Vol. 85

The literature lacks detailed information about the electrical properties of the plastic filaments used in 3D printing. This opens the way for research on characterizing the types of materials used in these filaments. In this work, a method for the extraction of the dielectric constant and loss tangent of materials is described. This method, which is suitable for characterizing any dielectric material, is then used to characterize 3D-printed samples based on different filament materials and infill densities over a very wide frequency range [0.02-10 GHz]. The selected materials are Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS) and a semi-flex filament that combines the two important features of flexibility and endurance. These three types are the most commonly used in 3D printing. The two$-$line technique is applied to extract the complex permittivity of the material under test (MUT) from the propagation constant. This method employs the uncalibrated scattering parameters with different types of transmission line for any characteristic impedance. A rectangular coaxial transmission-line fixture has been used to validate the theoretical work through simulations and measurements involving the 3D filament samples.

This paper presents a novel engineered artificial dielectric superstrate for improving the radiation characteristics of a CPW-fed planar antenna. Even though the permittivity of the material used for the superstrate is only 4.4, it attains an effective permittivity of more than 18 because of the periodic pattern printed on it. Due to the high value of effective permittivity an improvement in radiation pattern, impedance matching and gain of the antenna are obtained. From the measured results an impedance bandwidth of 374 MHz from 2.453 GHz to 2.827 GHz is observed for the antenna loaded with superstrate. The periodic pattern is fabricated on a substrate of thickness 1.6 mm, and it occupies an area of 56.45×42.48 mm².

In order to energize the biomedical implantable electronic devices wirelessly for in vivo health monitoring of patients in an isolated, outdoor and inaccessible environment, an alternate driving energy source is highly desirable. In pertinent to this, a photovoltaic driven wireless energizing system has been explored. The system is designed to convert solar energy to a high frequency energy source so as to facilitate energy transfer through resonant inductive link to the automated bio-medical sensing system allied with the receiver unit. The received power is observed to be 286 mW for the coil separation gap of 3 cm and load value of 40 Ω at the resonant frequency of 772.3 kHz. The automated biomedical smart sensor is competent to acquire the body parameter and transmit the consequent telemetry data from the body to the data recording segment. The real-time body temperature parameter of different living beings has been experimented, and to ensure the accuracy of the developed system, the observed parameter has been matched with a calibrated system. The proposed scheme can be suitable for monitoring wirelessly other in vivo health parameters such as blood pressure, bladder pressure, and physiological signals of the patients.

A wireless power transfer system based on magnetic resonant coupling (MRC) is preferred in many applications as it provides good balance between power transfer efficiency and physical separation distance. However, wireless power transfer to multiple loads through magnetic resonance coupling demands time due to the noteworthy advancement in consumer portable electronic devices. However, operating multiple loads corresponding to their optimum power level is a major concern which mostly depends on the position of the receiving coils with respect to the transmitting coil. This article presents an experimental investigation to find the best suited position of the multiple receiving coils corresponding to a spirally configured transmitting coil for powering multiple loads at their optimal power level. Through this technique multiple electronic devices can be powered up not only in one direction but also in both directions with their optimal power level. The findings will greatly assist the design of a resonant wireless power transfer system for powering multiple loads.

In this paper, a design method that employs simulated annealing (SA) algorithm to create stub structure of a dual-layer microstrip patch antenna for circular polarization is presented. Firstly, based on established controls of SA algorithm, a series of stub structures have been created automatically on the stacked parasitic element - (Split Ring Resonator) SRR of antenna. The desired stub structure is chosen according to the generation of orthogonal modes that produce circular polarization through the electromagnetic coupling to the driven patch with an SRR-shaped slot. Then, a dual-layer microstrip patch antenna with a Z-shaped stub and left-hand circularly polarized (LHCP) characteristic is obtained by employing the assisted design. The designed antenna is simulated, optimized, fabricated, and measured. The results show that the microstrip patch antenna with Z-shaped stub has a simulated minimum axial ratio of 1.64 dB at 2.4 GHz, and the measured peak gain can be up to 5.87 dBi.

