Search

This paper proposes a method to localize multiple partial discharge (PD) sources in air-insulated substation by using radio frequency (RF) antenna sensors combining with clustering algorithm, which solves the problem that multiple PD or interference sources are difficult to localize in air-insulated substation (AIS). Our research group made four omnidirectional RF antenna sensors, the detection frequency band was 250 MHz-3 GHz, the voltage standing wave ratio (VSWR) of the RF antenna in the detection frequency band was less than 2, which meets the detection requirements. The scenes of multiple PD sources in AIS were simulated in the laboratory, the time difference of arrival (TDOA) was collected through four RF antennas, and the clustering effects of K-means and Two Step algorithms were compared. Based on the normal distribution characteristics of TDOAs and the better Two Step algorithm, a $3\sigma $ -Two Step algorithm was proposed to process TDOAs and output the centers of TDOAs. Newton iterative algorithm was used to solve the localization equations. The results show that the average localization error of two PD sources was 0.21 m and that of three PD sources was 0.45 m. The PD localization tests were carried out in an actual AIS in China, the proposed method localized a corona discharge on a post insulator and a corona discharge on a disconnector. Through the verifications with an ultraviolet camera, it was obtained that the localization errors at each position were within the range of 0.6-2 m. [ABSTRACT FROM AUTHOR]

In this article, a novel low-cost frequency scanning-based synthetic aperture radar (F-SAR) system is proposed for high-resolution imaging. F-SAR scheme is demonstrated for personal screening for the first time. A hybrid scanning model is presented to illuminate the human body, namely, frequency control beam steering in cross-track and mechanical scanning in along-track. A frequency scanning-based tomographic SAR focusing algorithm is proposed. Accordingly, a power spectrum estimation algorithm in cross-track and synthetical aperture processing in along-track are compounded in the signal processing framework. Unlike a variety of multiple input multiple output (MIMO) array imaging which illuminates the object by switching different channels sequentially over separate time intervals, the F-SAR concept sweeps across all swaths over each chirp by employing a frequency scanned beam. Herein imaging time and hardware cost can be significantly cut down by dimensionality reduction from the MIMO system to a single input single output (SISO) system. Furthermore, to fulfill the particular scheme of the F-SAR system, a novel combo antenna module, leaky-wave slotted waveguide combined with a cylindrical lens, is proposed and achieved at 78–92-GHz band, by which a steering fan-beam focused at the object under test (OUT) plane is radiated. The radiation beam is focalized by the cylindrical lens accompanied by frequency sweeping, while is diffused in along-track. The frequency-controlled beam-steering concept and the fan-beam focusing mechanism are verified by the chamber measurements. The measured scanning range is 23°. Beamwidth of 11–16 mm is obtained at the focal plane. Beam steering in cross-track together with mechanical scanning in along-track can attain a field of view (FoV) of 0.54 2 $\text{m}^{2}$. Through-clothes imaging of person-borne concealed objects and the real-time capability are demonstrated by experiments. Resolutions in both along-track and cross-track can reach 5 mm. [ABSTRACT FROM AUTHOR]

This letter presents a novel image-based vital sign detection strategy for trapped persons based on the optimized two-dimensional (2-D) ultrawideband (UWB) radar deployment. The main novelty is that the slow-time images based on 2-D radar deployment are created to continuously screen the trapped persons with periodic micromotions in a specific area. According to the optimized deployment, multiple UWB life-detection monostatic radars are distributed and work in a time-division-multiplexing mode. These radars are sequentially controlled and activated to capture information from all possible wave incidents and scattering angles. The 2-D radar deployment is designed and optimized using the multiple-input and multiple-output (MIMO) array topology technique. The vital sign is modeled as the slow-time image, and multiple images might contain the periodic weak responses from the trapped persons. Proof-of-principle experiments were carried out based on an optimized 2-D UWB radar deployment. All observation points in this deployment are sequentially selected to complete the transmission and reception of the UWB monostatic radar. Finally, the experimental results validate the effectiveness of the proposed image-based vital sign strategy on the azimuth locations of the trapped persons. [ABSTRACT FROM AUTHOR]

