Volume 77, Issue 5-6

In this letter, a new microwave sensor of the coaxial resonant cavity with a single-open-ended circuit loaded capacitor is proposed and used to detect the liquids’ complex permittivity. The improved cavity has a higher internal electric field and smaller size when compared with the cylindrical cavity, which gives the sensor a high sensitivity in measuring liquids’ complex permittivity. A coaxial resonant cavity operating in 1.9 GHz was designed in this work. The silicone hose used for the test is inserted vertically from the center of the cavity, and the liquids under test (LUTs) are guaranteed to be 2 ml each time. The dielectric properties of LUTs will cause perturbation to the internal electric field of the cavity. By analyzing the measured data, the sensitivity of the cavity is 0.12%, and the relative errors of the real part of the measured value and the reference value are 3.67%. which shows the measured value has a good agreement with the reference value.

In this paper, a quad-band polarization- and incident-angle independent low-profile metamaterial absorber is proposed. The design consists of three square rings one into another and one plus-shaped slot structure. The size of the unit cell is 11 × 11 mm 2 and is printed on an FR-4 substrate having a thickness of 1 mm. It provides 99.2%, 97.6%, 99.3%, and 99.9% absorption at 3.55 GHz, 5.27 GHz, 7.57 GHz, and 11.57 GHz, respectively, thus covering the S, C, and X bands. The surface current distribution of the proposed absorber is also shown at the four resonating frequencies to get a better insight into the design. Moreover, the stability of the proposed design is also validated with different incident angles (for both TE and TM modes) and polarization angles. In addition, a prototype of the proposed absorber structure is also fabricated and then verified experimentally.

To obtain radiation pressure of a hybrid chiral structure, we derive the transfer matrix method and optical force densities from the Maxwell stress tensor for a planar layered bianisotropic media. The key derivations are how to get wavevectors and field components of each layer, transfer matrices connecting four eigenwaves of adjacent chiral media, as well as the force densities expressed by co- and cross-polarized reflection and transmission coefficients. After the validation of the methods and programs is performed, the radiation pressure of a layered biaxial bianisotropic chiral slab is studied. The effects of linearly and circularly polarization incident waves, incident angle, thickness, opposite handedness (optical activity), anisotropy, gain and loss of chiral media on the radiation pressure are discussed. Our work elucidates the mechanism of light-chiral media interactions, provides better understanding of chiral detection, optical trapping, and biophysics.

This research focuses on an improved automatic target recognition algorithm for solving the classification challenge of ground-moving targets from pulsed-Doppler radar. First, it was studied how decision-making intervals affect the proposed algorithm. Second, the altering of the data augmentation process was investigated. Third, a consideration of the three time-frequency signal representations and finally the use of different deep learning models for the classification issues were examined. It is proven that the proposed algorithm can efficiently recognize all targets enclosed in the publicly available RadEch dataset, with 4 s of radar echoes. When the decision-making time is only 1 s, a classification probability of 99.9% was obtained, which is an improvement related to the other research studies in this area. Furthermore, when the decision-making time is reduced 16 times the classification accuracy is reduced by only 1.3%. Moreover, the proposed algorithm was successful on another dataset enclosing ground-moving targets from comparable pulsed-Doppler radar.

This paper reports investigations on the effect of array size on the RCS reduction bandwidth of checkerboard metasurfaces (CMS). Three CMSs, one on a Rogers substrate and the remaining on FR4, are considered. While the usual phase deviation criteria are used for the designs on both the substrates, additionally a set of modified criteria recently proposed are used for the FR4 substrate-based designs. While three different sizes – 120 mm 2 , 240 mm 2 , and 480 mm 2  – are considered for the simulation-based investigations for all the structures, an additional size of 600 mm 2 is also considered for one of them. The 8 and 10 dB RCS reduction bandwidths drop as array size increases. The bandwidth reduction is attributable to mutual coupling, as has been reported in an earlier study. As therefore expected, all of the three structures, for all sizes, present the same RCS reduction bandwidth when a mutual coupling mitigation technique is incorporated. For 10 dB RCS reduction bandwidth, this value approaches that estimated by using a mutual coupling independent semi-empirical equation that holds for infinite arrays.

The purpose of this study was to analyze and synthesize L-shaped compact microstrip antennas (LCMA) and T-shaped compact microstrip antennas using regression-based machine learning algorithms (TCMA). This was accomplished by simulating 3808 LCMAs and 900 TCMAs operating at UHF and SHF frequencies with different physical and electrical characteristics. The acquired data was utilized to create a data set containing the antennas’ physical and electrical characteristics, as well as their resonant frequencies in the TM 010 mode. Four baseline regression models and seven machine learning models were developed to determine the resonance frequency of antennas and the values of the physical parameters required for a particular frequency. To examine the efficacy of machine learning models, three-dimensional LCMAs and TCMAs were created using polylactic acid (PLA) and felt-based flexible substrates, as well as copper tape. The results illustrate the feasibility of using machine learning models for LCMA and TCMA analysis and synthesis.

