Jennifer T. Bernhard

Pen‐on‐Paper Flexible Electronics

Figure 1 . a) Optical image of a rollerball pen loaded with a conductive silver ink. The background shows conductive text written on Xerox paper. b and c) SEM images of the side and top views of the rollerball pen. d) Optical image of the rollerball pen tip, captured during writing a conductive silver track on a Xerox paper. Printed electronics constitute an emerging class of materials with potential application in photovoltaics, [ 1 ] transistors, [ 2 , 3 ] displays, [ 4–6 ] batteries, [ 7 ] antennas, [ 8 ] and sensors. [ 9 , 10 ] Recent attention has focused on paper substrates as a low-cost, enabling platform for fl exible, lightweight, and disposable devices. [ 11–13 ]

Conformal printing of electrically small antennas on three-dimensional surfaces

J. J. Adams ,[+] Prof. J. T. Bernhard Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801, USA E-mail: jbernhar@illinois.edu Dr. E. B. Duoss ,[+,++] T. F. Malkowski ,[+] Dr. B. Y. Ahn , Prof. J. A. Lewis Department of Materials Science and Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801 USA E-mail: jalewis@illinois.edu Dr. M. J. Motala , Prof. R. G. Nuzzo Department of Chemistry University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA [+] These authors contributed equally to this work. [++] Presently at Lawrence Livermore National Laboratory, Center for Microand NanoTechnology, Livermore, CA 94550 USA

Integration of packaged RF MEMS switches with radiation pattern reconfigurable square spiral microstrip antennas

This work describes the integration of commercially available packaged radio frequency microelectromechanical system (RF MEMS) switches with radiation pattern reconfigurable microstrip antennas. Most applications of RF MEMS switches consider the switches as only circuit elements. In contrast, the implementation of packaged switches in this particular antenna must address not only the simple open/closed behavior of the switches but also their impact on the radiation characteristics of the reconfigurable antenna. Here, two Radant MEMS single-pole single throw (SPST) SPST-RMSW100 (packaged RF MEMS) switches are used to reconfigure the radiation patterns of a resonant square spiral microstrip antenna between endfire and broadside over a common impedance bandwidth. Switch insertion, matching network design, and other issues are addressed. Results for both simulated and measured antennas, as well as recommendations for future work in this area, are provided.

A pattern reconfigurable microstrip parasitic array

This communication presents a novel linearly polarized pattern reconfigurable microstrip parasitic array. Specifically, this antenna uses four switches (currently copper strips for proof of concept) to reconfigure the radiation pattern into three variations over a shared 2:1 VSWR bandwidth, and has potential applications in mobile communication devices and large phased antenna arrays. Both measured and simulated results of a microstrip parasitic array are provided. The effects of changes in physical dimensions and directions for future work are also discussed.

Analysis and design of broad-band single-layer rectangular U-slot microstrip patch antennas

A wide operating bandwidth for a single-layer coaxially fed rectangular microstrip patch antenna can be obtained by cutting a U-shaped slot on the patch. This antenna structure has recently been found experimentally to provide impedance bandwidths of 10%-40%, even with nonair substrates. However, design rules for this antenna have not yet been presented. This paper develops principle design procedures through examination of the structures multiple resonant frequencies as well as the radiation and impedance properties of different antenna geometries. The approximate design rules are derived by analysis of former experiments, method of moments (MoM) simulations, and measurement results. Simulations and measurements of several antennas designed using these new rules are presented and directions for further study are discussed.

A novel radiation pattern and frequency reconfigurable single turn square spiral microstrip antenna

This paper presents a novel pattern and frequency reconfigurable microstrip antenna that uses switched connections. The basic antenna operates with linear polarization around 3.7 GHz. One set of connections provides a re-directed radiation pattern while maintaining a common operating impedance bandwidth with the baseline configuration. The second set of connections results in operation at a higher frequency band at 6 GHz with broadside patterns. Measured results of the three antenna configurations are provided. Potential applications of this reconfigurability and directions for future work are discussed.

Directional Modulation Technique for Phased Arrays

A directional modulation (DM) technique using a phased array to produce the modulation is presented. By phase shifting each element correctly, the desired amplitude and phase of each symbol in a digital modulation scheme can be produced in a given direction with data rates determined by the switching speed of the phase shifters. Because this signal is direction-dependent, the technique offers security, as the signal can be purposely distorted in other directions. DM also enables an array to send independent data in multiple directions. When using an array with driven elements, the phase shifts can be determined from simple calculations rather than time-consuming simulations or measurements. Mathematical analysis and experimental results are presented.

Performance Study of Pattern Reconfigurable Antennas in MIMO Communication Systems

We explore the potential benefits of using pattern reconfigurable antennas in multiple-input multiple-output (MIMO) communication systems. First, theoretical capacity increases are calculated in a typical indoor multipath environment assuming ideal, fully reconfigurable antennas and compared to cases using theoretical isotropic antennas. Next, a real reconfigurable antenna built into a multiple element antenna system for MIMO use is described and analyzed to investigate the possible effects of beam tilts on capacity. Finally, this system is used to quantify the possible capacity improvements due to both antenna diversity and antenna gain that are enabled by antenna pattern reconfigurability in a scientifically reproducible environment that includes antenna coupling.

Directional reconfigurable antennas on laptop computers: Simulation, measurement and evaluation of candidate integration positions

This study reports on the integration of a novel reconfigurable microstrip antenna capable of reconfiguring both its radiation pattern and frequency response onto a generic laptop computer structure. The purpose of such an exercise is to provide the relevant information necessary to integrate high performance antennas onto structures that can be used in ad hoc communication scenarios as well as other demanding applications. To pre-evaluate candidate antenna locations on the laptop chassis, an electromagnetic visibility study (EVS) is performed. Once integrated into candidate positions that have been analyzed by the EVS, the operation of the antenna on the host structure is measured and assessed with consideration to several realistic electromagnetic environments. The resulting performance and packaging issues are discussed. A formalized procedure for the integration of the antenna onto any host chassis using the EVS as a tool is also included.

Demonstration of Directional Modulation Using a Phased Array

A four-symbol modulation is created by repeated switching of phase shifters in a phased array, in a technique known as directional modulation (DM). The phase shifts are chosen to minimize the bit error rate (BER) in a line-of-sight channel in a desired direction while maximizing the BER elsewhere. A DM transmitter is demonstrated in an anechoic chamber, and results are compared with a traditional baseband QPSK modulation using the same phased array. Experiments indicate that the DM transmitter creates a narrower region of low BERs around the desired direction than the traditional phased array while maintaining high BERs in the sidelobe regions.