Equal Amplitude Research Articles

Ka-Band Huygens Antenna Array With Very High Aperture Efficiency and Low Sidelobes

A Ka-band Huygens antenna array with extremely high aperture efficiency (AE) and low sidelobe levels is reported for 5G millimeter-wave (mm-wave) wireless applications. The basic array element is an innovative Huygens subarray consisting of two open rectangular waveguides that form an aperture consisting of a 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 set of orthogonal, tightly coupled electric and magnetic elements separated by a virtual gap that are balanced, in- phase, and radiate Huygens cardioid patterns. A larger 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times16$ </tex-math></inline-formula> element array is then realized with 64 of these 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 subarrays. With excitations of equal amplitude, the full broadside-radiating array achieves an AE up to 97.5% in the operating bandwidth, which is very close to the 100% limit associated with an ideal uniform aperture distribution. Moreover, a highly efficient and compact feed network with tapered-amplitude and in- phase excitations from the array center to its edges is designed to achieve sidelobe and backlobe levels less than −20 dB. The −10 dB impedance bandwidth covers 26.7–29.65 GHz, and the peak realized AE (RAE) reaches 82%. A full-aluminum array prototype was fabricated with standard machining processes and tested. The measured performance characteristics agree well with their simulated values, confirming the efficacy of their designs.

A Compact Broadband Circularly Polarized Wide-Slot Antenna With Axial Ratio Bandwidth Encompassing LTE 42 and LTE 43 Standards of 5G Mid-Band

This study presents a compact broadband wide-slot antenna with broadband left-hand circular polarization compatible with both LTE 42 and LTE 43 standards of 5G mid-band applications. The proposed antenna is fabricated on an FR4 dielectric substrate with overall dimensions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.41\lambda _{o}\times 0.36\lambda _{o}\times 0.02\lambda _{o}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{o}$ </tex-math></inline-formula> is the free space wavelength at the resonant frequency of the antenna. The antenna ground plane is etched to form a square radiating slot with a pair of rectangular ground stubs that are diagonally placed inside the slot. On the other side of the antenna, the feed line is loaded by horizontal and vertical stubs to improve the coupling between the feed line and the square slot. To generate a circular polarization, the feeding stubs cooperate with the pair of rectangular ground stubs to excite the radiating slot of the antenna at two different feeding points whose currents have approximately equal amplitude and 90° phase shift. The measured impedance bandwidth (BW) of the proposed wide-slot antenna is 16.2% (580 MHz along the band 3.3-3.88 GHz), while the observed axial ratio bandwidth (ARBW) is 12.2% (440 MHz in the 3.4-3.84 GHz band). The measured gain values are found to be larger than 2.5 dB along both standards of the 5G mid-band applications.

Влияние шумов с различными спектрами на течения вязкой несжимаемой жидкости

The results of an experimental study of the effects of noises on flows in a rotating spherical layer are presented. Noise is introduced into the flow in the form of random fluctuations of the inner sphere rotational rate relative to a time constant mean value. The flow velocity was measured with a laser Doppler anemometer. It was found that the noises of the equal amplitude, but with different spectra cause the generation of mean flows of different intensity. It is shown that the increase in the average velocities under the action of the noise is larger for the stable flows compared to unstable ones.

Attentional capture is modulated by stimulus saliency in visual search as evidenced by event-related potentials and alpha oscillations

This study used a typical four-item search display to investigate top-down control over attentional capture in an additional singleton paradigm. By manipulating target and distractor color and shape, stimulus saliency relative to the remaining items was systematically varied. One group of participants discriminated the side of a dot within a salient orange target (ST group) presented with green circles (fillers) and a green diamond distractor. A second group discriminated the side of the dot within a green diamond target presented with green circle fillers and a salient orange square distractor (SD group). Results showed faster reaction times and a shorter latency of the N2pc component in the event-related potential (ERP) to the more salient targets in the ST group. Both salient and less salient distractors elicited Pd components of equal amplitude. Behaviorally, no task interference was observed with the less salient distractor, indicating the prevention of attentional capture. However, reaction times were slower in the presence of the salient distractor, which conflicts with the hypothesis that the Pd reflects proactive distractor suppression. Contrary to recent proposals that elicitation of the Pd requires competitive interactions with a target, we found a greater Pd amplitude when the distractor was presented alone. Alpha-band amplitudes decreased during target processing (event-related desynchronization), but no significant amplitude enhancement was observed at electrodes contralateral to distractors regardless of their saliency. The results demonstrate independent neural mechanisms for target and distractor processing and support the view that top-down guidance of attention can be offset (counteracted) by relative stimulus saliency.

