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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.

ThThis letter proposes a novel four-dimensional multi-probe anechoic chamber (4D-MPAC) method for emulating time-domain non-stationary channel models of over-the-air (OTA) testing. The proposed method adds time dimension to the 3D-MPAC system, so that the channel model with spatial parameters changing over time can be emulated. In addition, 4D power angular spectrum similarity percentage (4D-PSP) as a figure of merit to evaluate the accuracy of the channel reconstruction is proposed for the first time. Based on the 4D-PSP, genetic algorithm (GA) is designed to reduce the number of active probes and testing cost. Furthermore, a dynamic motion scenario in a street is modeled by ray tracing simulation, where the time-domain non-stationary channel model is reconstructed by the proposed method with a small number of probes.

In this study, we propose a method for generating an angular spectrum using array radar and physiological component analysis. We develop physiological component analysis to separate radar echoes from multiple body positions, where echoes are phase-modulated by propagating pulse waves. Assuming that the pulse wave displacements at multiple body positions are constant multiples of a time-shifted waveform, the method estimates echoes using a simplified mathematical model. We exploit the mainlobe and nulls of the directional patterns of the physiological component analysis to form an angular spectrum. We applied the proposed method to simulated data to demonstrate that it can generate a super-resolution angular spectrum.

Background Image-based cell analytic methodologies offer a relatively simple and economical way to analyze and understand cell heterogeneities and developments. Owing to developments in high-resolution image sensors and high-performance computation processors, the emerging lensless digital holography technique enables a simple and cost-effective approach to obtain label-free cell images with a large field of view and microscopic spatial resolution. Methods The holograms of three types of cells, including MCF-10A, EC-109, and MDA-MB-231 cells, were recorded using a lensless digital holography system composed of a laser diode, a sample stage, an image sensor, and a laptop computer. The amplitude images were reconstructed using the angular spectrum method, and the sample to sensor distance was determined using the autofocusing criteria based on the sparsity of image edges and corner points. Four convolutional neural networks (CNNs) were used to classify the cell types based on the recovered holographic images. Results Classification of two cell types and three cell types achieved an accuracy of higher than 91% by all the networks used. The ResNet and the DenseNet models had similar classification accuracy of 95% or greater, outperforming the GoogLeNet and the CNN-5 models. Conclusions These experiments demonstrated that the CNNs were effective at classifying two or three types of tumor cells. The lensless holography combined with machine learning holds great promise in the application of stainless cell imaging and classification, such as in cancer diagnosis and cancer biology research, where distinguishing normal cells from cancer cells and recognizing different cancer cell types will be greatly beneficial.

Angular spectrum (AS) methods enable efficient calculation of wave propagation from one plane to another inside homogeneous media. For wave propagation in heterogeneous media such as biological tissues, AS methods cannot be applied directly. Split-stepping techniques decompose the heterogeneous domain into homogeneous and perturbation parts, and provide a solution for forward wave propagation by propagating the incident wave in both frequency-space and frequency-wavenumber domains. Recently, a split-step hybrid angular spectrum (HAS) method was proposed for plane wave propagation of focused ultrasound beams. In this study, we extend these methods to enable simulation of acoustic pressure field for an arbitrary source distribution, by decomposing the source and reflection spectra into orthogonal propagation direction components, propagating each component separately, and summing all components to get the total field. We show that our method can efficiently simulate the pressure field of arbitrary sources in heterogeneous media. The accuracy of the method was analyzed comparing the resultant pressure field with pseudospectral time domain (PSTD) solution for breast tomography and hemispherical transcranial-focused ultrasound simulation models. Eighty times acceleration was achieved for a 3-D breast simulation model compared to PSTD solution with 0.005 normalized root mean-squared difference (NRMSD) between two solutions. For the hemispherical phased array, aberrations due to skull were accurately calculated in a single simulation run as evidenced by the resultant-focused ultrasound beam simulations, which had 0.001 NRMSD with 40 times acceleration factor compared to the PSTD method.

