Terahertz and Millimetric Rectennas

In recent years, the energy market has witnessed increasing demand on green electromagnetic energy resources to meet the next generation devices requirements. While energy harvesting in the lower gigahertz band has witnessed many improvements leading to market-ready solutions, the terahertz harvesting is, still, in an immature state. As will be demonstrated later, the electromagnetic radiation frequency identifies the theory of operation and so the rectifiers are categorised, into lower and upper frequency bands. While the theoretical framework for the lower frequency rectifiers is more "uniform", there are many theories to explain the rectifier operation for upper frequency bands. For the latter case, Simmons and the transfer matrix method models are chosen and elaborated in more details. An optimisation framework that deploys the transfer matrix method to calculate the voltage-current relationship of a tunnelling diode and improve the relevant figures of merit will be also suggested. New and novel techniques leading to optimized wireless energy transmission will be elaborated. In this context, the time-modulated array technique will be considered and studied, for a range of frequencies extending to 28 GHz, as a possible substitution to the lossy linear phased array control circuits. The novel frequency-diverse array technique, leading to distance-dependent radiation pattern behaviour, will be also discovered. A market-ready solution for an efficient 2.4 GHz energy-harvesting device is presented and tailored to work in harsh electromagnetic environments. Starting from a simple and generic rectifier model, the design is upgraded to reach an end-product prototype together with its measurements in a real-world scenario. In the end, an efficient and fast simulation method capable to calculate the received power by wireless sensors is also presented. Thanks to the integral solver simulation, the results are more accurate than typical finite difference simulation and are obtained much faster as demonstrated in the corresponding chapter

RF Systems Design for Simultaneous Wireless Information and Power Transfer (SWIPT) in Automation and Transportation

This work presents some recent solutions that exploit the wireless power transfer (WPT) technology for energizing moving vehicles and machinery tools. Such technology is currently experiencing unprecedented interests in non-traditional RF/microwave sectors fields, such the industrial automation and the railway transportation safety. Near-field electromagnetic coupling solutions are presented showing that, in order to obtain efficient performances for broad ranges of operating conditions, the nonlinear electromagnetic co-design of the entire WPT system, from the energy source to the receiver load, needs to be carried out. This technology can be combined with wireless data transfer, thus realizing integrated systems able to simultaneously control the energy transfer and the transmission of data. The adopted operating frequencies are in the MHz range, which is only recently considered for this kind of applications. In particular this work focuses on three different systems: the first one demonstrates the constant powering of “on the move” industrial charts at 6.78 MHz, regardless of the relative position of the transmitter and the receiver sub-systems; the second one presents a novel design of a balise transportation system adopting a high efficiency GaN-based transmitter designed to keep its performance over a wide range of loading conditions; the last one consists of the simultaneous wireless power and data transfer, to a rotating machinery tool, automatically controlled by the powering system based on the coexistence of frequency-diverse inductive and capacitive couplings

Harvesting electromagnetic energy in the V-band using a rectenna formed by a bow tie integrated with a 6-nm-thick Au/HfO2/Pt metal-insulator-metal diode

In this paper, the first demonstration of a bow-tie antenna integrated with a metal-insulator-metal (MIM) diode for electromagnetic energy harvesting in the V-band (i.e., 40-75 GHz) is presented. We have designed, simulated, fabricated, and fully characterized a 60-GHz rectifying antenna (rectenna) based on a vertical Au-HfO2-PtMIM diode with reduced differential resistance. The dielectric used for the MIM structure is a 6-nm-thick amorphous HfO2 grown by atomic layer deposition. For the fabricated MIM device, we report here a current density of 3 x 10(4) A/cm(2) that exceeds the previous values presented in the literature. The vertical MIM-based rectenna is able to efficiently harvest up to 250 mu V from an impinging modulated millimeter-wave signal with -20 dBm of available power, thus offering a voltage responsivity of over 5 V/W. The reported results indicate that the proposed approach is well suited for future low-power solutions much sought after for the energetically autonomous 5G terminal equipment

