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State-of-the-art myoelectric hand prostheses provide multi-functional control but lack somatosensory feedback. To accommodate the full functionality of a dexterous prosthesis, the artificial sensory feedback needs to convey several degrees of freedom (DoF) simultaneously. However, this is a challenge with current methods as they are characterized by a low information bandwidth. In this study, we leverage the flexibility of a recently developed system for simultaneous electrotactile stimulation and electromyography (EMG) recording to present the first solution for closed-loop myoelectric control of a multifunctional prosthesis with full-state anatomically congruent electrotactile feedback. The novel feedback scheme (coupled encoding) conveyed proprioceptive (hand aperture, wrist rotation) and exteroceptive information (grasping force). The coupled encoding was compared to the conventional approach (sectorized encoding) and incidental feedback in 10 non-disabled and one amputee participant who used the system to perform a functional task. The results showed that both feedback approaches increased the accuracy of position control compared to incidental feedback. However, the feedback increased completion time, and it did not significantly improve grasping force control. Importantly, the performance of the coupled feedback was not significantly different compared to the conventional scheme, despite the latter being easier to learn during training. Overall, the results indicate that the developed feedback can improve prosthesis control across multiple DoFs but they also highlight the subjects’ ability to exploit minimal incidental information. Importantly, the current setup is the first to convey three feedback variables simultaneously using electrotactile stimulation while providing multi-DoF myoelectric control with all hardware components mounted on the same forearm.

Background: Piriform aperture is anterior opening of the nasal cavity formed by bones of the viscerocranium and knowledge about differences between genders is important for forensic scientists, anthropologists, orthopedists, neurosurgeons and vascular surgeons. The aim of this study was to examine gender differences of piriform aperture on 3D models of human skulls originating from Bosnian population using the geometric morphometric method. Materials and methods: The study was conducted on 211 3D models of human skulls of known gender. 3D models were obtained by laser scanning. We analyzed the gender differences of piriform aperture using geometric morphometrics method. On 3D models we marked four landmarks on piriform aperture in the Landmark editor program, after which we analyzed its gender differences in MorphoJ program. Results: The first PCA axis described 40.398% of total variability of piriform aperture. The greatest gender variability was present in the position of the landmark rhinion. Discriminant functional analysis of the shape and size of the piriform aperture allowed the gender determination with 64.03% accuracy for male and 70.83% accuracy for female gender. The size of the piriform aperture showed a statistically significant difference between genders. Discriminant functional analysis of the shape of the piriform aperture without affecting size enabled gender determination with 59.71% accuracy for male and 62.5% accuracy for female. Conclusions: Analysis showed statistically significant differences in the shape and size of piriform aperture between genders. The accuracy for gender determination based on piriform aperture was higher in females.

To understand the relationships between channel size and ion selectivity, we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthroline-...

Wireless communications with extremely large-scale array (XL-array) correspond to systems whose antenna sizes are so large that conventional modelling assumptions, such as uniform plane wave (UPW) impingement, are longer valid. This paper studies the mathematical modelling and performance analysis of XL-array communications. By deviating from the conventional modelling approach that treats the array elements as sizeless points, we explicitly model their physical area/aperture, which enables a unified modelling for the classical discrete antenna arrays and the emerging continuous surfaces. As such, a generic array/surface model that accurately takes into account the variations of signal phase, amplitude and projected aperture across array elements is proposed. Based on the proposed model, a closed-form expression of the resulting SNR with the optimal single-user MRC/MRT beamforming is derived. The expression reveals that instead of scaling linearly with the antenna number M as in conventional UPW modelling, the SNR with the more generic model increases with M with diminishing return, which is governed by the collective properties of the array, such as the array occupation ratio and the physical sizes of the array along each dimension, while irrespective of the properties of the individual array element. Additionally, we have derived an alternative insightful expression for the optimal SNR in terms of the vertical and horizontal angular spans. Furthermore, we also show that our derived results include the far-field UPW modelling as a special case. One important finding during the study of far-field approximation is the necessity to introduce a new distance criterion to complement the classical Rayleigh distance, termed uniform-power distance (UPD), which concerns the signal amplitude/power variations across array elements, instead of phase variations as for Rayleigh distance.

This communication presents a design of a dual-band circularly polarized antenna with structure reuse for 1U CubeSat applications. It is a challenging to design an antenna with the limited space of a CubeSat platform. To improve the space utilization, an antenna is designed inspired by the concept of structure reuse. A meshed-like-structure is designed, which works as the radiator of a microstrip antenna at UHF band. However, it works as a partial reflective sheet for a Fabry-Perot resonator cavity antenna at C band. Therefore, a microstrip patch antenna and a Fabry-Perot resonator cavity antenna share only single aperture. A shaped ground is used to decrease the resonance at the lower band. Then, the aperture of the antenna is only 0.3λ0 × 0.3λ0, which makes it easy to integrate with a 1U CubeSat. The measurement reveals that the antenna has a common bandwidth of (|S11| < -10 dB, AR < 3 dB) 1% and 1.4%, an isolation higher than 35 dB and 20 dB, a peak gain of 5.82 dBic and 13.75 dBic at UHF and C band, respectively. The frequency ratio of these two bands reaches 6.4. The above properties make the proposed antenna suitable for a CubeSat system.

Compton imaging is the main method for locating radioactive hot spots emitting high-energy gamma-ray photons. In particular, this imaging method is crucial when the photon energy is too high for coded-mask aperture imaging methods to be effective or when a large field of view is required. Reconstruction of the photon source requires advanced Compton event processing algorithms to determine the exact position of the source. In this study, we introduce a novel method based on a Deep Learning algorithm with a Convolutional Neural Network (CNN) to perform Compton imaging. This algorithm is trained on simulated data and tested on real data acquired with Caliste, a single planar CdTe pixelated detector. We show that performance in terms of source location accuracy is equivalent to state-of-the-art algorithms, while computation time is significantly reduced and sensitivity is improved by a factor of ∼5 in the Caliste configuration.

