Benefit from the high resolution, penetrating and all weather advantages of millimeter-wave (MMW) imaging, MMW imaging plays an important role in remote sensing, security inspection, navigation, etc. Among the MMW imaging systems, synthetic aperture imaging radiometer (SAIR) utilizes aperture synthetic technology to achieve higher imaging resolution, but the perception information is insufficient, resulting in poor image quality. In order to improve the image quality of passive SAIR MMW image effectively, we propose a novel multichannel depth convolutional neural network (MDCNN) in this paper. Aiming at the characteristics of original MMW images with more noise in low-frequency information and less features in high-frequency information, wavelet transform is incorporated into the MDCNN to obtain the high and low frequency components firstly. Then, dense residual block and skip connection technology are adopted to denoise and enhance target information in the four independent channels respectively. Finally, high quality MMW images are synthesized by inverse wavelet transform. The simulation results show that the reconstructed images of MDCNN have better image quality (such as image contour and texture details) than other deep learning-based methods.
In order to obtain the analytical expression of the position of sparse array sensors under the condition of a given total array sensor number, a sparse array design method based on direct-connection of 4 uniform linear arrays (DCUA4) is proposed. By using the only known parameter of the total array sensor number, the sensor number and spacing parameters of four subarrays are obtained by mathematical operation, then the four subarrays are directly connected to realize the design of sparse array. It is proved that the aperture of the sparse array is large, and there are no holes. Because all the sensors are allocated to four subarrays, the number of small spacing sensor pairs in the array is controlled The performance of the proposed array is simulated based on the spatial smoothing MUSIC (SS-MUSIC) algorithm. The simulation results show that the proposed DCUA4 can produce a large virtual array aperture, realize high-precision direction of arrival (DOA) estimation under underdetermined conditions, and resist the influence of low mutual coupling.
In this paper, a rectangular embedded dual band Electromagnetic Band Gap (EBG) structure at frequencies 2.45/5.8 GHz useful in industrial, scientific, and medical (ISM) band for various wearable applications is proposed. The main intent of this work is to design a dual band EBG to reduce specific absorption rate (SAR). The unit cell which is a part of the EBG structure is formed using a rectangular patch. It has a U shaped rectangular slot and a stretched strip with a rectangular patch at end. EBG unit cell simulation is accomplished by solving eigen mode problem in High Frequency Structure Simulator (HFSS). EBG structure has to be suitably designed and fine tuned for specified band stop property to reduce surface waves. It must improve front to back ratio (FBR). With placing antenna on human body, frequency detuning occurs which is undesirable thus emphasizing the need of improvement in impedance bandwidth. This improvement can be achieved by a suitable design of EBG structure. In this work, the proposed EBG structure is integrated with a dual-band monopole antenna at frequencies 2.45/5.8 GHz for wearable application. The evaluation of antenna performance on a four layer body model is carried out. Simulations are used to demonstrate EBG array structure effectiveness for the reduction of Specific Absorption Rate (SAR) on the four layer body model. Computed SAR values for tissue in 1 g and 10 g are within standard prescribed limits. It is concluded that the proposed dual band antenna is appropriate for wearable applications. Proposed EBG array is fabricated and integrated with a twin E-shaped monopole antenna. The measurement of reflection coefficient, radiation pattern, and transmission coefficient of fabricated EBG array is carried out. The measured and simulated results show good agreement. Antenna performance in the event of bending condition and on-body condition is assessed.
With the development of communication technology, people's requirements for information transmission rate are getting higher and higher. Compared with the previous sub 6G frequency band, terahertz communication has a larger bandwidth and a higher rate. This paper studies the influence of azimuth angle of arrival (AoA) and azimuth angle of departure (AoD) on the received signal strength in the 220 GHz-320 GHz frequency band, as well as the influence of the signal passing through different obstacles, different dry humidity and material thickness on the signal power.
This article introduces a unique dual-band notched Ultra Wide Band (UWB) Multiple Input Multiple Output (MIMO) antenna. The planned MIMO antenna has two identical Mushroom-shaped radiators with a combined dimension of 18×34×1.6 mm3. Inverted L-structured stubs are joined to the antenna's ground to provide enhanced port isolation. The proposed antenna achieves improved isolation of -23 dB over 3.08-12.8 GHz bandwidth. Two novel strips are extruded in the antenna's ground and mushroom-shaped radiator to introduce a notched WiMAX band (3.37-4.30) and WLAN (5.08-5.80) GHz band. The presented antenna's peak gain is achieved from 2 to 4.8 dBi, and the antenna's radiation efficiency is attained between 78 and 90% except for (3.37-4.30) GHz and (5.08-5.80) GHz stopped bands.
