Microwave induced thermoacoustic imaging (TAI) is a hybrid imaging technique combining microwaves and ultrasound waves to achieve both superior spatial resolution and high image contrast. Here, we present results from a hybrid finite element model and an experimental setup using a microwavem peak power of less than 5 kW (average power of only 4.5 W), significantly less than for comparable imaging performance in previous works. Microwave pulses with a duration less than 1 μs are used to excite ultrasound waves with a frequency higher than 1 MHz. Experimental measurements show agreement with simulation results using hybrid finite element modeling capturing microwave heating and acoustic wave propagation. Simulations suggest targets with a conductivity of approximately 0.9 S/m yield the strongest thermoacoustic signatures. Both B-mode images and time-reversal based reconstructed images are obtained and clearly demonstrate the enhanced contrast and high resolution by exploiting the dielectric absorption properties of microwaves and the sub-millimeter resolution of ultrasound. The use of a time reversal algorithm on recorded data demonstrates the effectiveness of TAI for biomedical applications. Standing wave patterns are identified in targets and their relation to the target characteristics and their effect on the resulted images are investigated. The novelty of this work is in lowering the microwave average power while still being able to detect induced acoustic signals, along with developing a numerical model to provide an insight into the imaging process and analyze anomalies in image reconstruction.
In this work, a Complementary Folded Triangle Split Ring Resonator (CFTSRR) loaded triband mobile handset planar antenna is presented. The proposed antenna consists of a dumbbell-shaped radiating element and two CFTSRR metamaterial unit cells. The dumbbell-shaped radiating element resonates at 5 GHz. The presence of CFTSRRs additionally offers two lower band resonance. The CFTSRR-1 and CFTSRR-2 exhibit negative permittivity at 1.8 GHz and 2.4 GHz, respectively. The proposed antenna is designed to resonate at 1.8 GHz (GSM1800 MHz), 2.4 GHz, and 5 GHz (IEEE802.11ax) for voice and Wi-Fi applications of the mobile handset, respectively. The proposed antenna demonstrates compactness up to 88.6% at 1.8 GHz. The parametric studies are investigated to optimize the antenna in desired frequency bands by using Ansys HFSS19 software. The simulated and measured results are discussed. The measured result shows -10 dB reflection coefficient with bandwidth about 250 MHz (1.6 GHz-1.85 GHz), 50 MHz (2.375 GHz-2.425 GHz), and 225 MHz (4.925 GHz-5.15 GHz) which are 14.5%, 2%, and 5% respectively around their center frequencies. The measured maximum gain is approximately 1.7 dBi, 8 dBi, and 11.5 dBi for 1.8 GHz, 2.4 GHz, and 5 GHz, respectively.
In this paper, a compact tri-band microstrip filter is designed and fabricated for application in wireless communication systems such as Bluetooth, WIMAX (World Wide Interoperability for Microwave Access), and WLAN (Wireless Local Area Network). In the proposed filter, three resonators, i.e., Stub-Loaded Resonator (SLR), Stepped-Impedance Resonator (SIR), and Square Split Ring Resonator (SSRR), are used. The dimensions of the proposed filter are equal to 16.2×12.3 mm2 or 0.219λg×0.166λg. These dimensions indicate that the proposed structure has reduced the size by about 40% compared to the conventional samples. This is the main advantage of the proposed filter. Finally, in order to investigate analysis and simulations, the proposed filter is fabricated. The results prove correctness of the design, analysis, and simulations.
A wide Ka-band frequency agility synthesizer with low phase noise and high frequency stability is presented in this paper, which serves as the emission source of transmitter and the local oscillator (LO) of receiver in fully electronic millimeter wave (MMW) imaging system. In order to improve operating frequency and shorten hopping time, a novel method is proposed in this synthesizer. By mixing direct digital synthesis (DDS) with multiple phase locked loops (PLLs) and multiplying the mixed signal, a high output frequency with low phase noise and rapid frequency hopping is realized. The experimental results show that the frequency synthesizer achieves frequency resolution of 1 MHz from 27 to 32 GHz and phase noise of -95 dBc/Hz at 10 kHz carrier offset. In addition, the frequency switching time is 2 μs, and broadband spurs do not exceed -60 dBc.
