Damiano Patron

On the Use of Knitted Antennas and Inductively Coupled RFID Tags for Wearable Applications

Recent advancements in conductive yarns and fabrication technologies offer exciting opportunities to design and knit seamless garments equipped with sensors for biomedical applications. In this paper, we discuss the design and application of a wearable strain sensor, which can be used for biomedical monitoring such as contraction, respiration, or limb movements. The system takes advantage of the intensity variations of the backscattered power (RSSI) from an inductively-coupled RFID tag under physical stretching. First, we describe the antenna design along with the modeling of the sheet impedance, which characterizes the conductive textile. Experimental results with custom fabricated prototypes showed good agreement with the numerical simulation of input impedance and radiation pattern. Finally, the wearable sensor has been applied for infant breathing monitoring using a medical programmable mannequin. A machine learning technique has been developed and applied to post-process the RSSI data, and the results show that breathing and non-breathing patterns can be successfully classified.

Sectorized Antenna-based DoA Estimation and Localization: Advanced Algorithms and Measurements

Sectorized antennas are a promising class of antennas for enabling direction-of-arrival (DoA) estimation and successive transmitter localization. In contrast to antenna arrays, sectorized antennas do not require multiple transceiver branches and can be implemented using a single RF front-end only, thus reducing the overall size and cost of the devices. However, for good localization performance the underlying DoA estimator is of uttermost importance. In this paper, we therefore propose a novel high performance DoA estimator for sectorized antennas that does not require cooperation between the transmitter and the localizing network. The proposed DoA estimator is broadly applicable with different sectorized antenna types and signal waveforms, and has low computational complexity. Using computer simulations, we show that our algorithm approaches the respective Cramer-Rao lower bound for DoA estimation variance if the signal-to-noise ratio (SNR) is moderate to large and also outperforms the existing estimators. Moreover, we also derive analytical error models for the underlying DoA estimation principle considering both free space as well as multipath propagation scenarios. Furthermore, we also address the fusion of the individual DoA estimates into a location estimate using the Stansfield algorithm and study the corresponding localization performance in detail. Finally, we show how to implement the localization in practical systems and demonstrate the achievable performance using indoor RF measurements obtained with practical sectorized antenna units.

Design and harmonic balance analysis of a wideband planar antenna having reconfigurable omnidirectional and directional patterns

In this paper we discuss a novel reconfigurable antenna equipped using PIN diodes and analyze the harmonic distortions that may be generated. The design herein described is for a novel planar antenna that can generate omnidirectional and directional radiation patterns by switching between microstrip elements. Based on the equivalent circuit model of the antenna, we have performed a harmonic balance circuit simulation to consider channel distortion due to employment of these reconfigurable antennas as part of a 2×2 MIMO system over broad bandwidth communication channel.

Optical Control of Reconfigurable Antennas and Application to a Novel Pattern-Reconfigurable Planar Design

This paper discusses techniques for optical control of reconfigurable antennas using commercially available devices. These techniques are applied to a pattern-reconfigurable planar antenna that integrates optical control circuitry to switch folded microstrip radiators arranged in each of the quadrants. By switching between the microstrip elements, the designed antenna can generate a single omnidirectional or four directional patterns, maintaining good impedance matching within the 2.4 GHz WiFi band. We investigated two possible strategies for optical control: 1) p-i-n photodectors based switching, and 2) phototransistor controlled RF p-i-n diodes switches. Extended numerical and experimental analysis was carried out for the latter technique, discussing advantages and limitations when employed as RF switch on reconfigurable antennas. Finally, measurements of input impedance and radiation patterns were collected to validate the proposed optically controlled antenna design and compared to standard electronic control.

A reconfigurable antenna with omnidirectional and directional patterns for MIMO systems

In this paper, we propose a novel pattern reconfigurable planar antenna for employment in a 2×2 multiple input, multiple output (MIMO) system. By switching between the microstrip elements, the antenna can generate a single omnidirectional mode or four directional modes. The design has been tuned for a frequency of 3.8 GHz and has a bandwidth of at least 400 MHz, depending on the configuration. The flexibility in directional and omnidirectional operation, in concert with the wide operating bandwidth, makes this antenna an ideal candidate for future MIMO systems. This paper presents the antenna array architecture as well as simulated return loss and mutual coupling.

