Anthony K. Amert

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.

A simulation and experimental study on packing of nanoinks to attain better conductivity

A simulation and experimental study on the packing of nanoinks has been carried out. Simulation predicted that the packing of two different sized monodispersed colloids would results in a more densely packed structure than a single sized monodispered colloid alone. The simulated results were confirmed by conducting experiments with two different sized-monodispersed silver colloids. A binary sized ink was printed in a rectangular pattern using a direct write method system and then the final pattern was sintered. The pattern was confirmed to be highly conductive and the final conductivity obtained from this pattern gave 47% of the bulk conductivity of silver.

Multiple superstrates technique for a broadband cavity resonance antenna (CRA)

A cavity resonance antenna (CRA) with three dielectric superstrates is examined and its performance is compared to those of the single superstrate CRAs of the lowest two resonances. The broadside directivity, bandwidth, and directivity-bandwidth product of all three antennas are investigated. When compared to the single superstrate CRAs, an appropriately designed three superstrate CRA can enhance to the maximum directivity, the bandwidth, or both, a result that is reflected as more than 75% increase to the directivity-bandwidth product in some cases. Theoretical results are validated by simulation using commercial numerical electromagnetics software.

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%.

Homogenization of periodic metamaterials by field averaging over unit cell boundaries: use and limitations

We revise the method of periodic metamaterials homogenization initially proposed by Pendry, Holden, Robbins and Stewart (PHRS). The shortcomings of the PHRS derivation of the basic formulae of their method are outlined, subtleties of the method implementation are discussed and the range of validity of both the PHRS method and its later modifications are analyzed. We then give a rigorous derivation of the PHRS averaging formulae in the static approximation and modify the PHRS method to account for the phase advance of an incident wave across the unit cells of metamaterials beyond the quasistatic regime. The advantages of our proposed method are illustrated by numerical calculations of the effective parameters of some periodic metamaterials.