Multiple-input-multiple-output synthetic aperture radar (MIMO-SAR) technology is an effective scheme to achieve there-dimensional (3-D) imaging in millimeter wave and terahertz band. Compared with the 2-D array, the system complexity and the number of array elements are greatly reduced. In this paper, an efficient image reconstruction algorithm in wavenumber domain based on phase shift migration (PSM) was proposed for MIMO-SAR 3-D real-time imaging application. By decomposing the range-wavenumber based on binomial approximation theory, the PSM operation can be achieved only by matrix multiplication and Fourier transform (FT) algorithm without time-consuming wavenumber accumulation. Proof-of-principle experiments were also carried out in 0.1THz band based on a MIMO-SAR prototype system. Both simulation and experimental results of different targets show that the image quality of the proposed algorithm is comparable to that of back-projection algorithm (BPA). The partial enlarged images of the imaging results validate that compared with the range migration algorithm (RMA) the proposed algorithm can achieve higher reconstruction accuracy with comparable efficiency. [ABSTRACT FROM AUTHOR]

Inspired by the circular-aperture synthetic aperture radar (Circular-SAR) imaging regime that can provide higher azimuth image resolution, the imaging regime employing the multiple-input–multiple-output (MIMO) arc array is proposed. Moreover, no efficient imaging algorithm is now available for these MIMO arc array setups. This article proposes a modified Omega-K algorithm for near-field azimuth image reconstruction based on the geometry transformation from the single-frequency MIMO arc array to the equivalent MIMO linear array. Note that this geometry transformation relies on the calculation of the phase difference and the definition of the corresponding compensation function. Compared with the single-input–single-output (SISO) arc scan requiring more elements, simulations with good agreement were performed to validate the azimuth image reconstructions of single/multiple targets. Although the computing efficiency of the proposed algorithm for MIMO arc array is lower than that of the traditional Omega-K algorithm for the SISO arc scan, it still has an obvious advantage relative to the traditional backprojection (BP) algorithm that is always taken as the gold standard. Furthermore, three realistic imaging geometries, including the metal strips at different radii, the tilted metal plate, and the human body torso cross section, were simulated to test the fidelity of the proposed reconstruction algorithm. Proof-of-principle experiments were also carried out based on an MIMO arc array with the help of one arc scanner. Finally, both simulation and experimental results validate the effectiveness of the proposed algorithm on azimuth image reconstruction quality. [ABSTRACT FROM AUTHOR]

This paper studies the methods of moving targets tracking based on a multi-beam tracking system in terahertz (THz) band, which is an initial attempt in this field. Taking the advantage of forming high resolution range profile of THz radar, a target geometric center tracking method is developed at first. However, the tracking performance is deteriorated by the severe angular glint and system disturbance. A further analysis on the experiment data finds a statistical correlation between the angular glint and the normalized amplitude variance, which is exploited to identify and exclude instable scatterers. A non-linear angular discrimination function is also established to deal with the anomalous measurement of the radar. Finally, an instable point exclusion method and a nonlinear angular discrimination method are proposed and combined to develop an improved tracking method, which can suppress angular glint and mitigate measuring perturbation, hence promoting the tracking performance. Proof-of-principle experiments are performed with a multi-beam tracking system working in 0.2 THz band. Tracking results of different targets demonstrate that the improved tracking method can effectively eliminate the tracking failure and significantly promote the tracking accuracy. [ABSTRACT FROM AUTHOR]

In this paper, the method of phase shift migration (PSM) for multi-input-multi-output sidelooking (MIMO-SL) was developed for fast image reconstruction in terahertz (THz) band. By investigating the relationship between the “explode fields” and the echoed data recorded in the MIMO-SL system, a data reorganization method in the wavenumber domain was developed to derive the “explode fields” based on the bistatic data. It is interesting to find that the reorganized MIMO-SL data measured in a certain frequency are equivalent to the “explode fields” in other frequency (“equivalent frequency”). By deriving and applying the modified phase shift factor at the “equivalent frequency,” a comprehensive MIMO-SL-PSM algorithm was established for the first time with fast transformation in the wavenumber domain. Proof-of-principle experiments in the 0.1-THz band were performed based on an MIMO-SL prototype system. The reconstructed images for different targets with high efficiency and quality demonstrate the theoretical results and the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This letter presents a two-dimensional near-field synthetic spectrum imaging algorithm based on a single-frequency sparse multiple-input–multiple-output (MIMO) array. By using an especially defined backward spreading function, the proposed algorithm migrates the scattered wave field under different illuminations. A synthetic spectrum can be obtained by synthesizing the spectrums of these migration results and then interpreted to the final reconstruction. The migration processing enables the algorithm to adapt to arbitrary apertures. Meanwhile, the influences of the limited aperture, the spreading loss, and the wavefront curvature in the near field are considered and compensated. High processing speed is achieved by using a large interpixel spacing during the migration processing and by the fast Fourier transform in the frequency-wavenumber (f-w) domain. Simulations and experiments are carried out, and the results demonstrate both the high-computational efficiency and the high flexibility for arbitrary sparse MIMO array apertures. [ABSTRACT FROM AUTHOR]

