Dimitris Psychoudakis

Topology design optimization of dielectric substrates for bandwidth improvement of a patch antenna

Most literature studies dealing with design optimization for RF applications focused to a large extend on size and shape optimization. So far, material and topology optimization has not been pursued primarily due to the challenges associated with the fabrication of inhomogeneous materials and the limited access to analysis tools. In this paper, we focus on optimum topology/material design of dielectric substrates for bandwidth enhancement of a simple patch antenna. First, the possibility of designing arbitrary dielectric constant materials using off-the-shelf dielectrics is presented as is necessary for the practical fabrication of inhomogeneous substrates. Then, a formal design optimization procedure is conducted using the solid isotropic material with penalization (SIMP) method by relying on a fast full wave finite element-boundary integral (FE-BI) simulator. The SIMP method is a mathematically well-posed topology optimization algorithm because a continuous density function is used to relate the cell variable to the actual material properties. This also allows for a formulation in a versatile optimization framework. Sequential linear programming (SLP) is used to solve the nonlinear optimization procedure with the sensitivity analysis based on the adjoint variable method. An important advantage of the proposed design optimization approach is its generality to handle multiple objectives and multidisciplinary problems. Using the proposed automated design procedure, inhomogeneous substrates are designed which allow for 250% bandwidth enhancement of the square patch antenna. Typically, only a few iterations are needed to reach convergence. Finally, the designed substrate is post-processed with image processing and fabricated using thermoplastic green machining.

A Portable Low-Power Harmonic Radar System and Conformal Tag for Insect Tracking

Harmonic radar systems provide an effective modality for tracking insect behavior. This letter presents a harmonic radar system proposed to track the migration of the Emerald Ash Borer (EAB). The system offers a unique combination of portability, low power and small tag design. It is comprised of a compact radar unit and a passive RF tag for mounting on the insect. The radar unit transmits a 5.96 GHz signal and detects at the 11.812 GHz band. A prototype of the radar unit was built and tested, and a new small tag was designed for the application. The new tag offers improved harmonic conversion efficiency and much smaller size as compared to previous harmonic radar systems for tracking insects. Unlike RFID detectors whose sensitivity allows detection up to a few meters, the developed radar can detect a tagged insect up to 58 m (190 ft).

Multiobjective Optimal Antenna Design Based on Volumetric Material Optimization

There is growing interest for small antennas that concurrently have higher functionality and operability. Multiobjective optimization is an important tool in the design of such antennas since conflicting goals such as higher gain, increased bandwidth, and size reduction must be addressed simultaneously. In this paper, we present a novel optimization algorithm which permits full volumetric antenna design by combining genetic algorithms with a fast hybrid finite element-boundary integral method. To our knowledge, this is the first time that a full three dimensional antenna design is pursued using concurrent shape, size, metallization as well as dielectric and magnetic material volume optimization. In comparison to previous optimization pursuits, our approach employs a wide-frequency sweep using a single geometry model, thus, enhancing speed, along with several discrete material choices for realizable optimized designs. The developed algorithm can be interpreted as a three dimensional Pareto optimization scheme and provides the designer with several choices among the best antennas, according to design goals and constraints. The final designs are associated with very thin (~0.01lambda) material substrates and yield as much as 15% bandwidth using a 0.1lambda--0.4lambda aperture subject to various gain and bandwidth requirements

Embroidered Multiband Body-Worn Antenna for GSM/PCS/WLAN Communications

A novel textile-based body-worn antenna covering the Global System for Mobile Communications/personal communications services/wireless local-area network frequency bands is presented. This antenna was made of densely embroidered metal-coated polymer fibers (e-fibers). These e-fibers are 15 μm thick and consist of high strength, flexible polymer cores with conductive silver coatings, providing mechanical flexibility and low loss at radio frequencies. When measured in free space, the textile antenna showed comparable performance to its copper counterpart, having ~ 2 dBi realized gain at all three bands. This textile antenna was simulated and measured on a full body phantom to determine the bodys influence on antenna performance, including frequency detuning and pattern shadowing. The measured radiation pattern of the body-worn antenna matched well with simulation at various on-body locations for the three bands. Field measurements were also carried out by mounting the antenna onto the shoulder of a jacket, and using it to replace the one of a cell phone. We found that the communication quality using the body-worn textile antenna was equivalent to the best location of the original cell-phone antenna. Therefore, this textile-based antenna provided for a more reliable body-worn communication when mounted on the bodys shoulder.