Wireless strain sensor through a flexible tag antenna employing inductively-coupled RFID microchip

Intensity variations of the backscattered power from an RFID tag have been demonstrated to be a potential wireless solution to measure material deformation. This paper discusses the design and performance of a flexible tag antenna equipped with novel inductively-coupled RFID microchip for use as a wireless strain sensor. Dielectric characterization of a flexible substrate has been carried out to properly design and simulate the proposed antenna design. Due to the balanced nature of this radiating element, differential scattering parameter measurements were performed to characterize the antenna input impedance. Finally, measurements of the backscattered power as a function of radial deformations are also shown as a qualitative analysis of the strain sensing capabilities.

Improved design of a CRLH leaky-wave antenna and its application for DoA estimation

In this paper, we propose a composite right/left handed two port leaky-wave antenna (CRLH-LWA) having reduced size and enhanced beam steering capabilities. The antenna is made of a cascade of metamaterial CRLH unit cells, populated with varactor diodes. By properly designing the CRLH unit cell, the propagation constant has been optimized within the radiated zone achieving maximum beam steering and keeping a nearly constant gain for all of the beam configurations. Through a modified multiple signal classification (MUSIC) algorithm, we employed the antenna for direction of arrival (DoA) estimation. Validation of the algorithm along with the proposed CRLH-LWA has been conducted in an anechoic chamber and the estimated DoA results are in good agreement with the predicted angles.

Optical control of pattern-reconfigurable planar antennas

This paper presents a pattern-reconfigurable planar antenna that is optically controlled to switch in and out various composite printed circuit radiators in each of the quadrants. The designed antenna is able to generate a single omnidirectional or four directional patterns by switching between the microstrip elements, maintaining a good impedance matching over the entire 2.4 GHz WiFi band. By using commercially available optical devices, two different strategies were explored for the optical control: i) PIN photodetectors based switching, and ii) a photo-transistor controlled RF PIN diodes for switching. Different advantages and limitations of each technique are discussed, when implementing as single-pole-single-throw RF switches in the proposed composite antenna. The antennas characteristics are reported, where a matched input impedance and radiation patterns are achieved over WiFi frequency band.

Innovative propagation mechanism for inter-chip and intra-chip communication

SoC (System on chip) technology has rapidly developed in recent years, stimulating emerging research areas such as investigating the efficacy of wireless network interconnection within a single chip or between multiple chips. However the design of the on-chip antenna faces the challenge of obtaining high radiation efficiency and transmission gain due to conductive loss of the silicon substrate. A new on-chip propagation mechanism of radio waves, which takes advantage of the un-doped silicon layer, is developed in order to overcome this challenge. It was found that by properly designing the dimension of silicon wafer, the un-doped silicon layer is able to act like a waveguide. Most of the energy is directed to the approximately lossless the undoped silicon layer of high resistivity instead of attenuating in the doped silicon substrate or radiating to the air. HFSS modeling and simulation results are provided to show that efficiency, gain and directivity of the on-chip antenna are greatly improved. In addition, this type of antennas can be easily reconfigured, which as a result, makes wireless SoCs with wireless interconnects or even a wireless network on PCB (Printed Circuit Board) possible.

A Miniaturized Reconfigurable CRLH Leaky-Wave Antenna Using Complementary Split-Ring Resonators

Composite Right-/Left-Handed (CRLH) Leaky-Wave Antennas (LWAs) are a class of radiating elements characterized by an electronically steerable radiation pattern. The design is comprised of a cascade of CRLH unit cells populated with varactor diodes. By varying the voltage across the varactor diodes, the antenna can steer its directional beam from broadside to backward and forward end-fire directions. In this paper, we discuss the design and experimental analysis of a miniaturized CRLH Leaky-Wave Antenna for the 2.4 GHz WiFi band. The miniaturization is achieved by etching Complementary Split-Ring Resonator (CSRR) underneath each CRLH unit cell. As opposed to the conventional LWA designs, we take advantage of a LWA layout that does not require thin interdigital capacitors; thus we significantly reduce the PCB manufacturing constraints required to achieve size reduction. The experimental results were compared with a nonminiaturized prototype in order to evaluate the differences in impedance and radiation characteristics. The proposed antenna is a significant achievement because it will enable CRLH LWAs to be a viable technology not only for wireless access points, but also potentially for mobile devices.