This paper reports the control method for the core power of the China initiative Accelerator Driven System (CiADS) facility. In the CiADS facility, an intense external neutron source provided by a proton accelerator coupled to a spallation target is used to drive a sub-critical reactor. Without any control rod inside the sub-critical reactor, the core power is controlled by adjusting the proton beam intensity. In order to continuously change the beam intensity, an adjustable aperture is considered to be used at the Low Energy Beam Transport (LEBT) line of the accelerator. The aperture size is adjusted based on the Proportional Integral Derivative (PID) controllers, by comparing either the setting beam intensity or the setting core power with the measured value. To evaluate the proposed control method, a CiADS core model is built based on the point reactor kinetics model with six delayed neutron groups. The simulations based on the CiADS core model have indicated that the core power can be controlled stably by adjusting the aperture size. The response time in the adjustment of the core power depends mainly on the adjustment time of the beam intensity.

Apertures generally exist in the sandwich structures attributing to mechanical connection and lightweight, which might induce failure of such structures. Thus, it is required to realize the impact of aperture on mechanical behaviors of sandwich structures. If transverse shear deformations are unable to be described accurately, the reasonable prediction of dynamic behaviors of the form-core sandwich plates with apertures will meet severe challenges due to a large difference of transverse shear modulus at the adjacent layers. Thereby, such issue is less studied by using the efficient models and experimental testing, so an alternative sinusoidal-type finite element formulation is to be proposed to precisely predict dynamic response of the form-core sandwich structures with apertures. The proposed finite element formulation can meet beforehand compatible conditions of transverse shear stresses at the interfaces of adjacent laminates. In order to appraise strictly capability of the proposed model, experimental tests on natural frequencies of three groups of specimens with different apertures have been carried out. Moreover, four specimens in each group are tested to reduce the testing errors, which is less reported in the published literature. In addition, three-dimensional Finite Element Method (3-D FEM) is also selected to account for the good performance of the present model. Finally, the impact of aperture diameter on the natural frequencies of the sandwich structures is both experimentally and numerically investigated, which can serve as a reference for other researchers.

We describe a new type of ultra-wideband feed antenna based on nested coaxial waveguides. The feed is for radio astronomy applications and covers two closely spaced bands: 400–800 MHz and 900–1800 MHz. New design techniques are described for a three-cavity choke, a wideband iris matching network, and printed circuit board excitation structures. The design methods were developed to improve broadband impedance matching, to control radiation patterns, to separate bands, and to suppress unwanted waveguide modes. The feed has nearly constant beamwidth over the entire 4.5:1 frequency range and a stable phase center. On a f/D = 0.43 reflector antenna, the aperture efficiency exceeds 70% and the phase efficiency exceeds 95%. Other features include low ohmic loss and a compact, lightweight, and low-cost structure. Experimental results are shown for a scaled prototype to verify the design methodology. The methods described are general and can be applied to continuous frequency coverage on reflectors of different geometries.

BACKGROUND: Quantification of melanin pigment release in pigment dispersion syndrome as well as observations of melanin brightness changes can be valuable information in the management of this rare ocular disease. OBJECTIVES: Previous studies have focused on examining the iris pigment epithelium and aqueous humor. Therefore, the aim of this study was to examine the cornea. METHODS: A novel technique was developed for this purpose based on aperture photometry. Slit lamp digital video images of the cornea were recorded. A single frame from each video recording based on the quality was chosen for further processing and analysis. Aperture photometry was performed with AstroImageJ open source software. Aperture selection was performed automatically. Melanin particles displaying a signal-to-noise ratio above 20 were analyzed. RESULTS: A total of 16 melanin particles from the right eye of the patient participating in the study were detected and a further 9 melanin particles from the left eye. The examined area of the cornea measured 348 × 348 pixels in the image. Brightness differed by as much as 8.98 × among particles in the right eye and 2.03 × in the left eye. CONCLUSIONS: It seems feasible for this new method to be potentially used in the monitoring of patients with pigment dispersion syndrome and pigmentary glaucoma as well as in other ocular diseases.

We experimentally demonstrate an elliptical-aperture multimode diversity receiver to mitigate the impairment from anisotropic turbulence, which is emulated by employing an electrically-controlled heater. The anisotropy gradually decreases as the flow-level of the introduced airflow from fans increases. In contrast to circular-aperture reception, the elliptical-aperture multimode diversity receiver can effectively resist beam wander under anisotropic turbulence, reducing outage probability from 14.63% to 0.38% for detecting a dual-polarization 30-Gbaud QPSK signal. Without the aid of an adaptive optics system, this work demonstrates the feasibility of realizing an anisotropic-turbulence-resistant FSO link using multimode and multi-aperture diversity reception employing digital coherent combining techniques.

A novel methodology to create metallic waveguides with multilayer integrated vertical electromagnetic bandgap (EBG) structure is proposed in this paper, and the structure realizes low-cost millimeter-wave (mmWave) slot array antennas. A multilayer stack of easy-to-process thin metallic etching plates is introduced to design mmWave waveguide using compression-fit instead of diffusion bonding and welding assembly process. The electromagnetic (EM) wave leakage from the gaps between the metallic plates is suppressed using the vertical-EBG structure and anti-phasing feeding. The dispersion diagrams of the vertical-EBG unit cell are investigated to illustrate the suppression of leakage. Another leakage wave intercepting methodology is adopted by anti-phase feeding to prevent leakage wave from adjacent slot sub-arrays. Finally, two examples of 2×8 and 8×8 slot array antennas are presented to verify our design concept. The measured impedance bandwidths of the two antennas are 77.1-84.6 GHz (9.3%) and 78.6-84.9 GHz (7.7%), respectively. In addition, the 3-dB broadside gain bandwidths are 73.1 to 85.3 GHz (15.1%) and 76.8 to 84.4 GHz (9.4%), respectively. The results show aperture efficiencies up to 56.4%.

Airborne Distributed Coherent Aperture Radar (ADCAR) is one of the most promising next-generation radars to significantly improve target detection and discrimination abilities. However, time and phase synchronization among unit radars should be done before an ADCAR is intended to cohere on a potential target. To address this problem, a time and phase synchronization technique using clutter observations is proposed in this paper. Clutter returns from different azimuths and elevations on the surface of the earth are employed to calibrate system uncertainties. Two stages are mainly considered: a scene registration among range-Doppler units from different transmit/receive pairs is performed to enhance the clutter coherence in the first stage, followed by a joint estimation of those synchronization errors in the second stage. To relieve the computational burden, a novel Separable and Sequential Estimation (SSE) method is provided to separate the unknowns at the sacrifice of a range-Doppler unit. Moreover, performance analyses including the clutter coherence ability, estimation lower bound, and signal coherence loss are also performed. Finally, simulation results indicate that ADCAR time and phase synchronization is realized by using our methods.

