- 标题
- 摘要
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- 实验方案
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Performance Analysis of Fractional Fourier Domain Beam-Forming Methods for Sensor Arrays
摘要： The problem of estimating the direction of arrival (DoA) of multiple far-field moving targets, producing broad-banded chirp signals, in both active and passive mode of operation is addressed. As the chirp signal, commonly used in both radar and sonar systems is better processed in fractional Fourier domain, the detection is done using fractional Fourier transform (FrFT) in the proposed work. Subsequently, the DoA estimation is achieved using both conventional and subspace methods. Even though FrFT beamforming method has been studied in the past, its performance in respect of varying signal-to-noise ratios (SNRs) and multiple target detection has not been extensively analyzed yet. The results of simulation experiments reported in the present work show that FrFT enjoys better estimation accuracy over the conventional frequency domain beam-forming for chirp signals using Fourier transform (FT), in terms of computational efficiency, accuracy and resolution with low SNR, limited snapshots and sensors, and spatially coherent/multi-path signals. The performance metrics used for the study are (i) root mean square error, (ii) 3-dB beam width and (iii) CPU time for accuracy, resolution and computation time, respectively. It is seen from computer simulations that MUSIC outperforms other DoA estimation techniques from the performance curves for both active and passive systems.
关键词： direction of arrival estimation,chirp signal,Sensor arrays,beam-forming,fractional Fourier transform
更新于2025-09-09 09:28:46
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Structural, Optical, and Magnetic Properties of Hydrothermally Grown Fe-Doped ZnO Nanorod Arrays on Glass Substrate
摘要： In this paper, undoped and Fe-doped ZnO nanorod arrays were grown on glass substrate by a facile hydrothermal method. Structural, optical, and magnetic properties of the prepared nanorods were investigated. Structural investigation clearly showed that the prepared nanorods had single phase wurtzite structure without any secondary phases and the prepared undoped and Fe-doped nanorods were grown vertically. The optical characterization revealed that the optical band gap of ZnO nanorods was decreased by increasing the value of Fe concentration. Furthermore, the formation of diluted magnetic semiconductor nanorod arrays was verified. The origin of room temperature ferromagnetism is explained by the bound magnetic polaron concept.
关键词： Diluted magnetic semiconductors,Bound magnetic polaron,Nanorod arrays,Fe-doped ZnO
更新于2025-09-09 09:28:46
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High density GaAs nanowire arrays through substrate processing engineering
摘要： GaAs nanowires (NWs) vertically aligned were successfully fabricated through substrate processing engineering. High-density vertical GaAs NWs are grown on n-type Si (111) substrate by molecular beam epitaxy. Systematic experiments indicate that substrate pretreatment is crucial to vertical epitaxial growth of one-dimensional (1D) nanomaterials. The substrates etched using diluted buffered oxide etch (BOE) were explored to improve the NW density and vertical. We also find that the substrate processing engineering strongly affect the morphology of GaAs NWs. Finally, we demonstrate fabrication of GaAs NW arrays on Si surface by field-emission scanning electron microscopy (FE-SEM). This single-step process indeed offers a simple and cost-effective way to obtain a large area of GaAs NW arrays without using e-beam lithography (EBL) and/or nanoimprint lithography (NIL) processes. This work provided a new approach for hight density NW arrays.
关键词： GaAs nanowire arrays,self-catalyzed,buffered oxide etch,molecular beam epitaxy
更新于2025-09-09 09:28:46
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Theory and Design of a Retrodirective Rat-Race-Based RFID Tag
摘要： Movement towards mm-wave backscatter communications in radio-frequency identification (RFID) systems necessitates seeking designs that compensate for the path loss introduced by the radio channel. A viable, simple, and power-efficient solution is to equip RFID tags with retrodirective arrays, which guarantee reflection with maximal gain in the direction of incidence. In this paper, we build upon a previous work to design and implement an original retrodirective tag in which its feeding network is a properly-terminated rat-race coupler. We start by deriving the required terminations that ensure retrodirectivity. Then, we build a retrodirective tag and experimentally compare its radar cross section to that of a single-antenna tag. The measurements reveal that the radar cross section of the proposed retrodirective tag is, on average, approximately 6 dB more than that of a single-antenna tag while both tags have the same field-of-view. From the promising results in this paper, the proposed design is a potential candidate for next-generation microwave and mm-wave RFID tags because it is compatible with low-power reflection amplifiers (e.g., tunnel diodes), it can implement multiple modulation schemes without changing the circuit layout, and it can be implemented using only a single RF switch.
关键词： multi-modulation RFID tags,Retrodirective arrays,rat-race coupler
更新于2025-09-09 09:28:46
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Incoherent Synthesis of Sparse Arrays for Frequency-Invariant Beamforming
摘要： Frequency-invariant beamformers are used to prevent signal waveform distortions in real world applications like audio, underwater acoustics, and radar. Most of existing methods assume uniform arrays, and only few consider sparse designs, which may lead to higher performance in terms of robustness and directivity factor. We propose an incoherent approach that first determines for each frequency bin a sparse set of sensors positions. Subsequently, by using tools of dimensionality reduction and clustering, these selections are merged together yielding the optimal sensors on a sparse array layout. We present design examples of sparse linear and planar superdirective array designs. We show that the proposed incoherent sparse design obtains superior performance in terms of white noise gain, directivity factor, and computational load compared to a uniform array design and compared to a coherent sparse approach, where the sensors’ locations and the beamformer coefficients are optimized simultaneously for all frequencies.
