Massimo Del Prete

Time-Modulation of Linear Arrays for Real-Time Reconfigurable Wireless Power Transmission

This paper proposes a smart wireless power transmission method, based on a two-step procedure, exploiting real-time beaming of time-modulated arrays. The sideband radiation phenomenon, which is usually a drawback of these radiating systems, is favorably used for intentional wireless power transfer (WPT): in a first step to precisely localize the tag to be powered and in the second one to perform directive WPT. The approach is first theoretically discussed, then the numerical procedure, which integrates full-wave analysis of the antenna array with nonlinear simulation of the modulated nonlinear feeding network, is used to validate the principle of operation and to include nonlinearities and electromagnetic couplings affecting the whole system performance. The procedure allows a flexible design of the time-modulated-array-based WPT system, taking into account the impact of different array elements layout and spacing on localization and power transmission performance. Experiment of the first step is carried out in a real indoor environment at 2.45 GHz: a TI MSP430 drives a Schottky-diode-based network to provide proper modulated RF excitations of the array elements. Measurements show that the system is able to select tags to be energized randomly distributed in a 100 °-scanning range.

Energy-autonomous Bi-directional Wireless Power Transmission (WPT) and energy harvesting circuit

This work demonstrates a novel 2.45-GHz bi-directional circuit that can operate as both a wireless power transmitter and energy harvester. The circuit is based on a class-F oscillator/rectifier and is energy-autonomous since it does not need an external bias supply for either power transmission or power reception. Bi-directionality is exploited in two steps: the system first operates in rectifying mode with harvested DC voltages for biasing the oscillator; followed by the transmitting mode where the harvested DC power is used to start up oscillations. Conversion efficiencies for both configurations are higher than 50% for output/input RF power in the 10dBm range. This component can be exploited as a “power relay node” for distributed battery-less energy autonomous microsystems.

Exploitation of a dual-band cell phone antenna for near-field WPT

The same antenna, designed to exploit its far-field properties for communication purposes, can be suitably configured for simultaneously realizing wireless power transfer via its near-field properties. In this paper we analyze the near-field behavior of a pair of closely coupled transmitting and receiving dual-band printed monopole antennas, suitable for cell phones applications. The proposed architecture is based-on a frequency division approach, operating in the GSM900 and GSM1800 bands for data communications, and in the ISM 433 MHz for near-field power transfer. In this work we develop the theoretical and numerical demonstration of how it is possible to achieve both far-field performance and near-field power transfer efficiency (from 35% to 10%) for mobile phones located few centimeters apart.

Scavenging for Energy: A Rectenna Design for Wireless Energy Harvesting in UHF Mobile Telephony Bands

The development of distributed and ubiquitous electronic devices is an achievement of modern technology that has the potential to revolutionize many aspects of human life. Such electronic devices are being employed not only in consumer areas like home automation, intelligent transportation systems, and personal entertainment but also for health-care applications, such as noninvasive biomedical parameter monitoring, as well as industrial and military applications. A novel WEH for commercial telephony frequencies in the UHF band has been presented. The system, being based on a broadband slot antenna and a thin flexible substrate, weighs fewer than 15 g, which is far below the competition requirements and makes the harvester particularly appealing for realistic scenarios. Thanks to the proper design of the rectifier and the matching network, an excellent performance has been verified over the whole band, with a rectenna conversion efficiency of up to 60% and an EFoM equal to 37.6 dB for 2 μW/cm2 of incident power density.

Optimum Excitations for a Dual-Band Microwatt Wake-Up Radio

To enable pervasive exploitation of wireless sensor networks, semipassive wake-up radios (WuRs) are proposed to minimize the active time of the energy-hungry main communication radio. The most challenging feature is to enhance their sensitivity, the weakest activation signal the receiver is able to sense, which is limited by the minimum turn-on voltage of the diode-based detector. In order to operate the detector at even lower power levels, a strategy to optimize the modulated WuR excitations is presented, exploiting high-peak intermittent continuous waves while preserving the required average power per bit. The design and implementation of an ultralow-power detector, fed by a dual-band antenna and loaded by the WuR backend is presented: 2.45-GHz and 868-MHz operations of the same WuR are demonstrated, with added flexibility and interoperability among different communication bands. We show that a correct WuR activation is possible with an average power per bit as low as -63 dBm at 2.45 GHz and -65 dBm at 868 MHz. This is experimentally verified by a lab-level setup and confirmed by a system implementation based on off-the-shelf components only.