A synthesized strategy for achieving polarization-insensitive metalens is proposed by imposing identical parabolic phase patterns individually on two decoupled left-handed (spin up, σ+) and right-handed (spin down, σ-) circular polarization (CP) channels of an anisotropic scheme. This is enabled by synergizing dynamic phases and local geometric phases within 0° and 90° rotations. As a consequence, similar focusing behavior is expected when it is illuminated by a plane wave of arbitrary polarization since any incoming wave is a superposition of σ+ and σ- wave. Such an intriguing feature can be utilized to engineer a polarization-insensitive reflectarray/transmitarray in a shared aperture by placing a feeding source of different polarizations at its focal spot without altering the array aperture. Therein, the polarization of the meta-array is determined by its feeding which is readily to be changed in practice. For demonstration and possible applications, two reflectarrays composed of 50 × 50 elements at Ku band with one in normal and the other in offset configuration were designed and experimentally characterized. Numerical and experimental results illustrate that both reflectarrays are able to work in dual-linear (LP) and dual CP states by utilizing LP and CP horns of different orientations. Moreover, the versatile polarization-agile property does not pose significant penalty on its radiation performance and both reflectarrays exhibit a measured peak aperture efficiency of 63.8 and 39.6%, respectively near 14 GHz, and a 1dB gain bandwidth more than 11.8 %.

This paper presents a gain-equalized Ka-band Rotman lens-fed antenna by using phase gradient transmission lines (PGTLs). With PGTLs, the variation trend of the output progressive phase differences among the feeding ports are inverted. The aperture loss of the planar antenna array is then partially compensated by the efficiency of the lens when performing a wide-angle beam scanning. Hence, gain equalization is achieved among multiple beams with an acceptable gain degradation. To reduce the total size, the Rotman lens with PGTLs, the feeding networks, and the antenna array are stacked vertically. Meanwhile, the feeding network is implemented with substrate integrated coaxial lines, suppressing the parallel-plate-mode inside the multilayer structure. In order to validate the proposed design, a compact Rotman lens fed antenna operating at 24.75-27.5 GHz (FBW=10.5%) is designed and fabricated. The results show that the gain drop of the Rotman lens-fed multibeam antenna is reduced from 4.4 dB to 1.5 dB at the design frequency of 26 GHz, covering a wide angular range between ±56∘.

A novel reflectarray (RA) with ultra-low-profile and 2-bit phase quantization beam-steering ability is presented in this paper. To reduce the profile, a Leaky-wave feed is used to excite the RA with enhanced illumination efficiency. Moreover, simultaneous sum and difference patterns are also obtained to provide beam flexibility. The entire thickness of the proposed RA is less than 3% of that of the conventional front-fed RA with the same aperture. To increase the efficiency of the RA, a novel unit cell consisting of a polarizer layer and a reflection layer is developed, which is configured to provide polarization rotation and 2-bit phase shifts by using a hybrid of tunable polarization and discrete resonator. The operation principle, theoretical explanation, and implementation of the proposed antenna are elaborated in this work. To prove the design concept and beam scanning performance, an array with 9×7 unit cells operating at Ka-band is designed and simulated firstly. 2-D beam scanning within the range of ±30° has been verified. Then, a passive prototype with 9×67 unit cells is designed, fabricated and measured. Experimental results show aperture efficiency of 35.1% and illumination efficiency of 43.4%. The developed RA is scalable, and it provides a viable low-cost solution to develop low-profile, high-gain and beam-steering array antennas for satellite applications.

This work investigates the spectral quantum efficiency and inter-pixel crosstalk of a MWIR-LWIR dual band, HgCdTe-based focal plane array (FPA) photodetector (MWIR and LWIR stand for mid- and long-wavelength infrared bands). Pixels are $\text{10}\,\mu$ m-wide with truncated pyramid geometry and separated by deep trenches. Three-dimensional combined full-wave electromagnetic and electrical simulations in the drift-diffusion approximation allowed to describe the complex, standing-wave-like spectral features resulting from the light interference and diffraction due to the pixels and illuminating beam aperture. The inter-pixel crosstalk for the MWIR operation demonstrated to be very sensitive to the trench depth, in contrast to the LWIR electrooptical response, left almost unchanged. The present work also investigates the causes of performance worsening in the two IR bands when pixel pitch is reduced to $\text{5}\,\mu$ m, hence well below typical LWIR wavelengths and close to the diffraction limited operation.

This paper presents a shared-aperture dual-band dual-polarized antenna array for fifth-generation (5G) mobile communication. Within one radiating aperture, four higher-band (HB) patch antenna elements are placed over the lower-band (LB) full-wavelength slot antenna. The proposed array is miniaturized by bending the ground plane of the slot antenna. Suppression of cross-band mutual coupling and scattering is achieved by using the filtering performance of the slot antenna and a dual-function metasurface. The filtering performance of the slot antenna is realized using coupled microstrip lines inside the radiating slot and open-ended stubs on the feeding lines. The dual-function metasurface operates as an artificial magnetic conductor reflector in the LB and bandpass frequency selective surface in the HB. By placing the dual-function metasurface behind the slot antenna, the radiation of the slot antenna is enhanced in the LB but not HB, and the negative effect of its HB scattering on the HB antennas is reduced. The working mechanism is explained in detail. The measured and simulated results demonstrate that the proposed array has stable radiation patterns in the bands of 0.69-0.96 and 3.4-3.7 GHz with a high cross-band isolation of over 32 dB, and is more compact than the previous works.