Luminance white noise electroretinograms (wnERGs) in mice.

To record and analyse electroretinograms (ERGs) to luminance stimuli with white noise temporal profiles in mice. White noise stimuli are expected to keep the retina in a physiologically more natural state than, e.g., flashes. The influence of mean luminance (ML) was studied. Electroretinograms to luminance temporal white noise (TWN) modulation (wnERGs) were measured. The white noise stimuli contained all frequencies up to 20 Hz with equal amplitudes and random phases. Responses were recorded at 7 MLs between -0.7 and 1.2 log cd/m2. Impulse response functions (IRFs) were calculated by cross correlating the averaged white noise electroretinogram (wnERG) responses with the stimulus. Amplitudes and latencies of the initial trough and subsequent peak in the IRFs were measured at each ML. Fourier transforms of the IRFs resulted in modulation transfer functions (MTFs). wnERGs were averaged across different animals. They were measured twice and the responses at identical instances in the 1st and 2nd recordings were plotted against each other. The correlation coefficient (r 2 repr) of the linear regression quantified the reproducibility. The results of the first and second measurement were further averaged. To study the underlying ERG mechanisms, the ERG potentials at the different MLs were plotted against those at the lowest and highest ML. The correlation coefficients (r 2 ML) were used to quantify their similarities. The amplitudes of the initial (a-wave-like) trough of the IRFs increased with increasing ML. The following positive (b-wave-like) peak showed a minimum at -0.4 log cd/m2 above which there was a positive correlation between amplitude and ML. Their latencies decreased monotonously with increasing ML. In none of the IRFs, oscillatory potential (OP)-like components were observed. r 2 repr values were minimal at a ML of -0.1 log cd/m2, where the MTFs changed from low-pass to band-pass. r 2 ML values increased and decreased with increasing ML when correlated with responses obtained at the highest or the lowest ML, respectively. White noise electroretinograms can be reliably recorded in mice with luminance stimuli. IRFs resemble flash ERGs superficially, but they offer a novel procedure to study retinal physiology. New components can be described in the IRFs. The wnERGs are either rod- or cone-driven with little overlap.

Sidelobe Suppression for Leaky-Wave Antennas Using a Complementary Paired Configuration

In this letter, an effective method is proposed to suppress the overall sidelobes for period-modulated leaky-wave antennas (PM-LWAs). The radiation mechanism of the high sidelobes in PM-LWAs is thoroughly investigated by space harmonic (SH) analysis of the aperture field. It is found that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n = 0$</tex-math></inline-formula> SH in PM-LWAs occupies a larger proportion of power than that in periodic LWAs (P-LWAs), resulting in a higher sidelobe level (SLL) in PM-LWAs than that in P-LWAs. An SLL suppression method for PM-LWAs is proposed based on even SH cancellation, which is realized by aligning inversed period modulations in a pair of PM-LWAs. Exciting the PM-LWA pair with equal amplitudes and reversed phases, all radiations from the even SHs are cancelled out and hence the overall sidelobes including the first sidelobe and grating lobe are efficiently suppressed. Prototypes are designed, simulated, fabricated, and experimentally measured. Measured results agree well with simulations, which verify the theoretical predictions. The overall sidelobes are suppressed by more than 10 dB in almost the entire forward region. The radiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n = - 2$</tex-math></inline-formula> SH (grating lobe) and the first sidelobe is reduced by more than 20 and 3.4 dB, respectively.

