This paper describes a method of designing Frequency Selective Absorber (FSA) which has a transmission band between two neighboring absorption bands. The proposed FSA is composed of a lossy layer on the top and a lossless layer at the bottom. The transmission characteristic is produced by the parallel LC resonators embedded in the lossy layer while the absorption ability is realized by the lumped resistors constructed in the lossy layer. An equivalent circuit model (ECM) is developed and discussed for a better understanding of this method. An FSA prototype is fabricated and measured for demonstration. Experiments show that the proposed FSA has a transmission band at the center frequency of 8.14 GHz, which agrees well with simulation. Both transmission and refection coefficients from 4.5 GHz to 7.5 GHz and from 9.1 GHz to 11.3 GHz are under -10 dB, which indicate good absorption in these frequency bands. In addition, the performance of the proposed FSA demonstrates a low sensitivity with respect to the polarization of incident EM waves and is maintained well when the incident angles range from 0˚ to 45˚.

High frequency measurements at 50 MHz-10 GHz were performed for the first time using interdigitated electrodes on a low temperature co-fired ceramic substrate to analyze fungal spores. Wet and dry spore generation methods were evaluated and tested with two different fungal species. The dry generation method was found feasible for RF measurements, since the component capacitance increased 14-21% in the 2-6 GHz range, but for the wet generation method the capacitance decreased only slightly (<1%). Based on these initial results the RF measurements have the capacity to evaluate the quantity of fungal spores but not to identify their species.

A printed dual-port coplanar waveguide (CPW)-fed antenna is proposed for wideband communication systems. The antenna includes two identical hybrid trapezoidal-elliptical radiating elements that are printed perpendicular to each other. Also, two orthogonal CPW lines are used to feed the antenna. In order to achieve broadband dual-polarized operation with a compact size, the geometrical parameters of the antenna are optimized by using Ansoft HFSS. The antenna was fabricated and tested. Reasonable agreement between the simulation and experimental results is obtained. The fabricated prototype with a small size of 25×53 mm² can cover the wide operating frequency band from 2.4 to 18 GHz (reflection coefficient less than -10 dB) for both ports. The measured isolation is better than 25 dB over the entire operating bandwidth. Moreover, the measured results show that the proposed antenna can provide omnidirectional radiation patterns with a good orthogonal polarization operation, reasonable gain, high radiation efficiency, and constant group delay.

Ground penetrating radar (GPR) may be used to detect cracks in a buried pipe. Using GPR, there are only a few techniques, such as statistical approach robust principal component analysis (RPCA). to detect cracks in buried objects. Buried nonmetallic pipe crack detection is an important application for GPR to analyze the structural health of underground pipelines. The strength of a reflected signal may be feeble from a cracked location as compared to position with respect to that from other positions of the pipe. Currently, crack detection is a challenging task, especially when the buried pipe is nonmetallic, and soil moisture varies. In this paper, the problem of crack detection in a PVC pipe using GPR is attempted. It is a challenge to detect small sized cracks in an underground PVC pipe because the GPR image is flooded with correlated background signal or clutter, and the image patterns are typically irregularly distributed. In order to efficiently detect the crack in a buried PVC pipe, a novel adaptive crack detection algorithm has been developed with the help of covariance of real GPR data and covariance of normal distributed synthetic Gaussian data. Results are evaluated and validated to show the effectiveness of crack detection algorithm.

The study done in this paper focuses on the detection of breast cancer by neuronal approach, by rotating the transmitting antenna from 15°, 30°, 45°, 60°, 75° to 90° relative to its initial position which is of 0° (i.e. to the opposite of the reciving antenna). We have generated our database by using a CST electromagnetic simulator for each antenna location. Then the learning and test phases of our artificial neural network (ANN) are done for seven antennae locations using two learning algorithms which are: the Scaled Conjugate Gradient Back-propagation (Trainscg) and the Gradient Descent with Momentum (Traingdm). A comparative study was conducted for all the seven cases. The results obtained are very satisfying and show that the best location of the transmitter antenna is at 60° and that the learning algorithm Trainscg gives better results than Traingdm.

