This work presents a fast direct solver strategy allowing full-wave modeling and dosimetry at terahertz (THz) frequencies. The novel scheme leverages a preconditioned combined field integral equation together with a regularizer for its elliptic spectrum to enable its compression into a non-hierarchical skeleton, invertible in quasi-linear complexity. Numerical results will show the effectiveness of the new scheme in a realistic skin modeling scenario.
Ischemic stroke is one of the important causes of neurological morbidity and mortality. After ischemic stroke occurs, blood perfusion is decreased. Timely restoration of blood flow to ischemic brain tissue is the key to treatment. In this paper, a wireless cerebral blood flow (CBF) monitoring system based on inductive sensing technology is proposed, which collects CBF data through CBF sensor and LDC1612 EVM module. The STM32F103C8T6 microcontroller and ATK-ESP8266WiFi module wirelessly transmits CBF data to the host computer for real-time display. Physical experiment was designed to explore the monitoring range and depth of the system, analyze the amplitude information of the periodic beat signal. To verify the feasibility of the wireless CBF monitoring system based on inductive sensing technology to monitor CBF. The results of physical experiments show that the system introduced in this paper can monitor the pulse signal of CBF at medium depth. The wireless CBF monitoring system based on inductive sensing technology has been preliminarily verified to be able to monitor the pulse signal of CBF. Interference caused by wired is avoided. It is expected to achieve real-time continuous monitoring of CBF in patients with ischemic stroke, assisting diagnosis and treatment.
Bandwidth enhancement of a comb-line array antenna for millimeter (mm)-wave automotive radar applications is proposed. The proposed antenna consists of 12 radiating elements, 13 parasitic elements and 12 slots, which staggered up and down on the feeding line. By adjusting the width and the length of each radiating element, the antenna achieves a low sidelobe. Meanwhile, a wide impedance bandwidth is obtained by adding parasitic elements. The proposed antenna is fabricated and measured. The simulation and measurement are in good agreement. Experimental results show that the antenna has a 10-dB impedance bandwidth over 75.1-80.3 GHz with a low sidelobe level of -18.9 dB.
K-/Ka-Band is significant block of spectrum in the satellite communication. In this design, K-/Ka-band circular-polarized shared-aperture phased array antenna is proposed. The center frequency of high and low band is 19.5 GHz and 29 GHz, and the operational bandwidth is 3 GHz and 5 GHz, respectively. Dual-band shared-aperture uniform arrays is designed with the square lattice. A wide-angle scanning of ±60° in both operating bands can be obtained.
In this paper, propagation measurements of a quad-polarized multiple-input multiple-output (MIMO) channel are conducted in different multipath environments, including a realistic office room with different transmission distances and the reverberation chamber (RC), and the Rician K-factors and fading characteristics are analyzed based on the measured channel data. It is found that the Rician K-factor and channel distribution highly depend on the scattering components of different multipath environments. In the rich multipath environment, the scattered components make the strongest contribution, leading to a small K-factor, and the quad-polarized channel is better fitted as the Rayleigh distribution. With the enhancement of the contribution of direct components in total received signal, the K-factors become larger, and the channel varies from Rayleigh to Rician channel. Moreover, the differences of the K-factors between different polarizations become larger in the less scattered environment, which indicates the K-factor is also influenced by the polarization and radiation characteristics of the antennas.
In this paper, an improved wide-band source reconstruction method based on numerical Green’s function (NGF) and interpolation algorithm is proposed to avoid repetitive computation and effectively reduce computation cost compared to conventional source reconstruction method. Due to ill-posed nature of inverse problem, Tikhonov regularization technique gathered with the generalized cross-validation (GCV) method is used in the proposed SRM at a single frequecy point. To expand the proposed algorithm to wide band, adaptive frequency sampling (AFS) is applied to determine the supporting frequency points used in the interpolation algorithm which improves computational efficiency. The core method of AFS is bisection searching. Three numerical examples of printed circuit boards are shown in the last part of this paper to validate accuracy of proposed method both in near field reconstruction and far field reconstruction.
