The idea of wireless power transfer (WPT) has been around since the inception of electricity. In the late 19th century, Nikola Tesla described the freedom to transfer energy between two points without the need for a physical connection to a power source as an ?all-surpassing importance to man? [1]. A truly wireless device, capable of being remotely powered, not only allows the obvious freedom of movement but also enables devices to be more compact by removing the necessity of a large battery. Applications could leverage this reduction in size and weight to increase the feasibility of concepts such as paper-thin, flexible displays [2], contact-lens-based augmented reality [3], and smart dust [4], among traditional point-to-point power transfer applications. While several methods of wireless power have been introduced since Tesla?s work, including near-field magnetic resonance and inductive coupling, laser-based optical power transmission, and far-field RF/microwave energy transmission, only RF/microwave and laser-based systems are truly long-range methods. While optical power transmission certainly has merit, its mechanisms are outside of the scope of this article and will not be discussed.

Harvesting Wireless Power: Survey of Energy-Harvester Conversion Efficiency in Far-Field, Wireless Power Transfer Systems

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Rfid Handbook Fundamentals And Applications In Contactless Smart Cards And Identification

Radio waves carry both energy and information simultaneously. Nevertheless, radio-frequency (RF) transmissions of these quantities have traditionally been treated separately. Currently, the community is experiencing a paradigm shift in wireless network design, namely, unifying wireless transmission of information and power so as to make the best use of the RF spectrum and radiation as well as the network infrastructure for the dual purpose of communicating and energizing. In this paper, we review and discuss recent progress in laying the foundations of the envisioned dual purpose networks by establishing a signal theory and design for wireless information and power transmission (WIPT) and identifying the fundamental tradeoff between conveying information and power wirelessly. We start with an overview of WIPT challenges and technologies, namely, simultaneous WIPT (SWIPT), wirelessly powered communication networks (WPCNs), and wirelessly powered backscatter communication (WPBC). We then characterize energy harvesters and show how WIPT signal and system designs crucially revolve around the underlying energy harvester model. To that end, we highlight three different energy harvester models, namely, one linear model and two nonlinear models, and show how WIPT designs differ for each of them in single-user and multi-user deployments. Topics discussed include rate-energy region characterization, transmitter and receiver architectures, waveform design, modulation, beamforming and input distribution optimizations, resource allocation, and RF spectrum use. We discuss and check the validity of the different energy harvester models and the resulting signal theory and design based on circuit simulations, prototyping, and experimentation. We also point out numerous directions that are promising for future research.

Fundamentals of Wireless Information and Power Transfer: From RF Energy Harvester Models to Signal and System Designs

In this paper, various ambient energy-harvesting technologies (solar, thermal, wireless, and piezoelectric) are reviewed in detail and their applicability in the development of self-sustaining wireless platforms is discussed. Specifically, far-field low-power-density energy-harvesting technology is thoroughly investigated and a benchmarking prototype of an embedded microcontroller-enabled sensor platform has been successfully powered by an ambient ultrahigh-frequency (UHF) digital TV signal (512-566 MHz) where a broadcasting antenna is 6.3 km away from the proposed wireless energy-harvesting device. A high-efficiency dual-band ambient energy harvester at 915 MHz and 2.45 GHz and an energy harvester for on-body application at 460 MHz are also presented to verify the capabilities of ambient UHF/RF energy harvesting as an enabling technology for Internet of Things and smart skins applications.

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Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless Sensor Platforms

In this paper, various ambient energy-harvesting technologies (solar, thermal, wireless, and piezoelectric) are reviewed in detail and their applicability in the development of self-sustaining wireless platforms is discussed. Specifically, far- field low-power-density energy-harvesting technology is thor- oughly investigated and a benchmarking prototype of an embedded microcontroller-enabled sensor platform has been successfully powered by an ambient ultrahigh-frequency (UHF) digital TV signal (512-566 MHz) where a broadcasting antenna is 6.3 km away from the proposed wireless energy-harvesting device. A high-efficiency dual-band ambient energy harvester at 915 MHz and 2.45 GHz and an energy harvester for on-body application at 460 MHz are also presented to verify the capa- bilities of ambient UHF/RF energy harvesting as an enabling technology for Internet of Things and smart skins applications.