Due to the exponential growth of the number and scale of wind farms, wind turbine clutter has become the main factor that limits the detection performance of weather radar systems. As a consequence of the rapid rotation of wind turbine blades, conventional ground clutter filters are ineffective at removing wind turbine clutter (WTC). An improved range-Doppler joint interpolation for WTC suppression is proposed in this paper. The proposed algorithm firstly exploits the frequency-domain transformation technique to improve the signal-to-noise ratio (SNR), so that the interpolation algorithm can recover the weather signal in the case of low SNR. Then, the weather signals recovered by one-dimensional interpolation in range domain and Doppler domain are calculated, respectively, and the two-dimensional joint interpolation is performed based on two-dimensional weighted coefficients calculated via a least mean squares criterion. Theoretical analysis and simulation results show that the proposed algorithm effectively suppresses the wind turbine clutter and significantly reduces the bias in radial velocity estimation caused by WTC contamination in low SNR environments.

A metamaterial sensor that can be applied to detect water content in emulsified oil is proposed, which is reusable in experiment and nondestructive to the sample. Electric field of the original absorber is researched to guide the design of microfluidic. Also, its equivalent circuit model is proposed to validate its ability as a sensor. The calculated sensitivity of the sensor is 339 MHz/ε'_r in the range of 11.26 GHz to 10.044 GHz, indicating its potential for detecting the emulsified oil. The experimental results reveal the reliable process of detection and the linear relationship between frequency shift and water content. This work provides a fast and convenient solution to check the quality of lubricant oil to some extent, which is relatively valuable to modern machinery.

A novel high-swing Class-C VCO with an amplitude feedback loop is presented. The amplitude feedback loop is used to ensure the start-up of the VCO which also makes the proposed VCO always have an optimal phase noise against the PVT variations automatically. The proposed circuit is implemented in a 65 nm CMOS process. The VCO has exhibited a measured phase noise of -128.6 dBc/Hz at 1 MHz offset from the 1.52 GHz carrier frequency with a 1.4 mW power consumption. The variation of measured phase noise at 1 MHz offset is less than 2.3% while temperature changes from -40˚C to 100˚C.

As a kind of complicated targets, the nonrigid vibration of aircraft, their attitude change, and the rotation of their ro-tating parts will induce complicated nonlinear modulation on their echoes from low-resolution radars. These kinds of modulation play an important role in target classification. However, due to the influence of clutter and noise, these kinds of modulation have the characteristics of fuzziness and randomness. As a quantitative to qualitative conversion model based on traditional probability statis-tics theory and fuzzy theory, backward cloud model can be used to model and analyze the modulation characteristics of the conven-tional low-resolution radar echoes from aircraft targets. By considering the sample values of the echo data as individual cloud drop-lets, the paper extracts the cloud digital features such as the expectation, entropy and hyper-entropy of each group of echo data, and investigates the application of these features in aircraft target classification based on support vector machine. The research results show that the backward cloud model can describe the aircraft echoes well, and the echo cloud digital features can be effectively used for the classification and identification of aircraft targets.

The hybrid magnetic bearings (HMB) stabilize suspension in equilibrium position by providing bias flux through permanent magnets. The loss generated during operation causes the temperature of the HMB to rise, which affects the stability of the magnetic bearing. In this paper, the loss and temperature of HMB are analyzed by finite element analysis software. The results show that the loss of HMB is mainly distributed in the rotor part, and the temperature of the rotor part is obviously higher than that of the stator part. The relationship between the structural parameters such as air gap length and pole width, and the loss of HMB is obtained by finite element analysis. According to the analysis results, the structural parameters are optimized by GAPSO. After optimization, the loss and temperature of HMB are significantly reduced.

In this paper, a compact planar mono-band multiple input multiple output (MIMO) antenna with four monopole elements is presented for X-band satellite applications (7.2-7.8 GHz). The MIMO antenna resonates at 7.5 GHz, with high isolation (more than 26 dB) between its ports. It consists of a four closely arranged symmetric monopole antennas with edge-to-edge distance of 7.2 mm (0.18λ). In the top face, different forms are loaded at the rectangular patch. U slot defected ground structure (DGS) has embedded in the ground plane. The prototype of the proposed MIMO antenna is simulated, fabricated and measured to examine the performance of this antenna in terms of S parameters, radiation patterns, the envelope of correlation coefficient (ECC) and the diversity gain (DG). As a result, the presented antenna has a high isolation (S₁₂ < -26 dB) at 7.5 GHz with impedance bandwidths is about 430 MHz (7.28 GHz-7.71 GHz), which covers the X-band applications. The diversity gain is about 10, and the envelope correlation coefficient of antenna is less than 0.02 which means that the antenna has high performance at the resonance frequency.

