In coaxial magnetic gear (CMG), magnetic modul ation ring is composed of a modulator and a connecting bridge. The torque performance of the magnetic gear are affected by the different structures of the magnetic modulation ring. In this paper, fifteen different kinds of magnetic modulation rings with different structures are proposed; they consist of three different shapes of modulators and five different locations of connection bridges. By using the two-dimensional finite element method (FEM), the magnetic flux density, magnetic line distribution, static torque, and steady-state torque of the CMG with different structures of magnetic modulation ring are analyzed. The results show that the innermost bridge has the least effect on the torque and torque ripple of the CMG, while the outermost bridge has the opposite effect. The torque capacity of the circular modulator and arc modulator is higher than that of the square modulator, and the circular modulator helps to reduce the inner torque ripple, while the square modulator helps to reduce the outer torque ripple. This paper can provide some references for the design of the magnetic modulation ring.
Magnetic micro-robots are used widely in a narrow space, such as internal inspections and desilting of slender pipelines, minimal- or non-invasive diagnoses and treatments of various human diseases in blood vessels, and micro-manipulations, micro-sensing fields. Magnetic micro-robots are usually driven by several electromagnetic coils. It is essential to understand the magnetic field and magnetic forces acting on micro-robots to drive the magnetic micro-robots more effectively. In this paper, the finite element method is applied to simulate the magnetic field generated by a coil assembly. Moreover, a three-dimensional magnetic force simulation is also performed to reveal the magnetic forces acting on a cylindrical magnetic micro-robot. Experimental measurements validate the simulated results. A Hall sensor is used to measure the magnetic field along the coil assembly's axial and radial direction. The micro-robot is glued to a connecting rod, fixing a force sensor to measure the magnetic forces acting on it. The measured results are in good accordance with the simulated ones, which prove the validity of the simulation. The results from this study show potential to provide a reference to magnetic micro-robot applications.
A Ku-band long linear helical subarray (LLHS) for a high-power cylindrical conformal array antenna has been developed. The LLHS consists of 80 helical antennas can be used to constitute conformal array of cylindrical surface. Through the research on the embedded probe structure, the adjustment of the coupling ability of different types of unit probes and the sealing method of the whole feeding, the problems of large feed reflection, the uneven coupling amount of the unit probe in the rectangular waveguide system are solved, and the LLHS which can be used in the high-power conformal array is realized. The LLHS which is 52.35λ length can obtain 25.2 dB gain, 2.31 dB axis ratio, 90% aperture efficiency, -15.65 dB reflection at 12.5 GHz, and the reflection is lower than -14 dB during 12-13 dB. In addition, it could handle a pulse power of 166 MW under vacuum condition.
Radio frequency (RF) energy harvesting technologies have attracted different efforts from researchers to employ low energy in powering portable electronic devices. In this article, an Ultra-Wide Band (UWB) antenna based on a Vivaldi fractal antenna backed with a Metamaterial (MTM) array is exemplified for RF-energy harvesting in the modern 5G networks. The antenna is connected to a full wave rectifier circuit to obtain a rectified DC current. It is found that the exemplified antenna provides a maximum output voltage of 1.4V and 1.3 V at 3.1 GHz and 4 GHz, respectively, when the incident RF power is around 17 Bm. The measured results and simulations show excellent agreement. The antenna is printed a flexible Kodak photo paper of 0.5 mm thickness with εr = 2 and loss tangent of 0.0015. The numerical simulations are conducted using CST MWS and HFSS software packages. The proposed antenna structure is fabricated using an ink jet printing technology based on conductive silver nanoparticle ink. Finally, from the obtained measurements after the comparison to their simulations, the proposed antenna is covers the frequency band from 2.4 GHz up to 20 GHz with a gain of 1.8 dBi at 3.1 GHz and 4 dBi at 4 GHz.
We firstly derived the simplified formulas for calculating attenuation constants of surface wave in double-layer magnetic absorbing sheets (MASs). The fabricated two kinds of magnetic absorbing sheets, having advantages in the low and high frequency range respectively, were used to design a group of 0.5 mm-thick double-layer sheets. Numerical calculation results show that the surface wave attenuation constants of double-layer absorbing sheet with a proper combination of the two MASs can be significantly enhanced in the whole frequency range, compared to those single-layer sheets of the same thickness. Furthermore, the simulations of mono-static RCS reduction of the metal slab coated with double-layer MAS well confirm the calculation analysis. This work demonstrates that it is feasible for double-layer magnetic absorbing sheet to enhance the surface wave attenuation ability and broaden application frequency range.
