In this work, magnetic metallic cobalt nanoparticles with an average particle size of 28 nm were processed as a dry powder with surface coating material and other organic additives to form a screen-printable ink to be cured at 110 °C. EFTEM and TGA-DSCMS-analyses were used to measure the thickness of the polymer, its coverage on cobalt nanoparticles and the inorganic solid content of the ink. The resolution of the printed patterns and the print quality were evaluated by surface profiler, FESEM and optical microscopy. The relative permeability of the thick film patterns with good printability was measured with a shorted microstrip structure over the frequency range of 0.2 to 4 GHz and complex permeability values were calculated from measured scattering parameter data. The ink attained real part of complex permeability values of up to 5.13 at 200 MHz with 70 wt.% of magnetic filler. The developed ink can be utilized in various printed electronics applications such as antenna substrates and magnetic sensors.

In this paper, we consider the imaging of thin dielectric inclusions completed embedded in the homogeneous domain. To image such inclusion from boundary measurements, topological derivation concept is adopted. For that purpose, an asymptotic expansion of the boundary perturbations that are due to the presence of a small inclusion is considered. Applying this formula, we can design only one iteration procedure for imaging of thin inclusions by means of solving adjoint problem. Various numerical experiments without and with some noise show how the proposed techniques behave

In this paper the definition of characteristic impedance for lossless microstrip and coplanar lines has been considered. It has been shown that due to a significant value of the displacement current related to longitudinal component of the electric field, impedance definition becomes ambiguous. Such ambiguity can cause considerable errors in design procedure. This effect is especially noticeable in the coplanar lines, in opposite to microstrip ones. To confirm the validity of the applied algorithm (spectral domain approach) the propagation coefficients and characteristic impedances have been compared to values obtained from commercial software.

This paper proposes a radio frequency identification (RFID) based collision-free robot docking in cluttered environment. Physical distance estimation sensors are fused to the developed degree of arrival (DOA) guided robot docking system, and collision-avoidance function is implemented based on the vector field histogram technique. Additionally, new simple but efficient DOA filtering algorithm is developed based on the gain control according to the improved robot control algorithm, which enables the robot to move continuously. The experimental results show that the robot can move to target transponder even though the estimated DOA is blocked by obstacles. The success rate does not reach satisfactory level due to the limitation of the employed sensors and collision-avoidance algorithm, but it is proved that the collision-free docking becomes available without any priori map and reference stations.

A new adjustable Electromagnetic Band-Gap (EBG) structure whose frequency response is controllable by adjusting spacer height is proposed. The finite difference time domain method is adopted for the simulations. Results show that the desired frequency response can be selected by adjusting the spacer height. The effects of the air-gap on the polarization dependent and conventional EBG structures have been investigated both theoretically and numerically. The agreement between the theoretical calculations and numerical results is reasonably good.

In this paper, a novel hybrid dielectric resonator (DR) antenna for Ultrawideband (UWB) short-range wireless communications is proposed. The proposed antenna consists of a microstrip fed monopole loaded with a half cylindrical dielectric resonator antenna of Rogers RO3010 mounted on RT5880 substrate with a finite ground plane. The microstrip line fed monopole antenna is on the other side of the substrate. Compared to the conventional circular cylindrical DR mounted on a finite ground plane (reference antenna), the proposed antenna has a reduction in the antenna size by about 30% with a bandwidth increase by about 22% than the reference antenna. The proposed antenna has a good impedance bandwidth. In addition, the proposed antenna has a quite higher and more stable gain than that of reference antenna. Moreover, the antenna has a good omni-directional radiation patterns in the H-plane. The proposed antenna is considered a good candidate for UWB short-range wireless communication systems.

A bandwidth improvement method in reflectarray antennas by using closely space elements, i.e. unit-cell sizes smaller than λ/2, has been investigated both numerically and experimentally in this paper. A new definition of phase error has been introduced to analyze the broadband mechanism of closely spaced phasing elements. Through full wave EM simulations, it is revealed that closely spaced elements achieve a smaller phase error over the band. Based on these theoretical studies two Ka-band reflectarrays were fabricated and their performance was measured across the frequency range of 30 to 34 GHz. It is demonstrated that the reflectarray designed with closely spaced elements achieves a notable improvement in gain bandwidth performance.