Co-Design of Dielectric Resonator Antenna and T-Shaped Microstrip Feeding Network for Back-Radiation Suppression

In practice, the broadband feeding network on the back side of an antenna can have a nonnegligible effect on the antenna's back radiation due to the feeding network's radiation contribution. Thus, a back-radiation cancellation scheme is proposed by co-designing the antenna and its feeding network to solve this problem. The antenna and its feeding network can be viewed as a two-element array. Their radiation toward the antenna's backward direction can cancel each other when both have equal amplitude and opposite phases along the back direction. A differential fed dielectric resonator antenna (DRA) through a rat-race coupler ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${180}^\circ $</tex-math></inline-formula> hybrid coupler) and a T-shaped broadband differential feeding network are compared and analyzed to verify the proposed scheme. In addition, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1\!\times\!4$</tex-math></inline-formula> DRA array with a T-shaped broadband differential feeding network in a previous work (where the feeding network's radiation effect on the back side was overlooked) is used for experimental validation of the proposed scheme. Simulations and measurements demonstrate significant back-radiation suppression than the ideal differential feeding network.

Floquet scattering through a parity–time symmetric oscillating potential

We investigate the scattering of a particle from a trapping potential that is subjected to weak, parity–time symmetric periodic drivings. Using the Floquet theory, we derive the scattering matrix and calculate the transmittance of the incident particle. When the driving is purely coherent, our calculation recovers the known result and the transmission spectrum shows the familiar, bound-state-induced Fano resonances. When the driving is purely incoherent, we find the Fano resonances still occur, but the lineshape of each resonance is reversed compared to the coherent-driving counterpart. Intriguingly, the transmission resonances disappear when both the coherent and incoherent driving fields are present with equal amplitudes. This phenomena can be seen as a manifestation of the non-reciprocal coupling of Floquet channels in the frequency domain. Notably, when the frequency up-conversion is absent, the transmission is such as if there is no driving at all, even when the driving strength increases.

Reservoir Computing with Charge-Trap Memory Based on a MoS2 Channel for Neuromorphic Engineering.

Novel memory devices are essential for developing low power, fast, and accurate in-memory computing and neuromorphic engineering concepts that can compete with the conventional complementary metal-oxide-semiconductor (CMOS) digital processors. 2D semiconductors provide a novel platform for advanced semiconductors with atomic thickness, low-current operation, and capability of 3D integration. This work presents a charge-trap memory (CTM) device with a MoS2 channel where memory operation arises, thanks to electron trapping/detrapping at interface states. Transistor operation, memory characteristics, and synaptic potentiation/depression for neuromorphic applications are demonstrated. The CTM device shows outstanding linearity of the potentiation by applied drain pulses of equal amplitude. Finally, pattern recognition is demonstrated by reservoir computing where the input pattern is applied as a stimulation of the MoS2 -based CTMs, while the output current after stimulation is processed by a feedforward readout network. The good accuracy, the low current operation, and the robustness to input random bit flip makes the CTM device a promising technology for future high-density neuromorphic computing concepts.

Coded information storage pulsed laser based on vector period-doubled pulsating solitons

Pulsating soliton is a unique local structure in nonlinear dissipative system. Different from the pulse train with equal amplitude generated by conventional average soliton, the amplitude of pulsating soliton shows a remarkable periodic fluctuation behavior. With the help of the interaction between vector solitons, vector solitons with rich multi-period pulsation phenomena are successfully obtained in the experiment and numerical simulation. Then, based on the phenomenon of multi-period pulsation of vector solitons under polarization modulation, a simple and stable information storage fiber laser is designed. By changing the rotation angle of the polarization controller to adjust the polarization state in the cavity, the regulation of vector period-doubled pulsating soliton is flexibly realized. In addition, an automatic identification program is designed to process the pulse data with binary coding, so as to realize the information storage function based on vector period-doubled pulsating soliton. This result promotes the application prospect of vector solitons in optical communication, information storage and other fields.

