Focusing RF-on demand by logarithmic frequency-diverse arrays

The radiating systems exploiting the frequency diversity of the antennas are powerful architectures, that can have a big impact on wireless power transmission applications, but their characterization is merely theoretical. This paper offers a deep and critical numerical analysis of frequency- diverse arrays and shows the advantages of the family with logarithmic distribution of the frequency for radio-frequency energy focusing goals. For the first time, these systems are analyzed through a Harmonic Balance-based simulation combined with the full-wave description of the array made of eight planar monopoles: the rigorous results confirm the potentialities of these complex radiating systems, in particular show how the time-dependency of the radiating mechanism can be favorably deployed

Smart beamforming for energy-aware wireless power transmission

In wireless power transfer (WPT) applications the weakest contribution to the overall link efficiency is the effective selection of the zone to be powered. Hence, the need for smart transmitting architectures is strong. In this contribution, two promising families of highly-reconfigurable arrays are presented: first, time-modulated arrays are considered as a powerful tool for selective WPT, through the exploitation of the sideband radiation phenomenon; frequency-diverse arrays are, then, proposed for a smarter radiation, able to focus the beam in range, too. In both these cases, the accurate nonlinear/electromagnetic analysis approach, relying on the Harmonic Balance technique, demonstrates its effectiveness

Energy focusing through layout-based frequency-diverse arrays

This paper offers a computationally efficient strategy for the delicate analysis of frequency-diverse arrays. This family of radiating systems shows a radiation mechanism dependent on both angle and range thanks to the different frequency radiated by each array element: for this reason, it can simultaneously focus and steer its beam, thus providing a strategic capability for wireless power transfer applications. Despite the array architecture described in this paper is the standard one, it represents a cumbersome task from the circuit analysis point of view. The full-wave analysis combined with an effective exploitation of the Harmonic Balance technique allows, for the first time, the accurate estimation of the dynamic behavior of this promising radiating system

Smart beamforming techniques for “on demand” WPT

This chapter focuses on smart radiating solutions for wireless power transfer (WPT) purposes, being the energy-aware transmission of power the weakest and less efficient step in the entire link budget estimation. The exploitation of time as additional degree of freedom in the transmitting array synthesis makes time-modulated arrays (TMAs) potential candidate for future telecommunication applications, as WPT: their almost real-time ease of reconfiguration allows an agile and dynamic transmission of the signal/energy. Moreover, TMAs rely on a peculiar radiation phenomenon: the possibility to deploy additional radiating frequencies, besides the fundamental radio-frequency (RF) carrier, generated by the superposition of the carrier itself and the low frequency used to drive the nonlinear switches placed at each antenna port. This sideband radiation can be favorably exploited thus making TMAs multiharmonic radiators at the same time: a smart WPT procedure relying on this capability is demonstrated. The importance of a complete software tool, combining full-wave and nonlinear circuit techniques for the accurate estimation of TMAs complex regime, is also highlighted in the chapter

A Logarithmic Frequency-Diverse Array System for Precise Wireless Power Transfer

The exploitation of frequency diversity in array systems is theoretically discussed in the literature for wireless power transfer applications, because of the unique capability of energy focusing. In this paper the family of frequency-diverse arrays with logarithmic distribution of the frequency is deeply investigated through an accurate numerical approach: an efficient Harmonic Balance-based simulation is combined with the full-wave description of the array made of eight planar monopoles. The obtained results confirm the energy focusing potentiality of these radiating systems, even in presence of their intrinsic time-dependent radiation. A preliminary set-up of the complex control system architecture is presented

An orientation-independent UHF rectenna array with a unified matching and decoupling RF network