The problem of transient free convection in an open cavity containing two elastic thin fins is studied in this paper. The left surface is heated, and the right surface is in opening, which is in contact with the environment air. The dimensionless forms of the governing equations for continuity, momentum and heat transfer in the fluid and structures domains are written in Arbitrary Lagrangian–Eulerian (ALE) formulation. The governing equations are solved by the finite element method (FEM). The governing parameters considered are the oscillating fin direction, fin amplitude and length with several flexibility values and aperture sizes. The results show that a maximum heat transfer enhancement occurs at the suitable parameters between the aperture size and the fins oscillating direction.

Extremely large-scale multiple-input multiple-output (XL-MIMO) communication aims to further significantly boost the antenna size over the current massive MIMO systems, for which conventional far-field assumption with uniform plane wave (UPW) model may become invalid. This paper studies the near-field modelling and performance analysis for multi-user XL-MIMO communication. With the spherical wavefront phase modelling, and also by taking into account the variations of signal amplitude and projected aperture across array elements, the performance of the three typical beamforming schemes are investigated, namely the maximal-ratio combining (MRC), zero-forcing (ZF), and minimum mean-square error (MMSE) beamforming. For the special case of two users, we analytically show that the signal-to-interference-plus-noise ratio (SINR) of all the three beamforming schemes increases as the channels’ squared-correlation coefficient decreases. Furthermore, compared to existing UPW model where inter-user interference (IUI) can only be suppressed in angular domain, XL-MIMO enables a new degree-of-freedom (DoF) for IUI suppression by distance separation, even for users along the same direction. Simulation results are provided to validate the modelling and performance analysis of multi-user XL-MIMO communications.

This paper presents a dual-polarized Frequency-scaled Ultra-wide Spectrum Element (FUSE) array on a triangular lattice, precision-machined from an Aluminum block as a self-supporting structure, similar to all-metal Vivaldi arrays reported by the authors in past work. Whereas dual-polarized FUSE arrays normally consist of offset radiator pairs conforming to the ubiquitous square-lattice egg-crate configuration and capacitively coupled at the ends to achieve ultra-wideband operational frequency ranges, this work is novel in that it uses conventional manufacturing to directly machine the dual-polarized FUSE array on a triangular lattice instead. Triangular lattices for dual-polarized wideband arrays are uncommon in the literature and have the benefit of 15.5% reduction in element counts over a square lattice aperture of the same footprint and upper frequency of operation, making this a useful development for applications requiring minimum element counts, i.e., reduced cost/weight. In this paper, embedded element performance predictions for the dual-polarized triangular-lattice FUSE array are presented and validated with measurements of a hardware prototype. Results show similar overall grating-lobe-free performance to a square lattice FUSE array of the same footprint and operational frequencies reported in earlier work. The asymmetries of the triangular lattice result in relative performance degradation vs. square lattice FUSE arrays as a trade-off to the benefit of reduced element counts for apertures of similar size.

Real-time, three-dimensional (3D), passive acoustic mapping (PAM) of microbubble dynamics during transcranial focused ultrasound (FUS) is essential for optimal treatment outcomes. The angular spectrum approach (ASA) potentially offers a very efficient method to perform PAM, as it can reconstruct specific frequency bands pertinent to microbubble dynamics and may be extended to correct aberrations caused by the skull. Here we assesses experimentally the abilities of heterogeneous ASA (HASA) to perform trans-skull PAM. Our experimental investigations demonstrate that the 3D PAMs of a known 1 MHz source, constructed with HASA through an ex vivo human skull segment, reduced both the localization error (from 4.7±2.3 mm to 2.3±1.6 mm) and the number, size, and energy of spurious lobes caused by aberration, with modest additional computational expense. While further improvements in the localization errors are expected with arrays with denser elements and larger aperture, our analysis revealed that experimental constraints associated with the array pitch and aperture (here 1.8 mm and 2.5 cm, respectively) can be ameliorated by interpolation and peak finding techniques. Beyond the array characteristics, our analysis also indicated that errors in the registration (translation and rotation of ±5 mm and ±5°, respectively) of the skull segment to the array can led to peak localization errors of the order of a few wavelengths. Interestingly, errors in the spatially dependent speed of sound in the skull (±20 %) caused only sub-wavelength errors in the reconstructions, suggesting that registration is the most important determinant of point source localization accuracy. Collectively, our findings show that HASA can address source localization problems through the skull efficiently and accurately under realistic conditions, thereby creating unique opportunities for imaging and controlling the microbubble dynamics in the brain.

In this paper, we propose a traveling-wave endfire antenna based on the first higher-order transmission line (TL) mode, and it features wide bandwidth, high gain, and large aperture efficiency. We propose two essential conditions for the realization of the proposed wideband endfire antenna. Firstly, the dispersion curve of the first higher-order mode should be made close to that of the air line across a wide frequency band. Secondly, the fundamental mode should be suppressed to allow single higher-order mode operation across a wide frequency band. Following these principles, we provide a design for an endfire antenna based on a periodically slotted parallel stripline, where the periodic meandered slots suppress the fundamental mode and hence allow single higher-order mode radiation. To verify the proposed approach, a prototype has been designed and fabricated. The antenna can achieve endfire radiation within a 1:2 frequency band (8.5-17.5 GHz), with an average gain of 10.7 dBi, and large aperture efficiency up to 6.38 dBi/λ20.

A broadband low-profile folded transmitarray is proposed and investigated, in which a novel wideband transmission polarizer (TP) is used to realize low-profile design. The proposed TP, mainly consisting of a differential-fed grid-slotted patch antenna, can realize high-efficiency transmission and polarization selection simultaneously within a wideband frequency range. Moreover, the proposed TP can realize linear transmission phase because of the true-time delay (TTD) technique. Owing to the function of polarization selection and linear transmission phase, the TP can be used as antenna element for a folded transmitarray. A 140-element folded transmitarray (FTA) is designed and fabricated by combining the TP with a broadband polarization rotation reflecting surface (PRRS). The measured radiation patterns agree well with the simulated results, and a peak gain of 24 dBi and maximum aperture efficiency of 44.7% are achieved. Furthermore, -1 dB and -3 dB gain bandwidth with 25.9% and 33.3% are also experimentally demonstrated in the proposed FTA, respectively.

