Impulse Response Time Research Articles

Accurate Measurement of Frozen Soil Depth Based on I-TDR

In this study, a new method for determining the depth of frozen soil, Impulse Response Time Domain Reflectometry, is discussed. This method uses the principle of impedance measurement and the law of time–frequency domain convolution to convert the frequency-domain reflection signal into a time-domain signal and accurately determines the soil freezing front by measuring the difference between the impedance of frozen soil and unfrozen soil. The advantage of this method is that it solves the problems of small bandwidth, long rising edge time, and large measurement errors in the traditional TDR method to effectively improve the measurement accuracy of the soil-freezing front. Under laboratory conditions, soils of different textures (sand, loess, black soil, and red soil) were selected for experimental determination, and the results showed that compared with the traditional TDR method, the RMSE of the I-TDR method was small, and the method was applicable under different soil texture conditions, which could provide a new method for monitoring frozen soil in cold areas. In addition, the application of this method has important guiding significance for improving the efficiency of winter irrigation water, especially for guiding agricultural production, farmland irrigation, drainage engineering construction, meteorological frozen soil monitoring, and other aspects in cold and arid areas.

An unsupervised learning damage diagnosis method based on virtual impulse response function and time series models

As it contains the inherent properties of the structure and is insensitive to variation of the input, the transmissibility function (TF) is widely used for structural damage detection under ambient excitation. However, in TF-based methods, the selection of the optimal damage sensitivity band often requires access to vibration data under different operating conditions, which is not conducive to unsupervised learning. In order to accommodate unsupervised learning and extract more damage information, this paper proposes a data-driven unsupervised damage detection method based on the virtual impulse response function (VIRF) and time series model (TSM). In this method, the VIRF is used as a damage-sensitive feature (DSF), the TSM is used for low-dimensional feature extraction of the VIRF, and the distance metric of the model coefficients is used to detect the occurrence of anomalies. The study analyses the type of TSM applied to VIRF and uses the parameter adjusted cosine similarity (PACS) as a more accurate statistical distance tool for the model coefficients. The application of two well-known benchmark structure experiments verifies the accuracy and practicality of the proposed method in damage detection under minor operational variations and ambient excitations. The comparative analysis and detection results indicate that the proposed method is advantageous in qualitatively quantifying the extent of the damage. Structural anomalies can be detected in both linear and nonlinear damage scenarios.

The impulse response of optic flow-sensitive descending neurons to roll m-sequences.

ABSTRACTWhen animals move through the world, their own movements generate widefield optic flow across their eyes. In insects, such widefield motion is encoded by optic lobe neurons. These lobula plate tangential cells (LPTCs) synapse with optic flow-sensitive descending neurons, which in turn project to areas that control neck, wing and leg movements. As the descending neurons play a role in sensorimotor transformation, it is important to understand their spatio-temporal response properties. Recent work shows that a relatively fast and efficient way to quantify such response properties is to use m-sequences or other white noise techniques. Therefore, here we used m-sequences to quantify the impulse responses of optic flow-sensitive descending neurons in male Eristalis tenax hoverflies. We focused on roll impulse responses as hoverflies perform exquisite head roll stabilizing reflexes, and the descending neurons respond particularly well to roll. We found that the roll impulse responses were fast, peaking after 16.5–18.0 ms. This is similar to the impulse response time to peak (18.3 ms) to widefield horizontal motion recorded in hoverfly LPTCs. We found that the roll impulse response amplitude scaled with the size of the stimulus impulse, and that its shape could be affected by the addition of constant velocity roll or lift. For example, the roll impulse response became faster and stronger with the addition of excitatory stimuli, and vice versa. We also found that the roll impulse response had a long return to baseline, which was significantly and substantially reduced by the addition of either roll or lift.

Modeling of UV diffused-LOS communication channel incorporating obstacle and its applicability analysis.

Existing studies of the ultraviolet (UV) channel mainly focus on non-line-of-sight (NLOS) scenarios, while line-of-sight (LOS) scenarios are generally neglected since obstacles sometimes block them. To fill this gap, a UV diffused-LOS channel model in the presence of an obstacle is proposed for the first time, to the best of our knowledge. For easy interpretation, the whole derivation is combined with four typical positions of the obstacle. Moreover, the applicability of the proposed model is investigated via comparison with the classical Monte Carlo simulation model, where the transceiver elevation angle and azimuth angle are always kept optimal. Calculation and simulation results show that when the obstacle thickness is relatively small, the channel attenuation of the UV diffused-LOS system is lower than that of the UV NLOS system with the variation of obstacle width, height, and distance between transceiver and obstacle. In addition, an expression of the impulse response time of the diffused-LOS channel with the obstacle is also derived for tractable analysis.