This paper presents a miniature antenna optimized for an environment agnostic positioning system. Based on the principle of multiple standard positioning techniques, the proposed terminal is using the low-power LR1110 integrated circuit. With the dimension of 50 × 40×10 mm3, the antenna supports LoRa communication standards at 868 MHz, GNSS communication standards at 1575 MHz, and WiFi/BLE at 2400 MHz. In particular, the antenna structure at 1575 MHz is integrated within a CE2354 battery holder and operates as a circularly polarized design. With these properties, the proposed antenna is suitable for wearable positioning devices.
wideband linearly-polarized unit cell for beam-steering transmitarray based on polarization rotation is proposed. As beam-steering capability is important for 5G/B5G communication, in this work, PIN diodes are used to modify the design proposed in [1], resulting in a reconfigurable 1-bit unit cell. Besides, a central slot has also been added to the top and bottom layers to improve matching, and an additional thin layer of substrate has been added for DC routing. The proposed unit cell achieves a fractional bandwidth of 18.7% under the criteria that reflection coefficient is less than −10 dB and phase difference is within 180° ± 10°. Also, the insertion loss is less than 1.6 dB throughout the entire operating band.
In era of the fifth-generation(5G) and beyond, millimeter wave (mm-Wave) techniques provide solutions for high data rate and large bandwidth [1]. The broadband mm-Wave antenna covering several frequency bands are crucial to wireless communication systems due to the limited footprint of the terminals. For broadband mm-Wave antenna designs, the losses should be as low as possible. This makes the dielectric resonator (DR) antenna (DRA) a good candidate for mm-wave antenna designs due to the compact size, low loss, high efficiency, and high degree of design flexibility [2], [3].
In this paper, the use of a tunable capacitor is proposed to reconFigure the resonance frequency of a miniature antenna. The antenna design at 868MHz is described and validated by a 3D electromagnetic simulation. As expected, the operating frequency can be controlled by changing the shunt capacitor value.
We investigate ratios of singular values of wireless multiple input multiple output (MIMO) channel matrices. Under certain practically feasible assumptions, we can find expressions that serve as a lower bound for these singular value ratios (SVRs) for the line of sight (LOS) path. The computation of the lower bounds only requires knowledge of the distance between transmitter and receiver and a summary statistic of the size of the arrays. We empirically show the validity of these lower bounds for general antenna array configurations with simulations and measurements. A possible use case for SVRs and their lower bounds is identifying the LOS path in a channel impulse response, which is a problem in localization.
This paper validates a calibration procedure applied on a microwave imaging (MWI) kernel based on the combination of pre-computed simulated data and available S-parameters measurements. The assessed technique compensates for the image degradation caused by mild and non-modeled features of the imaging device, such as the unavoidable manufacturing discrepancies in the antenna array. The testing considers a synthetically mimicked experimental scenario of a hemorrhagic stroke condition and a realistic scanner prototype. This approach allows a thorough comparative assessment of the calibration effect on the electric field estimation used by the MWI algorithm, hardly achievable with measurements. The results show the capability of the calibration procedure to reduce the retrieved images’ distortions and artifacts compared to the non-calibrated approach, being an essential milestone toward its application in real-life scenarios.
When the scatterer is magnetic, the magnetization phenomenon exists. There are two different models— magnetization electric current (MEC) and magnetization magnetic current (MMC)—used to depict the magnetization phenomenon. The volume equivalence principle based on the MEC model is simply reviewed. The volume equivalence principle based on the MMC model is proved rigorously. The difference between the MEC-based and MMC-based convolution integral formulations (CIFs) are clarified, and the advantages of the MMC model is emphasized. The MMC-based CIF derived in this paper is applicable to both “the scatterer placed in the free-space environment” and “the scatterer placed in the non-free-space environment”. The MMC-based CIF is valuable for many numerical applications, such as the method of moments (MoM) and characteristic mode analysis (CMA) for scattering problem.
A pattern reconfigurable antenna is proposed in this paper, which can be reconfigured between omnidirectional and bidirectional radiation modes. The antenna employs split-ring patches for bidirectional radiation and a monopole for omnidirectional radiation. A ground is placed off center with the antenna to help improve the omnidirectional radiation. A circular ring is etched on the ground for bidirectional radiation. Two pairs of orthogonal vertical split rings (VSRs) are introduced for bandwidth enhancement of the monopole mode. A feeding structure with two PIN diodes is developed to reconFigure the antenna. The antenna achieves an overlapped bandwidth of 12.7% for omnidirectional and bidirectional modes.
