Spatial Azimuth Research Articles

Spatiotemporal energy regulation strategy for enhancing SNR and spatial resolution in the damage detection with SH0 waves

The fundamental shear horizontal (SH0) wave, which can be generated by electromagnetic acoustic transducers (EMATs), is widely used in the structural health monitoring fields owing to its non-dispersive nature and the ability to detect over long distances. However, current SH0 wave methods hardly achieve the excellent signal-to-noise ratio (SNR) of the echo signals and satisfactory spatial resolution to defects due to the co-restriction between them. To address these issues, a spatiotemporal energy regulation strategy (STERS) is proposed in this paper to optimize energy distribution in the temporal and spatial dimensions. First, spatiotemporal pulse compression technology (STPCT) is proposed to improve both SNR and spatial range resolution for defect detection. Second, a staggered dual-exciter employing two sets of excitation signals is designed to improve the spatial azimuth resolution. Besides, a double sidelobe suppression algorithm (DSSA) is proposed to suppress sidelobe issues arising from the application of STPCT, thereby further improving the performance of STPCT. Finally, multiple simulations and experiments are executed to demonstrate the advantages of the proposed damage detection system. Results show that our methods can achieve comprehensive improvement in SNR, spatial range resolution, spatial azimuth resolution, and sidelobe suppression ability.

Spatial positioning method based on UWB antenna array layout

Aiming at the problem of spatial positioning of dynamic targets in traditional power systems, this paper provides a cost controllable and high precision UWB antenna array layout method for spatial positioning to solve the problems of low precision and multiple restrictions of ultra wideband in spatial environment. First, a base station is set in each area. The base station contains a group of UWB antenna arrays composed of multiple antenna pairs. The distance L from the base station with the location tag is accurately measured through the UWB. Then, the UWB antenna array uses the PDOA phase difference principle to measure the direction of the signal. Finally, the spatial azimuth of the UWB signal from the tag to be located relative to the base station is calculated. The feasibility of the proposed method is verified by an example, which can significantly improve the positioning accuracy. The proposed method can provide strong technical support for intelligent operation and maintenance of power system and safe production.

Quantification of rupture directivity effects on strong ground motion during the 8 January 2022 MS6.9 Menyuan earthquake in Qinghai, China

On 8 January 2022, an MS6.9 earthquake occurred in the Menyuan county, Qinghai province at the northeastern margin of the Tibetan Plateau. A dense observatory network consisting of accelerographs and intensity meters has obtained many acceleration recordings in this region, which previously had only a few strong motion recordings. Using acceleration data recorded by 141 accelerographs and micro-electro mechanical system (MEMS)-based intensity meters within 100 km of the causative fault, we investigated the spatial distribution and attenuation characteristics of the near-source ground motion during this event. The observed response spectra were compared with the prediction obtained using the NGA-West2 models. It was found that, in the long-period section of >1.0 s, the acceleration response spectra in the rupture forward direction (southeast of the epicenter) were greater than the prediction, while observations on the northwest side were lower than the prediction. Through the spatial distribution of the ground motion and quantitative analysis of the residuals, we found that the rupture directivity effects on the ground motions were controlled by the spatial azimuth relative to the fault and the along-strike projected length of the rupture, which mainly affected the long-period portion of the >1.0 s. In the rupture forward direction, the spectral accelerations (SAs) with periods of 1.0–10.0 s were enhanced to 1.18–1.56 times the average. In the backward direction (northwest of the epicenter), the SAs with periods of 1.0–10.0 s were only 0.63–0.86 times the average. The rupture directivity effects during the MS6.9 (MW6.6) earthquake exhibited an obvious period-dependence and narrowband characteristics, and the amplification effects were the strongest at 5.0 s. The amplification factors in the straight forward directions were underestimated by the empirical model. Two typical velocity pulse records were observed in the rupture forward direction, and their response spectra were significantly amplified at long periods of greater than 1.0 s, with peak amplification values of 4.0–6.0 near the characteristic period of the pulses. This amplification was related to the resonance excited by a specific periodic pulse. Our study provides a reference of quantifying near-source effects for both moderate and major shallow crustal earthquakes by using MEMS recordings in this region.

