Time-domain Pulse Research Articles

Time-domain acceleration-based pulse characterization of 2023 Kahramanmaraş earthquakes

Time-domain acceleration-based pulse characterization of 2023 Kahramanmaraş earthquakes

Nondestructive testing of chips faults based on Terahertz pulse time-domain reflection technology

Traditional methods for defect and fault detection in integrated chips have various shortcomings. This study uses terahertz pulse time-domain reflection technology to detect two types of packaged chips with unknown faults and microstrip circuit chips with multiple open circuit faults from different manufacturers. It has achieved qualitative discrimination of internal fault types in packaged chips and precise positioning of fault locations in microstrip circuit wires. When the length of the test line is 27mm, the positioning error is only 1 %. The research results indicate that terahertz pulse time-domain reflection technology has the ability to detect internal faults in integrated chips.

The Relation between Soil Moisture Phase Transitions and Soil Pore Structure under Freeze–Thaw Cycling

The process of soil moisture phase transitions (SMPT) under freeze–thaw cycling is considered a key factor driving changes in soil pore structure. However, there is still no consensus on which indicators related to SMPT affect the soil pore structure. The objectives of this study were to compare SMPT and soil pore characteristics under freeze–thaw cycling, and to analyze the inherent relationship between them as affected by different bulk densities. Hence, we employed thermal pulse time-domain reflection technology (T-TDR) and X-ray CT scanning technology (X-CT) to quantitatively study the process of SMPT and pore characteristics of soil core samples (60 mm diameter, 100 mm height) repacked with three different bulk density levels: 1.10 g·cm−3 (NC), 1.30 g·cm−3 (LC) and their combination (1.10 g·cm−3 for upper half, 1.30 g·cm−3 for lower half, SC) under freeze–thaw cycling. Our results showed that compared with NC, the porosity of LC’s 0–5 cm soil column decreased by 0.070 cm3·cm−3, the imaged porosity (ϕ>60μm) decreased by 0.034 cm3·cm−3, and the maximum soil ice content (MIC) decreased by 0.030 cm3·cm−3. The pores within the range of 200−300 mm (ϕ2) and 300–400 mm (ϕ3) contribute the most significantly to ϕ>60μm (50–60%). Soil initial moisture content (IMC) and MIC explained 50.1% of the change in ϕ2, and the bulk density explained 49.3% of the change in ϕ3. During the melting process, higher moisture content promotes the thaw collapse of soil particles, resulting in a decrease in ϕ>60μm. The mean pore radius of the limiting layer (MRLL) and the hydraulic radius (HR) show that changes in bulk density from 1.10 g·cm−3 to 1.30 g·cm−3 do not have significant differences. Our results show the relationship between SMPT and pore structure change during freeze–thaw cycles as affected by initial soil bulk density and moisture condition.

Half-Wave Voltage Measurement Method Based on SI and Time-Domain Pulse Intensity Demodulation

Half-Wave Voltage Measurement Method Based on SI and Time-Domain Pulse Intensity Demodulation

Quantum correlation and squeezing in pulses propagating in dispersion oscillating fibers

We consider the squeezing and correlation of quantum fluctuations in pulse pairs arising due to soliton fission in dispersion oscillating fibers. The dispersion oscillation acts as a time-domain pulse splitter. After the split, the pulses interact via their tails and acquire nonzero correlations. We analyze the correlation pattern using Karhunen–Loève mode expansion. The regime of high intrapulse and interpulse correlations can be described using single Karhunen–Loève mode. The regime with partial pulse-to-pulse correlation requires to take into account at least two Karhunen–Loève modes. We found that the soliton fission in dispersion oscillating fibers allows to generate squeezed states with highly correlated fluctuations in the output pulses.

