radar applications. © 2013 IEEE.

RF energy harvesting is attracting widespread interest to meet the goal of providing sustainable energy sources for future growth and protection of the environment. In order to demonstrate the feasibility of RF energy harvesting, RF field investigations and analysis of maximum available power in the suburbs of Melbourne, Australia are conducted. Measurement results and analysis indicate that broadcasting system at 540 MHz (with 20 MHz bandwidth) and 100 MHz (88-108 MHz) are great scavenging sources. These frequency ranges provide stable RF signal levels and low propagation loss, produce maximum available power to a range of locations. In addition, broadcasting bands offer a great deal of flexibility to deploy simple and cost-effective implementations, which is of paramount importance for optimal power harvesting systems. © 2012 EUROPEAN MICROWAVE ASSOC.