关键词： Frequency-invariant beamformer,superdirective beamformers,differential microphone arrays,sparse design
更新于2025-09-09 09:28:46
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Automatic Monitor-Based Tuning of an RF Silicon Photonic 1X4 Asymmetric Binary Tree True-Time-Delay Beamforming Network
摘要： Photonic beamforming networks are promising candidates to achieve power-efficient transmission in future cellular communication systems. However, sensitivity to process and temperature variations necessitates an automatic calibration solution to enable robust operation. This paper demonstrates fully automatic monitor-based tuning of an integrated optical ring resonator-based 1X4 asymmetric binary tree optical beamforming network (OBFN). The proposed monitor-based tuning algorithm compensates fabrication variations and thermal crosstalk by controlling micro-heaters individually using information from electrical monitors. This algorithm is demonstrated on an OBFN that operates at 30 GHz with 2 GHz bandwidth and is fabricated in a standard silicon photonics foundry process. Successful calibration of the OBFN from a severely degraded initial response to the well-defined group delay responses required for a targeted radiating angle over 60? (?30? to 30?) in a linear beamforming antenna array is achieved. This fully automatic tuning approach opens the possibility of employing silicon OBFNs in real wideband mm-wave wireless communication systems.
关键词： optical ring resonators,thermal crosstalk,photonic integrated circuits,phased arrays,RF photonics,optical beamforming,true time delays,Microwave photonics
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (SAM) - Sheffield (2018.7.8-2018.7.11)] 2018 IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (SAM) - Symmetric Sparse Linear Array for Active Imaging
摘要： Sparse sensor arrays can achieve significantly more degrees of freedom than the number of elements by leveraging the co-array, a virtual structure that arises from the far field narrowband signal model. Although several sparse array configurations have been developed for passive sensing tasks, less attention has been paid to arrays suitable for active sensing. This paper presents a novel active sparse linear array, called the Interleaved Wichmann Array (IWA). The IWA only has a few closely spaced elements, which may make it more robust to mutual coupling effects. Closed-form expressions are provided for the key properties of the IWA. The parameters maximizing the array aperture for a given even number of elements are also found. The near field wideband performance of the array is demonstrated numerically in a coherent imaging scenario.
关键词： active sensing,Interleaved Wichmann Array,mutual coupling,Sparse sensor arrays,coherent imaging
更新于2025-09-09 09:28:46
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Ultrasound-assisted successive ionic layer adsorption and reaction synthesis of Cu2O cubes sensitized TiO2 nanotube arrays for the enhanced photoelectrochemical performance
摘要： In this paper, Cu2O cubes with high photoelectrochemical activities were deposited on the surface of TiO2 nanotube arrays by the ultrasound-assisted successive ionic layer adsorption and reaction (SILAR) method. The elemental composition and morphology were characterized by XPS and SEM. The TiO2 NTs/Cu2O showed excellent photoelectric conversion and photoelectrocatalytic (PEC) removal of organic dyes and Cr(VI). The results confirmed that the SILAR deposition cycle greatly influenced the visible light response and PEC properties, and the TiO2 NTs/Cu2O (6) prepared with 6 SILAR cycles showed the optimal visible light photocurrent (1.08 mA/cm2), visible light photovoltage (-0.044 V/cm2), solar PEC degradation efficiencies of MO (77.62%), RhB (61.83%) and MB (98.30%), and PEC reduction of Cr(VI) (97.16%). The TiO2 NTs/Cu2O photoelectrodes would show prospective applications in solar cells and waste-water treatment due to the significantly enhanced photoelectrochemical performance.
关键词： Photocatalysts,TiO2 nanotube arrays,Cu2O cubes,SILAR,Photocurrent
更新于2025-09-09 09:28:46
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[IEEE 2018 15th European Radar Conference (EuRAD) - Madrid, Spain (2018.9.26-2018.9.28)] 2018 15th European Radar Conference (EuRAD) - Multiplier-less Correlator for Noise SAR Imaging
摘要： Correlation function estimate using one-bit reference signal is described and results of FPGA-based implementation of multi-channel time-integrating correlator without multiplication operation (multiplier-less correlator) is described. Results of experimental evaluation of the suggested multiplier-less relay correlator in Innovative Integration X6-1000M board with Xilinx Virtex-6 FPGA and arbitrary waveform generator Euvis AWG472 are presented.
关键词： Relay Correlator,Field Programmable Gate Arrays,Noise Radar,Radar Imaging,Synthetic Aperture Radar
更新于2025-09-09 09:28:46
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Experimental determination of reference pulses for highly segmented HPGe detectors and application to Pulse Shape Analysis used in $\gamma$γ-ray tracking arrays
摘要： For the first time, bases of signals delivered by highly segmented HPGe detectors, for identified hit locations, have been determined in situ, that is in the actual accelerator-target-detection system conditions corresponding to data acquisition during a physics experiment. As a consequence, these bases include all the genuine features and alterations of the signals induced by the experimental setup, e.g. diaphony, electronic response, specificity of individual crystals. The present pulse shape bases were constructed using calibration source data taken at the beginning of the AGATA campaign at GANIL. An experiment performed at GANIL using the AGATA γ-ray detector together with the VAMOS spectrometer was used to validate the bases. The performance of the bases when used for pulse-shape analysis has been compared to the performance of the standard bases, composed of pulse shapes generated by a computer simulation used for AGATA. This is done by comparing the Doppler correction capability. The so-called Jacobian method used to generate the in situ bases also produces correlations that can be applied to locate in a direct way (no search algorithm) the location where a γ-ray interacted given that only one segment is hit. As about 50% of all pulse-shape analysis is performed on crystals with only one segment hit this will allow for a large reduction in the needed computer power. Different ways to improve the results of this prospective work are discussed.
关键词： HPGe detectors,Doppler correction,γ-ray tracking arrays,VAMOS spectrometer,Pulse Shape Analysis,AGATA
更新于2025-09-09 09:28:46