Risk prediction of pulse wave for hypertensive target organ damage based on frequency-domain feature map

The application of deep learning to the classification of pulse waves in Traditional Chinese Medicine (TCM) related to hypertensive target organ damage (TOD) is hindered by challenges such as low classification accuracy and inadequate generalization performance. To address these challenges, we introduce a lightweight transfer learning model named MobileNetV2SCP. This model transforms time-domain pulse waves into 36-dimensional frequency-domain waveform feature maps and establishes a dedicated pre-training network based on these maps to enhance the learning capability for small samples. To improve global feature correlation, we incorporate a novel fusion attention mechanism (SAS) into the inverted residual structure, along with the utilization of 3 × 3 convolutional layers and BatchNorm layers to mitigate model overfitting. The proposed model is evaluated using cross-validation results from 805 cases of pulse waves associated with hypertensive TOD. The assessment metrics, including Accuracy (92.74 %), F1-score (91.47 %), and Area Under Curve (AUC) (97.12 %), demonstrate superior classification accuracy and generalization performance compared to various state-of-the-art models. Furthermore, this study investigates the correlations between time-domain and frequency-domain features in pulse waves and their classification in hypertensive TOD. It analyzes key factors influencing pulse wave classification, providing valuable insights for the clinical diagnosis of TOD.

TIPS-pentacene organic field-effect transistor for optoelectronic neuromorphic simulation

Biological learning and memory of visual information are carried out through the regulation of synaptic weight by visual neuron synapses. Replicating the cognitive processes and light-induced adaptability of the human brain holds immense significance for the advancement of artificial intelligence. Here, we propose an organic photoelectric synaptic transistor based on 6,13-bis(triisopropylsilylethynyl) pentacene. The device showcases a memory window greater than 20 V and current on/off ratio of 106. Synaptic behavior transition is exhibited from short-term plasticity to long-term plasticity under photoelectric pulse modulation, including paired-pulse facilitation, spike time dependent plasticity, spike number dependent plasticity and optical enhancement/electrical inhibition. In addition, we simulate the learning and adaptation process of the synaptic device after long-term light stimulation, and recognize visual information by perceiving light pulses in different time domains.

Time Domain Simulated Characterization of the Coplanar Waveguide in an On-Chip System for Millimeter Waveform Metrology

We investigate the time domain characterization of a coplanar waveguide (CPW) based on an on-chip electro-optic sampling (EOS) system for millimeter waveform metrology. The CPW is fabricated on a thin layer of low-temperature gallium arsenide (LT-GaAs), and the substrate material is GaAs. A femtosecond laser generates and detects ultrashort pulses on the CPW. The forward propagating pulses are simulated using a simplified current source for the femtosecond laser at different positions on the CPW for the first time. Then, the influences of the CPW geometry parameters on the measured pulses are discussed. The varying slot width has larger influences on the amplitude of millimeter wave pulses than the center conductor width and the pumping gap. Finally, in the frequency range of 10 GHz to 500 GHz, the transfer functions calculated by the time domain pulses are in good agreement with the transfer functions calculated by the frequency domain ports. The above results are important for improving the measurement precision of the millimeter waveform on the CPW for millimeter waveform metrology.

Highly precise timing alignment of multi-wavelength interleaved cavity-less pulse sources with FROG.

Strictly uniform time interval between adjacent channels is a crucial requirement for the multi-wavelength interleaved (MWI) pulse sources, which difficult alignment can be easily solved by what we believe to be our novel method based on frequency-resolved optical gating (FROG). By utilizing highly precise measurements from FROG, which provide fully two-dimensional information of the pulses in time and frequency domain, we can intuitively identify the time mismatches between different channels in the MWI pulse sources. This enables us to directly align the timing of each channel with sub-picosecond resolution at the first time. MWI pulse sources with total repetition rate of 20.8 GHz (four wavelengths) and 41.6 GHz (eight wavelengths) are precisely aligned by the proposed method, this achievement will pave the way for advancements in photonic analog-digital converters (PADC), high-speed optical communications and so on.