The superposition of basic non-diffracting beams triggered new research hotspots lately, laying opportunities for long-distance wireless optical communication. The Lommel-Gaussian (LMG) beam formed by the superposition of Bessel-Gaussian light not only possesses non-diffraction feature, but also has tunable symmetry. With the help of Poynting vector analysis, we observed a smaller radial energy flow component during the propagation of the high order symmetrical LMG beam, which allows it to maintain the original beam profile over long distance. Thanks to the energy oscillation of the mainlobe and sidelobes, the mainlobe blocked by the symmetrical LMG beam can be restored. Also, the random phase screen with angular spectrum method is used to describe the beam behaviors in turbulence. The results show that the symmetry LMG is preferred in free space optical communication, and the asymmetric LMG performs poorly due to asymmetric energy transfer.

Passive cavitation mapping, which generates images using bubble acoustic emission signals, has been increasingly used for monitoring and guiding focused ultrasound surgery. Passive cavitation mapping can be used as an adjunct to magnetic resonance imaging to provide crucial information on the safety and efficacy of focused ultrasound surgery. The most widely used algorithm for passive cavitation mapping is delay-and-sum. One of the major limitations of delay-and-sum is its suboptimal computational efficiency. Although frequency-domain delay-and-sum can partially resolve this issue, such an algorithm is not suitable for imaging the evolution of bubble activity in real time and for cases in which cavitation events occur asynchronously. This study investigates a transient angular spectrum approach for passive cavitation mapping. The working principle of this approach is to back propagate the received signal to the domain of interest and reconstruct the spatial-temporal wave field encoded with the bubble location and collapse time. The transient angular spectrum approach is validated using an in silico model and water bath experiments. It is found that the transient angular spectrum approach yields similar results to delay-and-sum, but it is one order of magnitude faster. The results obtained by this study suggest that the transient angular spectrum approach is promising for fast and accurate passive cavitation mapping.