This paper presents the power density evaluation and power mapping performance of a novel magnetic geared double-stator permanent magnet generator (DSPMG) which is proposed to address problems of mechanical geared generators for low-speed power generation applications. The operating principle is based on three PM rotors consisting of prime permanent-magnet (PM) poles in the middle rotor and field PM poles in the inner and outer rotors respectively. To evaluate the power density performance, a 2-D finite-element method (FEM) is used to predict the performance of the generator, and a demonstrator prototype is fabricated and evaluated experimentally. The power density characteristics of the proposed generator are analyzed and reported. The measured results agree closely with the simulated ones to verify the validity of the magnetic geared generator design. Finally, a measurable comparison is conducted with other published prototype magnetic gear machines to demonstrate its benefits of higher power density and smaller volume size.

In this paper, the design and implementation of a three-layer linear polarization converter having broadband and asymmetric transmission (AT) properties is demonstrated. A 3.2 mm thick transmission-type polarization converter with two separate operating frequency bands is obtained with a cut-wire sandwiched by two layers of diagonal split-ring resonator (DSRR). The asymmetric transmission property can be realized by rotating the upper and lower DSRR dislocation, and its physical mechanism can be explicated by the Fabry-Pérot-like interference effect. Experimental results are presented and compared to numerical simulations, and they demonstrate that the proposed polarization converter has a significantly polarization conversion ratio over 0.8 in frequency bandwidths 8-11 GHz and 17-21 GHz for the forward and backward incidences. The proposed polarization converter has a great potential to be used as an asymmetric transmission radome or diode-like device in microwave domain.

In this paper, a novel planar waveguide with quasi-TEM mode for periodic structure measurement applications is proposed. Unlike conventional parallel double conductor transmission lines (PDCTL) which suffer from mismatch to 50 ohms, high insertion loss in higher frequency band, the proposed planar waveguide consisting of an F4B substrate, s metal conductor line, and a metal base has easy access to match to 50 ohm through a special transition region and also has a satisfactory insertion loss in a wide band. The metal conductor line etched on one side of the F4B substrate, and the metal base is parallel to mimic a perfect electric wall, where a ``fake'' infinite plane is realized. The proposed planar waveguide has wide measurement bandwidth with the reflection coefficient below -15 dB, which cannot be realized by a standard rectangular waveguide. Good agreements between the simulated and measured results are obtained. In addition, a simple periodic structure is designed as an example. The transmission characteristics of the periodic structure are simulated and compared in two different methods, namely, standard periodic structure simulation method in free space and proposed planar waveguide method. All the measured results demonstrate the validation of our designed planar waveguide, which is convenient and economic for periodic structure measurement applications.

The proposed microstrip antenna is based on fractal techniques and designed for wireless applications. The radiating element is an A-shaped triangle on which fractal concept is applied. Fractal concept is applied on the proposed A-Shaped Fractal Microstrip Antenna (ASFM-Antenna), similar to English alphabet letter A. Further the analysis and verification of result is achieved by testing the fabricated antenna and also comparison of simulated and experimental results. Von Koch's snowflake concept is used in which a single line is divided into four new lines, and it is done at each side of the triangle. This step is repeated. In this paper, a two-iteration Koch generator is used, thus the proposed antenna is designed. Simulations are carried out using commercially available HFSS (High Frequency Structure Simulator) based on finite element method. The antenna is simulated and fabricated, and results are recorded. It is found that simulated and experimental results are in close agreement with each other. The antenna resonates at 11.44 GHz, 13.178 GHz, 15.482 GHz, 19.902 GHz and 23.529 GHz. Hence, X-band [8.2-12.4 GHz], Ku-band [12.4-18 GHz] and K-band [18-26.5 GHz] are the frequencies of operating bands under consideration.

In this paper, we report the formulation to account for dielectrics in a first principles multipole-based cable braid electromagnetic penetration model. To validate our first principles model, we consider a one-dimensional array of wires, which can be modeled analytically with a multipole-conformal mapping expansion for the wire charges; however, the first principles model can be readily applied to realistic cable geometries. We compare the elastance (i.e. the inverse of the capacitance) results from the first principles cable braid electromagnetic penetration model to those obtained using the analytical model. The results are found in good agreement up to a radius to half spacing ratio of 0.5-0.6, depending on the permittivity of the dielectric used, within the characteristics of many commercial cables. We observe that for typical relative permittivities encountered in braided cables, the transfer elastance values are essentially the same as those of free space; the self-elastance values are also approximated by the free space solution as long as the dielectric discontinuity is taken into account for the planar mode.