The vibration and noise problems caused by the radial electromagnetic force of the Bearingless Switched Reluctance Motor (BSRM) severely restrict its wide application. The purpose of this paper is to research the electromagnetic vibration and noise of Single-Winding Bearingless Switched Reluctance Machine (SWBSRM). Firstly, the radial electromagnetic force, which is the excitation source of electromagnetic vibration, is analyzed. Secondly, the three-dimensional (3D) model of stator structure is established by ANSYS finite element analysis (FEA) software, and its modal analysis is carried out to obtain its modal shape and corresponding modal frequency, which provides a reference and basis for researching the mechanical vibration of the SWBSRM. Finally, the harmonic response field analysis and sound field analysis model are established, and the vibration and noise of the motor under radial electromagnetic force are analyzed by using the magnetic-solid weak coupling analysis method.

In this paper, an integrated switchable and tunable bandpass filter is designed, simulated, and fabricated. This integrated bandpass filter is able to switch as well as tune in the ultra-wideband (UWB) as well as 2.4 GHz band. At first, a UWB bandpass filter is developed which consists of two bent shorted quarter-wavelength stubs and a connecting half-wavelength stub. Subsequently, a 2.4 GHz bandpass filter is realized by connecting another half-wavelength stub on top of the UWB filter. RF pin-diodes are used for switching the bands between UWB and 2.4 GHz bandpass filter. The switchable bandpass filter converts into a tunable filter by changing the inductance or the length of shorted stubs through the pin diodes. A detailed parametric analysis is done for calculating different stubs lengths of the UWB as well 2.4 GHz bandpass filter. The simulation results show a high rejection level of >40 dB at the lower frequency and a low insertion loss of 0.8 dB in the passband for UWB filter. For 2.4 GHz bandpass filter, the simulation results show an insertion loss of 0.42 dB and a 3 dB bandwidth of 796 MHz. The filter is fabricated on a Rogers 4003 substrate, and the measurement results of the switchable filter in the UWB band show an insertion loss of 2.1 dB and a 3 dB bandwidth of 7 GHz. In the case of 2.4 GHz bandpass filter, the insertion loss is 0.78 dB.

In this paper we revisit the condiagonalization of the Sinclair backscattering matrix, to overcome the Huynen decomposition issues, so as to correctly extract scatterer polarimetric properties. The correct extraction of scatterer polarimetric properties will lead to the correct classification of the scatterer predominant scattering mechanism. Huynen used the congruence transformation by a special unitary matrix to diagonalize the Sinclair matrix into a real and nonnegative diagonal matrix. He also expressed the special unitary matrix in terms of the polarization ellipse parameters and associated them with the scatterer orientation, asymmetry, and skip angle. Unfortunately, this association was found misleading. As a result, it makes the scatterer classification ambiguous, for it is based on the scatterer skip angle and the diagonal matrix. To overcome these ambiguities, we perform the diagonalization procedure founded on the consimilarity transformation by a special unitary matrix, as proposed by Lüneberg. In order to correctly extract the scatterer asymmetry degree and orientation, we express the special unitary matrix in terms of an asymmetry operation and a pure rotation operation. Moreover, we integrate the scatterer skip angle in the diagonal matrix of the consimilarity transformation by having it complex, leading to an unequivocal scatterer characterization.

This paper studies the nonlinear effects induced by a TVS limiter on an entire system illuminated by a high power electromagnetic (HPEM) pulse through a simple model. The relations between the load responses and the incident electric field under different conditions are obtained numerically. The results show that the TVS limiter not only protects the circuit which it is intended to but also may increase the response of the other end which is connected to the circuit by a transmission line. The nonlinear effect of the TVS limiter on the other end is dependent on the incident direction of the external HPEM pulse, TVS location, line length, electric field level, and shielding cavity. When the effective coupling length (ECL) of a load is longer than the line length, or its coupling with external HPEM is much weaker than the other end, its response will be affected by the other end connected with a TVS limiter and will become nonlinear. The addition of a shielding cavity will increase the effect because the cavity will increase the duration of the field which results in a larger ECL. Due to the nonlinear effect of the TVS limiter, special attentions, such as considering different incident directions as many as possible in the real testing and setting more margins, should be paid in the protection design.