New accurate approximation is proposed using integral expressions for evaluating the magnetic force between cylindrical permanent magnet arrays. The magnetic field distribution is calculated analytically by using Coulombian model. In this paper, every cylindrical magnet is divided into elementary cuboidal magnets.The accuracy can be controlled by regulating the value of elementary cuboidal permanent magnets ``N''. The approximation can also be used to calculate the force interaction in the cylindrical linear single-axis-actuator. We confirm the validity of magnetic force calculation by comparing it with other methods and measurements. The calculation results are in very good agreement with measured values, which indicates the feasibility of our approximation.
An Electric Ring Resonator (ERR) loaded Sierpinski Square Gasket Fractal (SSGF) antenna for multiple frequency band application is proposed, fabricated, and measured. The CPW-fed antenna consists of a Multi-mode Electric Ring Resonator (MERR) which is fixed on reverse side of the substrate and iterated Sierpinski gasket fractal derived from a square patch which is stamped on top of an FR4. Multi-bands can be obtained by placing a single multi-mode ERR beneath the CPW structure of the antenna. Each resonating frequency band can be easily tuned by properly changing the dimensions of the ERR structure. Instead of ERR's quasi-lumped capacitance, reconfigurability of the low, middle, and high frequency bands can be achieved by using a pair of Digital Variable Capacitors (DVCs)inserted into the middle of the ERR's rings corresponding to the chosen mode. The bandwidth is enhanced using four iterations of square radiating patch, modified feed line, and multi-mode electric ring resonator-loaded ground plane. More specifically, the impedance matching of the CPW fed antenna is improved by introducing transitions between the microstrip feed line and the Sierpinski square gasket. The numerical results show that the proposed antenna has good impedance bandwidth and radiation characteristics in the operating bands at 3.08/5.81/8.02/12.13/15.56\,GHz which cover the frequency spectrum of WiMAX, WiFi/WLAN(IEEE 802.11a), IEEE 802.16e, X-band uplink, S/C/X/Ku and K band with return loss of better than 10 dB.
In this paper a novel design to reduce mutual coupling in circular patch antennas is proposed. A circular MIMO antenna with a dumb-bell shape parasitic element is inserted between the two circular patch antennas thereby reducing the mutual coupling. It has been observed that the proposed design produces a multi-band characteristics at 3.1 GHz, 6.2 GHz & 7.7 GHz. At the tri-band frequencies impedance bandwidths (IBW's) are around 90 MHz, 320 MHz, and 540 MHz. The process involves cutting rectangular slits on each side of a circular patch and placing a dumb-bell shaped parasitic structure to reduce the transmission coefficient (S12) to -40.75 dB. It is observed that the antenna parameters are greatly improved in terms of ECC, diversity gain, directivity, group delay and peak gain which are 0.005, 9.973 dBi, 6.14 dBi, 10.81±1 nsec and 3.59 dBi. The results of experimental validation and numerical analysis are presented. The antenna design can be used for wireless communication as well as all C-band applications.
A compact wideband circularly polarized (CP) square slot antenna for universal ultra high frequency (UHF) RF identification (RFID) handheld reader applications is proposed, fabricated, and tested. The antenna is coplanar waveguide (CPW) fed by an inverted Z-shaped feeding line. By inserting four stubs in diagonal directions and two inverted T-shaped strips inside the square slot, broadband CP operation, wide axial ratio bandwidth, and good impedance matching are achieved. The measured < -10 dB impedance bandwidth is from 706 MHz to 1007 MHz (301 MHz, 35.1%). The measured 3-dB axial ratio (AR) is 427 MHz (745-1172 MHz, 44.5%). The maximum measured gain of the proposed antenna is 4.8 dBi. The proposed antenna has wide impedance bandwidth, wide axial ratio bandwidth, and small size. The dimensions of the antenna are only 120×120×1.6 mm3. The impedance bandwidth and AR bandwidth performances of the proposed antenna can easily cover the UHF RFID band as whole.
