Keith W. Whites

A Direct-Write Printed Antenna on Paper-Based Organic Substrate for Flexible Displays and WLAN Applications

This paper presents the design, fabrication and measurements of a direct-write printed low-cost and flexible inverted-F antenna on an ultra-low-cost paper-based organic substrate for wireless local area network (WLAN) and flexible display applications. Innovations include the study and utilization of paper as a high-frequency substrate for the first time in the gigahertz (GHz) range, the fabrication technology for the direct-write printing of the antenna as a flexible RF electronic device, and the investigation of antenna flexibility in conjunction with flexible displays. Although paper substrates exhibit relatively high dielectric losses (tanδ ~ 0.065 at 2.45 GHz), the maximum realized gain of the fabricated antenna is measured to be + 1.2 dBi giving a total efficiency ~ 82%. Simulated results of the antennas return loss and radiation patterns agree well with the measurements, and can lead to a whole new class of flexible low-cost electronic devices of the future.

Non-aqueous synthesis of silver nanoparticles using tin acetate as a reducing agent for the conductive ink formulation in printed electronics

We have developed a process for the synthesis of silver nanoparticles protected with a passivating shell of dodecylamine in toluene media using tin(II) acetate as a reducing agent. Based on the electrochemical series, during the reduction process Sn(II) oxidizes into Sn(IV) which reduces Ag(I) into Ag(0). The nucleation and growth processes result in particles with diameters in the range 5–20 nm. This simple non-aqueous one pot synthesis can be easily scaled up to produce grams of nanoparticles in a matter of hours. The particles can also be dispersed in many non-aqueous solvents which make them a suitable candidate for many applications. Characterization of the end product using TEM, UV-Vis spectroscopy, and powder X-ray diffraction verified the presence of a silver metallic core whereas TGA confirmed the presence of a dodecylamine shell. The resulting particles were used in non-aqueous conductive ink formulation. The ink was used to print conductive tracks on flexible substrates like Epson photo paper and polyimide (Kapton) using an Aerosol Jet based printing technique.

Miniaturization of the Biconical Antenna for Ultrawideband Applications

A miniaturized, ultrawideband antenna for the 3.1 to 10.6 GHz frequency band is presented. The antenna is designed to have a low profile to enhance integration onto existing structures and a low directivity pattern for body worn applications. A systematic process to miniaturize the well-known biconical antenna is illustrated by adding several different geometric features that reduce the size of the antenna. After miniaturization, the vertical height of the antenna was reduced by over 60% while maintaining electrical performance. Prototype antennas were manufactured using low cost plastic injection molding and dipping processes to facilitate transition to mass production and to enhance the durability of the antenna. The simulated and measured reflection coefficient of the antenna show good agreement. Measured antenna gain patterns verify that the manufacturing process employed is capable of producing low loss antenna structures. Lastly, time domain short pulse measurements of the antenna verify that it does not appreciably distort radiated signals in the azimuthal plane.

Bandwidth Enhancement of the Resonant Cavity Antenna by Using Two Dielectric Superstrates

We propose a novel approach to enhance the bandwidth of the high directivity of the resonant cavity antenna (RCA) by applying two dielectric layers as superstrates. The approach is based on creating two cavities corresponding to two operating frequency bands that combine to form a single wide band of operation. The RCA design is discussed in a methodological manner to determine the thicknesses of the superstrates, the separation distance between them, and the separation distance to the ground plane. We show that the proposed technique is capable of enhancing the bandwidth from 9% of the single superstrate RCA to 17.9% of the two superstrate RCA, with only 0.1-dB reduction of the maximum directivity (17.5 dBi). The presented design method can be replicated for any RCA with any directivity level and type of primary feeding. The performance of the analytically designed antenna is validated by simulation using commercial numerical electromagnetics software.

The Puck Antenna: A Compact Design With Wideband, High-Gain Operation

We develop a high-gain antenna with wideband operation and compact size by placing a small dielectric superstrate (puck) in front of the feeding antenna. The antenna performance is a combination of the leaky-wave effect, naturally existing in this type of antennas, and the edge diffraction effect occurring at the puck perimeter. Compared to the typical resonant cavity antenna utilizing a large superstrate, the proposed puck antenna has nearly four times enhanced performance (gain-bandwidth combination) while using a square puck of side slightly smaller than two wavelengths (at the design frequency). Further enhancement is achieved by making the puck circular in shape in order to add the diffracted fields in phase. The study is conducted through full-wave simulations and validated through measurements in the Ku band. The effect of puck misalignment is then discussed as a potential practical issue. Last, the ground plane is optimized for maximum antenna performance and relatively acceptable values of aperture efficiency (up to 51%).

