Method Of Echo Research Articles

Non-contact three-dimensional emissivity distribution measurement method of M8 LiDAR echo

Non-contact three-dimensional emissivity distribution measurement method of M8 LiDAR echo

A Numerical Simulation Method of Radar Echo From a High-Speed Target

The radar echo signal of a high-speed target is simulated in this letter. Using the Lorentz transformation, the linear frequency modulation pulse radar signal is transformed from the laboratory coordinate system into a moving system. The near-zone scattered fields and the far-zone echo signals are solved by the finite-difference time-domain (FDTD) algorithm in the moving system that is kept the same velocity as the target. Subsequently, transform the echo signal back to the laboratory system. Meanwhile, this letter combines the graphic processing unit parallel technique with the Lorentz–FDTD method to realize the simulation of a high-speed target excited by a large time-width signal and extracts the one-dimensional(1-D) range profile of the target. The validity of the proposed method is verified by the analytical results of a high-speed target excited by arbitrary directions incident waves. The numerical examples show that the motion's effects on the range information of the radar signal are nonnegligible for high-speed objects.

An Improved Meteor Echo Recognition Algorithm for SuperDARN HF Radar

The SuperDARN HF radars can be used for meteor observation and inversion of mid-upper atmosphere neutral wind using observed meteor echo Doppler velocities. Aiming at the problem that the extraction of meteor echo based on echo power, Doppler velocity and spectral width is rough and contains ionospheric echo, this paper optimizes the extraction algorithm of meteor echo. Based on the AgileDARN HF radar’s digital characteristics, the observation method of meteor echo was improved, and we designed a meteor observation mode without changing the hardware system: using a meteor observation with a 7.5 km range resolution and a 2 s integration time, we extracted the Doppler characteristics of different echo types at meteor echo ranges; according to these features, the extraction algorithm of meteor echo was optimized. By analyzing the measured data, the characteristics of diurnal variation, power distribution, Doppler velocity distribution and spectral width distribution of meteor echo extracted by the optimization algorithm were obtained. The meteor echo characteristics obtained by the improved algorithm are more consistent with the theoretical analysis; thus, the improved algorithm is better than the SuperDARN high frequency radar meteor echo extraction algorithm and has good performance. The meteor echo extraction algorithm presented in this paper can extract the meteor echo more accurately, so that the atmospheric neutral wind can be retrieved more accurately. At the same time, the proposed algorithm is not only applicable to AgileDARN HF radar meteor observation mode data, but also to AgileDARN and SuperDARN normal mode data, which is beneficial to expand the data application of SuperDARN radars.

Collection Method of Arbitrary Laser Echo Based on STM32

When LIDAR measures the water depth, in most cases the echo signal is more complex, with more backscattering, and it is difficult to observe different parts of the waveform separately, especially the underwater echo signal. Therefore, this paper uses an STM32 controller to design a signal generator to send out pulse signals, which act on the detection device PMT in the LIDAR detection system to control the start and stop of the PMT receiving channel. By adjusting the frequency, duty cycle, and other parameters of this signal generator, the arbitrary part of the waveform can be collected, and the waveform is not disturbed. Using the STM32 instead of a traditional signal generator can reduce system power consumption and load capacity.

Oil spill extraction from X-band marine radar images by power fitting of radar echoes

ABSTRACT Oil spills cause great environmental damage and the ability to identify them accurately is important to prompt oil spill response. A power fitting method of radar echo is proposed in this paper to detect oil spills on sampled X-band marine radar images. In this method, first, the marine radar image is pre-processed, including coordinate transform and noise reduction. Then, the difference between the pre-processed radar image and power fitting result is obtained. Finally, oil spills are extracted by using a mean filter, the Otsu method, and connected component analysis. The proposed oil spill detection method was used on radar images sampled after an oil spill accident in the coastal region of Dalian, China, on 21 July 2010. The proposed method can detect oil spills without manual participation, and the extracted oil spills are comparable to visual interpretation.