In this article, a microstrip-fed stepped open slot antenna is presented which is suitable for GSM 1800, WiFi, WiMAX, PCS, and ITM-2000 applications. The proposed geometry is composed of a circle-shaped tuning stub, a feed structure, and deformed ground plane. The proper tuning of resonating modes (fr1, fr2, fr3 and fr4) and wideband frequency response are acquired by adjusting the dimension of stairs, tuning the stub and an elliptical slot. The experimental result demonstrates that this antenna covers the frequency range from 1.375 to 5.6 GHz with measured fractional bandwidth (BW(%)=200 * (fh - fl)/(fh + fl) of 121.14% for S11<-10 dB. This antenna also exhibits resonance at frequencies (measured) 1.625, 2.52, 2.82, 3.75, 4.67, and 5.42 GHz. After investigating the surface current distribution, the mathematical equations are deduced for simulated resonating frequencies of 1.35, 2, 3.8, and 5.22 GHz. Due to asymmetry in structure, asymmetric far-field patterns are found in E-plane with omnidirectional patterns in H-plane.
This paper proposes and implements a novel class of inductor-capacitor-capacitor wireless coordinative DC motor drives, which not only performs selective wireless power to motors, but also achieves power equalization to ensure the same operation for isolated robotic arms. The key is to make use of the selective wireless power transfer with several resonant frequencies and then use only one transmitter with the inductor-capacitor-capacitor compensation network to provide multiple-frequency transmission without relying on the switched-capacitor array. In order to provide simultaneous and independent wireless power to different motors and hence achieve the desired coordinative motion, a time-division multiplexing scheme and burst firing control are newly employed. Thus, the wireless power transfer system with multiple receivers can achieve better flexibility and simplicity. Both finite element analysis and experimental results are given to verify the validity of the proposed inductor-capacitor-capacitor wireless coordinative DC motor drive. As a result, the motors can achieve independent motion with 1200 rpm and simultaneous motion with 400 rpm when the torque is 10 Ncm, and the operating frequencies are set at 110 kHz and 130 kHz.
The average downlink data-rate in massive Multiple Input Multiple Output (MIMO) networks within realistic urban environments is characterized by means of ray-tracing simulations. The links between the receivers and transmitters are mostly established through rooftop propagation, which requires special treatment due to multiple diffractions near the optical boundaries. The bidirectional ray-tracing method is utilized in order to simulate these effects accurately. The average downlink data-rate is also calculated according to an empirical rooftop propagation model and the differences as well as the similarities with the bidirectional ray-tracing results are demonstrated. Additionally, an iterative Shooting and Bouncing Rays (SBR) algorithm, which improves the computational efficiency of the bidirectional ray-tracing, is introduced. The algorithm aims to maximize the number of rays, which contribute to the result, by setting specific launch directions. The results show that noticeable improvements in the computation time are possible.
In this paper, a wideband polarization diversity multi-input multioutput (MIMO) antenna system is proposed. The structure of the proposed antenna consists of four wideband coplanar waveguide (CPW)-fed monopole antennas with a common ground plane and radiated element. The simulated and measured -10 dB impedance bandwidth is 20% (2.25-2.75 GHz), which covers WiFi (2.4 GHz) and LTE (2.6 GHz) frequency bands. The MIMO antenna system is applied to both an indoor and outdoor wireless access point (WAP) at the covered frequency bands. Due to the common structure of elements in the proposed MIMO antenna, an acceptable mutual coupling between the antennas ports is critical. Hence, a new parasitic element structure is presented to improve mutual coupling between the antenna ports. Acceptable values for the coupling coefficient (<-14 dB) are achieved by adding the parasitic element. The presented antenna system provides a nearly omnidirectional radiation pattern with an orthogonal mode of linear polarization. The results show a polarization diversity gain of 10 dB and an envelope correlation coefficient of less than 0.2. Moreover, each antenna port possesses peak gains of 5.33-6.97 dBi and efficiencies of 51.5-57%. A comparison between the simulation results and experimental measurements reveals good agreement between the two, confirming the validity of the proposed design.