Bandwidth enhancement of the cavity resonance antenna (CRA) using multiple dielectric superstrate layers

The ray-tracing method is applied to study the radiation of a cavity resonance antenna (CRA) with both single and multiple dielectric superstrate layers. The behavior of the broadside directivity is investigated by analyzing the reflection phase of the antenna superstrates. To enhance the bandwidth of the CRA and maintain its large broadside directivity, a multilayered superstrate of an increasing reflection phase with frequency is presented. When compared to the single-layered CRA, a bandwidth enhancement of more than 100% is attained using a multilayered CRA of three superstrate slabs. Theoretical results are validated by simulations using commercial numerical electromagnetics software.

Computation of Static Effective Permittivity for a Multiphase Lattice of Cylinders

A methodology is described to calculate the static effective permittivity for a two-dimensional multiphase lattice composed of dielectric and/or conducting circular cylinders. This methodology uses an accurate T-matrix method to determine the dipole moments of the cylinders immersed in a uniform electric field, and then computes the effective permittivity by relating the lattice to a macroscopic model. With this methodology, the multiple scattering solution for the infinite lattice is presented in a succinct matrix-vector notation and is valid for any lattice type. The static effective permittivity equation described in this work allows us to account for the effect of all mutual interactions between the cylinders. This methodology is used to calculate the static effective permittivity for a two-phase lattice of metallic inclusions. These results are compared with the Maxwell Garnett formula and another formula presented by Kharadly and Jackson. Three additional examples are presented including two-phase dielectric lattices, multiphase lattices, and clusters. The static effective permittivity in all three situations deviates from the Maxwell Garnett result at high-volume fractions, as expected. This deviation is the most obvious for the cluster lattice because of the significant mutual coupling between the cylinders, even at relatively low-volume fraction.A methodology is described to calculate the static effective permittivity for a two-dimensional multiphase lattice composed of dielectric and/or conducting circular cylinders. This methodology uses an accurate T-matrix method to determine the dipole moments of the cylinders immersed in a uniform electric field, and then computes the effective permittivity by relating the lattice to a macroscopic model. With this methodology, the multiple scattering solution for the infinite lattice is presented in a succinct matrix-vector notation and is valid for any lattice type. The static effective permittivity equation described in this work allows us to account for the effect of all mutual interactions between the cylinders. This methodology is used to calculate the static effective permittivity for a two-phase lattice of metallic inclusions. These results are compared with the Maxwell Garnett formula and another formula presented by Kharadly and Jackson. Three additional examples are presented including two-phase d...

Inkjet printed microwave frequency multilayer antennas

Direct-write technologies offer a new degree of freedom for developing complex multilayer microwave frequency devices (Whites et al., 2006). We have developed a technique incorporating multiple direct-write technologies to sequentially layer multiple materials to produce devices. In this process, Cima NanoTech silver conductive ink (Cima NanoTech Inc., 2006) is deposited with a FUJIFILM Diamtix DMP-2830 inkjet printer (FUJIFILM Dimatix Inc., 2006) and liquid polyimide is deposited using a nScrypt model 600 machine (nScrypt, Inc., 2006). Using this process a dual frequency band stacked patch antenna was fabricated as an example of microwave frequency devices that can be realized with sequentially layered direct-write of multiple materials.

Can ultrawideband antennas be miniaturized effectively by dielectric loading

A novel approach for miniaturization of disc monopole antennas is presented. The physical size of the antenna has been miniaturized by loading a dielectric material of high dielectric constant around the antenna in an intelligent manner. In order to maintain the impedance bandwidth characteristics, a spatial quarter wave transformer was applied. Simulations of the structure showed that the impedance bandwidth was conserved while the physical size of the structure was reduced by 58.4%.

A low-cost WLAN “Green” PIFA antenna on eco-friendly paper substrate

This work shows for the first time the practical application of paper as a substrate in real-life wireless local area network (WLAN) applications. Photographic paper is used here in the design, fabrication and testing of a printed inverted F-antenna (PIFA) operating at 2.45GHz. Although paper substrates exhibit relatively high dielectric losses (tanδ ∼ 0.07 at 2.45GHz), the maximum gain achieved by the fabricated antenna is +1.2 dBi and its total simulated efficiency is approximately 82% at resonance. The simulation results of the return loss, as well as the radiation pattern of the antenna agree with the corresponding measured results that are presented in this work.