Simulation method of pulse laser fuze echo in dust environment

Simulation method of pulse laser fuze echo in dust environment

Molecular velocity auto-correlations in glycerol/water mixtures studied by NMR MGSE method

Molecular dynamics in binary mixtures of water and glycerol was studied by measuring the spectrum of water velocity auto-correlation in the frequency range from 0.05−10 kHz by using the NMR method of modulated gradient spin echo. The method shows that the diversity of diffusion signature in the short spin trajectories provides information about heterogeneity of molecular motion due to the motion in the micro-vortexes of hydrodynamic fluctuation, which is especially pronounced for the mixtures with low glycerol content. As concentration of glycerol increases above 10vol%, a new feature of spectrum appears due to interaction of water molecules with the clusters formed around hydrophilic glycerol molecules. New spectrum exposes a rate thickening of molecular friction, according to Einstein–Smoluchowski–Kubo formula, which inhibits rapid molecular motions and creates the conditions for a slow process of spontaneously folding of disordered poly-peptides into biologically active protein molecules when immersed in such a mixture.

High‐speed moving target detection and tracking method based on speed estimation

During the detection and tracking of high-speed moving target by radar, the coherent accumulation and the energy accumulation of target echo signal are poor. In order to solve this problem, this study discusses speed estimation based on the Hough transform, correction across distance of radar echo signal and pre-tracking detection method based on dynamic programming. The authors propose an energy accumulation method of target echo based on speed estimation. Using this method, speed estimation accuracy reaches 98.87%, signal-to-noise ratio increases by 10 dB and the goal amplitude is 4.81 times more than the original amplitude. Simulation results show that this method can improve the energy accumulation effectiveness and improve detection and tracking ability of high-speed moving target by radar.

Analysis method of impact echo based on variational mode decomposition

The Impact Echo (IE) method is a widely used method for the detection of concrete structures. The signal has non-stationary characteristics. Empirical mode decomposition (EMD) is one of the typical ways of dealing with non-stationary signals. Due to EMD having mode overlap and a breakpoint effect, Variational Mode Decomposition (VMD) has been proposed to overcome these problems. In this study, VMD is introduced into the analysis of the concrete component detection signals, and the impact echo analysis method based on VMD and marginal spectrum is established. The proposed method to solve the marginal spectrum is used in order to analyze the numerical simulation model’s IE signal. This method is able to correctly obtain the main frequency. When compared with the traditional Fourier spectrum, the marginal spectrum that is based on the VMD method shows that the band width that is present in the main frequency is narrow. Even in the presence of a highly noisy background, the method is able to correctly obtain the main frequency. At last, through the detection signal analysis of the non-defective concrete specimen and the concrete specimen with the circular hole, the results show that the proposed method can distinguish the signal in the different defective states of the concrete structures, which has obvious advantages compared with the Fourier spectrum.

Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a t−3∕2 long-time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short spin trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.

Epr Spectroscopy of Adsorbed Spin-Labeled Peptides: Immobilization of Trichogin on the Titanium Oxide

The TOAC-spin-labeled peptide Trichogin GA IV adsorbed on the TiO2 surface is studied. It is shown that the continuous wave (CW) electron paramagnetic resonance (EPR) spectrum does not depend on temperature in a wide range of 77–300 K. A pulsed EPR method of electron spin echo (ESE) utilizing a two-pulse sequence (π/2-τ-π) is used to study temperature dependence of the phase relaxation time, TF. The TF values are found to change from 750 ns to 100 ns in the interval of 77–300 K. The pulsed electronelectron double resonance (PELDOR) measurements utilizing the pulse sequence((π/2)A,-T-πB,-(τ-T)-πA) show that the space distribution of spin labels on the surface remains uniform irrespective of the temperature, and provide the fractal dimension of the surface of 2.7±0.1. The obtained results testify that EPR pulse experiments can be used to study adsorbed spin-labeled molecules at room temperatures, i.e. not only at cryogenic temperatures.

A Frequency Domain Extraction Based Adaptive Joint Time Frequency Decomposition Method of the Maneuvering Target Radar Echo

The maneuvering target echo of high-resolution radar can be expressed as a multicomponent polynomial phase signal (mc-PPS). However, with improvements in radar resolution and increases in the synthetic period, classical time frequency analysis methods cannot satisfy the requirements of maneuvering target radar echo processing. In this paper, a novel frequency domain extraction-based adaptive joint time frequency (FDE-AJTF) decomposition method was proposed with three improvements. First, the maximum frequency spectrum of the phase compensation signal was taken as the fitness function, while the fitness comparison, component extraction, and residual updating were operated in the frequency domain; second, the time window was adopted on the basis function to fit the uncertain signal component time; and third, constant false alarm ratio (CFAR) detection was applied in the component extraction to reduce the ineffective components. Through these means, the stability and speed of phase parameters estimation increased with one domination ignored in the phase parameter estimation, and the accuracy and effectiveness of the signal component extraction performed better with less influence from the estimation errors, clutters, and noises. Finally, these advantages of the FDE-AJTF decomposition method were verified through a comparison with the classical method in simulation and experimental tests.