In this paper, a new design approach is presented for achieving a miniaturized quad-band microstrip patch antenna (MPA) suitable to be used for 915-MHz (UHF band), 2.45- and 5.8-GHz (ISM band), and 3.5-GHz (WiMAX band). The proposed antenna is called modified square spiral antenna (MSSA) which is composed of a modified dual-arm square spiral patch strip structure and a tapered-ground plane with coplanar wave-guide (CPW)-fed configuration to feed this antenna, all printed on the top side of an FR4 substrate. The proposed antenna is designed through intermediate systematic design steps of antennas starting from a conventional strip-fed rectangular MPA and ending by achieving MSSA. A CST Microwave Studio (CST MWS) is used to model the designed antenna and simulation results, in terms of return loss (S11), realized peak gain and efficiency, besides to radiation patterns, are obtained. To validate the design concept, the antenna structure is fabricated, and the simulated and measured S11 results nearly coincid with each other. The proposed antenna is characterized by miniaturized size of 28×28 mm2, and based on measured -10-dB S11 result, MSSA has four bands, band 1: 915-GHz (872-929 MHz), band 2: 2.45-GHz (2395-2510 MHz), band 3: 3.5-GHz (3470-3550 MHz), and band 4: 5.8-GHz (5698-5900 MHz).
In this paper, an electronically switchable ultra-wideband (UWB)/dual-band bandpass filter using defected ground structures (DGSs) is proposed. The proposed filter consists of meandered inter-digital coupled line sections, stepped impedance open stubs, coupled lines, and rectangular DGSs to realize high performance in the operation band with a compact size of 12.5 mm × 10 mm. The proposed filter is designed on an RT/Teflon substrate (εr = 2.2, h = 0.7874 mm). The main advantage of the proposed filter is the reconfiguration of ultra-wide bandpass filter to dual-band bandpass filter. UWB has passband from 3.6 GHz to 10.6 GHz with upper wide stopband attenuation better than 20 dB up to 18 GHz. The dual passbands extend from 3.8 GHz to 5 GHz and from 9.5 GHz to 10.8 GHz. This filter is able to provide interference immunity from unwanted radio signals, such as wireless local area networks (WLAN), worldwide interoperability for microwave access (WIMAX) that cohabit within the UWB spectrum, and X (Military) band of satellite from 7 GHz to 8 GHz. The state of filter can be changed by using switching matrix equipment (mini circuit, replacement of PIN diodes). To validate the design theory, an electronically switchable UWB/dual-band bandpass filter using DGSs is designed, fabricated, and measured. Good agreement is found between simulated and measured results.
Convolutional Neural Network (CNN) models applied to synthetic aperture radar automatic target recognition (SAR ATR) universally focus on two important issues: overfitting caused by lack of sufficient training data and independent variations like worse estimates of the aspect angle etc. To this end, we developed a lightweight CNN-based method named SARNet to accomplish the classification task. Firstly, a clock-wise data amplification approach is presented to generate adequate SAR images without requiring many raw SAR images, effectively avoiding overfitting in the course of training. Then a SARNet is devised to process the extracted features from SAR target images and work on classification tasks with parameters fine-tuning under comparative models. To enhance and structurally organize the representation of learned proposed model, various activation functions are explored in this paper. Furthermore, due to the pioneering conducted experiments, training samples in the MSTAR and extended MSTAR database are utilized to demonstrate the robustness and effectiveness of the lightweight model. Experimental results have shown that our proposed model has achieved a 98.30% state-of-the-art accuracy.
A compact multiple-input-multiple-output (MIMO) antenna with very high isolation is proposed for ultrawideband (UWB) applications. The antenna with a compact size of 30.1×20.5 mm2 (0.31λ0×0.λ0) consists of two planar-monopole antenna elements. It is found that isolation of more than 25 dB can be achieved between two parallel monopole antenna elements. For the low frequency isolation, an efficient technique of bending the feed-line and applying a new protruded ground is introduced. To increase isolation, a design based on suppressing surface wave, near-field, and far-field coupling is applied. The simulation and measurement results of the proposed antenna with the good agreement are presented and show a bandwidth with S11 ≤ -10 dB, S12 ≤ -25 dB ranged from 3.1 to 10.6 GHz making the proposed antenna a good candidate for UWB MIMO systems.