Time domain response of corrugated transmission lines

AbstractIn order to employ periodic corrugated microstrip lines for reducing or suppressing electromagnetic interference in high‐speed or high‐frequency circuits, a precise method is necessary to calculate and measure the characteristic impedance of periodic microstrip lines. The equation for characteristic impedance (depending on frequency) of lossless periodic microstrip lines was obtained based on the transfer matrix method. A time domain pulse was used to measure the instantaneous impedance of conventional microstrip lines, and when the instantaneous impedance does not change with distance, it can be identified as the characteristic impedance of microstrip lines. However, when the time‐domain pulses are employed to measure the instantaneous impedance of periodic microstrip lines, rapid oscillations occur with distance. Therefore, a standard for spacing between adjacent grooves in the microstrip line can be suggested by analysing the interaction between the time‐domain pulses and the microstrip line grooves. Once such a standard is satisfied, many grooves etched along the microstrip line would no longer be distinguished by the time‐domain pulses. Such a principle and method can be used to determine the instantaneous impedance for the microstrip lines that have periodic grooves. On the other hand, when several periodic structures with different lattice constants coexist on a microstrip line, they can also be distinguished via the instantaneous impedance. A time domain reflectometer was used for measuring the instantaneous impedance of periodic microstrip lines, and the measured results are in agreement with the theoretical analysis.

Use of Stepped Carrier Frequency in Fast Scan Mode to Detect Small Targets on the Sea Surface

To detect a small target on the sea surface, we propose a detection algorithm that operates in three steps: (1) representation of three-dimensional complex cube in the (radial range, pulse time, scan time) domain by using stepped carrier frequency in fast scan mode; (2) intrascan integration to transform complex cube from the pulse time domain to the radial velocity domain by using Fourier transform; and (3) interscan integration to detect a small target by using a conventional optimal coherent detector with a Fourier relationship between stepped carrier frequency and initial radial range, and a discriminator between a true target and false targets. The proposed method improves the ability to detect of a small target, and reduces the sensitivity to sea clutter despite relatively low radial range resolution. In experiments, our proposed method could perform accurate and robust detection of a small target.

Research on simulation method for nonlinear effects of airborne SAR electromagnetic interference

In order to simulate the nonlinear interference effect of high-power electromagnetic signals on airborne Synthetic Aperture Radar (SAR) imaging, the walk–stop geometric modeling of airborne SAR was established, and the range time-domain pulse coherence method was used to simulate SAR echo. By establishing a SAR receiver RF channel model, the interference mechanism of high-power electromagnetic signals is combined on RF front-end devices, the nonlinear effects on the echo signal when high-power electromagnetic signals enter the receiver are simulated, and finally the range Doppler algorithm is used to image the echo signal and the interference signal. A method for evaluating the interference effect of high-power electromagnetic signals on airborne SAR imaging using the correlation coefficient of images was proposed. The results showed that the change in the correlation coefficient of images before and after interference relative to the interference signal ratio was consistent with the image interference effect. The correlation coefficient showed a stepped trend with the change in the interference signal ratio, and there was a saturation effect after the interference effect reached a certain level.

Precise Multiple Frequency Identification Based on Frequency-to-Time Mapping and Cross-Correlation

We propose and demonstrate a microwave frequency identification system based on frequency-to-time mapping (FTTM) and cross-correlation. The unknown microwave signals and the bidirectional chirped microwave probe signal are mixed by using a dual-drive Mach-Zehnder modulator. The mixing products are equivalently selected by a dispersion induced photonic filter and converted into electrical pulses in time domain. The unknown frequency is measured by calculating the time interval of the pulses. Moreover, a scheme based on cross-correlation is proposed to eliminate the noise interference for the pulse position acquisition. Experimentally, single and multiple frequency identification from 2-14 GHz is successfully demonstrated, and the measured frequency errors are less than ±3 MHz.