Transition Time of Ultrasonic Wave as a Tool of Quality Evaluation of Layered Polymer Composites

AbstractObservation of behaviour phenomena of ultrasonic waves in an object allows for quality assessment, identification and location of discontinuity. Physical nature of acoustic processes is based on propagation of mechanical waves constituting a disturbance of equilibrium of the state of material. The acoustic process identified by selected characteristics can be a source of information about state of material, its structure, and properties, which is particularly important for systems exhibiting anisotropy properties, and such are layered polymer composites. They are special materials because their properties depend greatly on the manufacturing technology. Therefore, while conducting acoustic tests which use the influence of elastic properties and homogeneity of material structure for propagation of sound waves the adopted method of measuring characteristics which identifies propagation of ultrasonic wave phenomenon is of particular importance. The aim of the work was quality evaluation of layered polymer composites made by winding and press moulding by the method of echo and C-scan, using head Phased Array. Composites have been tested by thermal and fatigue degradation. Quality evaluation has been made based on the transition time of the ultrasonic wave and the bending strength.

Non-Destructive Testing of High Temperature Degraded Concrete Composite of Portland Cement CEM I 42.5 R and Gravel Aggregate 11/22 by Transverse Waves

This paper study applicability of non-destructive method of impact echo for diagnosis of high temperature degraded plain concrete. Impact echo method is often used for detection of defects, cracks, and non-homogeneity in constructions. It's based on impact-generated mechanical wave that propagate through the mass of testing specimen and is reflected and partially absorbed by voids and surface. In this paper, we present results of an experiment where test specimens of dimension 0.1 x 0.1 x 0.4 m were created with usage of coarse aggregate 11/22 mm. Specimens has been divided to 7 sets. First set of test specimens were kept at laboratory conditions as a reference. Next six sets were heated up to 1200 ° C. After this heating, the specimens were cooled spontaneously and then tested by impact echo method. We used a steel hammer as an exciter of mechanical wave, which has been transferred to signal by the piezoelectric sensor. Then we analyzed this signal and we focused on transverse waves. Results from non-destructive tests were compared with results from destructive tests.

Evaluation of renal oxygenation change under the influence of carbogen breathing using a dynamic R2 , R2 ' and R2 * quantification approach.

The purpose of this study is to demonstrate the feasibility of dynamic renal R2 /R2 '/R2 * measurements based on a method, denoted psMASE-ME, in which a periodic 180° pulse-shifting multi-echo asymmetric spin echo (psMASE) sequence, combined with a moving estimation (ME) strategy, is adopted. Following approval by the institutional animal care and use committee, a block design of respiratory challenge with interleaved air and carbogen (97% O2 , 3% CO2 ) breathing was employed in nine rabbits. Parametrical R2 /R2 '/R2 * maps were computed and average R2 /R2 '/R2 * values were measured in regions of interest in the renal medulla and cortex. Bland-Altman plots showed good agreement between the proposed method and reference standards of multi-echo spin echo and multi-echo gradient echo sequences. Renal R2 , R2 ' and R2 * decreased significantly from 16.2±4.4s-1 , 9.8±5.2s-1 and 25.9±5.0s-1 to 14.9±4.4s-1 (p<0.05), 8.5±4.1s-1 (p<0.05) and 23.4±4.8s-1 (p<0.05) in the cortex when switching the gas mixture from room air to carbogen. In the renal medulla, R2 , R2 ' and R2 * also decreased significantly from 12.9±4.7s-1 , 15.1±5.8s-1 and 27.9±5.3s-1 to 11.8±4.5s-1 (p<0.05), 14.2±4.2s-1 (p<0.05) and 25.8±5.1s-1 (p<0.05). No statistically significant differences in relative R2 , R2 ' and R2 * changes were observed between the cortex and medulla (p=0.72 for R2 , p=0.39 for R2 ' and p=0.61 for R2 *). The psMASE-ME method for dynamic renal R2 /R2 '/R2 * measurements, together with the respiratory challenge, has potential use in the evaluation of renal oxygenation in many renal diseases.