Maximum downward slope of sleep slow waves as a potential marker of attention-deficit/hyperactivity disorder clinical phenotypes

BackgroundAttention-Deficit/Hyperactivity Disorder (ADHD) is a highly heterogeneous diagnostic category, encompassing several endophenotypes and comorbidities, including sleep problems. However, no predictor of clinical long-term trajectories or comorbidity has yet been established. Sleep EEG has been proposed as a potential tool for evaluating the synaptic strength during development, as well as the cortical thickness, which is presumed to be altered in ADHD. We investigated whether the slope of the Slow Waves (SWs), a microstructural parameter of the sleep EEG, was a potential predictive parameter for psychiatric comorbidities and neuropsychological dimensions in ADHD. Methods70 children (58 m; 8.76 ± 2.77 y) with ADHD who underwent psychiatric and neurologic evaluations and a standard EEG recording during naps were investigated. After sleep EEG analysis, we grouped the extracted SWs in bins of equal amplitude and then measured the associations, through generalized linear regression, between their maximum downward slopes (MDS) and the individual scores obtained from clinical rating scales. ResultsThe presence of Multiple Anxiety Disorders was positively associated with MDS of medium amplitude SWs in temporo-posterior left areas. The Child Behavior Checklist scores showed negative associations in the same areas for small SWs. The presence of autistic traits was positively associated with MDS of high amplitude SWs in bilateral anterior and temporal left areas. The WISC-IV Processing Speed Index showed negative associations with MDS of small-to-medium SWs in anterior and temporal right areas, while positive associations in posterior and temporal left areas. ConclusionsConsistency of association clusters' localization on the scalp suggests that variations in the local MDS, revealing alterations of local synaptic strength and/or in daytime use of certain cortical circuits, could underlie specific neurodevelopmental trajectories resulting in different ADHD clinical phenotypes.

A circularly polarized pyramidal horn antenna based on substrate integrated waveguide

A circularly polarized pyramidal horn antenna based on substrate integrated waveguide (SIW) technology is proposed and developed for Ku-band applications. The proposed horn antenna is excited by the upper and lower SICL differential feed networks placed vertically to each other, so that two orthogonal waveguide modes with the equal amplitude are generated at the horn aperture. A 90° coupling network based on SICL technology is proposed to achieve a 90° phase difference between the two orthogonal waveguide modes, thus realizing the function of left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) of the horn antenna. In addition, in order to make the phase distribution of the horn aperture more uniform, a cross metal strip structure at the horn aperture is proposed, thereby improving the radiation efficiency. The proposed horn antenna is manufactured by using low-cost printed circuit boards (PCBs) process. The measured results show that the proposed circularly polarized pyramidal horn operates at center frequency 12.5 GHz, the measured gain is 8.4 dBi, the relative standing wave and axial ratio (AR) bandwidth are approximately 24% and 5%, respectively. And the radiation aperture efficiency is as high as 78.5%. The developed circularly polarized pyramidal horn antenna can be applied in the field of satellite communications.

Millimeter-Wave ±45° Dual Linearly Polarized End-Fire Phased Array Antenna for 5G/B5G Mobile Terminals

In this article, a millimeter-wave (mmWave) endfire phased array antenna with ±45° linear polarizations is proposed for fifth generation (5G)/B5G mobile communications. The proposed antenna achieves ±45° polarizations by utilizing a modified substrate integrated waveguide (SIW) slot polarizer. The polarizer generates dual orthogonal modes with equal amplitudes and a 0°/180° phase difference, thereby yielding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+ 45^{\circ }/- 45^{\circ }$ </tex-math></inline-formula> -polarization radiated waves in the far field. In a practical metal-framed mobile phone environment, the ±45 polarizations are verified to provide more balanced radiation patterns and, consequently, a higher polarization-multiple input multiple output (MIMO) efficiency. A prototype of the proposed 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 array is fabricated and measured, achieving a −10 dB impedance bandwidth of 23.4–30.0 GHz (covers 5G band of n257/n258), with an isolation better than 15.6 dB and a realized gain above 8.9 dBi in the operating bandwidth. A peak gain of 11.4 dBi and a 3 dB scanning range of 87° can be observed at 27.0 GHz. Furthermore, the prototype is characterized on a metal-framed mobile phone platform, experimentally demonstrating its superiority to conventional vertical/horizontal polarized (V-/H-pol) arrays. The validated advantages of the balanced radiation patterns and robust impedance matching make the proposed ±45°-polarization endfire antenna array a promising candidate for mobile terminals in the era of 5G/B5G.