On causality and aural impulse responses synthesized using the inverse discrete Fourier transform.

Causality is a fundamental property of physical systems and dictates that a time impulse response characterizing any causal system must be one-sided. However, when synthesized using the inverse discrete Fourier transform (IDFT) of a corresponding band-limited numerical frequency transfer function, several papers have reported two-sided IDFT impulse responses of ear-canal reflectance and ear-probe source parameters. Judging from the literature on ear-canal reflectance, the significance and source of these seemingly non-physical negative-time components appear largely unclear. This paper summarizes and clarifies different sources of negative-time components through ideal and practical examples and illustrates the implications of constraining aural IDFT impulse responses to be one-sided. Two-sided IDFT impulse responses, derived from frequency-domain measurements of physical systems, normally occur due to the two-sided properties of the discrete Fourier transform. Still, reflectance IDFT impulse responses may serve a number of practical and diagnostic purposes.

High Capacity Transmission in a Coupled-Core Three-Core Multi-Core Fiber

High-capacity, long-haul transmission over a coupled-core three-core multi-core fiber is investigated in a recirculating loop experiment. We report key system characteristics, such as the optimum launch power as well as the wavelength dependence and distance-evolution of mode-dependent loss and the impulse response time spread. We further performed two high data-rate, long-haul transmission demonstrations with more than 75 nm optical bandwidth in C- and L-bands over distances up to 4800 km. The reported data-rate of 172 Tb/s over 2040 km is the highest demonstrated in any multi-span transmission system employing optical fibers with standard cladding diameter of 125 micro-meter to date. Additionally, transmission of 81 Tb/s over 4800 km distance demonstrates the potential of using coupled-core multi-core fibers in combination with wideband optical signals over long-haul distances.

Intrinsic Control in Defects Density for Improved ZnO Nanorod-Based UV Sensor Performance.

Hitherto, most research has primarily focused on improving the UV sensor efficiency via surface treatments and by stimulating the ZnO nanorod (ZNR) surface Schottky barriers. However, to the best of our knowledge, no study has yet probed the intrinsic crystal defect generation and its effects on UV sensor efficiency. In this study, we undertake this task by fabricating an intrinsic defect-prone hydrothermally grown ZNRs (S1), Ga-doped ZNRs (S2), and defect-free microwave-assisted grown ZNRs (S3). The defect states were recognized by studying X-ray diffraction and photoluminescence characteristics. The large number of crystal defects in S1 and S2 had two pronged disadvantages. (1) Most of the UV light was absorbed by the defect traps and the e–h pair generation was compromised. (2) Mobility was directly affected by the carrier–carrier scattering and phonon scattering processes. Hence, the overall UV sensor efficiency was compromised based on the defect-induced mobility-response model. Considering the facts, defect-free S3 exhibited the best UV sensor performance with the highest on/off ratio, the least impulse response time, the highest recombination time, and highest gain-induced responsivity to 368 nm UV light, which was desired of an efficient passive metal oxide-based UV sensor. Our results were compared with the recently published results.

Optimal channel selection in parallel scheduling of heterogeneous network based on competitive channel non-cooperative game model

In order to improve the parallel scheduling performance and channel balance of heterogeneous network, an optimal channel selection algorithm for parallel scheduling of heterogeneous network based on competitive channel non-cooperative game model is proposed in this paper. In this algorithm, the channel model of heterogeneous network is constructed, and the impulse response frequency doubling technology is adopted to spread the heterogeneous network channels. The simulation results show that this proposed method can improve equalisation and anti-interference ability of channels in optimal channel selection in parallel scheduling of heterogeneous network and it provides the maximum channel transmission bit error rate of 0.35 and channel transmission bit error rate of 0 at signal-to-noise ratio of 50 dB, which indicates that the bit error rate of the receiving end is small. With this method, the end-to-end time delay in parallel scheduling of heterogeneous network is reduced and the channel impulse response time is about 0.4~0.6 seconds, which improves the stability and accuracy of parallel scheduling of heterogeneous network.