Usage of internal magnetic fields to study the early hydration process of cement paste by MGSE method

Internal magnetic field gradients, arising within the porous media due to susceptibility differences at the interfaces of solid and liquid as well as due to the contained magnetic impurities, can be employed by the method of modulated gradient spin echo to get insight into the velocity autocorrelation spectrum of liquid confined in the porous structure. New theoretical treatment of spin interaction with the radio-frequency field and the simultaneously applied static non-uniform magnetic field provides the formula that match well with the measurement of restricted diffusion of water in pores of cement paste. Its fitting to the experimental data gives the changes in the mean size of capillary pores, the spin relaxation and the magnitude of mean internal magnetic field gradients during the induction period and early acceleration stage of hydration processes at different temperatures.

Hardware-in-the-loop simulation technology of wide-band radar targets based on scattering center model

Hardware-in-the-loop (HWIL) simulation technology can verify and evaluate the radar by simulating the radio frequency environment in an anechoic chamber. The HWIL simulation technology of wide-band radar targets can accurately generate wide-band radar target echo which stands for the radar target scattering characteristics and pulse modulation of radar transmitting signal. This paper analyzes the wide-band radar target scattering properties first. Since the responses of target are composed of many separate scattering centers, the target scattering characteristic is restructured by scattering centers model. Based on the scattering centers model of wide-band radar target, the wide-band radar target echo modeling and the simulation method are discussed. The wide-band radar target echo is reconstructed in real-time by convoluting the transmitting signal to the target scattering parameters. Using the digital radio frequency memory (DRFM) system, the HWIL simulation of wide-band radar target echo with high accuracy can be actualized. A typical wide-band radar target simulation is taken to demonstrate the preferable simulation effect of the reconstruction method of wide-band radar target echo. Finally, the radar target time-domain echo and high-resolution range profile (HRRP) are given. The results show that the HWIL simulation gives a high-resolution range distribution of wide-band radar target scattering centers.

Two-photon echo method for observing electron zitterbewegung in carbon nanotubes

The phenomenon of zitterbewegung (ZB, trembling motion) of electrons is described in zigzag carbon nanotubes (CNT) excited by laser pulses. The tight binding approach is used for the band structure of CNT and the effect of light is introduced by the vector potential. Contrary to the common theoretical practice, no a priori assumptions are made concerning electron wave packet; the latter is determined as a result of illumination. In order to overcome the problem of various electron phases in ZB, a method of two-photon echo (2PE) is considered and described using the density function formalism. The medium polarization of CNT is calculated by computing exact solutions of the time-dependent electron Hamiltonian. The signal of 2PE is extracted and it is shown that, using existing parameters of CNT and laser pulses, one should be able to observe the electron trembling motion. Effects of electron decoherence and relaxation are discussed.

The Measurement Method of Echo Highlights in Low Frequency

Methods which are MVDR beam-forming, STMV beamforming and a method using MVDR beamforming with copy correlation are using to measure highlight of targets echoes at low frequency. Compared with conventional beam-forming, the three methods restrain noise and resist reverberation better. To reduce calculation, firstly, as the azimuth measured by using Split array cross-correlation beamforming the center, and then the neighboring area scanned using MVDR focused beamforming. Therefore, this highlight of echoes research measures have high precision and practical.

Gel‐like aspect of a miscible polymer mixture studied by small‐angle neutron scattering

AbstractBy employing small‐angle neutron scattering (SANS), we have investigated a miscible mixture of polystyrene (PS) and poly(vinyl methyl ether) (PVME) to answer the question of what a gel state is. The large difference in the glass‐transition temperatures (Tg's) of PS and PVME uniquely enhances dynamic asymmetry by a temperature change. In an intermediate temperature range between the two Tg's, SANS reveals two interesting findings: (1) the anomalous suppression of small‐angle scattering in a quiescent state and (2) an abnormal butterfly scattering pattern due to shear‐induced phase separation. In this temperature region, we have further confirmed experimentally that the mixture behaves in a gel‐like limit at which concentration fluctuations relax more quickly than rheological relaxation. With the gel‐like limit and enhanced dynamic asymmetry, which is required for the gel state, our two SANS findings can be interpreted within the theoretical framework of dynamical coupling between stress and diffusion. For comparison, we have studied a swollen real chemical gel of poly(N‐isopropyl acrylamide), in which covalent bonds crosslink chains heterogeneously. A combined method of SANS and neutron spin echo has been used to quantitatively determine the static inhomogeneity, which gives rise to a structure factor of a squared Lorentzian shape. The static inhomogeneity is closely related to the nonergodic feature of excess scattering when the gel is subjected to swelling or nondecaying abnormal butterfly scattering under deformation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3148–3164, 2004