In this article, a new approach has been demonstrated for the bandwidth enlargement of a substrate integrated waveguide (SIW) cavity-backed antenna. The proposed structure employs bilateral slots, instead of unilateral slots, which is a distinct approach, in contrast to traditional cavity antennas. The proposed antenna embodies SIW cavity with a height less than 0.017λ0 and thus holds low-profile planar geometry, while retaining lower losses and light weight. The non-resonant slot, at the bottom plate, produces two-hybrid modes (odd TE210 and even TE210). The quality factor (Q) of these hybrid modes is greatly reduced by loading the resonant slot cut at the top metallic plate of the SIW cavity which leads to achieving a wideband response. A sample is fabricated and investigated at X-band. It is shown that the experimental results are well-matched with the simulated ones. The measured impedance bandwidth of the proposed antenna is 860 MHz (8.6%). Moreover, it renders a maximum gain of 6.56 dBi at 9.78 GHz and 6.75 dBi at 10.35 GHz, within the operating bandwidth. The cross-polarization radiation levels of maximum -26 dB and -28 dB are obtained at the corresponding resonant frequencies, respectively.
To obtain three-dimensional (3-D) high-precision and real-time through-wall location under ambiguous wall parameters, an approach based on the extreme learning machine (ELM) which is a neural network is proposed. The wall's ambiguity and propagation effects are both included in the hidden layer feedforward network, and then the through-wall location problem is converted to a regression problem. The relationship between the scattered signals and the target properties are determined after the training process. Then the target properties are estimated using the ELM approach. Numerical results demonstrate good performance in terms of effectiveness, generalization, and robustness, especially for the kernel extreme learning machine (KELM) approach. Noiseless and noisy measurements are performed to further demonstrate that the approach can provide good performance in terms of stability and reliability. The location time, including the training time and the test time, is also discussed, and the results show that the KELM approach is very suitable for real-time location problems. Compared to the machine learning approach, the KELM approach is better not only in the aspect of accuracy but also in location time.
The design of a wideband antenna using truncated corners partial ground plane loaded with L-shaped stubs and inverted T-shaped slots has been presented in this manuscript. The different concepts and structures related to antenna designing have been employed to attain the optimized model of antenna. L-shaped stubs and inverted T-shaped slots incised in the structure of antenna improve the impedance matching and bandwidth of proposed antenna. The fed 50Ω microstrip line has been applied to the proposed structure for attaining distinct performance parameters like reflection coefficient, gain and radiation pattern. The distinct structures of proposed antenna have been juxtaposed, and it is found that the structure with L-shaped stubs and inverted T-shaped slots shows improved antenna performance parameters. The designed antenna exhibits the bandwidth of 133.04% (3.14-15.62 GHz) and 16.96% (18.56-2.0 GHz) with improved reflection coefficient and gain. The proposed antenna has also been fabricated and tested for validation of simulated and measured results, and found in good agreement with each other. The design of proposed antenna is carved on a low cost thick substrate with compact electrical size of 0.566λ x 0.452λ x 0.0301λ mm3 at 5.45 GHz frequency and can be used for different wireless applications in the frequency range 3.14-15.62 GHz and 18.56-22.0 GHz.
An elliptical array, composed of 10 uniform elliptical apertures as the radiating elements, is presented. Assume that each aperture in an electric conducting plane spreads on the elliptic orbit and is fed by the uniform plane wave in order to obtain a low SLL array pattern with high directivity, the elliptic orbit eccentricity and the angular position of each array element are stimulated. The applied parameters are determined by an elaborate optimization procedure. The utilized procedure, comprising the geometric computational technique (GCT), and angular positions excitation (APE) is stated in detail, respectively to determine a satisfactory eccentricity and the angular position of each element.
In this manuscript, the thermal effect on a lumped element balanced dual-band band-stop filter (BSF) has been discussed in detail for the first time. The response of a novel filter should maintain consistency over a wide range of temperature. Although any microwave filter in general is designed for room temperature condition, the filter is employed for applications where the operating temperature constantly changes. Therefore, it is necessary to check the reliability of the filter response within a specific temperature range based on its application. Modern simulation software helps to make an initial assumption about the filter performance at different thermal conditions before its lab testing or actual application. Here, a quantitative analysis has been provided to show how change in temperature contributes to the change in each component value of a lumped element filter. This analysis is followed by a simulation to show that a balanced lumped element filter exhibits lower loss than its single-ended counterpart. Also, as the temperature varies, the balanced design demonstrates less deviation in the loss value than a two-port design. Next, a balanced dual-band BSF prototype with center frequencies 1.151GHz and 1.366GHz (25℃)is characterized with a 4-port network analyzer under different temperature conditions. The experimental results exhibit a good match with the simulation results. For a variation of 80℃ in temperature, the maximum deviation obtained for the filter center frequency, absolute bandwidth (ABW) and insertion loss (Sdd21) are 5MHz, 2.8MHz and 2dB, respectively.