The characteristics of the range cell migration (RCM) under single-input-multiple-output (SIMO) bi-static geometry are studied and an omega-K algorithm for near-field 3-D imaging based on planar SIMO or multiple-input-multiple-output (MIMO) array is proposed. The RCM and the linear part of the range offset (RO) within SIMO data are corrected by employing a 3-D Stolt transformation. The residual range error is further compensated by phase multiplication and an image-domain interpolation. Reconstruction for a MIMO aperture can be achieved by adding together all the focusing results from its SIMO subarrays. The implementation details of the algorithm are described. The imaging resolution and the sampling requirements for a MIMO aperture are discussed. Since the RO correction is achieved by an approximate way, the spatial limitation for accurate reconstruction is also given. The imaging accuracy and the high efficiency of the algorithm are demonstrated both by simulations and experiments with various distributed targets based on planar MIMO arrays. Real-time 3-D imaging for planar SIMO/MIMO aperture is expected to be achieved by using the algorithm. [ABSTRACT FROM AUTHOR]

A modified omega-K algorithm for planar multiple-input-multiple-output (MIMO) array-based 3-D image reconstruction is proposed. By applying several proper approximations in wavenumber domain, the complex and time-consuming bistatic Stolt transformation within the traditional MIMO- $\omega \text{K}$ is changed into a relatively simple monostatic one, and therefore the amount of the interpolation given for the data is greatly reduced. Combining with multidimensional fast Fourier transformation, extremely high computation efficiency can be achieved. Implementation details are well described. The imaging accuracy and the high efficiency of the algorithm are demonstrated by a near-field imaging experiment with a flat mannequin target based on a planar MIMO array radar. [ABSTRACT FROM AUTHOR]

An optimization method for ultrawideband multiple-input-multiple-output (MIMO) planar array topology design, which can satisfy both uniformity and lower element shadowing principles, is proposed by extending our previous work. Two planar MIMO arrays, namely, the basic optimal array (BOA) and the extended optimal array (EOA) are optimized. The focusing and sidelobe-suppression properties of the BOA and the EOA are demonstrated to be superior to other two previous state-of-the-art planar MIMO arrays. The advantages of the two optimized arrays in 3-D imaging are further indicated by experimental results for different distributed targets. The validity of the proposed method is verified by the excellent performances of the BOA and the EOA. [ABSTRACT FROM PUBLISHER]

A novel ultra-wideband (UWB) linear array human respiration model and detection method is proposed to obtain vital sign feature (VSF) including azimuth, range, and respiration frequency. As the azimuth of the human being cannot be estimated by a single receiving channel, the new method generates new B-scans for different scanning angles. When the azimuth angle is determined by the azimuth estimation method, the corresponding new B-scans can be processed to obtain the range and respiration frequency. The new method not only estimates the azimuth angle of the human being, but also detects multiple respiration motions from the new B-scans instead of the traditional B-scans. Meanwhile, the implementation steps of the new method are fully illustrated both in free-space and rubble situation. Four free-space simulations are performed and prove the necessity of the new method using the UWB linear array. The results verify its capability for the azimuth estimation and the multiple VSFs detection. In addition, the scene with one person trapped in rubble is simulated to validate the new method for the rubble case with unknown permittivity. Furthermore, a practical experimental validation is performed in an artificial ruin to show the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

This letter presents a new method for localizing and identifying a target through walls with known wall parameters. A time-delay difference curve (TDDC) is utilized in this method for target localization and identification. The characteristic of the TDDC can be applied to estimate the incident angle and offset the influences in propagation path and propagation time delay brought from the wall. This letter analyzes the method and gives out the theoretical TDDC. Extensive simulations and experiments show the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Via analyzing the characteristics of life sign, a novel method of life detection based on constant false alarm ratio and clustering is proposed in this paper. The signal to noise and clutter ratio (SNCR) is greatly improved. The nonstatic clutter can be removed effectively. The good performance of the new method is proved numerically and experimentally. The range location and frequency information of life sign can be estimated automatically and accurately in low SNCR environment. [ABSTRACT FROM PUBLISHER]