This work describes the design of a rectenna array exploiting orthogonal, closely-spaced UHF monopoles for orientation-independent RF energy harvesting to energize a passive tag, designed for UWB localization, with wake-up radio (WUR) capabilities. To reach this goal, different RF networks are studied to simultaneously realize RF decoupling of the antenna elements and matching of the radiating elements to the non-linear network of rectifiers. The design is performed for a wide power range of the RF incoming signals that need to be exploited for both energizing the passive tag and for providing energy autonomy to a WUR sub-system, used to minimize the long-term power consumption during tag standby operations. Two meandered cross-polarized monopoles, located in close proximity, and thus highly coupled, are adopted for orientation-insensitive operations. The combining RF network is reactive and includes an unbalanced power divider to draw a fraction of the harvested energy to a secondary way for WUR operations. The performance of the harvester is first optimized by EM/non-linear co-design of the whole system over an interval of low RF power levels. The system has been realized and experimentally validated: the superior results obtained, in terms of both dc voltage and power, with respect to a standard single-monopole rectenna, justify the deployment of the presented tag for the energy autonomy of future generation radio-frequency identification tags for indoor localization

Highly-Reconfigurable Time-based Radiating Systems and Their Optimization

This work aims at underlying the high reconfiguration capability of time-modulated arrays (TMAs) and their potential use in future 5G networks, as well as at stressing the need for a rigorous design tool when the optimization of these arrays is performed. The architectural simplicity of TMAs offers, as a counterpart, a complex dynamic radiating mechanism whose accurate description can significantly impact on the optimum solution. For this reason, a review of the available simulation strategies of TMAs is provided, mainly focusing on a recently proposed tool able to take into account all the dynamic linear and nonlinear phenomena occurring during a time-based radiatio

Respiratory Activity Monitoring by a Wearable 5.8 GHz SILO With Energy Harvesting Capabilities

In this work, the design and the realization of a pocket-size sensor for breath rate detection are presented. Exploiting the self-injection locking radar technique, it is possible to perform FM-to-AM demodulation that allows the detection of the voltage peaks at the output of the sensor's receiving part. If compared with existing solutions, this device is of reduced dimensions and fully wearable; in fact, it can be worn by the user at a certain distance from the body at the chest position, and work without the need of any dedicated remotely synchronized anchor nodes nor bulky analyzers to be carried close by. As a more distinctive peculiarity, the receiving circuit is designed as an RF-to-DC rectifier in order to also enable the possibility to harvest energy that can be exploited, for instance, to feed a microcontroller unit and a transceiver with the aim of sending wirelessly the breath rate data to a laptop or a smartphone. Circuit simulations are corroborated by measurements in order to ensure the feasibility of the proposed solution

RF-powered low-energy sensor nodes for predictive maintenance in electromagnetically harsh industrial environments

This work describes the design, implementation, and validation of a wireless sensor network for predictive maintenance and remote monitoring in metal-rich, electromagnetically harsh environments. Energy is provided wirelessly at 2.45 GHz employing a system of three co-located active antennas designed with a conformal shape such that it can power, on-demand, sensor nodes located in non-line-of-sight (NLOS) and difficult-to-reach positions. This allows for eliminating the periodic battery replacement of the customized sensor nodes, which are designed to be compact, low-power, and robust. A measurement campaign has been conducted in a real scenario, i.e., the engine compartment of a car, assuming the exploitation of the system in the automotive field. Our work demonstrates that a one radio-frequency (RF) source (illuminator) with a maximum effective isotropic radiated power (EIRP) of 27 dBm is capable of transferring the energy of 4.8 mJ required to fully charge the sensor node in less than 170 s, in the worst case of 112-cm distance between illuminator and node (NLOS). We also show how, in the worst case, the transferred power allows the node to operate every 60 s, where operation includes sampling accelerometer data for 1 s, extracting statistical information, transmitting a 20-byte payload, and receiving a 3-byte acknowledgment using the extremely robust Long Range (LoRa) communication technology. The energy requirement for an active cycle is between 1.45 and 1.65 mJ, while sleep mode current consumption is less than 150 nA, allowing for achieving the targeted battery-free operation with duty cycles as high as 1.7%