Giuseppina Monti

Electromagnetic Energy Harvesting and Wireless Power Transmission: A Unified Approach

In this paper, a rigorous procedure for the circuit-level analysis and design of entire systems, developed to provide power wirelessly, is presented. A unified theoretical approach is first introduced, based on a two-port-equivalent circuit representation, to describe the wireless power transfer link when the transmitter and the receiver are either in the near-field or in the far-field region reciprocally. This approach allows one to compute in a straightforward manner the system figure of merit, namely the power transfer efficiency. Specific guidelines for the two configurations are then intensively discussed together with the adopted software tools based on the combination of full-wave analysis and nonlinear harmonic balance techniques. Several practical examples based on this design procedure are presented, demonstrating predicted and experimental behavior of unconventional devices for both near-field and far-field power transfer usage.

UHF Wearable Rectenna on Textile Materials

A wearable rectenna for operation in the ultra high frequency (UHF) band is presented. The proposed device consists of a compact patch antenna and a full-wave bridge rectifier, both fabricated with textile materials. The patch antenna has been realized by using an adhesive conductive fabric on a bi-layer substrate made of pile and jeans. As for the rectifier, it is on a layer of jeans on the back-face of the antenna. Experimental data referring both to the patch antenna and to the rectenna are reported and discussed. From measurements performed with an incident power density of 14 μ/cm2, it is demonstrated that the rectenna here presented exhibits a conversion efficiency higher than 20% over the frequency range 860-918 MHz with a maximum of about 50% at 876 MHz.

Design of a 3-State Reconfigurable CRLH Transmission Line Based on MEMS Switches

Based on the use of micro electro-mechanical system (MEMS) switches this paper presents a composite right/left-handed (CRLH) transmission line (TL) with a reconflgurable behaviour. The design strategy here adopted consists on the use of metal-insulator- metal (MIM) capacitors and short-circuited stubs resulting in a very compact and monolithic CRLH unit cell well suited for phase shifter applications.

COMPACT MICROSTRIP ANTENNA FOR RFID APPLICATIONS

This work presents a planar antenna for Ultra-High- Frequency (UHF) Radio Frequency Identiflcation (RFID) Tags to be applied on metallic surfaces. The proposed radiating structure consists of a short-circuited patch antenna designed with a fractal geometry, resulting in a very compact and cost efiective Tag. Showing a very good platform tolerance, such a Tag is also suitable for application on difierent kinds of materials (metal, glass, etc.).

X-Band Planar Rectenna

This letter presents a novel X-band planar rectenna (i.e., a rectifying antenna). The proposed device consists of a slot antenna and a microstrip rectifying circuit. A realization on a low-cost FR4 substrate, using a surface-mount Schottky barrier diode (the HSMS-8202 diode by Avago Technologies) as the rectifying element, is proposed. Measurements performed at 9.3 GHz demonstrate that an RF-to-DC conversion efficiency of about 21% can be obtained with an input power density of 245 μW/cm2.

A Noninvasive Resonance-Based Method for Moisture Content Evaluation Through Microstrip Antennas

Several techniques for measuring the moisture levels of materials, particularly in the soil science area, are available. Nevertheless, the state of the art is rather lacking in moisture-sensing methods that are both inexpensive and noninvasive. The time-domain reflectometry (TDR)-based method, despite being a well-established low-cost technique for sensing moisture content, is intrinsically invasive due to the configuration of the probes that are commonly used. These considerations motivated the authors to investigate the adoption of simple inexpensive microstrip antennas as sensing elements for TDR-based moisture content measurements. For this purpose, the water content of the monitored material is sensed through the changes in the reflection scattering parameter S 11(f) of the antenna. In particular, the change in the resonant frequency of the antenna, which is evaluated through an appropriate processing of the TDR waveforms, is correlated with the water content of the material under investigation. The ultimate goal is to assess a sensing method that can be implemented for inexpensive real-time noninvasive monitoring applications.

Patch Antenna with Reconfigurable Polarization

A reconfigurable patch antenna consisting of a square patch with two cross-shaped diagonal slots is presented. The proposed design approach is based on the use of two pairs of switches in order to obtain both frequency and polarization reconfigurability. Specifically, three different polarization states have been obtained: a Right-Hand Circular Polarization, a Left-Hand Circular Polarization and a Linear Polarization. Experimental results, referred to a realization on a FR4 substrate of the layouts corresponding to the useful switch configurations, are reported.

Resonant Inductive Link for Remote Powering of Pacemakers

This paper presents a wireless power link for powering implantable medical devices. The proposed link operates at 403 MHz and exploits magnetic coupling between an external resonator and an implanted resonator to wirelessly provide power to implantable devices. Experimental results for remote powering of pacemakers are reported and the compliance with safety guidelines is discussed. It is demonstrated that the proposed wireless link is able to deliver up to 1 mW with an induced 10-g average specific absorption rate lower than 1.08 W/kg. This value is significantly below the 2-W/kg recommended limit, thus proving the suitability of the proposed system to be used to energize modern pacemakers.

Assessment of a TD-Based Method for Characterization of Antennas

Antenna-characterization measurements are traditionally performed in the frequency domain (FD) through a vector network analyzer (VNA) in an anechoic chamber. Nevertheless, the high cost of the required setup strongly limits the possibility of using this approach. Starting from these considerations, a time-domain (TD)-based approach for characterizing antennas without using an anechoic chamber is assessed. As a matter of fact, instruments operating in TD are usually less expensive than VNAs; nevertheless, with appropriate data processing, they provide as much information. Particularly, it is demonstrated that the selection of an optimal time windowing is the main factor that guarantees a high accuracy level in the corresponding FD. The proposed approach leads to the accurate evaluation of the reflection scattering parameter S 11(f) from time-domain reflectometry (TDR) data. The experimental validation is tested on a commercial radio-frequency identification (RFID) reader antenna, and the results are compared with reference VNA measurements performed in an anechoic chamber. The ultimate goal of this paper is to demonstrate that, through calibrated TDR measurements, along with an optimal time windowing, an accurate antenna characterization can be achieved.

BROAD-BAND DIPOLE FOR RFID APPLICATIONS

A novel planar dipole for Ultra-High-Frequency (UHF) Radio Frequency Identiflcation (RFID) systems is presented here. Referring to a realization based on the use of a chip produced by Texas Instruments, the proposed design approach has been numerically and experimentally investigated. Reported results demonstrate that the proposed antenna exhibits good radiation properties and matching (jS11j < i10dB) over the entire UHF RFID bandwidth (860{ 960MHz).