Brezlečna holografska mikroskopija je preprosta in kompaktna slikovna tehnika, ki jo sestavlja koherentni vir svetlobe in slikovno tipalo. Opazovani vzorec navadno postavimo čim bliže slikovnemu tipalu, na katerem nastane interferenčni vzorec, znan tudi pod izrazom hologram, ki je posledica interference med referenčnim nespremenjenim elektromagnetnim valom ter sipanim objektnim elektromagnetnim valom. Hologram vsebuje informacijo o amplitudi in fazi elektromagnetnega vala, ki jo je mogoče numerično rekonstruirati. Numerična rekonstrukcija nam v nasprotju s konvencionalno mikroskopijo omogoča naknadno ostrenje na poljubni fokusni razdalji, s čimer hologram nosi trirazsežno informacijo o opazovanih objektih. Za ostro rekonstrukcijo objekta je potrebno izbrati ustrezno fokusno razdaljo, ki je enaka fizični razdalji med objektom in slikovnim tipalom. Fokusno razdaljo lahko določimo ročno z vizualnim ocenjevanjem ali samodejno z uporabo metod samodejnega ostrenja. Algoritme samodejnega ostrenja vrednotimo na sintetičnih in eksperimentalno zajetih hologramih. Prvi so običajno modelirani z metodo kotnega spektra, ki je ista numerična metoda propagacije, kot se uporablja za rekonstrukcijo hologramov. To lahko prikrije nekatere napake, ki nastanejo kot posledica predpostavk numerične propagacije. Poleg tega metoda kotnega spektra ne more modelirati hologramov resnično trirazsežnih predmetov. V nasprotju s tem pa lahko na eksperimentalno zajete holograme vpliva šum in drugi artefakti, ki so posledica neusklajenosti med parametri eksperimentalne postavitve in parametri pripadajočega modela, kot so valovna dolžina svetlobe in velikost slikovnega elementa. Prav tako v tem primeru ne poznamo točne razdalje med objektom in slikovnim tipalom. V magistrskem delu smo predlagali objektivno vrednotenje algoritmov samodejnega ostrenja na hologramih, ki jih modeliramo z Miejevo teorijo in metodo T-matrik. Prednost obeh metod je modeliranje hologramov trirazsežnih sferičnih objektov. Implementirali smo različne algoritme samodejnega ostrenja in jih kvantitativno ovrednotili ter primerjali glede na natančnost določanja fokusne razdalje in časovno učinkovitost. Za potrebe izvajanja iterativnega algoritma za samodejno ostrenje v realnem času smo s pomočjo knjižnice PyOpenCL implementirali algoritme za izvajanje na grafičnih procesorskih enotah. Naša najboljša implementacija algoritma samodejnega ostrenja dosega srednjo absolutno napako 1,61 µm, pri čemer ena iteracija algoritma na hologramu velikosti 1024×1024 traja 330 µs. To omogoča obdelavo približno 20 hologramov na sekundo. Rezultati predstavljajo odlično izhodišče za uporabo v mikrofluidičnih aplikacijah, kjer je za sledenje ter določanje velikosti in lomnega količnika mikroskopskih delcev potrebno izvajanje v realnem času. Prav tako smo preučevali različne arhitekture modelov globokega učenja za napoved fokusne razdalje, premera in lomnega količnika mikroskopskih delcev. Z modeli globokega učenja, ki jih naučimo s sintetičnimi hologrami, modeliranimi na podlagi Miejeve teorije, smo za fokusno razdaljo dosegli najboljšo srednjo absolutno napako 1,60 µm. Srednja relativna napaka napovedi premera je bila pod 0,5 %, srednja relativna napaka napovedi fokusne razdalje in lomnega količnika pa celo pod 0,05 %. Obdelava enega holograma velikosti 150×150 je trajala približno 0,1 ms. Lensless holographic microscopy is a simple and compact imaging technique which comprises a coherent light source and an imaging sensor. A sample is usually placed as close as possible to the imaging sensor, on which an interference pattern between the reference and object electromagnetic wave is formed. The interference pattern is also commonly known as a hologram. The hologram encapsulates information about the amplitude and phase of the electromagnetic wave, which can be numerically reconstructed. In contrast to the conventional microscopy, the numerical reconstruction enables refocusing at desired focus planes effectively providing three-dimensional information about the scene. For a correct object reconstruction, a focus plane must be selected, which corresponds to the exact distance between the object and imaging sensor. The focus plane can be selected manually with visual inspection or automatically using an autofocusing method. Autofocusing algorithms are evaluated on synthetic and experimentally acquired holograms. Synthetic holograms are commonly modelled with the angular spectrum method, which is the same numerical propagation method as used for the reconstruction of holograms. Unfortunately, this may conceal some errors, that stem from the presumptions of the propagation method. In addition, angular spectrum method cannot model holograms of truly three-dimensional objects. In contrast, experimentally acquired holograms can be affected by noise and artefacts resulting from mismatch between parameters of the experimental setup and parameters of the propagation model, such as source wavelength and pixel size. Furthermore, the exact distance between the object and the imaging sensor is not known. In this work, we objective evaluate autofocusing algorithms on holograms modelled by Mie theory and T-matrix method. Both methods can model holograms of truly three-dimensional spherical objects. We implemented different autofocusing algorithms, which were objectively evaluated and compared according to the accuracy of the estimated focal plane and computational cost. Subsequently, we presented a proof-of-concept real-time implementation of the iterative autofocusing algorithm based on the PyOpenCL framework for execution on graphics processing units. Our best implementation resulted in an average absolute error of 1.61 µm, while the computational time for 1024×1024 holograms was 330 µs per iteration. This allows processing of approximately 20 holograms per second. The results provide promising starting point for use in real-time microfluidic applications for tracking and analysis of size and refractive index of microscopic particles. Furthermore, we studied different deep learning architectures for predicting the focus distance, diameter and refractive index of microscopic particles. Models trained on synthetic holograms modelled with Mie theory allowed estimation of the focus distance with a mean absolute error of 1.60 µm. The mean relative errors for the estimation of diameter and refractive index were less than 0.5% and 0.05%, respectively. The estimation time for a hologram of size 150×150 was approximately 0.1 ms.