Wireless power transmission system (WPTS) based on electromagnetic induction is a promising way to power a gastrointestinal capsule robot (CR) for wireless diagnosis, which typically consists of a one-dimensional (1-D) power transmitting coil (PTC) to excite an alternating magnetic field and a three-dimensional (3-D) power receiving coil (PRC) to induce signal. However, it is difficult to apply a 3-D PRC to practical medical applications since the oversize bodily form of the mounting receiver brings the extra challenge of design for microCR. This paper proposes a novel WPTS with space-saving architecture by combining a two-dimensional (2-D) power transmitting coil (PTC) outside the human and 1-D PRC onboard the CR, which can permit CR to accomplish the mission of exploring the intestinal space with wireless energy supplying owing to small size related to 1-D PTC. The analytical expressions of the magnetic flux density, magnetic field orientation, and uniform magnetic field excited by the designed PTC are derived. Simulated and experimental outcomes are implemented to achieve the desired magnetic field strength and direction by changing the transmission current of PTC, which verifies the feasibility and effectiveness of developed methods. And the magnetic field uniformity is greater than 44%. It can basically cover the 20 cm×20 cm area of the human abdomen at all times, which can permit the operational requirements of the CR in the practical case.
We propose the design of a dual-band nano-structured polarizer that allows the transmission of two different linear polarizations within different frequency bands. A broad-band transmission window in the visible range exists for the x-polarization, whereas the y-polarization transmits efficiently in the near-infrared range. The transmittance exceeds 80% for the target polarization in both cases under normal incidence. This operation is achieved by an orthogonally patterned metallic surface having a long metal wire along the x-axis with four other small metal wires along the y-axis and allowing for a strong localized slit resonance to operate in the desired passband. The appropriate metal length and air gap choice lead to intense slit resonances in the spectral region of choice. The proposed design can be optimized for either ultrawide single band operation or dual-band perpendicular polarization operation.
In this paper, a novel dual-frequency circularly polarized (CP) antenna applied to BDS system is presented. CP radiation is achieved by etching slotted circular patches of complementary open-loop resonators, which are excited by a feeding network consisting of a double-layer power divider. The circular patch is miniaturized by a complementary split-ring resonator (CSRR) etched on the patch. The overall dimension of the antenna is only 0.32λ0×0.32λ0×0.0104λ0, where λ0 is the corresponding free space wavelength at 1.268 GHz. The proposed antenna has 50 MHz (1.25-1.30 GHz) and 60 MHz (1.53-1.59 GHz) impedance bandwidth and 20 MHz (1.25-1.27 GHz) and 20 MHz (1.55-1.57 GHz) axial ratio bandwidth, respectively. The antenna profile is low, which is easy to install. Because of these performance indexes, the antenna has superior practicability in BDS system.
The electrical representation of the contactless power transfer (CPT) system with a coaxial transformer for the power traction in the rotary drilling system is presented. The air gap in the rotary transformer can lead to a lot of leakage inductance, so that the series-series (SS) compensation capacitors are used to increase the efficiency and the capability of the system. Moreover, the frequency response of the SS compensated CPT system is analyzed, and the transfer characteristics of the CPT system are revealed at different resonant frequencies. It is shown that the phase angle of the input impedance at resonant frequency determines the operation mode of the CPT system. At resonant frequency ω0, the system can operate in constant-current (CC) mode, whereas at resonant frequency ωH, it can work in constant-voltage (CV) mode. In the application of the drilling system, the CV mode owning good load regulation is more preferred than the CC mode for a wide range of load variation. At last, the analysis result is verified by experiment. The experimental results indicate that the CPT system in the CV mode can produce a 30~35 V voltage output and can transfer maximum power 180 W with an efficiency of 78.5%. The proposed CPT system can well meet the requirement of power supply in the drilling system.
In this article, a miniaturized antenna with a Koch fractal defected ground structure (KFDGS) is proposed for C/X and Ku-band applications. The performance of an inset-fed lambda/2 patch antenna is examined using an iterated KFDGS etched on the ground plane. A conventional antenna operated at 16 GHz with a return loss of -34.31 dB is constructed, followed by a tri-band miniaturized antenna operating at 6.35, 9, and 13.05 GHz with a return loss of -22.41, -25.05, and -28.54 dB in order to achieve miniaturization of 60.31%, 43.75%, and 18.43% respectively. An antenna is designed on a Roger RT Duroid substrate, fabricated, and tested with dimensions of 12×14×0.8 mm3, and its impact on reduction in size performance has been evaluated with measured peak directivity and gain of 3.07 and 2.80 dBi at 6.35 GHz, 4.78 and 4.65 dBi at 9 GHz, and 7.73 and 7.76 dBi at 13.05 GHz, respectively. A good agreement is found between the measurements and simulations.