Medical telemetry applications rely heavily on biomedical implanted antennas. These biomedical implanted devices can enhance and monitor patients’ daily life circumstances. A low-profile, downsized size implanted antenna operating at 915 MHz in the industrial, scientific, and medical (ISM) band is suggested in this research. The antenna is a simple slotted patch supplied by a 50-impedance coaxial probe. The radiator is made up of two slotted parasitic patches with one square-shaped outer radiator are manufactured on a Roger Droid RT5880 substrate with a standard height of 0.254 mm ( ε r  = 2.2, tan δ  = 0.0009). The entire dimension of the given antenna is 11 × 11 × 0.2514 mm with an electrical size of 0.049 λ g  × 0.049 λ g  × 0.0011 λ g . The antenna spans a bandwidth of 0.82–1.05 GHz when working inside muscle tissues (25.13 percent). The antenna’s calculations and experimental findings are quite similar. The computed specific absorption rate (SAR) values inside muscle of above 1 g mass tissue are 7.25 W/kg, according to the data. The stated SAR values are lower than the limit set by the Federal Communications Commission (FCC). As a result, the proposed small antenna is a strong contender for biological implantable applications.

Modern communication systems require an antenna with miniaturized size and large bandwidth with high data rate. In this article, a circular monopole antenna is presented with hexagonal patch on both sides of microstrip feedline and an I- shaped rectangular slot etched at the center of feedline to provide impedance matching. The modified loaded ground reduces the coupling between ground plane and radiation patch. This antenna has compact dimension of 30 mm × 25 mm with electrical size of 0.25 λ  × 0.20 λ. This antenna has been designed and simulated in HFSS commercial software and fabricated on FR4 substrate of thickness 1.6 mm with relative permittivity 4.4, loss tangent of 0.02. The experimental results are compared with simulated one, which are in close agreement. It attains a frequency band ranging from 2.4 to 56.6 GHz with reflection coefficient <−10, percentage bandwidth of 183.72%, Bandwidth Ratio (BR) 23.58:1, and Bandwidth Dimension Ratio (BDR) of 3674.40. The peak gain and radiation efficiency of this antenna is 12.77 dBi and 98.82% at 45.84 and 5.6 GHz respectively. Time domain analysis has been done, which proclaims that the proposed antenna has SWB characteristics. It may be useful for high data rate transmission, medical imaging, and other SWB applications.

Small size of the implantable antenna is the major concern in Implantable Medical Devices. A compact implantable wideband radiator working at the ISM band is proposed for biotelemetry applications. The overall dimension of the proposed radiator is 10 mm ⁎ 15 mm ⁎ 0.8 mm and the thickness includes substrate and superstrate thickness. The Coaxial feeding method is employed here. The inner and outer diameter of the coaxial feed is 1 and 1.5 mm respectively. The design process starts with a creation of rectangular patch of size 10 mm ⁎ 15 mm and the coaxial feed is located at (2.5, 7). Then slot like loops are introduced on a rectangular patch. This compact size is achieved by introducing small loops on a rectangular patch along with triangular cuts at the bottom right and top-left of the patch. The antenna is simulated with a tissue model (Skin, Fat, Muscle, Bone) and measured with a Body Equivalent Fluid (phantom). The −10 dB bandwidth is obtained over 1340 MHz (1.66–3 GHz) and the fractional bandwidth of 54.7% at the ISM band. The simulated gain and radiation efficiency of the radiator are −13.5 dBi and 3.15% respectively. The measured return loss of the proposed antenna is −30.53 dB and the SAR value averaged over 1 g tissue is 302.6 W/kg with 1 W input power. When compared to the previous works mentioned in the literature the proposed antenna displays wider bandwidth, high gain, low SAR and high radiation efficiency.

The driving power of the local oscillator (LO) determines whether the mixers can work in an optimal state. Implementing high-power LO sources is challenging for transceivers in the terahertz band beyond 100 GHz. In this paper, a cross-coupled oscillator based on Cascode amplifiers is proposed. Using the principle of current-reuse, a high-power doubler-embedded cross-coupled local oscillator is designed by combing a frequency doubler and a cross-coupled oscillator. The circuit is processed by 55-nm CMOS technology. With a supply voltage of 1.6 V, the output power reaches −1.3 dBm at 156 GHz, and the DC-to-RF efficiency is 2.1%. In addition, this local oscillator has been used in an up-conversion mixer.