This article reports a very efficient Frequency Selective Surface (FSS) with Convoluted Square Loop (CSL) shape is designed for applications in the X-band. They are designed on the surfaces of an FR-4 substrate. Frequency selective surface (FSS) is a combination of a periodic structure designed to selectively absorb, reflect, and transmit the electromagnetic (EM) waves. FR-4 material provides durability and flexibility. A convoluted square loop structure reduces the size of the unit cell, and it also has a better stability with good gain. So, a CSL patch with a CSL FSS array with a slot on dual FR4 substrates is introduced for the improvement in overall gain and bandwidth. As per the design parameters, a structure is designed at 10GHz. This structure is designed with ANSYS HFSS. The proposed antenna structure has a return loss of -36.424 db, and VSWR value is 1.0307. The measurement results show a gain improvement of 6.266db and bandwidth of 5.882 db.
Aiming at the problem of look direction error in the desired signal, a novel robust adaptive beamforming method based on covariance matrix reconstruction is proposed. Firstly, the Sparse Bayesian Learning (SBL) is performed to acquire the true signal direction and the spatial spectrum simultaneously. Secondly, the SBL spatial spectrum is used to reconstruct the interference-plus-noise covariance matrix. Compared with other reconstruction algorithms, this approach can realize the position estimation without any optimization procedures. Theoretical analysis, simulation results and water pool experiments demonstrate the effectiveness and robustness of the propose algorithm.
In this manuscript, a porous one-dimensional Photonic Crystal (1D-PhC) based sensor is designed for bio-chemical sensing application (i.e. hemoglobin concentration). The alternate layers of silicon are considered for design optimization, where, the porosity is introduced to obtain the desired index contrast value. The sensing capability of the proposed design is enhanced by modifying the dispersion property of the structure. For this, a defect middle layer is deliberately introduced. The number of layers, defect layer optical thickness and porosity values are optimized to confine a defect mode of desired wavelength. Finally, the detailed analysis of proposed structure is carried out. This provides the average sensitivity of around 323nm/RIU (0.05nm/(g/L) along with considerably higher FOM of 517RIU-1.
In order to provide high quality of service broadcasting systems, predicting the electric field strength in all the receiving points and generating the coverage map of the transmitter are svery important. Uniform Theory of Diffraction (UTD) based ray theoretical models could be used to predict the electric field and generate the coverage map in a short time. In order to eliminate the non-successive obstacles in the scenario and to reduce the computation time of UTD Model, Convex Hull (CH) technique is used for the first time. After this point, this model is named as Uniform Theory of Diffraction with Convex hull (UTD-CH) Model. Moreover, how operating frequency, obstacle height and the distance between the obstacles affect the coverage map of optimum base station location are researched by using UTD based models. In this study, UTD, Slope Uniform Theory of Diffraction (S-UTD), Slope Uniform Theory of Diffraction with Convex Hull (S-UTD-CH), and UTD-CH models are used for comparisons. Furthermore, computation times of UTD based models are compared.
The thinning methods were usually used to simplify the array complexity by turning off some of the radiating elements in large planar arrays which lead to unavoidable reduction in the directivity. In this paper, an alternative method is used to simplify the array complexity by partitioning a large array into two contiguous subarrays. The first subarray is in circular planar shape in which its elements are uniformly excited, while the second subarray in which its elements surround the circular subarray, and they have significant impacts on the array radiation features and are chosen to be adaptive. The desired radiation characteristics are then obtained by optimizing only the adaptive elements which are far less than the total number of the original array elements. Since the majority of the elements in the proposed array are uniformly excited, its directivity and taper efficiency are found very close to that of the benchmark solutions. Simulation results verify the effectiveness of the proposed array.
This paper considers utilizing radar multipath returns to locate a target in an L-shaped non-line of sight (NLOS) environment and proposes a NLOS target localization algorithm based on grid matching. The algorithm first establishes a multipath propagation model based on real data from an L-band single-input single-output (SISO) ultra-wideband (UWB) radar. Then, it calculates the times of arrival (TOAs) of each grid based on the multipath propagation model and matches the grid which is closest to the measured TOAs of round-trip multipath returns. Both simulation and real-data experiment results validate the effectiveness of the multipath model and the proposed localization algorithm.