In the research of radar-based human motion classification and recognition, the traditional manual feature extraction is more complicated, and the echo dataset is generally smaller. In view of this problem, a method of human motion recognition in small sample scenarios based on Generative Adversarial Network (GAN) and Convolutional Neural Network (CNN) models is proposed. First, a 77 GHz millimeter wave radar data acquisition system is built to obtain echo data. Secondly, the collected human motion echo data is preprocessed, the micro-Doppler features are extracted, and the range Doppler map (RDM) is used to project the velocity dimension and accumulate the two-dimensional micro-Doppler time-frequency map dataset of the human motion frame by frame. Finally, the deep convolution generative adversarial network (DCGAN) is constructed to achieve data augmentation of the sample set, and the CNN is constructed to realize automatic feature extraction to complete the classification recognition of different human motions. Experimental studies have shown that the combination of GAN and CNN can achieve effective recognition of daily human motions, and the recognition accuracy can reach 96.5%. Compared with the manual feature extraction, the recognition accuracy of CNNs is improved by 7.3%. Compared with the original data set, the system recognition accuracy based on the sample augmentation data set is improved by 2.17%, which shows that the GAN has an excellent performance in human motion recognition in small sample scenarios.
This paper presents a design of a right hand circularly polarized x-band reflectarray antenna (RA) at a center frequency 12 GHz. The reflectarray is fed by a linearly polarized dipole antenna. The proposed reflectarray antenna can be used for CubeSat applications. The reflecting elements have the shape of a pentagon. This shape is chosen to convert the incident linearly polarized fields to the required circular polarization. A dipole antenna is used as linearly polarized (LP) feeding element for the proposed reflectarray. This dipole antenna is tilted w.r.t the x-axis by an angle 45˚ to introduce nearly equal polarizations in x and y directions on the aperture of the reflectarray. Each reflecting element is adjusted to produce a phase shift 90˚ between the reflection coefficients in x and y directions. The required reflected phase is realized by adjusting a scaling factor (SF) for the pentagonal patch in x direction to the corresponding SF in y axis. This phase difference is responsible for polarization conversion of the incident plane wave into circularly polarized reflected wave. The reflectarray is designed with focal to-diameter (F/D) ratio equals unity. In this work, an efficient technique is discussed for modelling the reflectarray designed. This technique is based on developing a Visual Basic Script file for allocating the reflecting elements with their corresponding dimensions in their location on the simulation tool. This script file is used directly by the simulation tool (HFSS) to draw the complete model automatically. This procedure has a significant role on simplifying the modeling of complicated structure like the proposed reflectarray. The proposed reflectarray antenna is simulated at 12 GHz. The obtained axial ratio (AR) is found to be 2.1 dB, and peak gain is 18 dBi. The antenna is also fabricated and measured for verification.
In this paper, an ultra-wide band modified slot-sinuous antenna has been designed to enhance bistatic radar cross section (RCS) response. The design procedure consists of adding three or five parasitic ellipses openings to each of the slot-sinuous arm cells. The parasitic ellipsis allows to control bistatic RCS without impacting antenna radiation characteristics. Parasitic ellipses opening dimensions are small compared to the relative wavelength of the signal on each active region of the antenna. Ellipses deploy over the entire sinuous arms are scaled by the same expansion coefficient used to design the antenna itself. In the proposed design, ellipses parameters such as ellipses axis, radial position, and relative angle position on the sinuous cell are key parameters to be optimized for bistatic RCS reduction. The total number of designing parameters is finite, but their combination is infinite, which leads to the possibility of designing different antennas based on the required designing goals. The proposed solution and the results presented in this work show the applicability of the designing parameters to control bistatic RCS on active region antennas.
Traditional genetic algorithm identification of permanent magnet synchronous wind generator (PMSWG) parameters is easy to fall into local optimum, resulting in low accuracy of parameter identification results and slow convergence, which reduces the accuracy of parameter tuning of proportional-integral (PI) controller. Aiming at this problem, a chaotic mapping simulated annealing genetic algorithm (CMSAGA) for identifying PMSWG parameters is proposed. The traditional genetic algorithm (GA) has the ability of global random search, combined with the probability breakthrough characteristic of the simulated annealing (SA) algorithm, which avoids the parameter identification result falling into the local optimum and finally tends to the global optimum. With the increase of iteration times, the initial population is mapped with tent chaos mapping theory, and the optimal value of the population is disturbed in each iteration to increase the diversity of the population, making the proposed algorithm converge faster and improve the accuracy. Experiments show that the proposed algorithm has good accuracy and convergence speed, PMSWG stator resistance, stator winding d-q axis inductance and permanent magnet flux can be identified.