Ambient RF Energy-Harvesting Technologies for Self-Sustainable Standalone Wireless Sensor Platforms This paper presents various ambient energy-harvesting technologies and investigates their applicability in the development of self-sustaining wireless platforms.

Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe.

Wireless Power Transmission: R&D Activities Within Europe

In this article, the different challenges and open issues regarding WPT systems have been presented considering both the transmitting and receiving ends. The challenges in the receiving side include the accurate modeling of the rectifying elements, the adequate selection of the rectifier topology, and the joint optimization of antenna and rectifier circuit. The challenges in the transmitting side are mainly in the improvement of the dc-to-RF conversion efficiency and in the selection of the optimum transmitted signal waveform. The final goal of most of these challenges is to take advantage of the nonlinear nature of the rectifying elements in order to maximize the RF-to-dc conversion efficiency in the receiving end of WPT systems.

Optimum behavior: Wireless power transmission system design through behavioral models and efficient synthesis techniques

Summary form only given, as follows. This paper presents an approach to signal excitation specially designed to improve the DC power obtained in a RF to DC converter and consequently its RF-DC efficiency conversion. In this sense, a multi-sine signal is used as the excitation, and it is proved either theoretically, by simulations and by measurements, that a multi-sine signal with 0° phase relationship between the tones present better DC values in energy harvesters, when compared with a single tone excitation with the same input power

Maximizing DC power in energy harvesting circuits using multi-sine excitation

Traditionally, wireless power is delivered through single-carrier, continuous-wave (CW) signals. Most research efforts to enhance the efficiency of wireless power transfer systems have been confined to the circuit-level design. However, in recent years, attention has been paid to the waveform design for wireless power transmission. It has been found that signals featuring a high peak-to-average power ratio (PAPR) can provide efficiency improvement when compared with CW signals. A number of approaches have been proposed, such as multisines/multicarrier orthogonal frequency division multiplex (OFDM) signals, chaotic signals, harmonicsignals, ultrawideband (UWB) signals, intermittent CW (ICW) signals, or white-noise signals. This article reviews these techniques with a focus on multisines/multicarrier signals, harmonic signals, and chaotic signals. A theoretical explanation for efficiency improvement is provided and accompanied by experimental results. Circuit design considerations are presented for the receiver side, and efficient transmission architectures are also described with an emphasis on spatial power combining.

Boosting the Efficiency: Unconventional Waveform Design for Efficient Wireless Power Transfer

Fully passive wireless networks are a key-enabling technologies for the internet of things. Backscatter radios are a hypothesis to design these passive wireless networks. Backscatter modulation allows a remote device to wirelessly transfer information without requiring a traditional transceiver. Instead, a backscatter device leverages a carrier transmitted by an access point or base station. Nevertheless, the traditional approach is to use amplitude shift keying or phase shift keying backscatter solutions which limits the data rate of the sensors, since it transfers only one bit per symbol period. We propose a novel modulator, which employs a Wilkinson power divider with a phase shift in one of the design branch and two transistors acting as switches in order to generate M-quadrature amplitude modulation backscatter modulation. The design strategy for high level order backscatter modulations will be explained and a design approach will be presented in this manuscript.

Alirio Boaventura

Papers

Wireless Power Transmission: R&D Activities Within Europe

Optimum behavior: Wireless power transmission system design through behavioral models and efficient synthesis techniques

Maximizing DC power in energy harvesting circuits using multi-sine excitation

Boosting the Efficiency: Unconventional Waveform Design for Efficient Wireless Power Transfer

Quadrature Amplitude Backscatter Modulator for Passive Wireless Sensors in IoT Applications