We propose a circularly polarized microstrip patch antenna using artificial magneto-dielectric (AMD) substrate. The proposed antenna has a square patch with dual feeding point using Wilkinson power divider in order to achieve circularly polarized radiation pattern. The AMD substrate is constructed by single sprit ring resonators, which are arrayed in both x and y directions. The designed antenna has the characteristics of the axial ratio less than 1.7 dB, the peak gain of 0.55 dBic, and the right handed circular polarized radiation pattern at Korea UHF RFID service band. The sizes of the antenna and radiating patch are 100 mm×100 mm×5.2 mm and 65 mm×65 mm (0.199λ₀×0.199 λ₀), respectively.

A thick metal microstrip diplexer is presented. The circuit is based on compact folded half wavelength resonators and uses a source/load-multi-resonator coupling method providing improved performance and greater design flexibility. Source/load coupling with multiple resonators introduces additional transmission zeros, and this coupling is enhanced by using high-aspect-ratio metal structures. Tall, narrow metal arms connected to the ports and extended to the non-adjacent resonators provide effective multi-resonator bypass coupling. The high-aspect-ratio diplexer fabricated using polymer-based deep X-ray lithography and 0.22 mm thick metal electroplating demonstrates the advantages of thick metal structures for coupled resonator applications.

To describe propagation of polarized electromagnetic wave within a disperse random medium a new Monte Carlo based technique with an adopted vector formalism has been developed. The technique has been applied for simulation of coherent backscattering of circularly polarized optical radiation from a random scattering medium. It has been found that the sign of helicity of circular polarized light does not change for a medium of point-like scatterers and can change significantly for the scatterers with the higher anisotropy. We conclude that the helicity flip of the circular polarized light can be observed in the tissue-like media. We find that this phenomenon manifests itself in case of limited number of scattering events and, apparently, can be attributed to the pulse character of incident radiation rather than to the specific form of scattering particles.

In this study, transmission characteristics of a novel THz wire waveguide --- conical metal wire with dielectric coating at 0.1-1 THz are studied. The investigation results show that the coated conical wire with virtually low attenuation and high energy concentration is a promising candidate as THz transmission medium. The calculation results agree well with that of simulation such as high frequency structure simulation (HFSS), which is based on the finite element method. In this paper, a novel transition from a coaxial line to the coated conical metal wire is designed. Although coaxial probe excitation has been used in microstrip lines and rectangular waveguides in microwave, millimeter-wave frequency domains, the present study shows that it is also an effective method to excite conical wire at THz frequency. As shown in the investigation results, the return loss of coax-conical wire transition is better than 20 dB from 0.1-0.5 THz, and the insertion loss is as low as 1 dB (the total length is 15 mm). It is a promising THz transition structure.

An accurate and flexible three-dimensional Volterra Time Domain Integral Equation (TDIE) algorithm is presented and implemented here to model the time-dependent electromagnetic field of arbitrarily shaped dielectric bodies. This development is motivated by the need for a modern high-resolution numerical tool that is capable of providing a full and comprehensive investigation of devices containing a diverse range of feature sizes or boundaries, in all three space dimensions plus time. Stability, accuracy and convergence of the algorithm are discussed and verified by means of canonical working examples.

This article presents a simple structure for reducing mutual coupling between two diversity planar monopole antennas for WLAN 5.2/5.8 GHz applications. The structure has two λ/4 (λ-wavelength in the substrate) slots cut into the ground plane between the two monopoles. In 0.5 λ_o (λ_o,-wavelength in the air) of the antenna spacing, mutual coupling was -33.3, -21.1 dB at 5.2, 5.8 GHz, respectively. The lowest mutual coupling of -33.3 dB was achieved at 5.2 GHz, which is 20.8 dB improvement over the reference.