The effect of the width of the angular spectrum (numerical aperture) of a broadband-frequency wave-field probing a layered object on the signal of an autocorrelation low-coherence interferometer (ALCI) under spatially coherent and incoherent illumination of the entrance pupil is considered. It is found that under incoherent illumination an increase in the width of the angular spectrum of the field leads to a decrease in the amplitude, a change in the shape and position of the measuring signals of the interferometer due to decorrelation of the object field partial components which have reflected from various interlayer boundaries inside the object. In the case of coherent illumination, the ALCI signal is formed in a confocal mode, which leads to the amplitude extraction of the measurement signals are determined by the mutual correlations between a partial component reflected from the boundary on which the probing field was focused, and partial components of this field which have reflected from other boundaries within the object. This effect makes it possible to determine parameters of the internal layered structure of an object doing without apriori structure-related information. In this case, an increase in the numerical aperture of the probing light beam leads to an increase in the systematic error in determining the optical thicknesses of the layers, which can be estimated on the basis of the obtained expressions.

Acoustic hologram enable the capability in the acoustic pattern control and drive many applications of ultrasound. However, hologram has not been applied to ultrasound imaging because the medical application of acoustic holograms is limited owing to the sound reflection and scattering at the acoustic holographic surface and its internal attenuation. In this study, we propose an acoustic holographic computing method and present a disc-shaped hologram with a central hole comparing with a conventional hologram using the iterative angular spectrum approach. The results show that the transducer with hole hologram achieves the required focusing effect with the full width at half maximum about $1.5\lambda $ , high sensitivity increased by 92.7%, and a low two-way insertion loss with −15.8 dB compared to conventional hologram. Pulse-echo and ultrasonic imaging are achieved by a transducer with two holograms which shows new applications of acoustic hologram in ultrasound.

This paper presents an empirical study of the uplink and downlink azimuth angle of arrival (AoA) in an urban micro (UMi) scenario at 28 GHz. At present, most UMi measurements are conducted in the downlink and then the uplink situation is inferred assuming channel reciprocity. Although the channel correlation coefficient of the uplink and downlink can be as high as 0.8, this does not mean that they are the same. Only a real uplink measurement can accurately describe its channel conditions, and this is what this study does. A receiver equipped with a rotatable horn antenna is mounted at the base station and the user terminal, respectively, in simulating the uplink and downlink. To improve the angular resolution, we extract the multipath components (MPCs) using the space-alternating generalized expectation-maximization algorithm. Also, a spatial lobe approach is used to cluster the MPCs in the power angular spectrum. By matching MPCs with objects in the environment, we find that direct propagation and first-order reflections are dominant in line-of-sight and non-line-of-sight cases. By comparing our measurement with those in standard channel models, we verify that the AoA of clusters follows a Gaussian distribution in the uplink and downlink. In addition, a two-dimensional Gaussian distribution for ray AoA and power is established to reflect their correlation.

This paper presents a simulation study of the outdoor and indoor propagation losses utilizing 5G small cells at suggested millimeter-wave frequencies of 26 GHz, 28 GHz, and 38 GHz. The environment of this study is conducted with penetration loss of new and old building characteristics. The simulation is performed with help of 3D ray tracing model NVIDIA OptiX engine and MATLAB. The targeted frequencies are 26 GHz, 28 GHz, and 38 GHz that specified by International Telecommunication Union ITU-R organization. The simulation routes are investigated in term of signal strength at multiple receiving points. The strength angular spectrum are represented for fixed points and the power receiving delay is presented by their attributes. The simulated responses showed an efficient and sufficient outdoor and indoor service might be provisioned at 26 GHz and 28 GHz. The received signals at 28 GHz and 38 GHz are found around 4.5 dB and 11 dB with comparison with signal received level at 26 GHz. However, at 38 GHz the indoor signal strength and power receiving delays demonstrate a weak signal reception which offers a poor solution to indoor user by outside fixed base station.