A novel strategy is proposed to design microstrip antenna arrays with two wide bands for high frequency applications using any-layer HDI PCB technology. This technology makes it possible to stack multiple layers of substrates and micro-vias. Several antennas are designed and taped out to illustrate the new procedure. The antennas cover two wide frequency bands with a large separation ratio of 2.2:1, from 28 to 30 GHz and from 57 to 71 GHz. Measurement results show a matching better than 10 dB over both bands, and an intra-band coupling lower than -28 dB. Measured gains and radiation patterns for the arrays all show a good agreement with simulations.

This paper presents a new method for 3-D localization of an acoustic source signal by estimating its azimuth-angle, elevation-angle, and radial range. The proposed method exploits a spatially spread acoustic vector sensor, which is composed of a tri-axial velocity vector sensor and an isotropic pressure sensor. Unlike the spatially collocated case, the self-normalization of spatially spread acoustic vector sensors response is no longer independent of the source location, resulting in the inapplicability of the widely used self-normalization estimators [5], [30], [32]. The present work considers the near-field propagations path attenuation and phase difference among the sensor components and derives a source location estimation method without resorting to the self-normalization operation. Also, the proposed method is applicable to any non-free-space propagation models at arbitrarily unknown path-loss exponent. In comparison with the existing methods, where the velocity vector sensor is spatially collocated, the proposed method can offer improved performance estimation due to the inherent extension of the vector sensors spatial aperture in the spread structure.

Borehole sonic tools with an array of receivers provide estimates of plane wave velocities and dispersion characteristics associated with guided modes across receiver apertures ranging from 0.6 to 1.8 m. In addition, borehole resistivity imaging tools can be used to determine thin lamination thicknesses of about 5-10-cm interbedded in a reservoir. Recently, ultrasonic tools have been demonstrated to measure compressional and shear velocities across thin laminations using transit time of corresponding refracted headwaves along the borehole surface. However, mass densities of laminations cannot be determined from transit times of headwaves. Inversion of borehole flexural or Stoneley-guided mode dispersions yields three effective alteration parameters that include elastic stiffnesses and mass densities of laminations. These parameters are defined in terms of fractional changes in the Lame constants and mass density of the laminate from those of a reference homogeneous formation weighted by the ratio of laminate and formation thicknesses probed by the propagating wave. Since the laminate thickness is estimated from a borehole resistivity imaging tool, and formation thickness probed is determined from the sonic tool receiver aperture, ratios of the laminate to formation thicknesses are known inputs to the inversion workflow. Consequently, changes in the two Lame constants and mass density of the laminate can be estimated from those in the reference formation. Estimates of the compressional and shear moduli together with the mass density of laminate provide a complete elastic characterization that are of value in estimating compressional and shear impedances of the laminate.

Differs from conventional phased-array, frequency diverse array (FDA) employs a frequency increment across the array elements and thus produces a range-angle-dependent beampattern. This additional range dependence finds applications in target detection/localization, high-resolution synthetic aperture radar (SAR) imaging, and SAR deceptive jamming. To capture the essence behind those applications, we analyze the range, angle, and Doppler resolution capabilities of FDA radar signal via ambiguity function. As conventional ambiguity function is defined for a single-input single-output (SISO) signal, we extend it to the generalized ambiguity function for FDA radar signal, parameterized with the range, angle, and Doppler shifts of a target. Both theoretical analysis and numerical results show that the FDA radar with a large frequency increment has potentials in high-resolution ranging but will suffer from additional range ambiguity within the range bin and Doppler ambiguity. Moreover, the use of frequency increment brings FDA radar a virtual transmit aperture but decreases the directional gain.

Multiple aperture interferometric synthetic aperture radar (MAI) can measure ground displacements along SAR track. However, MAI measurements may suffer from severe ionospheric error, especially for long-wavelength SAR sensors. This study presents a new approach, azimuth split-spectrum interferometry (AziSSI), to correct ionospheric errors in MAI measurements. The proposed method can straightforwardly resolve ionospheric phase delay by exploiting two subband MAI interferograms with different centroid frequencies. We utilized two groups of ALOS-1 PALSAR images, which cover the 2008 Wenchuan earthquake containing strong coseismic ground deformation and a stable coast region in Chile, respectively, to test the proposed method. Experimental results show that the AziSSI method can successfully recover the coseismic displacements induced by the Wenchuan earthquake and circumvent the azimuth stripes for the Chile case's MAI measurements. The maximum ionosphere-induced azimuth shifts are about 2.2 m for the Wenchuan case and 2.5 m for the Chile case. We validated the correction performance of the AziSSI method with the Wenchuan case by comparing the compensated azimuth displacements with the simulated deformation from a forward fault slip model and coseismic global positioning system (GPS) measurements. The validations show that the deformation patterns after the ionospheric correction are consistent with the simulations of the sinistral slip of the causative fault. The root-mean-square error between the GPS and MAI measurements is reduced from 0.77 to 0.28 m before and after the ionospheric correction, indicating that AziSSI can significantly compensate ionospheric errors for MAI.

Spaceborne synthetic aperture radar (SAR) can operate at various modes, including stripmap mode, spotlight mode, sliding spotlight mode, and Terrain observation by progressive scans (TOPS) mode. These four imaging modes can be regarded as unified, differing in rotation-center ranges. To uniformly focus the data of these four imaging modes in real-time, this article proposes a real-time unified focusing algorithm (RT-UFA) for the multi-mode SAR via azimuth sub-aperture complex-valued image combining and scaling. The imaging processing can be performed while the data are being recorded. In the first stage of imaging, sub-aperture complex-valued images with relative low-resolution can be obtained by the cascade of the extended chirp scaling (ECS) and azimuth dechirp. Then, these complex-valued images are coherently combined by shifting the integer number of pixels, and thus the full-resolution image of all the recorded data can be obtained. The azimuth scaling and the pixels shifting in the RT-UFA are analyzed in detail. Simulation and SAR data results are presented to validate the analysis and RT-UFA.