A compact ultra-wideband microstrip-fed planar monopole antenna with dual band-notch characteristic is presented. Dual notched frequency bands are achieved by embedding an M-slot in the radiating patch and a W-slot in the ground beneath the feeding line. And the characteristics of the dual band-notched can be controlled by adjusting the length and position of the corresponding slot. Experimental results show that the proposed antenna, with compact size of, has an impedance bandwidth of 2.75~11.30 GHz for VSWR less than 2.0, except two notched bands of 3.25~4.20 GHz and 5.23~6.10 GHz. Moreover, this antenna exhibits good omnidirectional radiation patterns in the H-plane, stable antenna gains over the operation band, and perfect group delay in the time-domain.

The possibility of using non-Foster circuit to expand the bandwidth of a monopole antenna is investigated theoretically. Beginning with an inductor-loaded monopole antenna resonating at different frequencies by changing the value of the loaded inductor, we show that a frequency-dependent inductor is needed to enhance the bandwidth of the monopole antenna. The curve for the reactance of the frequency-dependent inductor versus frequency is fitted, which enlightens us to use a non-Foster reactive circuit to realize the frequency-dependent inductor. Based on the above studies, a monople antenna loaded with a non-Foster circuit is presented. Simulated results demonstrate that the input reactance of the loaded antenna becomes stable and approaches zero, which favors the impedance matching and extends the bandwidth to a certain extent. Finally, a passive (Foster) matching circuit is designed to improve the bandwidth further. A 0.69-m monopole antenna with 2.0:1 VSWR in the frequency range 30--150 MHz is designed and investigated.

This paper presents analysis and design of a Gaussian backscatter antenna with ring focus feed. The curvature of main reflector is Gaussian, and the subreflector is a portion of an ellipse. The antenna has axial symmetry. A backscattering technique is used with the main reflector to achieve wide beamwidth. The input parameters of the proposed antenna are derived in closed form. Physical theory of diffraction (PTD) is used to analyze the radiation pattern of the proposed antenna and verified with experimental results. The effects of the support structures on the radiation patterns of the proposed antenna have been investigated experimentally. The proposed antenna can produces high gain and wide beamwidth (coverage angle θ=±65°). This antenna can be used for realizing earth coverage beam in LEO satellite or indoor wireless LAN applications.

The paper describes pulse-based ultra-wideband (UWB) microwave imaging experiments for breast cancer detection using heterogeneous breast phantoms with dielectric properties mimicking the human breast. Three homogeneous and seven heterogeneous breast phantoms are used in tumor detection experiments. The phantoms have dielectric permittivity and conductivity higher than previously reported experiments, as well as clutters to represent the glandular tissue in human breast. The experiments are conducted in time-domain with pulse generator and real-time oscilloscope.

In this study, a general method for analyzing the multilayer optical planar waveguides with photonic metamaterial is presented. The propagation characteristics of TE waves guided by the film with both the permittivity and permeability less than zero are investigated theoretically. The formulae for the electric fields of TE modes in this structure have been proposed. Typical numerical results for dispersion characteristics are shown. The analytical and numerical results show excellent agreement.

This paper studies the left-handed behavior in conventional 2-port coupled line networks. The propagation parameters of 12 periodic structures, each has a different coupled line configuration, have been derived and the left-handed bands have been determined. Two structures were fabricated and measured to confirm the composite right/left handed (CRLH) characteristics. Measurements and EM simulations were in a very good agreement with the developed theory. In the light of the proposed theory, a geometrical circuit model was also proposed for split ring resonator (SRR). The model is capable to predict its performance over a wide band.

A dual-feed dual-polarized dielectric resonator antenna (DRA) with high isolation is proposed in this paper. The high isolation is achieved by using two hybrid feeding mechanism: one port having an H-shaped aperture coupled feed and the other with two out-of-phase probe feeds. The antenna is designed to operate at around 5.2 GHz for WLAN (Wireless Local Area Network) applications and experimental results show that it has more than 35 dB isolation over the entire impedance bandwidth. Good symmetric broadside radiation patterns with low cross polarizations are observed in the two principal planes, and in addition, the front-to-back (F/B) ratios for Port 1 and Port 2 are 10 and 18 dB, respectively.