Wireless charging is a technology of transmitting power through an air gap to electrical devices for the purpose of energy replenishment. The recent progress in wireless charging techniques and development of commercial products have provided a promising alternative way to address the energy bottleneck of conventionally portable battery-powered devices. However, the incorporation of wireless charging into the existing wireless communication systems also brings along a series of challenging issues with regard to implementation, scheduling, and power management. In this paper, we present a comprehensive overview of wireless charging techniques, the developments in technical standards, and their recent advances in network applications. In particular, with regard to network applications, we review the static charger scheduling strategies, mobile charger dispatch strategies and wireless charger deployment strategies. Additionally, we discuss open issues and challenges in implementing wireless charging technologies. Finally, we envision some practical future network applications of wireless charging.

Wireless Charging Technologies: Fundamentals, Standards, and Network Applications

This paper reviews the development of energy harvesting for low-power embedded structural health monitoring (SHM) sensing systems. A statistical pattern recognition paradigm for SHM is first presented and the concept of energy harvesting for embedded sensing systems is addressed with respect to the data acquisition portion of this paradigm. Next, various existing and emerging sensing modalities used for SHM and their respective power requirements are summarized followed by a discussion of SHM sensor network paradigms, power requirements for these networks, and power optimization strategies. Various approaches to energy harvesting and energy storage are discussed and limitations associated with the current technology are addressed. The paper concludes by defining some future research directions that are aimed at transitioning the concept of energy harvesting for embedded SHM sensing systems from laboratory research to field-deployed engineering prototypes. Finally, it is noted that many of the technologies discussed herein are applicable to powering any type of low-power embedded sensing system regardless of the application.

/pdf/energy-harvesting-for-structural-health-monitoring-sensor-40xb7fid8o.pdf

Energy Harvesting for Structural Health Monitoring Sensor Networks

Efficient nonlinear optical interactions are essential for many applications in modern photonics. However, they typically require intense laser sources and long interaction lengths, requirements that often render nonlinear optics incompatible with new nanophotonic architectures in integrated optics and metasurface devices. Obtaining materials with stronger nonlinear properties is a crucial step towards applications that require lower powers and smaller footprints. Recently, a new class of materials with a vanishing permittivity, known as epsilon-near-zero (ENZ) materials, has been reported to exhibit unprecedented ultrafast nonlinear efficiencies within sub-wavelength propagation lengths. In this Review, we survey the work that has been performed on ENZ materials and the related near-zero-index materials, focusing on the observation of various nonlinear phenomena (such as intensity-dependent refraction, four-wave mixing and harmonic generation), the identification of unique field-enhancement mechanisms and the study of non-equilibrium dynamics. Degenerately doped semiconductors (such as tin-doped indium oxide and aluminium-doped zinc oxide) are particularly promising candidates for ENZ-enhanced nonlinear optical applications. We conclude by pointing towards possible future research directions, such as the search for ENZ materials with low optical losses and the elucidation of the mechanisms underlying nonlinear enhancements. Materials with vanishingly small dielectric permittivity, known as epsilon-near-zero materials, enable strong ultrafast optical nonlinear responses within a sub-wavelength propagation length. This Review surveys the various observations of nonlinear phenomena in this class of materials.

Nonlinear optical effects in epsilon-near-zero media

A system for wireless power transmission may include one or more charging panels and one or more powered devices. The charging panel may include a pilot analysis circuitry, processor and power transmitter. The pilot analysis circuitry may be configured to analyze the magnitude and phase of a pilot signal from the powered device, based on which the processor may be configured to determine a complex conjugate of the pilot signal. And the power transmitter may be configured to cause radiation of a focused wireless power beam to the powered device in accordance with the complex conjugate of the pilot signal and via one or more antenna elements. The charging panel may be one of a plurality of spatially-distributed charging panels each of which includes respective antenna elements that may form an array of antenna elements configured to collaboratively radiate wireless power as a distributed, retro-reflective beamformer.

Wireless Power Transmission

Transparent conducting oxides have recently gained great attention as CMOS-compatible materials for applications in nanophotonics due to their low optical loss, metal-like behavior, versatile/tailorable optical properties, and established fabrication procedures. In particular, aluminum-doped zinc oxide (AZO) is very attractive because its dielectric permittivity can be engineered over a broad range in the near-IR and IR. However, despite all these beneficial features, the slow (>100  ps) electron-hole recombination time typical of these compounds still represents a fundamental limitation impeding ultrafast optical modulation. Here we report the first epsilon-near-zero AZO thin films that simultaneously exhibit ultrafast carrier dynamics (excitation and recombination time below 1 ps) and an outstanding reflectance modulation up to 40% for very low pump fluence levels (<4  mJ/cm2) at a telecom wavelength of 1.3 μm. The unique properties of the demonstrated AZO thin films are the result of a low-temperature fabrication procedure promoting deep-level defects within the film and an ultrahigh carrier concentration.