Experimental study on explosion overpressure and flame propagation characteristics of simulated vertical dome oil tank

In order to study the development law of gasoline-air mixture explosion in vertical dome oil tank, a series of experiments are carried out in simulated oil tank. It is found that the development of overpressure in internal field can be divided into three stages: the overpressure rising stage, the overpressure relief stage and the overpressure oscillation and attenuation stage. The maximum overpressure peak, average overpressure rise rate and maximum overpressure rise rate in internal field all increase first and then decrease with the increase of gasoline vapor volume fraction. However, the formation time of the maximum overpressure peak, the maximum negative overpressure and the average pressure relief rate have opposite numerical trends. All of these peaked at the initial gasoline vapor volume fraction of 1.7%. The external field pressure wave of gasoline-air mixture explosion has a great relationship with spatial azimuth. With the increase of proportional distance, the pressure wave of external field at any angle shows the exponential decay law in form of Pext=kR−α. The relationship among the maximum overpressure peak, distance and direction can be uniformly expressed by a formula. With the increase of gasoline vapor volume fraction, the maximum overpressure peak at the nearest measurement point in the direction of dome opening increases first and then decreases, and the formation time of the maximum overpressure peak changes in the opposite trend, which can be expressed by cubic polynomials. The flame propagation of gasoline-air mixture explosion can be divided into three stages: the in-tank development stage, the vent explosion stage and the free burning stage. In addition, affected by fluid instability during explosion propagation, the positive feedback mechanism makes the development of explosion more and more intense.

Super-resolution performance studies for orbital-angular-momentum-based imaging radar

ABSTRACT Vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM), whose unique wavefront distribution exhibits angular diversity characteristics, which provides a richer degree of freedom for information modulation. Although several works have reported that the EM vortex imaging has superior performance in target detection and imaging with azimuthal super-resolution, the underlying physical mechanism needs to be further developed. This article offers a solution to significantly refine the imaging resolution for conventional real-aperture imaging radar (CRAIR) using multiple OAM-carrying beams. Firstly, it is deduced that the various spatial frequency distributions and time-varying phase wavefront distributions of OAM beams promote the realization of OAM-based imaging radar (OAMIR) super-resolution imaging. Secondly, a scheme for adjusting the directivity of EM vortex beam is proposed, which can effectively acquire most spatial frequency components of the probed target, resulting in the target can be illuminated simultaneously by the main lobes of various beams carrying different topological charges. Thirdly, the point-spread function (PSF) comparison for CRAIR and OAMIR is carried out by theoretical analysis and numerical simulation, and the spatial azimuth resolution for OAMIR is derived. Finally, the signal mathematical model for OAMIR is established and analysed. Simulation results validate that the proposed OAM-based imaging paradigm breaks through the Rayleigh limit associated with conventional real-aperture imaging technology and achieves imaging performance superior to OAMIR in previous works.

The application rule of half-wave signal magneto-optical modulation in spatial azimuth measurement

The purpose of this study is to summarize the application rule of half-wave signal magneto-optical modulation in azimuth measurement, and obtain the limit on modulation signal when establishing the azimuth measurement model. After analysis on the azimuth measurement system principle, the model of modulated signal are present according to Malous law, the application feasibility of the four half-wave signal magneto-optical modulation in azimuth measurement are discussed respectively, the azimuth measurement models based on mixed signal are present, and the reason why the AC signal cannot be used to establish the azimuth measurement model is analyzed.