A Long-Distance RF-Powered Sensor Node with Adaptive Power Management for IoT Applications

We present a self-sustained battery-less multi-sensor platform with RF harvesting capability down to −17 dBm and implementing a standard DASH7 wireless communication interface. The node operates at distances up to 17 m from a 2 W UHF carrier. RF power transfer allows operation when common energy scavenging sources (e.g., sun, heat, etc.) are not available, while the DASH7 communication protocol makes it fully compatible with a standard IoT infrastructure. An optimized energy-harvesting module has been designed, including a rectifying antenna (rectenna) and an integrated nano-power DC/DC converter performing maximum-power-point-tracking (MPPT). A nonlinear/electromagnetic co-design procedure is adopted to design the rectenna, which is optimized to operate at ultra-low power levels. An ultra-low power microcontroller controls on-board sensors and wireless protocol, to adapt the power consumption to the available detected power by changing wake-up policies. As a result, adaptive behavior can be observed in the designed platform, to the extent that the transmission data rate is dynamically determined by RF power. Among the novel features of the system, we highlight the use of nano-power energy harvesting, the implementation of specific hardware/software wake-up policies, optimized algorithms for best sampling rate implementation, and adaptive behavior by the node based on the power received.

A 2.4 GHz-868 MHz dual-band wake-up radio for wireless sensor network and IoT

Wake-up radio is an emerging technology with the ambitious goal of reducing the communication power consumption in smart sensor networks and Internet of Things. This reduction in power consumption will enable a new generation of applications which could achieve a longer lifetime than is achievable today. Wake up radios are required to work with a low power budget and should exhibit low latency coupled with high sensitivity and addressing capabilities. Typically they are combined with existing radio transceiver and power management techniques to reduce the overall communication power while maintaining the same communication performance. This paper presents a dual band (2.4GHz and 868MHz) wake up radio with the above mentioned characteristics. The dual band solution is exploited to increase the flexibility of the wake up radio, allowing interoperability with the two most common frequencies used in Wireless Sensors Networks and Internet of Things. Simulation results present a system able to exploit the two bands with sensitivity as low as -53dBm at 868MHz and -45dBm at 2450MHz. Experimental results on power consumption demonstrate the low power consumption of the proposed solution with only 1.276μW of power consumption in listening mode. The addressing is performed by an ultra low power on board PIC microcontroller with 40nW of power consumption when the wake up radio is in listening mode and only 70 μW when the data are received and parsed.

A 2.45-GHz Energy-Autonomous Wireless Power Relay Node

This paper describes the design and experimental characterization of a battery-less bidirectional 2.45-GHz circuit operating in oscillator mode as a wireless power transmitter or in rectifier mode as an energy harvester, with a measured efficiency greater than 50% in both operating states. The dc voltage harvested in rectifier mode provides the drain bias for the oscillator. The FET-gate self-bias mechanism is exploited in both functionalities, thus eliminating external gate bias. Bi-directionality is based on the time-reversal properties of a transistor oscillator. Energy autonomy is possible at received RF power levels as low as -4 dBm, by means of a bias-assisting feedback loop, consisting of a single matched low-power diode in shunt configuration. A hybrid prototype is demonstrated with the ability to operate as an energy-autonomous power relay node by switching between transmit and receive power modes.

A dual-band wake-up radio for ultra-low power Wireless Sensor Networks

Wake-up radio is an emerging technology for smart sensor networks and the Internet of Things with the ambitious goal of minimizing the power needed to communicate, thus enabling a new generation of applications. Wake-up radios should exhibit low latency coupled with high sensitivity, addressing capabilities with ultra-low power budget. They may be combined with existing radio transceivers and power management units to reduce the overall communication power while maintaining a high performance. This paper presents a 2.45 GHz and 868 MHz wake-up radio with the above mentioned characteristics. Dual band is exploited to increase the flexibility of the wakeup radio, allowing interoperability with the two most common bands used in Wireless Sensors Network and Internet of Things. Simulations results present a system with sensitivity as low as -55 dBm at 868 MHz and -53 dBm at 2.45 GHz.

Experimental analysis of power optimized waveforms for enhancing wake-up radio sensitivity

To minimize energy consumption of state-of-the-art wireless sensor nodes, asynchronous communication transceivers are adopted, which make use of an ultra-low power wake-up radio (WUR) to minimize the active time of the energy-hungry main communication radio. This work contributes to the ambitious goal of pushing over the minimum average RF power needed to operate the WUR, thus enabling energy-efficient communication in larger areas. To reach this goal a dual-band rectifier, optimized to be loaded by an ultra-low power comparator, is used as WUR detector. Its behavior is experimentally tested under several power-optimized excitation formats. By selecting the proper excitation format the base-band comparator is enabled starting from average RF-power as low as -64.5 dBm.