Application of the digital matched-filter technique to ultrasonic non-destructive testing

Acoustic-pulse compression is obtained in systems with different timebandwidth products by applying the digital matched-filter technique to ultrasonic non-destructive testing. The signal is linearly frequency -modulated (LFM) pulse and the digitized electrical-excitation signal itself is used as a digital matched filter. Experimental results are in good agreement with theory. Suppressions of side lobes achieve -41.9 dB and -41.5 dB for the Hamming and Gaussian weighted signals respectively. It shows that the application of the digital matched-filter technique improves the performances of a ultrasonic testing system explicitly.

Outage Probability and Achievable Rate Analysis for Massive MIMO Downlink with Mixed-DAC and MF Precoding

This paper analyses of the outage probability and the achievable rate of massive multi-input-multi-output(MIMO) systems, in which the base station(BS) is equipped with digital-to-analog-converters(DACs) of mixed-level resolution. And the matched-filter(MF) precoding is used on the BS. Closedform expressions are derived by the distribution of user-interference power and other statistical properties in the signal-to-interference-plus-noise-ratio. Then, the combination of mixed-DACs resolution profile is chosen about outage probability and achievable rate with the BS energy consumption. And the resolution configurations between the outage probability and the achievable rate and the BS energy consumption are given. Meanwhile, Effects of related parameters and channel errors are analysed about outage probability and achievable rate. The numerical results show that the correctness of the formula derivations. As the number of users increases the system's achievable rate increases and the outage probability decreases. The selected resolution configuration system has better comprehensive performance.

Near-field triggering of microearthquakes along the Longitudinal Valley fault in eastern Taiwan

Dynamic earthquake triggering as a well-documented phenomenon can provide valuable information for studying the stress loading cycle from failure on faults.In this study,seismicity rate changes were investigated in the Longitudinal Valley fault(LVF)following the 2019 M_(L)5.2 Hualien earthquake,which occurred offshore in eastern Taiwan.After the matched filter technique was applied to continuous waveform data,twice as many microearthquakes were newly detected in the vicinity of the LVF compared with the number listed in the Taiwan Weather Bureau catalog.Seismicity rates in the northern segment of the LVF increased immediately following the Hualien mainshock,which indicated dynamic triggering during the passage of seismic waves.Statistical analysis suggested that following seismic events might be attributed to fault slipping or creeping.These findings show that the observation of earthquake triggering can provide valuable assistance in monitoring the stress perturbations of active faults.

Data replenishment of five moderate earthquake sequences in Japan, with semi-automatic cluster selection

Missing early aftershocks following relatively large or moderate earthquakes can cause significant bias in the analysis of seismic catalogs.In this paper,we systematically address the aftershock missing problem for five earthquake sequences associated with moderate-size events that occurred inland Japan,by using a stochastic replenishing method.The method is based on the notion that if a point process(e.g.,earthquake sequence)with timeindependent marks(e.g.,magnitudes)is completely observed,it can be transformed into a homogeneous Poisson process by a bi-scale empirical transformation.We use the Japan Meteorological Agency(JMA)earthquake catalog to select the aftershock data and replenish the missing early events using the later complete part of each aftershock sequence.The time windows for each sequence span from 6 months before the mainshock to three months after.The semi-automatic spatial selection uses a clustering method for the epicentral selection of earthquakes.The results obtained for the original JMA catalog and replenished datasets are compared to get insight into the biases that the missing early aftershocks may cause on the Omori-Utsu law parameters’estimation,characterizing the aftershock decay with time from the mainshock.We have also compared the Omori-Utsu law parameter estimates for two datasets following the same mainshock;the first dataset is the replenished sequence,while the second dataset has been obtained by waveform-based analysis to detect early aftershocks that are not recorded in the JMA catalog.Our results demonstrate that the Omori-Utsu law parameters estimated for the replenished datasets are robust with respect to the threshold magnitude used for the analyzed datasets.Even when using aftershock time windows as short as three days,the replenished datasets provide stable Omori-Utsu law parameter estimations.The p-values for all the analyzed sequences are about 1.1 and c-values are significantly smaller compared to those of original datasets.Our findings prove that the replenishment method is a fast,reliable approach to address the missing aftershock problem.

Characteristics of the AE Distribution and Triggering Mechanism of a Simulated Meter-Scale Fault after Stick-Slip Events

With the more complete acoustic emission(AE)catalog improved by the multi-channel AE matched-filter technique(MFT),we study the spatiotemporal evolution of the AE activities after laboratory stick-slip events incorporate with the slip data recorded by displacement transducers on an^1.5 m granite fault.The results show that the number of the AE events identified by MFT is about 9 times larger than that of the traditional method.A logarithmic expansion of early AE events along the fault strike is observed as a function of time,whereas the fault does not slip in the same manner.Thus,we related the expansion of the early AE events along the fault to the stress transfer caused by the adjacent AE events.Moreover,there is a good correlation between the cumulative number of the later AE events and the amount of fault slip.It suggests that the stress change caused by the continuous slip of the simulated fault after the stick-slip events response for the later AE events near or on the simulated fault.

3D S-Wave Velocity Structure of the Crust and Upper Mantle

In this paper, 238 Rayleigh wave path data are selected and processed by the matched-filtering frequency-time analysis technique and the grid dispersion inversion method to obtain the 3D S-wave velocity structure of China mainland and its adjacent sea regions. The results show that the velocity structure relates to geotectonic division, Bouguer gravity anomaly is basically controlled by the relief of Moho discontinuity, the buried depth of LVL in upper mantle concerns the surface heat flow deeply. In this paper, authors indicate the main characteristics of the velocity structure in tectonic active and stable regions.