In this paper, congruent and near-stoichiometric LiNbO3:Fe (CLN:Fe and SLN:Fe) crystals are prepared through Czochralski and Vapour-transport-equilibration techniques, and the temporal evolution of the photoinduced light scattering (PILS) in both crystals are studied at different temperatures by using an in-situ dynamic angular spectrum technique. It is found from a series of in-situ dynamic angular spectra that, the PILS angular distribution becomes narrow with the time elapsed in both crystals but the narrowing extent and its temperature dependence are quite different in the congruent and near-stoichiometric LiNbO3:Fe crystals. The narrowing of the PILS angular distribution is suggested to be connected with the competition between the noise gratings with the different wave vectors, and the distinct PILS characteristics in the two crystals are explained by the crystal conductivity varying with both the temperate and Li composition of the crystal. In particular, at the high temperatures above 170 °C two columns of PILS distributing in the angular regions of − 7° ~ − 17° and − 17° ~ − 25° are found in the congruent LiNbO3:Fe crystal but none in the near-stoichiometric LiNbO3:Fe crystal. The prolonged temporal evolution of these two columns of PILS are attributed to the competition between the two groups of noise gratings formed by the high-concentration protons with low mobility in the congruent LiNbO3:Fe crystal.

In this paper we show the equivalence of near-field beamforming and backward-wave reconstruction algorithm. The proof is carried out analytically with two different approaches, using the principle of stationary phase from a signal processing point of view and the angular spectrum representation as an electromagnetic point of view. A comparison of the time complexity of the near-field beamforming and backward-wave reconstruction algorithm is given. A detailed discussion of the constraints required for a digital implementation is presented, leading to limitations for the chosen system parameters, especially for the backward-wave reconstruction approach. An exemplarily scenario is simulated and processed, confirming the found equivalence between the two very different approaches of image reconstruction. An additional measurement with a 120 GHz radar showcases the capabilities of both algorithms and validates our findings.

In order to improve the disadvantages that the detection range is close and the probe beam is difficult to be used effectively in the traditional ptychography system, the terahertz ptychography experimental system based on focused Gaussian beam was proposed. Based on the principle of ptychography and using the angular spectrum transmission theory, a focused Gaussian beam was used to replace the diffracted beam generated by the traditional aperture. The feasibility of this replacement was verified through computer simulation experiments, and the corresponding imaging experiments were completed. The numerical simulation results show that it is feasible to carry out the terahertz ptychography using a focused Gaussian beam in the 0.1 THz band, and the simulation and experimental results verify the feasibility of the system. Under the condition of detection distance of 50 mm, the theoretical depth resolution reaches to λ/4, and the experimental system depth resolution is λ/2, which fully demonstrates the effectiveness of this ptychography system.

Purpose The aim was to quantitatively validate the hybrid angular spectrum (HAS) algorithm, a rapid wave propagation technique for heterogeneous media, with both pressure and temperature measurements. Methods Heterogeneous tissue-mimicking phantoms were used to evaluate the accuracy of the HAS acoustic modeling algorithm in predicting pressure and thermal patterns. Acoustic properties of the phantom components were measured by a through-transmission technique while thermal properties were measured with a commercial probe. Numerical models of each heterogeneous phantom were segmented from 3D MR images. Cylindrical phantoms 30-mm thick were placed in the pre-focal field of a focused ultrasound beam and 2D pressure measurements obtained with a scanning hydrophone. Peak pressure, full width at half maximum, and normalized root mean squared difference (RMSDn) between the measured and simulated patterns were compared. MR-guided sonications were performed on 150-mm phantoms to obtain MR temperature measurements. Using HAS-predicted power density patterns, temperature simulations were performed. Experimental and simulated temperature patterns were directly compared using peak and mean temperature plots, RMSDn metrics, and accuracy of heating localization. Results The average difference between simulated and hydrophone-measured peak pressures was 9.0% with an RMSDn of 11.4%. Comparison of the experimental MRI-derived and simulated temperature patterns showed RMSDn values of 10.2% and 11.1% and distance differences between the centers of thermal mass of 2.0 and 2.2 mm. Conclusions These results show that the computationally rapid hybrid angular spectrum method can predict pressure and temperature patterns in heterogeneous models, including uncertainties in property values and other parameters, to within approximately 10%.