This paper presents a 3D printed extended hemispherical lens antenna for Body Centric Communications in 60 GHz band. The prototype consists of a 3D printed lens made of Polylactic Acid with three planar broadside patch antenna elements used as a source for the lens. The direction of the main beam antenna is switched by changing the excitation of source elements. The measured overlapping impedance bandwidth of the fabricated antenna is from 57.27 GHz to 60 GHz with reflection coefficient better than -10 dB. The main beam direction switches in broadside direction with 3 dB angular coverage from -29.2° to +30° by changing the radiating elements at 60 GHz. The measured gain is 15.28 dBi at 60 GHz. The beam switching capabilities and high gain with broadside radiation characteristics make the proposed antenna a suitable candidate for off-body links at 60 GHz. The effect of placing the antenna structure over the body is also studied in this paper. The body to off-body link measurement is successfully demonstrated with extended lens over the body and an open-ended waveguide as an external node.
In this study, a double reentrant cavity sensor (DRECS) loaded with ring gaps is proposed to characterize the displacement that the metal plate is inserted into the DRECS. The conventional substrate-parasitic-capacitance of DRECS in the substrate integrated waveguide (SIW) configuration, which has no contribution to the sensitivity, is successfully eliminated by using a symmetric double reentrant cavity. The ring gaps are introduced in SIW DRECS to effectively suppress the fringe electric field around the post, and enlarge the range of displacement measurements. Additionally, a displacement model, which is characterized by the quantitative relationship between the resonant frequency of DRECS and insertion depth inside DRECS, is theoretically established with the help of the electric field distribution and the equivalent circuit of the DRECS. A prototype of the designed sensor is fabricated and measured. The sensor work at 1.5-3.1 GHz and the measured results are in good agreement with the simulated ones from the displacement model. The measurement results indicate that the sensor has a displacement test range of 27 mm and Q-factor of over 150, and can achieve high sensitivity of 58 MHz/mm.
Group delay distortions are critical for high quality transmissions in today's communication system. In this paper, we have proposed design and analysis of defected microstrip line-based Negative Group Delay Circuits (NGDCs) to compensate for group delay distortions. Initially, a tunable pulse shaped defection based NGD structure is designed wherein a variable resistor connection allows group delay tunability. The proposed design is able to generate a group delay (GD) tuning from 0 to -4.8 ns at 2.7 GHz as the resistance is varied from 1 kΩ to 1 MΩ. Further, we embedded two stubs to implement the switchable multi-band feature on the proposed NGDC design. The NGDCs are fabricated, and the measured results confirm the proposed concept. Lastly, we designed a tunable compact NGDC with inverted-U stubs inscribed inside a microstrip line. It generated GD tunability at different frequency bands with the aid of a variable resistor and switched the frequencies as required.
The article describes the problem of spatial separation of devices operating in the same frequency range. The possibility of focusing electromagnetic fields in several specified regions of space is considered. The proposed method for focusing the electromagnetic field can be an additional method for separation devices that operate in the same frequency range. The system under consideration, consisting of space, radiating antennas and focusing points, is represented as an abstract multipole with the number of inputs equal to the number of radiating antennas and with a set of outputs equal to the number of focusing points. A coordinate system has been introduced that makes it possible to calculate the distances between radiation and focusing points. A method for calculating complex transmission coefficients between emission points and reception points is described. An analytical expression is obtained, a system of linear algebraic equations, which makes it possible to calculate the necessary amplitudes and phases of signals supplied to radiating antennas. A model in a computer-aided design system containing 56 radiating antennas is presented. 9 focus points were set, and 4 of them should have maxima of the electromagnetic field. The simulation confirmed the theoretical calculations. A method for optimizing the calculations of the initial amplitudes and phases by eliminating the elements of the characteristic matrix is considered. This made it possible to reduce the number of elements in the characteristic matrix.
It is commonly believed that electromagnetic waves cannot propagate in lossy conductive media and that they quickly decay inside such media over short length scales of the order of the so-called skin depth. Here we prove that this common belief is incorrect if the conductive medium is stratified. We demonstrate that electromagnetic waves in stratified lossy conductive media may have propagating character, and that the propagation length of such waves may be considerably larger than the skin depth in homogeneous media. Our findings have broad implications in many fields of science and engineering. They enable radio communication and imaging in such strongly lossy conductive media as seawater, various soils, plasma and biological tissues. They also enable novel electromagnetic metamaterial designs by mediating the effect of losses on electromagnetic signal propagation in metamaterials. Our results demonstrate a new class of inherently non-Hermitian electromagnetic media with high dissipation, no gain, and no PT-symmetry, which nevertheless have almost real eigenvalue spectrum.