Ultrafast anisotropic dynamics of hyperbolic nanolight pulse propagation.

Polariton pulses-transient light-matter hybrid excitations-traveling through anisotropic media can lead to unusual optical phenomena in space and time. However, studying these pulses presents challenges with their anisotropic, ultrafast, and nanoscale field variations. Here, we demonstrate the creation, observation, and control of polariton pulses, with in-plane hyperbolic dispersion, on anisotropic crystal surfaces by using a time-resolved nanoimaging technique and our developed high-dimensional data processing. We capture and analyze movies of distinctive pulse spatiotemporal dynamics, including curved ultraslow energy flow trajectories, anisotropic dissipation, and dynamical misalignment between phase and group velocities. Our approach enables analysis of polariton pulses in the wave vector time domain, demonstrating a time-domain polaritonic topological transition from lenticular to hyperbolic dispersion contours and the ability to study the polariton-induced time-varying optical forces. Our findings promise to facilitate the study of diverse space-time phenomena at extreme scales and drive advances in ultrafast nanoimaging.

Progress in application of terahertz time-domain spectroscopy for pharmaceutical analyses.

Terahertz time-domain spectroscopy is an analytical method using terahertz time-domain pulses to study the physical and chemical properties of substances. It has strong potential for application in pharmaceutical analyses as an original non-destructive, efficient and convenient technology for spectral detection. This review briefly introduces the working principle of terahertz time-domain spectroscopy technology, focuses on the research achievements of this technology in analyses of chemical drugs, traditional Chinese medicine and biological drugs in the past decade. We also reveal the scientific feasibility of practical application of terahertz time-domain spectroscopy for pharmaceutical detection. Finally, we discuss the problems in practical application of terahertz time-domain spectroscopy technology, and the prospect of further development of this technology in pharmaceutical analyses. We hope that this review can provide a reference for application of terahertz time-domain spectroscopy technology in pharmaceutical analyses in the future.

Wave scattering by an array of moored floating flexible plates resting on an elastic foundation in the reference of blocking dynamics

Surface gravity wave scattering by an array of floating flexible plates having free/moored edges and resting on a Winkler foundation are studied within the framework of flexural gravity wave blocking. The impact of the floating plates having moored edges compared to that of free edges along with the occurrences of Bragg reflection are analyzed. The study reveals that wave reflection is oscillatory in nature irrespective of the number of plates. Further, the amplitude of wave reflection increases for smaller frequency and decreases for higher frequency in the presence of Winkler foundation. The study depicts the occurrences of removable discontinuities at the blocking frequencies and the existence of a smaller number of extrema in wave reflection outside the blocking limits than within the said limits. Besides, the number of sub-harmonic peaks between two consecutive harmonic peaks in wave reflection depends on the wave frequency, plate length and gap between the consecutive plates. Moreover, the free surface elevations and the floating plate deflections exhibit certain irregularity within the blocking frequencies. The free surface elevation and floating plate deflection in the presence of compressive force wave blocking exhibit the recurrence of scattering of wave pulses in the linear time domain.

All-optical digital-to-analog conversion based on time-domain pulse spectrum encoding

An all-optical digital-to-analog conversion (DAC) scheme based on time-domain pulse spectrum encoding is proposed and experimentally demonstrated. In this approach, the ultrafast optical pulses are first time-broadened and frequency-chirped based on wavelength-to-time mapping and then segmented and power weighted in both time and spectrum domains to produce the multi-band optical carrier. The optical carrier is intensity-modulated by the serial digital inputs to realize the time-domain pulse spectrum encoding. Each spectrum-encoded pulse is then time-compressed to achieve the incoherent weighted intensity summation of digital bits within each word. This approach generates the multi-band optical carrier and achieves the corresponding incoherent intensity summation using all-fiber structure; the system configuration is greatly simplified. Moreover, the time-domain pulse spectrum encoding could efficiently exploit the superwide spectrum resource offered by ultrafast optical pulses and potentially improve the system conversion resolution. A proof-of-concept experiment of a 4-bit DAC system based on time-domain pulse spectrum encoding is carried out, and the obtained results validate the feasibility of the proposed approach. In addition, the system performance in terms of the effective number of bits is investigated.