This paper presents a gain enhanced wide azimuth beam automotive antenna using half-mode substrate integrated waveguide (HMSIW) cavity for automotive applications. The antenna is separated into two HMSIW cavities by electrical via walls. The two HMSIW cavities are excited through differential feeding, including a 180 delay line in the center of the antenna. The antenna was operated in TM11 mode and investigated using aperture theory based on the cavity model. The antenna size is small enough to mount in the rear-view mirror, which has a long rectangular shape. For comparison, the proposed antenna and a conventional 1 2 microstrip square patch antenna array were fabricated to the same dimensions. Then, these antennas were tested to provide validation. The tested results were consistent with the simulation results. The tested results show that the antenna, with the overall dimensions of 70 mm 35 mm 1.52 mm (1.380 0.690 0.030), operates at 5.9 GHz. The gain of the antenna is 9.49 dB, and the azimuth beam width is 74.0. The proposed antenna has a wider azimuth beam width (74.0) than a conventional 1 2 square patch array antenna (42.0) with similar gain and size.

This article presents a hybrid 3-D electromagnetic (EM) full-wave inversion (FWI) method for the reconstruction of subsurface objects illuminated by an antenna array with the limited aperture. The 3-D linear sampling method (LSM) is first used to qualitatively reconstruct the rough shapes and locations of the subsurface objects. Then, the 3-D convolutional neural network (CNN) U-Net is used to further refine the images of the unknown objects. Finally, the Born iterative method (BIM) is implemented to quantitatively invert for the dielectric parameters of subsurface inhomogeneous objects or multiple homogeneous objects in the restricted image regions. Numerical simulations show that, compared with the pure FWI method BIM, the proposed hybrid method can reconstruct subsurface 3-D objects from limited-aperture EM data with both higher accuracy and lower computational cost. In addition, the proposed hybrid method also shows a strong antinoise ability for the reconstruction of multiple subsurface objects.

Currently, in the spaceborne synthetic aperture radar (SAR) community, the sliding spotlight mode has been widely applied to achieve high-resolution imaging. However, limited by the system pulse repetition frequency (PRF), it is usually impossible to realize a large-scale coverage at the same time. The technique of azimuth multichannel alleviates the PRF restriction by receiving additional spatial samples proportional to the number of Rx channels. A system combining the technique of azimuth multichannel with sliding spotlight SAR is able to achieve ultrahigh-resolution and wide-swath imaging simultaneously. In the advanced multichannel sliding spotlight mode, some problems may occur. First, azimuth beam progressive steering leads to an enlarged Doppler bandwidth over N· PRF, and conventional azimuth multichannel reconstruction algorithms developed for the stripmap mode are, thus, not directly suitable for the sliding spotlight mode. Second, the phase characteristics of multichannel sliding spotlight SAR is different from that of multichannel stripmap SAR due to the time variation of the system Doppler centroid. Third, processing of spaceborne multichannel sliding spotlight SAR experimental data shows that the convolution function used in the full-aperture reconstruction method is closely related to the antenna phase configuration strategy of the phased array antenna system. Therefore, an improved processing frame is required for the multichannel sliding spotlight SAR, reexamining the validity of assumptions, such as the stop-go-stop approximation and that of a noncurved trajectory during the relatively long aperture time. Recently, as an exploratory study, a dual-channel sliding spotlight experiment was conducted with the Gaofen-3 (GF-3) SAR. Two experimental data sets were acquired with different PRFs. In this article, the GF-3 payload and the experiment design are introduced, and a complete multichannel sliding spotlight SAR data processing chain is provided. The first imaging results of spaceborne multichannel sliding spotlight SAR are demonstrated.

For repeat-pass interferometric systems, temporal decorrelation (TD) is inevitable and cannot be ignored, and can lead to significant bias in the forest height estimation. The TD random volume over ground (TD + RVoG) model has been found to be a reasonable way to describe the scattering process over forest areas. In this letter, based on the TD + RVoG model, a new forest height estimation method is proposed for use with multibaseline polarimetric synthetic aperture radar interferometry (PolInSAR) data. First, the correlation between the ground-to-volume ratios (GVRs) associated with the different polarizations is parameterized according to the geometric interpretation of the RVoG model. An interferometric pair that is assumed to have no TD is then selected based on the eccentricity of the polarimetric coherence region, and the other interferometric pairs are fitted by the TD + RVoG model. E-synthetic aperture radar (E-SAR) P-band PolInSAR data sets affected by TD are used to prove the effectiveness of the proposed method. The experimental results show that the forest height results are improved by 25.90% when compared to the RVoG-based method.

International audience; We have measured the three-dimensional coordinates of retroreflecting glass spheres using a multilateration technique. To this end, the distances between each target and our measurement heads have been determined by an in-house prototype of electro-optical absolute distance meter. The used targets are spheres of glass refractive index n=2 and of diameter 14.2 mm. They offer a much larger aperture than corner cubes and a lower cost, but they present a low reflectivity. However, this paper shows that with a proper collimation of the laser beams it is possible to reach a range of operation of 20 m. The standard uncertainty on such distances is better than 11 µm, including the mechanical errors of the gimbal mechanisms of our aiming systems. This uncertainty has been validated thanks to a comparison with an interferometric bench. In addition, the measurement of the coordinates of 16 glass spheres using a self-calibration multilateration algorithm has also confirmed the performances of the developed system: the standard deviation on the position errors has been estimated to about 10 µm.

High-gain single-feed antennas are desired for current and future wireless systems. Slot-based highly overmoded cavity antennas are one solution, but the fact that they can only radiate broadside beams limits their applications. An innovative phase-control technique is developed for slot-based resonant cavity antennas that utilizes a planar array of closely-spaced, appropriately-sized metallic patches integrated into the very near field of their slot arrays. It facilitates the design and realization of the phase distribution over their radiating aperture that is required for them to generate single and/or multiple tilted beams pointed at specified directions. A TE(10)(11)(0)-mode slot-based cavity antenna is selected as the pathfinder system. A TE110-mode single-slot cavity antenna that is equivalent to the half-wavelength subsection of that cavity is introduced initially to monitor the phase radiated from each slot. The phase control surface is then carefully engineered to facilitate tilted output beams from the base design. The approach is validated with two subsequent tilted-beam systems. The first system achieves a single beam tilted to 30° with respect to the broadside direction. The second system is extended to produce two independently-directed titled beams pointing at –10° and 20°, respectively. All of the measured results agree well with their simulated values.