This paper investigates the performance of compact triple band-notched Multiple Input Multiple Output (MIMO) antenna for Ultra-Wideband (UWB) communication. Open-ended quarter wavelength slots are inserted on the radiators. These slots are used to obtain notch bands at WiMAX/C band, WLAN band and the X-band Satellite Communication System that ranges in 3.3-4.2 GHz, 5-6 GHz, and 7.2-8.6 GHz respectively. An I-shaped stub extends from the ground surface to minimize mutual coupling among radiating elements. Mutual coupling and Envelope Correlation Coefficient are found less than -15 dB and 0.2, respectively. The diversity characteristics like Mean Effective Gain Ratio and Total Active Reflection Coefficient are found around 1dB and less than -10.5 dB, respectively. The radiation efficiency of the radiator is more than 80% over the entire UWB frequency range. The proposed antenna is designed with the overall dimensions of 23×40×1.6 mm3.
Surface ship imaging technology is widely used in military and civilian applications. To resolve the problem of imaging moving target positioning blur on sea surface, this paper proposes a method for estimating the velocity of moving target using velocity synthetic aperture radar (VSAR). Firstly, the paper analyzes the imaging mechanism and constraints of VSAR method and establishes an imaging model based on phased array radar for surface ships. Then, the rate-frequency estimation method of the multi-antenna image domain is used to correct the azimuth offset, and the image moisture algorithm is used to estimate Doppler frequency modulation. Therefore, the adaptive focusing of the target image is completed. Finally, this method is used to simulate and calculate the surface motion ship to realize continuous dynamic imaging of the moving ship. Compared with the traditional single-channel SAR radar and track-interfering radar (ATI) algorithm, the rate-frequency estimation algorithm solves the shortcomings of the azimuth positioning accuracy and improves the positioning performance of the moving target ship under large-area sea conditions.
This paper presents a detailed analysis of the human body limb movement influence on the radiation pattern of a wearable antenna during different activities. The analysis is carried out at 3, 6, 9 GHz of the 3-10 GHz UWB range of frequencies. Simulations are carried out on a human body model in CST microwave studio with a compact wearable antenna to obtain the body-worn antenna radiation patterns for lower and higher frequencies. This study gives an insight into the variation of the radiation patterns of a compact UWB antenna depending upon the position of the wearable antenna on the body. Results conclude that the radiation pattern of the wearable antenna changes significantly in terms of shape, size, level of distortion and direction of maximum radiation with different limb movement activities and also depends upon the placement of the antenna on the limbs. The coverage area of the wearable antenna radiation pattern becomes highly directive and shrinks in coverage area for the shoulder/thigh node in comparison to the wrist/ankle wearable node by 10-15%. The bending of the limbs leads to deformation and reduction in area of the radiation pattern with values as high as 30-40% compared to free space scenario as the bending angle between the upper and lower arm/leg reduces. The analysis presented gives directional information regarding maximum radiation and the field strength of the radiation pattern for various activities performed. The present study reports results on the influence of the wearable antenna position, on detection and tracking performance of RF and microwave biomedical devices/sensors suitable for various healthcare applications such as tracking of human subject, patient monitoring, gait analysis, physical exercises, yoga, physiotherapy, and rehabilitation.
An effective numerical technique is demonstrated for the plane wave scattering from an infinite periodic array of hollow circular cylinders of finite length. The cylinders are made of infinitely thin perfect conductor and allocated in the axial direction. We formulate the boundary value problem into a set of integral equations for the unknown electric current densities flowing in the circumferential and longitudinal directions. Employment of the Galerkin method allows us to solve simultaneous linear equations for the expansion coefficients of the unknown current, from which we can find the field distributions in both far and near regions. The procedure of analytical regularization makes the linear system into the Fredholm second kind that is contributory to stable and rapidly convergent results. Resonance is detected as abrupt changes in the total scattering cross sections for each grating mode, and it is accompanied by the formation of circular cavity mode pattern in the cylinder.
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