It is crucial to choose the appropriate number of truncation in circular near-field to far-field transformation (CNFFFT) [1] . The accuracy of transformation would be inaccurate if the number of truncation is lack; There would be unnecessary cost calculation, on the other hand, if the number of truncation is too much. In this paper, the number of truncation in circular near-field to far-field transformation method is investigated. Firstly, the relationship of power spectrum and the number of truncation is acquired by Fourier Transform to process near-field scattering data. Secondly, the extrapolated results of different number of truncation are compared, where the number of truncation is chosen by the power spectrum. In this way, the appropriate number of truncation would be defined. The simulation result proves that it is proper to choose the number of truncation when the normalized power spectrum is reduced to -40dB.
Based on the complex and expensive circuitry of existing imaging equipment for short-range broadband millimeter wave in human security screening, the huge amount of holographic data, the long time-consuming algorithm, and the high maintenance cost, a short-range single-frequency millimeter wave accurate imaging method is proposed, which obtains the short-range millimeter wave image reconstruction information only through the echo data of a single frequency point. The imaging method uses convolutional neural networks for feature extraction and modeling of the target echo data, and the ComplexResUnet network architecture is designed for the holographic data characteristics, which can directly perform end-to-end short-range millimeter wave image reconstruction without other algorithms after training. The method is capable of extracting the target information at different scales by fusing the feature information at different scales to improve imaging quality. The effectiveness of the method is demonstrated through experiments and analysis.
The load-pull technique is a primary routine for designing and optimizing power amplifiers (PAs). However, most load-pull techniques only focus on the fundamental impedance while fixing the harmonic terminations, which limits the achievable high efficiency of PA designs. In this paper, a data-driven searching technique is proposed for high-efficiency PA design, which achieves high efficiency by proposing simultaneous novel fundamental and harmonic impedances. Use of practical circuit simulation results as training data, allows surrogate models to be constructed using least-square support vector regression. After that, a second-order ascending strategy is adopted to optimize the surrogate model to find optimum terminations. To verify the effectiveness of the proposed algorithm, a high-efficiency PA is designed. Simulation results show that the PA achieves a maximum power-added efficiency of 80.5 % at 2.6 GHz with an output power of 41.2 dBm and a gain of 13.2 dB.
Achieving unidirectional radiation with high gain at broadside direction is of particular interest for point-to-point communications, wireless power transfer, radar systems, and various other wireless systems [1] [2]. Conventional approaches frequently employ fabry-perot cavity [3] [4], horn [5], Yagi-Like multilayer antenna [6] to obtain high directivity. These designs are often designed at microwave band. Expect these antenna type, slot antenna is widely used in millimeter-wave band due to its advantages such as low profile, simple structure and can be easily used to conformal surface. However, traditional slot antenna suffer from narrow bandwidth and low antenna gain. There are some methods such as modify the shape of slot, adding parasitic element to enhance slot bandwidth. These methods can hardly be scaled to millimeter-wave band due to the fabrication limitation and high profile.
A compact dual broadband dual-polarized shared-aperture antenna array is proposed for base station applications. The shared-aperture antenna array consists of a dipole antenna operating at the lower band (LB) of 0.69-1.52 GHz, and a 2×2 antenna array operating in the higher band (HB) of 2.3-5 GHz. Low-pass partially reflective surfaces are introduced for the shared-aperture antenna to eliminate the influence of the LB antenna on the HB antenna array. The overall size of the antenna is about $0.30 \lambda_{L} \times 0.30 \lambda_{L} \times 0.17 \lambda_{L}(\lambda_{L}$. is the free-space wavelength of 0.69 GHz). The dual broadband shared-aperture antenna array achieves stable radiation patterns with average gains of 8 dBi for the LB antenna and 11 dBi for a column of two elements of the HB antenna. Owing to the dual broad bandwidth, low profile, and shared aperture, the proposed antenna array is promising for Sub-6 GHz mobile communication applications.