We present a study on beam coupling in radiating structures that support multiple simultaneous beams. The formation of multiple beams is relevant in modern wireless communication applications when diverse data streams can be sent from a single transmitter to users located in different directions. General expressions are provided that relate the coupling between radiated beams to the associated current distributions on the radiating aperture. When expanding the currents in terms of basis functions, the beam coupling can be also written in terms of coupling contributions due to each pair of basis functions. The analysis is applied to antenna arrays with different levels of mutual coupling between the array elements. More specifically, arrays of resonant elements, characterized by very low mutual coupling, are compared with arrays of connected elements, which are strongly coupled. We show that, even for a very high level of mutual coupling between individual array elements, it is possible to obtain orthogonal beams if the total current distributions associated with the beams are uncoupled.

Recently, a novel design scheme of low-earth-orbit spaceborne mini-synthetic aperture radar (MiniSAR) system is proposed to exploit the integrated transceiver to collect the azimuth periodic block sampling data by using alternated transmitting and receiving operations. Because such collected data are downsampled, the images recovered by the typical matched filtering (MF)-based methods have the problems of obvious azimuth ambiguities, ghosts, and energy dispersion. To find a suitable method for such data, with the help of sparse signal processing technique, we first introduce sparse synthetic aperture radar (SAR) imaging with l₁-norm regularization-based approximated observation method to recover the large-scale considered scene. To further improve the imaging performance, a novel approximated observation unambiguous sparse SAR imaging method via l $_{2,1}$ -norm is proposed. Compared with l₁-norm-based method, the recovered image by the proposed one achieves better imaging quality with reduced azimuth ambiguities and ghosts. Experimental results on simulated and real data validate the proposed method.

This study proposes a broadband dual-polarized solar cell phased array antenna. It is constructed by using crisscross distributed metal-meshed tie-shaped dipoles, an optical transparent glass substrate, feeding probes and ground probes, a solar cell, and a metal ground. The meshed tie-shaped dipoles are sputtered on the top surface of the glass substrate. Circular metal-meshed patches located at the crisscrossing points of the dipoles on the back surface of the glass substrate are introduced to extend the operational bandwidth of the solar cell antenna. The solar cell was placed on the ground of the antenna. We fabricated a sample of the solar cell antenna and measured the electromagnetic characteristics and its power output. The results of the measurements agreed with those of simulations. The proposed solar cell antenna array had a wide operational bandwidth of 2.5-5 GHz, a wide two-dimensional range of the phase scanning angle of ±45°, a high aperture efficiency of 68.9%–84.1%, and a high relative maximum output power ratio of 87.1% compared with a pure solar cell. It is scalable, and can be used in a self-sustained 5G wireless communication system for sub-6 GHz applications.

We propose a general method for designing wideband matching tapers in inhomogeneous media where phase velocity is coupled to the taper impedance profile. Such tapers are used to match wideband gradient index (GRIN) lens antennas. To simplify fabrication tapers are often constrained to physically uniform layers wherein commensurate line theory cannot predict the frequency response. Therefore, we present a new design algorithm which derives an effective permittivity $\epsilon_{eff}$ to equalize the electrical length of commensurate and non-commensurate line tapers. The algorithm provides a systematic design method with predictable frequency response for non-commensurate line tapers. Nevertheless, there are several unavoidable nonidealities present in such discretized tapers which we discuss and provide recommendations for mitigation. The algorithm is used to design a Klopfenstein taper with return loss better than 15 dB from 8 to 78 GHz. The design is fabricated and measurements agree with simulation across the WR90, WR28, and WR12 bands. An approximate efficiency formula is proposed which predicts aperture efficiency of taper-matched lenses without the need for time-consuming full-wave simulations. Various lenses are designed and compared to highlight the advantages of Klopfenstein tapers in GRIN lens design. The results demonstrate the usefulness of the proposed design method., Comment: 11 pages, 9 figures. Accepted June 5, 2021 for publication in IEEE Trans. Antennas Propag

Digital beamforming (DBF) is a state-of-the-art technique for high-resolution and wide-swath (HRWS) observation in synthetic aperture radar (SAR) imaging. Since azimuth high-resolution imaging will be a popular tendency in future SARs, DBF-SAR needs to become practical. A new problem arising in airborne DBF-SAR application is the aperture extension loss (AEL). Similar to the pulse extension loss, it is confirmed in our study that AEL will widen the point target responses and degrade the signal-to-noise ratio (SNR) improvement in airborne DBF-SAR. However, little work has been devoted to the compensation of the AEL effect. In this article, the effects of AEL are demonstrated and two compensation methods are proposed, discussed, and implemented for the processing of raw data. The above are demonstrated through simulations and an airborne experimental C-band azimuth high-resolution DBF-SAR. The results show that the AEL compensation removes the AEL effects and increases the SNR with the cost of higher impulse response sidelobes. Moreover, with this novel design scheme, it is demonstrated that azimuth ambiguity suppression can be implemented by elevation DBF.

Passive localization is important because of its strong concealment and long detection distance. Space-borne passive radiation source location technologies have contradicting characteristics of wide coverage and high-precision position. Hence, accurate target identification is difficult to realize. A novel measurement that utilizes passive synthetic aperture is presented in this letter to measure the time of the satellite's passing zenith precisely. In the beam coverage duration, the radiation carrier Doppler component is extracted and accumulated to synthesize an equivalent large virtual satellite antenna azimuth aperture. Taking advantage of the linear Doppler rate, a local matched filter is designed to implement a 2-D search. Doppler rate and zero Doppler point correspond to the target range and azimuth locations, respectively. The corresponding subastral point position radiation source can then be determined. Practical experiment results from an unmanned aerial vehicle platform demonstrated the effectiveness, wide coverage, and high-precision meter scale of the proposed method. Satellite data were also utilized to verify the feasibility of the system.