We propose photonic crystal substrates that support microstrip structures to mitigate the problem of spurious harmonics in microwave devices. The wave propagation in microwave transmission lines can be controlled by employing substrates that have modulated dielectric constant such that there exist forbidden spectral regions, which are known as bandgaps in the photonic crystal terminology. With proper selection of crystalline geometry, these bandgaps can be designed to suppress the spurious harmonics. To show the existence of bandgaps in microstrip structures, we present Bloch analysis with a bi-layered photonic crystal configuration of high and low permittivities. For a practical microstrip structure that incorporates a bi-layered photonic crystal substrate, we show suppression of spurious harmonics via circuit analysis and transmittance measurements. Furthermore, a 2.5 GHz coupled-line filter is designed on a photonic crystal substrate, and 30 dB second harmonic suppression at 5 GHz is experimentally demonstrated. With the current trend multiple device integration on single platform, the photonic crystal substrates can potentially provide the noise suppression and spurious harmonic rejection needed for microwave components occupying close proximity.
This paper investigates the problem of wave propagation on periodic building façade with ray tracing method. Compared with the common practice, which is to replace a complex building structure with a flat surface and cause reduction in simulation accuracy, in this research, the Uniform Theory of Diffraction (UTD) is utilized with ray tracing method to include diffraction effects on building facades in propagation simulation. Two scenarios have been modelled which are Moore Hall's façade and Malaysia shop houses respectively. First, the façade models were created based on real buildings, and propagation simulations were conducted for flat surface and knife edge approximations. Then, for different approximations, the accuracy of simulation results was further examined, which varied with the degree of simplification and the frequency of the signal. Also, the computation time was evaluated to consider the speed of simulation. This study is beneficial to the improvement of accuracy in propagation prediction and supports the development of ray-tracing propagation prediction software and the design of wireless communication system.
This paper describes an innovative technique for the quantitative reconstruction of the dielectric and conductivity distribution of objects in a microwave tomography framework using sparse data. The proposed method tries to extract information about the size, shape, localisation and dielectric distribution of various inclusions within the object under study using an iterative reconstruction methodology in the sparse domain. The proposed algorithm combines the Distorted Born Iteration method (DBIM) and a convex optimization technique for solving the inverse ill-posed problem. The Re-weighted Basis Pursuit (RwBP) algorithm is chosen as the convex optimization technique in this work. The performance of the proposed algorithm has been compared with the TV-norm method, and the results obtained are highly encouraging. The proposed method produces a significant reduction in the reconstruction error as compared to the TV norm method with an error value of 0.083 as against 0.32 in the case of TV norm in the presence of 25 dB noise. By accurately preserving the edges of the inclusions the proposed technique is found to provide an overall improvement in the reconstruction in terms of tissue differentiation (permittivity and conductivity), dimensions of inclusions, resolution, shape, size and coordinate localisation of inclusions. The proposed algorithm converges within 10-12 iterations as compared to other complex imaging algorithms available in the literature. Further, this proposed technique is validated using experimental data from an actual breast imaging setup. The three inclusions of 10 mm, 6 mm, and 3 mm have been localised with errors of 0.052, 0.04, and 0.09, respectively The results obtained from the real-time data show the applicability and feasibility of the proposed algorithm in breast tumor imaging application
Microwave staring correlated imaging (MSCI) is a promising technique for remote sensing due to its ability to achieve high-resolution microwave imaging without the limitation of relative motion between target and radar. In practical applications, unsteady quasi-stationary platforms, such as tethered aerostat, are often used as carriers of MSCI radar. However, these platforms cannot keep ideally stationary during the imaging process. The platform's motion caused by atmospheric effects will cause time-varying inaccuracy of observation positions. Although navigation systems can measure the platform's motion to compensate for the errors of observation positions, the imaging performance of MSCI may still suffer from degradation due to the measurement errors of navigation systems since MSCI is sensitive to model error. This paper focuses on MSCI based on the quasi-stationary platform with motion measurement errors. First, the MSCI model based on the quasi-stationary platform with motion measurement errors is established under the assumption that the translation and the rotation of the platform are uniform during a coherent imaging interval. Then we propose a self-calibration imaging method for MSCI based on the quasi-stationary platform with motion measurement errors. This method iterates over the steps of target reconstruction and motion measurement errors correction until convergent conditions are met. Simulation results show that the proposed method can correct the motion measurement errors and improve imaging performance significantly.
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