Compact Wide-Beam Circularly Polarized End-Fire Antenna Combining Ground Radiation Mode and Vertically Polarized Mode

A compact wide-beam endfire antenna with ground radiation mode and vertically polarized mode for circular polarization (CP) is presented in this article. The antenna is constructed based on a configuration of coupled-mode patch antenna (CMPA), which consists of two coupling cavities with a shorting wall, and can generate vertically polarized modes. The CP is realized through a pair of orthogonally polarized modes of horizontal and vertical polarizations. Meanwhile, rendering them acquires an equal amplitude and a 90° phase difference. The horizontally polarized radiation mode is realized through inserting a crossed ground slot. Offset probe feed is used to excite all the radiation modes and introduce an additional phase shift for the CP. A set of offset ground slots (OGSs) are then applied to perturb the electromagnetic coupling of the modes and adjust the phase and magnitude of the radiating electric fields (E-fields). Several effects are synthesized, which results in a wide-beam circularly polarized (CP) endfire radiation. Aiming to improve the radiation performances, a cavity-backed planar reflector was applied in the experiment. Simulated and measured results are detailed and analyzed, which demonstrate that the measured 3 dB axial ratio (AR < 3 dB) bandwidth (ARBW) ranges from 3.385 to 3.428 GHz (1.2%), and the peak gain can be up to 3.4 dBi if the planar reflector is added. The measured half-power beamwidth (HPBW) and 3 dB ARBW can be up to 88°/114° and 53°/112° at 3.4 GHz, respectively. The antenna size (excluding the reflector) is maintained at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.49\lambda _{0}\times 0.25\lambda _{0}\times 0.017\lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength in free space, performing a compact configuration.

Design of a Low-Cost, Low-Sidelobe-Level, Differential-Fed SIW Slot Array Antenna with Zero Beam Squint

This paper presents a low-cost, low-sidelobe-level, differential-fed, substrate-integrated waveguide (SIW)-based slot array antenna with zero beam squint. The antenna consists of two identical six-way unequal power dividers (PDs) and a 6 × 16 slot array and is realized on a single-layer substrate. The six-way unequal PD provides tapered amplitude and in-phase excitation for six SIWs, and each of them has 16 radiating slots. The 1 × 16 linear slot array on each SIW is excited using a differential feed to avoid undesired beam squinting across its operating band. A two-way hybrid waveguide (WG)-to-SIW E-plane PD is developed to provide equal amplitude and out-of-phase excitation for two six-way unequal power dividers. Moreover, metallic decoupling walls are implemented between two adjacent linear slot arrays to reduce E-plane external mutual coupling. An antenna prototype is fabricated and experimentally verified. The fabricated antenna shows that the measured −10 dB reflection bandwidth is 7.15% (9.57–10.28 GHz), with the achieved gain ranging from 20.30 to 21.92 dBi. A stable boresight beam is observed over the entire operating band. Furthermore, at the designed frequency of 10 GHz, peak SLLs of −29.1 dB and −29.4 dB are achieved in the E- and H-plane, respectively.

Helicity Conservation for Mie Optical Cavities

The study of helicity in the context of light-matter interactions is an increasing area of research. However, some fundamental aspects of the helicity content of light fields inside scatterers have been overlooked. In this work, we demonstrate that the helicity of light fields inside lossless spherical cavities cannot be either conserved or sign flipped as a result of a scattering event. The underlying reason is that the internal electric and magnetic Mie coefficients cannot simultaneously oscillate with equal amplitude and equal or opposite phase. Our analytical demonstration is fulfilled regardless of the refractive index, sphere size, and multipolar order. In addition, we show that the helicity of light fields inside lossy spheres can be conserved. This fact is in striking contrast to the behavior of the scattered field, whose helicity content cannot be conserved precisely when the sphere has losses. Finally, we show that the helicity content of internal fields can be flipped for materials with gain.