A synthesis problem of a 2D array of thin linear vibrators, whose geometric centers are located at the nodes of a flat rectangular grid with double periodicity solved. The problem can be formulated as follows. A 2D antenna array radiates monochromatic electromagnetic waves into free space. Suppose that the array radiation pattern (RP) can be scanned in space by varying complex surface impedances of separate vibrators. Then, it is necessary to determine vibrator surface impedances to control the direction of the RP maximum. The analytical solution of the impedance synthesis problem, as an alternative to a numerical solution of a two-dimensional equation system, was obtained under two assumptions: the vibrators are excited by electric currents of equal amplitudes, and the RP of each radiator does not differ from that of an isolated radiator. Verification of theoretical formulas will be done by comparing them with relations known for one-dimensional equidistant arrays.

A self-consistent time-domain travelling-wave model for the simulation of self-assembled quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) is developed. The 1-D time-domain travelling-wave model takes into consideration of time-varying QD optical susceptibility, refractive index variation resulting from intersubband free-carrier absorption, homogeneous and inhomogeneous broadening, and QD spontaneous emission noise source. Carrier concentration rate equations are considered simultaneously with the travelling wave model. Effects of temperature on optical susceptibility and carrier density in the active region are taken into account. The model is used to analyze the characteristics of 1.3-μm oxide-confined QD InAs-GaAs VCSEL. The field distribution resulting from time-domain travelling-wave equations, in both the active region and distributed Bragg reflectors, is obtained and used in finding the device characteristics including light-current static characteristics considering the thermal effect. Furthermore, the dynamic characteristics and modulation frequency response are obtained in terms of inhomogeneous broadening.

An annular-ring element for building a miniaturized bandstop frequency selective surface (FSS) structure which possesses a superior performance with respect to electromagnetic wave polarizations and incident angles is introduced in this paper. The proposed element has prominent miniaturization characteristics with a unit dimension of 0.061λ×0.061λ, where λ represents the free-space wavelength corresponding to resonant frequency. Miniaturization of the proposed FSS element is achieved by constructing special meandered strips in geometry and arranging lumped components between the elements. The advantage of this method lies in its great simplicity in tuning the resonant frequency of FSS by adjusting values of the printed capacitors rather than rebuilding the geometry. The obtained FSS also exhibits a stable performance in terms of angle stability and polarization insensitivity. Prototypes of the proposed FSS are fabricated and measured to verify design method. Measurements are well in line with simulation results.

In this paper, a broadband transition structure from microstrip line to slotline with band-notched characteristic is proposed. To match the 50 Ω microstrip line, 4 Chebyshev impedance transformations are used in the transition structure, and its bandwidth is widened. There is a fan-shaped radial line at the microstrip terminal. A U-shaped slot is etched on the microstrip line with stepped impedance matching to achieve band-notch characteristic. By changing the length of the slot, the band notch is realized at different frequencies. Simulation and optimization of the transition structure are made by using the high frequency simulation software HFSS in this paper to achieve the band-notch function at 3.37-3.84 GHz and 10.67-11.14 GHz. In the rest of the band, return loss S₁₁ is less than -15 dB, and voltage standing wave ratio (VSWR) is less than 1.5.

This paper proposes a two-dimensional (2-D) inverse synthetic aperture radar (ISAR) imaging method with nonuniformly obtained angle samples. A one-dimensional (1-D) radar image, a range profile, is obtained using frequency samples within a given bandwidth. 2-D ISAR images are then obtained by acquiring the Doppler spectrum using range profiles obtained from multiple observation angles having a constant interval. However, when ISAR images are obtained by applying the range-Doppler imaging method for a target scattered signal with nonuniform angle samples, a clear image cannot be obtained. In this paper, we propose a method to generate a covariance matrix from a nonuniform angle sample and obtain an ISAR image based on the multiple signal characterization (MUSIC) technique. The proposed method can be applied to the target scattering signal using a search radar, which observes target with nonuniform aspect angles. We present a scattering signal model of a target for the search radar and provide ISAR images obtained by applying the proposed method to simulated and measured data, respectively. Results reveal that the proposed method improves image quality and reduces computation time compared to the conventional method.