To undertake THz spectroscopy and imaging, and accurately design and predict the performance of quasi-optical components, knowledge of the parameters of the beam (ideally Gaussian) emitted from a THz source is paramount. Despite its proliferation, relatively little work has been done on this in the frame of broadband THz photoconductive antennas. Using primarily pinhole scanning methods, along with stepwise angular spectrum simulations, we investigate the profile and polarization characteristics of the beam emitted by a commercial silicon-lens-integrated THz photoconductive antenna and collimated by a TPX (polymethylpentene) lens. Our study flags the limitations of the different beam profiling methods and their impact on the beam Gaussianity estimation. A non-Gaussian asymmetric beam is observed, with main lobe beam waists along x and y varying from 8.4 $\,\pm\,$ 0.7 mm and 7.7 $\,\pm\,$ 0.7 mm at 0.25 THz, to 1.4 $\,\pm\,$ 0.7 mm and 1.4 $\,\pm\,$ 0.7 mm at 1 THz, respectively. Additionally, we report a maximum cross-polar component relative to the on -axis co-polar component of $-$ 11.6 dB and $-$ 21.2 dB, at 0.25 THz and 1 THz, respectively.

The emergence of beyond-licensed spectrum sharing in FR1 (0.45–6 GHz) and FR2 (24–52 GHz) along with the multi-antenna narrow-beam-based directional transmissions demand a wideband spectrum sensing in temporal and spatial domains. We referred to it as ultrawideband angular spectrum sensing (UWAS), and it consists of digitization followed by the characterization of the wideband spectrum. In this article, we design and develop a state-of-the-art UWAS prototype using universal software radio peripheral (USRPs) and LabVIEW NXG for validation in the real-radio environment. Since 5G is expected to co-exist with LTE, the transmitter generates the multidirectional multiuser wideband traffic via LTE specific single-carrier frequency division multiple access (SC-FDMA) approach. At the receiver, the first step of wideband spectrum digitization is accomplished using a novel approach of integrating sparse antenna-array with reconfigurable sub-Nyquist sampling (SNS). The reconfigurable SNS allows the digitization of noncontiguous spectrum via low-rate analog-to-digital converters, but it needs intelligence to choose the frequency bands for digitization. We explore a multiplay multi-armed bandit-based learning algorithm to embed intelligence. Compared with previous works, the proposed characterization (frequency band status and direction-of-arrival estimation) approach does not need prior knowledge of received signal distribution. The detailed experimental results for various spectrum statistics, power gains, and antenna array arrangements validate the functional correctness, superiority, and feasibility of the proposed UWAS over state-of-the-art approaches.

There exist a multitude of methods and processing steps for the numerical reconstruction of digital holograms. Because these are not standardized, most research groups follow their own best practices, making it challenging to compare numerical results across groups. Meanwhile, JPEG Pleno holography seeks to define a new standard for the compression of digital holograms. Numerical reconstructions are an essential tool in this research because they provide access to the holographically encoded 3D scenes. In this paper, we outline the available modules of the numerical reconstruction software developed for the purpose of this standardization. A software package was defined that is able to reconstruct all holograms of the JPEG Pleno digital hologram database, evaluating several core experiments. This includes Fresnel holograms recorded or generated in Fresnel or (lensless) Fourier geometries as well as near-field holograms, that require rigorous propagation through the angular spectrum method. Specific design choices are explained and highlighted. We believe that providing information on the current consensus on the numerical reconstruction software package will allow other research groups to replicate the results of JPEG Pleno and improve comparability of results.