In this paper, a novel broadband high-isolation dual-polarized antenna is proposed for 5G application. The proposed antenna consists of L-shaped elements, Γ-shaped feeding strips, and a box-shaped reflector. The use of simple L-shaped antenna elements not only simplifies the manufacturing process, but also greatly increases the isolation between the two ports. Stable gain and radiation patterns are achieved by using box-shaped reflectors. Results show that an impedance bandwidth of 50.6% for S₁₁ < -10 dB & S₂₂ < -10 dB from 3.1 to 5.2 GHz was achieved, and port to port isolation was higher than 45 dB within the bandwidth. The gains of the measured antenna were 8.7±1.1 dBi in the whole operating frequency band. In addition, stable radiation pattern with low cross polarization, low back radiation was achieved.

The excitation of surface plasmon on a metallic grating can be observed by varying the polar angle, accompanied by the absorption of incident light. The absorption occurs at a resonance angle which is sensitive to the refractive index of the liquid coated on the surface of the grating. As a result, an application in index sensing is developed. However, the sensitivity by varying the polar angle is almost at the same level as a conventional prism couple-based sensor through angular detection. In our new setup, we propose two methods to improve the sensitivity to refractive index change using an index sensor. Our first method is a slight modification of the conventional setup by varying the azimuth angle instead of the polar angle. Absorption of the incident is also observed while scanning the azimuth angle. The second method is to utilize phase detection to realize high resolution in finding the refractive index of liquids. In the phase detection, a good linearity is observed in the experimental results, with a resolution 10 times higher than that of a conventional setup.

A surface wave antenna operating in the 2.4 GHz band and efficient for launching surface electromagnetic waves at metal/dielectric interfaces is presented. Theantennaoperation is based on the strong field enhancement at the antenna tip, which results in efficient excitation of surface waves propagating along nearby metal surfaces. Since surface electromagnetic waves may efficiently tunnel through deep subwavelength channels from inner to outer metal/dielectric interface of a metal enclosure,this antenna is useful for broadband radio communication through various conductive enclosures, such as typical commercial Faraday cages.

In this paper, a control strategy based on second-order sliding mode is proposed for a permanent magnet synchronous motor (PMSM) drive system applying direct torque control with space vector modulation (DTC-SVM). This control strategy combines the principles of super-twisting algorithms, direct torque control, and space vector modulation, designed to overcome some obvious shortcomings, such as the large ripple of flux linkage and torque in traditional DTC, the poor robustness of traditional PI controllers, and the chattering of traditional sliding mode control. It gives the system good steady state and dynamic performance. The results show that the proposed method effectively solves the above shortcomings. Meanwhile, the control strategy effectively accelerates the dynamic response ability of the system and improves the robustness to parameter perturbation.

In this paper, a dual-polarisation shared-aperture duplex antenna is presented for satellite communications at the standard microwave Ku-band, based on the integrated filtering-antenna concept and co-design approach. The design relies on the use of resonators coupled to the radiating dual-band dual-polarisation antenna. The resonant patch antenna forms one pole of each channel filter, resulting in a third-order filter in the Rx channel and a second-order filter in the Tx channel. The Rx and Tx ports of the antenna take in horizontal and vertical linear polarisations, respectively. The integrated duplexer helps to increase the isolation between the ports and the selectivity of each channel. The integration between the filter and the antenna is achieved by electromagnetic coupling, without the need of external matching circuits. Thus it attains a compact footprint. The operation frequencies of the demonstrated duplexantenna are from 11 to 12.5 GHz (12.8%) for the downlink to the Rx port, and from 13 to 14.4 GHz (10.2%) for the uplink at the Tx port. High port-to-port isolation of over 40 dB is realized to reduce channel interference. Flat in-band average gains are achieved to be 8.3 and 8.6 dBi, for the low- and high-bands, respectively.