The aim of this paper is to present a compact coplanar waveguide (CPW) fed switchable UWB antenna as an antenna filter with adjustable notched frequency bands. Novel miniaturized tunable resonators are also presented to achieve notched bands. The antenna is made tunable in notched frequency bands without any modification in the basic structure. These stopbands are made tunable just by varying values of the capacitors according to our desired applications. The antenna structure is very compact having overall dimensions of 24×30.5 mm² with partial ground plane.The proposed small size, variable, low cost and low weight antenna with good propagation characteristics will pave the way for UWB wireless communication applications.

Ultrablack materials play an essential role in astronomical observation and many thermal applications. Many material systems such as vertically aligned carbon nanotubes have produced extraordinarily high absorption, but require complicated fabrication. Here we report a single step self-masked etching process performed on compressed-coal graphite plates on a silicon substrate, which produces an ultrablack material with 0.7% hemispherical reflectance in the visible region and specular reflectance below 0.7% between 850 nm and 10 μm. Nanoscopic pieces of silicon are ripped off the substrate and deposit on the graphite resulting in carbon nanoneedle structures, which grow linearly with etching time reaching a height of 5.7 μm after 60 minutes.

A wideband circularly polarized magnetoelectric dipole antenna fed by a Γ-shaped structure is investigated. In the design, a pair of vertical plates connected to ground work as a magnetic dipole, while a pair of rotationally symmetric horizontal plates with strips bent downward work as an electric dipole. And four metallic plates are vertically added on edges of the ground, forming a cavity reflector with four gaps to improve the axial ratio (AR) bandwidth. Measurements show that the antenna has a wide impedance bandwidth of 102% from 1.35 GHz to 4.2 GHz for voltage standing wave ratio (VSWR) ≤ 2 and a 3-dB AR bandwidth of 79.7% from 1.6 GHz to 3.72 GHz, over which the antenna gain varies from 5.4 dBic to 10.6 dBic. Furthermore, the antenna exhibits right-hand circular polarization and has good unidirectional radiation characteristic. The proposed antenna can be applied to wideband wireless applications.

An implantable magneto-electric antenna (IMEA) aiming for operation at ultra-wideband (UWB: 3.1-10.6 GHz) frequency spectrum is presented for biotelemetry usages for the first time. The IMEA is composed of a horizontal planar bowtie radiator, from whose middle the antenna is excited, and a vertically inclined rectangular radiator. The two radiators are complementary and correspond to electric and magnetic dipoles, respectively. The radiators are built over a square dielectric material (ε_r = 6, σ =0.0005) with a cavity for embedding suitable accompanying circuitry system. The IMEA with its biocompatible insulator (PEEK: ε_r = 3.2, tan δ = 0.01) measures 1456 mm³ in volume. HFSS software was used to carry out numerical optimization of the IMEA with a simple multilayered model of body tissue (Skin, Fat and Muscle) as the host environment. The simulated result of the proposed IMEA shows over 90% impedance bandwidth (S₁₁<-10 dB) and records a remarkable high gain of 2 dBi within 70% bandwidth. The radiation efficiency is around 50%, and a unidirectional radiation pattern with little back lobe is observed.

An LED array with 2N-1 lines and N rows is designed, which consists of red, blue, and far-red LEDs. The red and blue LEDs with N lines and N rows are uniformly and intervally arranged. The central distance between adjacent red and blue LEDs is d. The far-red LEDs are filled in-between every two lines of red and blue LEDs, which results in an array of far-red LEDs with N-1 lines and N rows. The central distance of adjacent far-red LEDs is also d. By using the imperfect Lambertian model, the irradiance distribution of the LED array with N being even and odd is derived in the reference plane, respectively. Also, solving equation of the optimal distance d is presented. Numerical results show that irradiance distributions of the three mixed-color, red, blue, and far-red lights of the LED array are uniform in the reference plane. Ratios of R/B and R/Fr are both relatively uniform in the reference plane. The ratio of R/B in the case of N being even is more uniform than that in the case of N being odd. However, the ratio of R/Fr is opposite.