Modern unmanned aerial vehicles (UAVs) perform a wide range of tasks in the military sphere. The expansion of the range of such tasks causes constant technical improvement of both the drones themselves and the means of countering UAVs. The direction of tactics and technics for using drones as part of a group is rapidly developing.The existing countermeasures have limited capabilities to detect UAV groups and resolve them in the group. Thus, there is an acute problem of group detection and resolving of UAV groups.At the stages of analysis and assessment of this problem, the requirements for the detection and resolving of UAV groups must be technically justified.The purpose of this article is to develop a method to improving the quality of detection and separation of UAVs as sources of radio emission (SRE), by improving the known method of technical justification of requirements based on the use of adaptive direction finders with superresolution.As result of the study, it was found that the steepness of the change of the weight vector signal in the area of directions on SRE is much greater than the steepness of the angular spectrum peaks at the output of the adaptive antenna array. This property was investigated and used to increase the angular resolution of the UAV’s SREs in adaptive direction finder. The estimation of the boundary angular resolution is obtained by using the weight vector signal as an angular power spectrum depending on the parameters of the input signal.

Shaping the intensity distribution of radiated electromagnetic (EM) fields in a given bounded target area is a challenging problem in EMs. Although some approaches have been explored for this purpose, most are limited to the synthesis of plane-wave fields or point-focused fields. In this communication, a field-shaping method based on angular spectrum projection and the linear superposition principle is presented. The proposed method allows radiated electric fields to be shaped with different desired intensity patterns in a given limited target area with the use of the same antenna array. Via this method, all element excitations of the antenna array can be analytically calculated, and not only is the element excitation computational time reduced, but the real-time control of shaped fields is also made possible. Full-wave simulations were carried out to illustrate the 1-D and 2-D electric field shaping within a small given target area. In the 1-D case, three types of shaped fields with different desired distributions are demonstrated. In the 2-D case, three kinds of origin-symmetric shaped fields with different intensity distributions are illustrated. Finally, shaped fields with more complicated 2-D intensity distributions, like “I”- and “X”-shaped patterns, are demonstrated, and are achieved directly by applying the linear superposition principle to multiple point-focused fields with spatially overlapping focal spots.

The angular spectrum approach (ASA)---a fast, frequency domain method for calculation of the acoustic field---enables passive source localization and modeling forward propagation in homogeneous media with high computational efficiency. Here we show that, if the medium is continuously stratified, a first-order analytical solution may be obtained for the field at arbitrary depth. Our simulations show that the stratified ASA solution enables accurate source localization as compared to the uncorrected ASA (error from 1.2$\pm$0.3 to 0.49$\pm$0.3 wavelengths) at scalings relevant to biomedical ($kL \sim$ 500, where $L$ is the length of the measurement aperture), underwater ($kL \sim$ 800), and atmospheric ($kL \sim$ 10) acoustic applications. Overall the total computation was on the order milliseconds on standard hardware (225$\pm$84 ms, compared with $78\pm63$ ms for the homogeneous ASA formulation over all cases). Collectively, the results suggest the proposed ASA phase correction enables efficient and accurate method for source localization in continuously stratified environments., Comment: arXiv admin note: text overlap with arXiv:1906.08156

Within the coupled wave method complemented by the quasi-optical approach, the feasibility of diffraction-mode selection over the transverse index in lasers with planar Bragg resonators is studied. Acceptable Fresnel parameters at which the diffraction losses from the Bragg-structure edges provide steady-state single-mode lasing with a narrow angular spectrum are determined. It is shown that the such stable lasing at high Fresnel parameters is achieved by shifting the operating transition frequency to the frequency of the longitudinal mode of a Bragg resonator with the highest Q-factor.

Flat nanophotonic devices hold a great potential to process diffractive optical information within ultra-thin submicron thickness. In particular, optical filtering of transmissive angular spectrum in the free space is an essential functionality in diffractive optics. Here, we propose a novel configuration and theoretical study of an ultrathin transmissive angular filtering metamaterial for the first time to the best of our knowledge. Based on the adiabatically tapered plasmonic waveguide metamaterial in the visible regime, full color angle-selective transmission is achieved near the optic axis including the representative blue (473 nm), green (532 nm), and red (633 nm) colors. By providing further analysis on bandwidth extension, we envision that the proposed flat angular filtering mechanism in the visible range promises practical value and potential for a variety of metamaterial-assisted compact diffractive imaging and sensing applications such as augmented or virtual reality displays and biomedical optical sensors.