Design and experiment of broadband electric field sensor for high-power sub-nanosecond pulse measurements

This paper briefly introduces the structure and working principle of the electric field sensor. And a conductive electric field sensor for measuring sub-nanosecond voltage pulse is designed. The sensor consists of coaxial transition section and integrated electric field probe. N-type connector and SMA connector are selected for input/direct output port and coupling output port respectively. The equivalent antenna area of electric field sensor measured by vector network analyzer is about 0.035cm2, and the 3dB bandwidth is more than 5GHz. The results show that the sensor can accurately measure the time-domain voltage pulse produced by the sub-nanosecond solid-state sources.

Prediction of pulse wave of target organ damage in hypertension based on multiple feature fusion

With respect to less efficiency and low accuracy of predicting on hypertensive target organ damage, this article proposes a fusion prediction model combining pulse-taking with inquiry diagnosis of traditional Chinese medicine to accomplish the efficient and non-invasive diagnosis. Regarding the class imbalance of inquiry diagnosis samples, an Eliminated random forest algorithm is proposed to select efficient features and reduce the impact of class imbalance on classification performance via cluster-based under-sampling algorithm. As to low discriminability of hypertensive time-domain pulse wave samples, time-domain pulse wave is transformed to the frequency-domain MFCC feature maps, and fuse feature maps of inquiry diagnosis scale for predicting hypertension target organ damage. In the article, the clinical 608 cases of hypertensive target organ damage are from Longhua Hospital affiliated to Shanghai University of Chinese Medicine and Hospital of Integrated Traditional Chinese and Western Medicine concerning pulse-taking and inquiry diagnosis. The evaluation indicators of 5-Fold cross-validation classification, i.e. F1-score, Accuracy, Precision, Sensitivity, AUC, are 97.31%, 98.72%, 97.71%, 97.04%, 99.13% respectively, which are higher than those of the other typical models. In addition, this article also studies the correlation between classification of pulse-taking or inquiry diagnosis and its features, and analyzes the feature importance ranking on pulse-taking and inquiry diagnosis, which aids clinicians to seek the occurrence mechanisms of hypertensive target organ damage, and find the effective measurements for timely prevention and treatment.

Real-Time Evaluation of Time-Domain Pulse Rate Variability Parameters in Different Postures and Breathing Patterns Using Wireless Photoplethysmography Sensor: Towards Remote Healthcare in Low-Resource Communities.

Photoplethysmography (PPG) signals have been widely used in evaluating cardiovascular biomarkers, however, there is a lack of in-depth understanding of the remote usage of this technology and its viability for underdeveloped countries. This study aims to quantitatively evaluate the performance of a low-cost wireless PPG device in detecting ultra-short-term time-domain pulse rate variability (PRV) parameters in different postures and breathing patterns. A total of 30 healthy subjects were recruited. ECG and PPG signals were simultaneously recorded in 3 min using miniaturized wearable sensors. Four heart rate variability (HRV) and PRV parameters were extracted from ECG and PPG signals, respectively, and compared using analysis of variance (ANOVA) or Scheirer-Ray-Hare test with post hoc analysis. In addition, the data loss was calculated as the percentage of missing sampling points. Posture did not present statistical differences across the PRV parameters but a statistical difference between indicators was found. Strong variation was found for the RMSSD indicator in the standing posture. The sitting position in both breathing patterns demonstrated the lowest data loss (1.0 ± 0.6 and 1.0 ± 0.7) and the lowest percentage of different factors for all indicators. The usage of commercial PPG and BLE devices can allow the reliable extraction of the PPG signal and PRV indicators in real time.