Epsilon-near-zero Al-doped ZnO for ultrafast switching at telecom wavelengths

Extreme tunability in aluminum doped Zinc Oxide plasmonic materials for near-infrared applications

https://patrickehopkins.files.wordpress.com/2011/02/pradhan2014aa.pdf

A transpiration cooling experiment using an optical heating method that provided a heat flux as high as 234 W/cm 2 on the surface of specimen for a scramjet engine was performed. In this experiment, 19-mm-diam sintered, powdered, stainless-steel tubes and a 25-mm square cross-sectional tube of perforated Inconel tube were used to investigate transpiration cooling effectiveness. The cooling effectiveness by transpiration for each specimen was measured and analyzed. As a result, the transpiration cooling mechanism appeared to be a promising approach to remove a large amount of heat from the engine wall. A preliminary analysis of the transpiration cooling mechanism and a scaling conversion study that translates the results from helium tests into the case when a hydrogen medium is used are included.

Transpiration Cooling Experiment for Scramjet Engine Combustion Chamber by High Heat Fluxes

The concept of microwave-driven smart material actuators was envisioned and developed as the best option to alleviate the complexity and weight associated with a hard-wire-networked power and control system for smart actuator arrays. The patch rectenna array was initially designed for high current output, but has undergone further development for high voltage output devices used in shape control applications. Test results show that more than 200 V of output were obtained from a 6 × 6 array at a far-field exposure (1.8 m away) with an X-band input power of 18 W. The 6 × 6 array patch rectenna was designed to theoretically generate voltages up to 540 V, but practically it has generated voltages in the range between 200 and 300 V. Testing was also performed with a thin layer composite unimorph ferroelectric driver and sensor and electro-active paper as smart actuators attached to the 6 × 6 array. Flexible dipole rectenna arrays built on thin-film-based flexible membranes are most applicable for NASA's various missions, such as microwave-driven shape controls for aircraft morphing and large, ultra-lightweight space structures. An array of dipole rectennas was designed for high voltage output by densely populating Schottky barrier diodes to drive piezoelectric or electrostrictive actuators. The dipole rectenna array will eventually be integrated with a power allocation and distribution logic circuit and microbatteries for storage of excessive power. The roadmap for the development of wireless power drivers based on the rectenna array for shape control requires the development of new membrane materials with proper dielectric constants that are suitable for dipole rectenna arrays.

Microwave power for smart material actuators

The concept of power transmission by a microwave is envisioned as the best option for alleviating the complexity associated with hard-wired control circuitry in controlling smart actuators and robots such as micro-aerial vehicles, biomimetic robots and space vehicles to produce remotely maneuverable capability. A flexible dipole rectenna array is conformably adaptable on the complex structure of vehicles used for practical applications of wireless power. For these applications, various flexible dipole rectennas and arrays were designed, fabricated and characterized over a frequency range of 9–12 GHz with 20 W and 200 W amplifiers through laboratory testing. The irradiance of the microwave power was measured. Also the irradiated power, the output power and the efficiency of the rectenna arrays were evaluated along with the microwave power and frequency. The maximum voltage of 65 VDC was observed from a series connected dipole rectenna array and the maximum current of 2.50 mA was obtained from a parallel connected rectenna array. The efficiency of dipole rectenna arrays ranges from 20% to 50% depending on the input power and the pole configuration. It was also demonstrated that the voltage, current and power output from a dipole rectenna array can be tailored by configuring the dipole rectenna elements in serial and parallel mode connections.

https://iopscience.iop.org/article/10.1088/0964-1726/15/3/017/pdf

Performance characterization of flexible dipole rectennas for smart actuator use

In exploiting the unique capabilities of smart actuators for applications in vehicle systems, even in unmanned or micro aerial vehicles, the power issues for smart actuators and devices have not been well addressed. This is due to the fact that the driving power for smart materials has not reached the level of the power specifications for conventional devices and systems. To answer the power issue, we have developed a wireless power transmission technology using a flexible rectenna system and implemented it for a microwave-powered aerial vehicle (MPAV) system. For this application, two flexible dipole rectennas were designed, manufactured and characterized over a frequency range of 9–12 GHz. These flexible dipole rectennas were attached and tested on the complex structure of small MPAVs. The maximum converted power output of a flexible dipole rectenna array was about 300 mA at 80 VDC. The power output from this rectenna was sufficient to run the propellers of the MPAV. Each electrically driven propeller requires approximately 2 W for operation.

https://iopscience.iop.org/article/10.1088/0964-1726/15/5/012/pdf

Kyo D. Song

Papers

Extreme tunability in aluminum doped Zinc Oxide plasmonic materials for near-infrared applications

Transpiration Cooling Experiment for Scramjet Engine Combustion Chamber by High Heat Fluxes

Microwave power for smart material actuators

Performance characterization of flexible dipole rectennas for smart actuator use

Microwave power transmission using a flexible rectenna for microwave-powered aerial vehicles