In order to increase the capacity of encrypted information and reduce the loss of information transmission, a three-dimensional &#x0028 3D &#x0029 scene encryption algorithm based on the phase iteration of the angular spectrum domain is proposed in this paper. The algorithm, which adopts the layer-oriented method, generates the computer generated hologram by encoding the three-dimensional scene. Then the computer generated hologram is encoded into three pure phase functions by adopting the phase iterative algorithm based on angular spectrum domain, and the encryption process is completed. The three-dimensional scene encryption can improve the capacity of the information, and the three-phase iterative algorithm can guarantee the security of the encryption information. The numerical simulation results show that the algorithm proposed in this paper realized the encryption and decryption of three-dimensional scenes. At the same time, it can ensure the safety of the encrypted information and increase the capacity of the encrypted information.

Due to the wave nature of light, resolution of optical imaging systems is limited to approximately half of the wavelength. The reason behind this limitation, known as diffraction limit, is the loss of information contained in evanescent waves at the far-field region. Here, we propose a new method to retrieve the information contained in evanescent waves in far field region resulting in a novel sub-wavelength imaging technique which can go beyond the diffraction limit. We theoretically prove that using interference of waves, between the target field and reference and reconstruction waves, one can apply a shift to the angular spectrum of the target field and convert a range of evanescent waves into propagating modes. Moreover, we demonstrate how these converted waves can be distinguished in far-field from other existing modes. Unlike previously developed sub-wavelength imaging techniques, the proposed method does not require either fluorescent materials or complex nano-structures to realize evanescent-to-propagating wave conversion. The performance of the method is numerically investigated illustrating a resolution of one-seventh of the working wavelength, which is much beyond the diffraction limit. The proposed technique can significantly simplify sub-wavelength imaging paving the road to develop practical low cost super-resolution imaging systems.

An updated fast solution in modeling quasi-optical beam waveguides is reported, where several mirror reflectors are utilized for the beam transformation. The fast Fourier transform Poynting vector ray tracing between virtual apertures (FFT-PVVAs) algorithm has been introduced and applied in modeling the reflected beam, based on the FFT-accelerated beam propagator between parallel apertures, and the Poynting vector ray tracing for the mirror reflection. However, for designing and optimizing a beam path with multireflectors, it is desired that the accumulated precision loss due to the Poynting vector ray tracing can be further reduced. As a modification, angular spectrum transform-based beam propagator between oblique apertures is introduced, so as to reduce the ray tracing path length. The improved method is named as FFT-PVVA-tilted propagation (FFT-PVVA-TP). As validation, beam propagation in a four-mirror beam waveguide is simulated by FFT-PVVA, FFT-PVVA-TP, and physical optics integration. Numerical results suggest that FFT-PVVA-TP provides clearly better accuracy after four times of beam reflection.

In this paper, a comprehensive study of millimeter-wave (mmW) imaging for far-field and near-field objects using 1-bit programmable metasurface (PMS) is presented. Theoretical PMS imaging simulation models are proposed by using plane-wave angular spectrum approach, in which two simulation models based on the flexible mmW beam-forming of PMS are developed. The first imaging model steers the high-gain beams electronically to scan over the region of interest, which is suitable for far-field object detection and surveillance. In the second model, randomly complex beams are generated that can sample the target objects in time domain, which is suitable for Fresnel region imaging. Physical optics theory is employed in the two imaging models for calculating reflected waves. Then, a 1-bit $20\times20$ PMS imager operating at 35 GHz is designed. The PMS imager is composed of a PIN-diode-loaded metasurface and a control board with 400 output channels. Finally, we measure 64 groups of randomly distributed fields using the planar near-field scanning technique in the anechoic chamber. Through imaging reconstruction, it is verified that the proposed PMS is a promising technique for mmW imaging with excellent performance.