The application rule of simple symmetrical wave signal magneto-optical modulation in spatial azimuth measurement

The purpose of the study is to summarize the application rule of sine wave and other simple symmetrical wave signal magneto-optical modulation in azimuth measurement, and acquire the limit on modulation signal when establishing azimuth measurement model. Firstly, we analyze the principle of traditional azimuth measurement system based on sine wave signal magneto-optical modulation, and establish the error free measurement model based on trigonometric function, after that we present the measurement models based on mixed signal with tangent, cosine and sine function, respectively. Secondly, we discuss the application feasibility of rectangle wave, triangle wave and sawtooth wave signal magneto-optical modulation in azimuth measurement respectively, and establish the azimuth measurement models based on rectangle wave and triangle wave signal modulation respectively, and analyze the reason why the sawtooth wave signal modulation cannot be applied in the azimuth measurement. Finally, we summarize the four simple signal magneto-optical modulation and acquire the requirements on modulation signal when establishing the azimuth measurement model based on simple wave single magneto-optical modulation. The study has an important guiding significance on the application of simple symmetrical wave magneto-optical modulation in azimuth measurement.

Spatial angular positioning device with three-dimensional magnetoelectric sensors

This paper reports on the development of a novel simple three-dimensional geomagnetic device for sensing the spatial azimuth and pitch positions by using three one-dimensional magnetoelectric sensors assembled along three orthogonal axes. This sensing device combines piezoelectric transducer plates and elongated high-performance Ni-based Metglas ribbons. It allows the simultaneous detection of all three orthogonal components of the terrestrial magnetic field. Output signals from the device components are provided in form of sine and/or cosine functions of both the rotation azimuth and the pitch angles, from which the total intensity as well as the inclination angle of the Earth's magnetic field is determined in an overall field resolution of better than 10(-4) Oe and an angle precision of ±0.1°, respectively. This simple and low-cost geomagnetic-field device is promising for the automatic determination and control of the mobile transceiver antenna's orientation with respect to the position of the related geostationary satellite.

基于正弦波磁光调制的空间方位失调角传递技术的改进

To enlarge the transmission scale and improve the transmission precision of an azimuth transmission system based on sine wave magneto-optic modulation,a new method of transmitting the azimuth in a large-scale and high-precision was established.The principle of the current azimuth transmission system was analyzed,and a double-angle formula was introduced to enlarge the transmission scale.A model to measure the azimuth was established according to analyzing the relationship between the azimuth and the extremum of the modulated light,and the measurement model was expatiated by comparing the extremums.A integrated method combined the approximation in little-scale with the looking-up table in large-scale was presented to calculate the arc tangent function in the model.Simulation results indicate that the theoretic transmission scale is widened obviously and the precision is improved.Experiment results show that the actual transmission scale is-64-64° and the transmission error is under 10″,which is better than those of the current methods.The method provides a new way to transmit the spatial azimuth in large-scales and high-precision.

利用原始光强信号实现空间方位失调角高精度传递新方法

利用原始光强信号实现空间方位失调角高精度传递新方法

基于磁光调制偏振光的空间方位失调角高精度测量新方法

基于磁光调制偏振光的空间方位失调角高精度测量新方法

Multibeam synthetic aperture radar for global oceanography

A single-frequency multibeam synthetic aperture radar concept for large swath imaging desired for global oceanography is evaluated. Each beam illuminates a separate range and azimuth interval, and images for different beams may be separated on the basis of the Doppler spectrum of the beams or their spatial azimuth separation in the image plane of the radar processor. The azimuth resolution of the radar system is selected so that the Doppler spectrum of each beam does not interfere with the Doppler foldover due to the finite pulse repetition frequency of the radar system.

The antipodal normal section

The geometry of the ellipse of normal section is studied in relation to widely separated points on the spheroid of reference. It is found that antipodal regions exist where spatial azimuth becomes inconsistent with the shorter surface distance of the normal section arc. A target height correction of 180o becomes apparent. An antipodal region for the chord is also investigated, this being where the method of determining position by means of chord length and spatial azimuth can lead to two solutions and is therefore not satisfactory.