Patch-antenna miniaturization using recently available ceramic substrates

The recent availability of high-contrast, low-loss ceramic materials provides us with possibilities for significant antenna miniaturization. This paper explores the use of low-temperature co-fired-ceramic (LTCC) substrates in producing a miniaturized patch-antenna design. Of particular interest in the design are parameters such as substrate thickness, input impedance, radiation efficiency, and bandwidth due to the high-contrast ceramic. We propose a thick substrate to increase bandwidth. However, the substrate is truncated to mitigate surface-wave loss, with possible texture to provide dielectric-constant control for improved impedance matching. Utilizing these proposed design modifications, a miniaturization factor of more than eight was achieved, with a return-loss half-power bandwidth greater than 9%. Moreover, respectable gain was maintained, given the achieved miniaturization

Design method for aperture-coupled microstrip patch antennas on textured dielectric substrates

Textured dielectric substrates made with multiple ceramics are now being introduced in antenna design. This paper presents a design technique for fabricating aperture-fed patch antennas with textured dielectrics. An example microstrip antenna is fabricated using this technique and measurements are compared to simulations. We show that by combining two ceramic materials a new composition is formed that has different properties from the original ceramics. These properties are measured and used in the fabrication of the antenna.

Conformal Asymmetric Meandered Flare (AMF) Antenna for Body-Worn Applications

A conformal body-worn antenna is presented for communications at 300 MHz. The antenna consists of a thin broadband flared-dipole element printed on a thin (0.1 mm) FR4 substrate without metallic backing or other shielding. The letter presents the design approach for tuning, matching, and mounting the antenna on the human body. Measurements are given for a human body phantom, and these are compared to simulations. Different antenna positions for improved coverage are also presented.

Flexible textile antennas for body-worn communication

This paper presents an embroidered body-worn antenna using conductive fibers (E-fibers). The antennas conductive surfaces were fabricated using precise and automated embroidering techniques to produce fully flexible and conformal antenna elements attached to regular fabrics and clothing. These E-fiber antennas offer desirable mechanical properties without undermining electrical performance for body-worn, on-clothing applications at radio frequencies (RF). In this study, we used an embroidered asymmetric meandered flare (AMF) dipole antenna to validate the textile antennas performance. Its excellent RF performance was found comparable to conventional printed antennas. Therefore, these new E-fiber antennas may be integrated into scarves, handbags, shirts, coats or hand bands for convenient carefree health monitoring and wideband communications.

Determining the Relative Permittivity of Deep Embedded Biological Tissues

Human tissue characterization, deep into the body, has been of interest for decades. X-rays are used for locating tumors. However, such surgery-free identification methods fail to verify whether tumors are benign or malignant without surgical extraction and testing of sample tissue. Moreover, X-ray scans do not allow for continuous time monitoring because frequent exposure to ionizing radiation and contrast agents is harmful to the human body. Probe methods do provide accurate approximation of the dielectric constant εr but requires direct access to the specimen, making them suitable only for in-vitro applications. On the other hand, while common wearable health monitoring systems are advantageous for everyday use, they are mainly focused on simple functions such as temperature, and heart rate monitoring.

Antenna Miniaturization Using Magnetic-Photonic and Degenerate Band-Edge Crystals

Engineered materials, such as new composites and electromagnetic bandgap and periodic structures have been of strong interest in recent years, due to their extraordinary and unique electromagnetic behaviors. This paper discusses how modified materials, inductive/capacitive lumped loads, and magnetic materials/crystals are impacting antenna miniaturization and performance improvements (e.g., bandwidth and gain reduction, multi-functionality, etc.). Dielectric design and texturing for impedance matching has led to significant size reduction and higher-bandwidth low-frequency antennas, for example. The recently introduced magnetic-photonic crystals (MPCs) and double band-edge (DBE) materials, displaying spectral nonreciprocity, are also discussed. Studies of these crystals demonstrated that magnetic-photonic crystals exhibit the interesting phenomena of (a) drastic slowing down of the incoming wave, coupled with (b) significant amplitude growth, while (c) maintaining minimal reflection at the interface with free space. The phenomena are associated with diverging frozen modes that occur around the stationary inflection points within the band diagram. Taking advantage of the frozen-mode phenomena, we demonstrate that individual antenna elements and linear or volumetric arrays embedded within the magnetic-photonic crystal and double band-edge structures allow for antenna sensitivity and gain enhancements