Various impeded flow particle receivers were proposed to prolong the particle residence time but always faced the risk of thermal deterioration and the difficulty of real-time particle velocity control. Herein, we reported a novel impeded flow particle receiver to solve above problems and further have the potential to control the particle velocity distribution, which could provide a heat source with better stability, better uniformity and higher temperature for subsequent thermal power generation and other thermal applications. In this receiver, the friction along the path and the gate valves at outlet act as the obstruction structures to allow the particles to move slowly and controllably in the form of a sliding-bed, which is why we call this receiver a sliding-bed receiver. The sliding-bed receiver's structural validity and operational characteristics at different working conditions were detailly investigated with both experimental and numerical methods. Experimental results showed that the outlet particle temperature and efficiency could reach 847 °C and 77.2% under a solar simulator of 4 kW. An optical and thermal coupling model was developed and revealed an improved particle temperature of 1350 °C and efficiency of 82% under higher incident power. The effects of the effects of the incident power distribution, the particle velocity distribution and the quartz glass on aperture on the receiver performance were detailly analyzed, which could also help optimize the design and operation of other particle receivers such as free-falling particle receivers.

This communication deals with the design of discrete apertures for wireless power transfer (WPT) within the Fresnel region, and provides some design guidelines to enhance WPT efficiency. In fact, although the aperture excitations optimization problem given two specific continuous or discrete apertures has been already researched, the effect of antenna arrays design choices (such as the number of antenna elements or their spacings) on the WPT efficiency has not been investigated yet. In order to do that, WPT efficiency formulation has been theoretically analyzed to understand the different antenna parameters contributions to the power transmission efficiency (PTE). After that, the problem of the array excitation optimization in the sense of maximum PTE has been revisited including cases with or without perfect impedance matching. Finally, different array designs and relative achievable PTEs have been compared systematically, and it is shown that arrays with inter-element spacing in the order of 0.3λ-0.4λ (tightly coupled arrays) provide the largest PTE (also for oblique WPT cases) when the array excitation is calculated taking into account the impedance mismatching.

Synthetic aperture radar (SAR) is an advanced ground-observing remote sensing technology, and high-resolution wide-swath (HRWS) imaging has always been the goal of SAR. In general, an improved azimuth resolution requires a large pulse repetition frequency (PRF), resulting in high system requirements. To overcome this difficulty, azimuth multichannel technology has gradually developed, achieving HRWS imaging and decreasing the PRF by increasing the spatial sampling, i.e., increasing the number of antenna subapertures in the azimuth. This article proposes a theoretical architecture that generates multiple virtual receiving apertures in the azimuth rather than real apertures. The virtual receiving apertures are formed by multiplying the azimuth signals by linear phase histories provided by vortex beams carrying different orbital angular momentum (OAM) modes. Vortex beams with different OAM modes have different oblique phase wavefronts, so virtual receiving positions are generated in the along-track direction. This approach aims to reduce the PRF without increasing the azimuth real receiving aperture. Simulation results demonstrate the effectiveness and limitations of the method. Finally, to overcome the inherent limitations of the method, two possible implementation schemes are proposed.

Synthetic aperture radar (SAR) human-imaging technology has been widely used in the fields of security screening and activity recognition. However, most of the existing methods aim at stationary human targets, resulting in severe restrictions on their potential applications. In this article, an SAR imaging method for walking human is proposed with short aperture terahertz (THz) radar. This method is based on a modified wavenumber domain approximate algorithm (mωka), whose interpolation mapping is modified according to the approximation of region of interest (RoI). Because the nonrigid motion phase error caused by the walking human would lead to severe deformation and blur in imaging results, a compensation processing is essential. To figure it out, the fractional Fourier transform combined with the maximum and minimum generalized likelihood ratio test (FrFT-mmGLRT) is devised in this article. Within a short aperture time, the nonrigid motion of walking human can be approximately assumed as a superposition of the rigid movements of different human body parts. Particularly, by taking advantage of the superposition property of FrFT, the motion phase errors of different human body parts are distinguished and estimated by jointly searching for the peaks of FrFT energy spectrum. Furthermore, the mmGLRT-based composite imaging technique is utilized to obtain a whole body result from the compensated results of different body parts. Finally, numerical simulation and real experiments are conducted to verify the feasibility and capability of the proposed method for walking human SAR imaging.

Translational compensation is a crucial step in inverse synthetic aperture radar (ISAR) imaging. However, nonparametric compensation methods may collapse under the condition of a low signal-to-noise ratio (SNR), and high-order parametric compensation methods usually have a large computational load. In this article, two cascaded integration methods are proposed to solve the problems above based on the generalized Radon-Fourier transform (GRFT). The first method models the translational motion as polynomial and utilizes the proposed subaperture GRFT (SAGRFT), which is a fast implementation of the GRFT, to estimate the translational parameters. The SAGRFT divides the full aperture into several subapertures and realizes coherent integration by implementing moving target detection (MTD) within subapertures and the GRFT among subapertures. In addition, the distribution property of the blind speed side lobes (BSSLs) generated by the SAGRFT is analyzed. On this basis, the second method based on metaheuristic algorithms is proposed to further accelerate the parameter estimation process and solve the BSSLs problem. The proposed methods can not only play a role in stealth target imaging but also be utilized in near-Earth asteroid (NEA) imaging in radar astronomy. Finally, the numerical simulations of asteroid imaging and the experimental results of plane imaging are demonstrated to verify the performance advantages of the proposed methods.

Azimuth multichannel synthetic aperture radar (SAR) working in the sliding spotlight mode can effectively achieve ultrahigh resolution and wide swath imaging. However, multichannel sliding spotlight SAR echoes with large pulse bandwidth and azimuth steering angle are difficult to reconstruct and process due to the large range frequency-dependent Doppler centroid varying frequency support. To resolve this problem, two azimuth preprocessing approaches both based on the range frequency-dependent deramping strategy are proposed in this article. In both approaches, echoes are handled by a range frequency-dependent azimuth deramping function at first, which assign the signal measurements to unambiguous Doppler frequencies. Afterward, in the first preprocessing approach, azimuth multichannel raw data can be reconstructed and combined before azimuth upsampling in the conventional two-step preprocessing technique. The other way to handle the deramped multichannel raw data is the modified full aperture azimuth multichannel sliding spotlight reconstruction approach, which embeds azimuth multichannel reconstruction into azimuth convolution between the deramped raw data and the selected range frequency-dependent azimuth deramping function. Furthermore, the azimuth data in the second approach should be resampled to obtain a uniform azimuth sampling interval. Computational complexity and effects on the following imaging algorithm of both approaches are analyzed and compared. Simulation results validate the proposed two azimuth multichannel preprocessing approaches.