THz rectennas and their design rules

The increasing demand for more efficient energy harvesting solutions has urged research for better harvesting solutions than the presently-available ones. While p-n junction solar cells have become commercially widespread, they are expensive and suffer from poor efficiency figures hardly reaching 20%. Other radiation-electricity converters such as rectennas have a theoretical limit in excess of 80%. However, no efficient rectenna solution for the terahertz frequency band has been commercialized or presented in the academic literature. In fact, there are many obstructions to an efficient solution. The aim of this paper is to address the key points towards an efficient and commercially-available solution by briefly reviewing the relevant literature and so identifying five factors that should be addressed in order to reach an efficient solution

Wireless Power Transfer Using Smart Antenna Techniques

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TIME-BASED ARRAYS FOR PRECISE TAGS LOCALIZATION

The paper describes a time-modulated compact antenna array suitable for future 5G IoT applications. Each antenna is selectively activated in order to localize tagged objects, randomly distributed in harsh electromagnetic environments, in almost real-time. The system positively exploits a well-known property of the time-modulation technique: the simultaneous radiation at both the carrier frequency and the sideband harmonics created by the superposition of the nonlinear switches driving (or modulation) frequency. Despite their architectural simplicity, these arrays are potential candidate for modern wireless applications because of their ease of reconfiguration. This paper shows some results of a two-element array for localization purposes

Optimization of a 27 MHz Wireless Power Transmitter for Unknown Receiver

This work describes the design of a WPT transmitter connected to a planar coil, designed by EM simulation, for the near-field wireless power transfer (WPT) of 25 W at 27 MHz to an almost unknown receiving section. A class-E inverter in GaN technology has been adopted to achieve constant current condition and high performance for its load-independent operation. A careful control of the overall efficiency of the WPT systems is provided during the different steps of the optimization process. The manuscript highlights the importance of the realistic description of both the amplifier and the loop for the sake of the project reliability

RF energy on-demand for automotive applications

This work proposes the design of a Wireless Power Transfer (WPT) system in the 2.4 GHz band, suitable for remotely energizing low-power wireless sensors located in highly complex environments from the electromagnetic propagation point of view. This is the case of many industrial scenarios such as industrial machineries or automotive engines, to enable remote monitoring, predictive maintenance and components diagnosis. A co-designing method was used to obtain a system of independent RF sources embedded in the complex environment, with the aim of being at the same time miniaturized for easy integration into the environment, and of having the ability for providing energy wirelessly in a pervasive way. The validation of the project shows that even wireless sensors located in critical and NLOS (Non-line-of-sight) positions, placed in key points of the engine compartment and in contact with parts that need to be monitored, can be successfully energized by the proposed approach. This enables battery-less sensors to be powered and to simultaneously communicate with a gateway in order to monitor vital engine parameters. A communication among the gateway and a number of battery-less sensor nodes is demonstrated exploiting low-power LoRa (Long Range) nodes working in the same frequency band of the RF powering system

Efficient Simulation Method for Wireless Power Transfer

With the development of the internet of things, it becomes necessary to wirelessly power distributed sensors. However, it is not straightforward to accurately estimate the available wireless power at certain points in a specific propagation scenario using traditional methods. This is due to the compro- mised accuracy for large problems and the long time required to run their simulation. In this paper, we present a novel model to accurately calculate the received power by distributed RF sensors using the wave integral equation solver and a developed calculation method using reciprocity theorem. The model is tested in a prototype to simulate a propagation scenario in harsh electromagnetic environments with a reverberation-like behaviour. The propagation scenario consists of a transmitter placed ahead of the prototype aperture and a receiver is moved inside the prototype and the obtained results are compared from both simulation and measurement to rigorously investigate their accuracy and model performance. Based on comparison with measurements and benchmarking with the time domain results, the proposed model is superior for both time and accuracy as it is 20 times faster and gives closer results to measurements than its time domain counterpart