Coherent infrasound generation using an air-propane burner

An invaluable tool in characterization of any receiver, propagation path, or detection system, is a source with known and repeatable signal characteristics. This talk will discuss development and evaluation of a coherent (non-explosive, periodic, with controlled duration) infrasound source with frequency capabilities in the sub-hertz to several hertz band. Design of a practical sound source within this band is a difficult engineering challenge. The simple source equation, which will govern any portable human-fabricated infrasound source due to the long wavelengths, shows this fundamental difficulty. As frequency decreases volume displacement must increase by the squared inverse factor of frequency in order to maintain an equal pressure amplitude at equal range. For this reason, the authors investigate utilizing the high energy density available in gas combustion to periodically displace large volumes of air within the open atmosphere. Prototype testing has verified the capability of generating continuous signals at a fundamental frequency of 0.25–1.5 Hz in the farfield—or ranges from the source where pressure and particle velocity are roughly in-phase. Harmonics of this fundamental are also generated throughout the 0.25–4.0 Hz band with reasonable signal-to-noise ratio. Development of the infrasound source prototype as well as experimental testing and results will be discussed.

A Novel Terahertz Detector Based on Asymmetrical FET Array in 55-nm Standard CMOS Process.

This paper reports a novel, one-dimensional dense array of asymmetrical metal-oxide-semiconductor field-effect-transistor (MOSFET) THz detector, which has been fabricated in GlobalFoundries 55-nm CMOS technology. Compared with other technologies, the Si-based complementary metal-oxide-semiconductor (CMOS) dominates in industrial applications, owing to its easier integration and lower cost. However, as the frequency increases, the return loss between the antenna and detector will increase. The proposed THz detector has a short-period grating structure formed by MOSFET fingers in the array, which can serve as an effective antenna to couple incident THz radiation into the FET channels. It not only solved the problem of return loss effectively, but also greatly reduced the detector area. Meanwhile, since the THz signal is rectified at both the source and drain electrodes to generate two current signals with equal amplitude but opposite directions, the source drain voltage is not provided to reduce the power consumption. This leads to a poor performance of the THz detector. Therefore, by using an asymmetric structure for the gate fingers position to replace the source drain voltage, the performance of the detector in the case of zero power consumption can be effectively improved. Compared with the symmetrical MOSFET THz detector, Rv is increased by 183.3% and NEP is decreased by 67.7%.

Using the spectral approach in image and arbitrary data processing

Introduction: The transfer of image processing operations to the spectral region is considered. Due to the duality of information representation, coding, filtering, compression and other transformations are possible both in the space of an object and in the region of spatial frequencies, in relation to its spatial spectrum. Purpose: To evaluate the efficiency of performing image processing operations and arbitrary digital information in the spectral domain. Results: A method for spectral holographic coding is proposed, which provides a gain in noise immunity by 7–8 dB and has less complexity of coding and decoding when changing redundancy over a wide range. During the coding process, the source data block is replaced by a code word, which is a linear one-dimensional hologram of a virtual point source. For transmission over a communication channel, we synthesize a signal with a given spectrum, the shape of which is a one-dimensional hologram, with its values rounded to one bit and the hologram itself being a sequence of zeros and ones – one means the presence of the corresponding harmonic in the spectrum, zero means the absence. To create a signal with such a line spectrum, it suffices to add a set of harmonics of equal amplitude with numbers corresponding to the position numbers of the units in the hologram. This operation is one of the types of orthogonal frequency division multiplexing, characterized in that the frequencies of the orthogonal subcarriers are in a multiple ratio, and amplitude shift keying is used as digital modulation. We propose a spectral method for image compression based on a detailed analysis of the spatial spectrum of an image and the removal of a large number of insignificant areas from it. Practical relevance: The reduction in the amount of information and, accordingly, the size of the image can be 4–8 times or more with a slight decrease in image quality.

Spin-current in a Magnetic Semiconductor Tunnel Junction: Effect of External Bias Voltage

This paper investigates spin-current transport in a GaMnAs/GaAs/GaMnAs magnetic semiconductor tunnel junctions under applied bias voltages. The 30-band k.p approach is used to describe the materials within the heterostructure, incorporating both spin-orbit and exchange interactions. We use the transfer-matrix formalism to derive numerical solutions for the wave functions. At specific bias values, we calculate the polarization of the spin-current component along the z direction of the structure. We show oscillations of the two spin-current components perpendicular to the magnetization with equal polarization amplitude and characteristic period. The polarization amplitude varies around 10%, reflecting the typical polarization in such type of material. The oscillation period - which relates to the Larmor frequency for spin precession - increases with the bias voltage values.