Case study: Measurement and treatment of severe flutter echo caused by a barrel-vaulted sanctuary ceiling

This case study centers on a recently constructed church with a barrel-vaulted sanctuary ceiling exhibiting excessive reverberation times and flutter echo. Reverberation times in excess of 5 s in the speech frequency range were observed at locations along the tiled center aisle, along with correspondingly elevated sound pressure levels and a highly non-diffuse sound field. Preliminary measurements, which included covering the reflective center aisle, substantiated the hypothesis that the acoustical behavior was caused by the interaction between the center aisle and the barrel-vaulted ceiling. The proposed recommendations for retrofitting the space to improve intelligibility along the aisle were modified with a view toward attaining an acceptable reduction in the reverberation times while retaining the spacious acoustical quality of the sanctuary. Additional acoustical measurements were performed prior to and following the completion of the recommended treatment. This case study describes the series of measurements and presents results of the treatment, in terms of reverberation time, impulse response decay curves, impulse response time waveforms and spectrograms, and sound pressure level measures. The unique characteristics of flutter echo due to the barrel-vaulted ceiling before and after the successful acoustical treatment are described.

Системний аналіз біонічної нейромережі контрастування сигналів

There are known the biologic or bionic models of contrasting neuronet on the basis of the Mach's optic strips, or the optical end effect, where of folding signals go through the process of illumination of the image. It is discovered, that the specific physical model of neuronet is given a demonstration of contrast as the line filter process. This is a many functional process contrast of the image or the signal а for other systems with its own assignment. That will be explained in more detail to the signaling contrast of in the different applications of nature, in science and technology. The systemic analysis of the neuronet and processes in the space frequency range, or in the usual frequency do the main of the permissive details, especially the process of viewing the contour image, the indicators of aptitude and parametric.Review of the neuronet structure and the neurons linkages “on” or “of” in admittance of adaptation system to the middle level of image and economics of the process.In addition, the structure of the neural network contrasting shows that the retina has a direct connection with the brain and memory. It can perform image processing similar to that of the Duhamel integral. Moreover, having in mind a large set of weight functions as impulse characteristics, you can get the desired output image. Such a neural system is adaptive for different purposes, or criteria’s. It can replace the entire set of required systems. To do this, it is enough to quickly change them in time impulse response and the purpose of the system.The neuronet and process contrast modeling permit to the extension the line filtration range of the images.

EKF/UKF-based channel estimation for robust and reliable communications in V2V and IIoT

Cyber-physical systems (CPSs) are characterized by integrating computation, communication, and physical system. In typical CPS application scenarios, vehicle-to-vehicle (V2V) and Industry Internet of Things (IIoT), due to doubly selective fading and non-stationary channel characteristics, the robust and reliable end-to-end communication is extremely important. Channel estimation is a major signal processing technology to ensure robust and reliable communication. However, the existing channel estimation methods for V2V and IIoT cannot effectively reduce intercarrier interference (ICI) and lower the computation complexity, thus leading to poor robustness. Aiming at this challenge, according to the channel characteristics of V2V and IIoT, we design two channel estimation methods based on the Bayesian filter to promote the robustness and reliability of end-to-end communication. For the channels with doubly selective fading and non-stationary characteristics of V2V and IIoT scenarios, in the one hand, basis extended model (BEM) is used to further reduce the complexity of the channel estimation algorithm under the premise that ICI can be eliminated in the channel estimation. On the other hand, aiming at the non-stationary channel, a channel estimation and interpolation method based on extended Kalman filter (EKF) and unscented Kalman filter (UKF) Bayesian filters to jointly estimate the channel impulse response (CIR) and time-varying time domain autocorrelation coefficient is adopted. Through the MATLAB simulation, the robustness and reliability of end-to-end communication for V2V and IIoT are promoted by the proposed algorithms.

Fouling detection in a shell and tube heat exchanger using variation of its thermal impulse responses: Methodological approach and numerical verification

A new method for fouling detection in a heat exchanger is proposed. This method is based on the sensitivity of its impulse response (time version of its transfer function) with fouling. The concept is validated here numerically for a shell and tube heat exchanger in steady state regime, perturbed thermally by a transient surface source. This method is presented here, on a theoretical ground. It can be implemented online, whatever the geometric and structural characteristics of the setup. It only requires the use of regular temperature sensors and actuators. The only condition concern the equations of the model of the heat exchanger which have to be linear with time invariant coefficients.

Recovery of Differential Equations from Impulse Response Time Series Data for Model Identification and Feature Extraction

Time recordings of impulse-type oscillation responses are short and highly transient. These characteristics may complicate the usage of classical spectral signal processing techniques for (a) describing the dynamics and (b) deriving discriminative features from the data. However, common model identification and validation techniques mostly rely on steady-state recordings, characteristic spectral properties and non-transient behavior. In this work, a recent method, which allows reconstructing differential equations from time series data, is extended for higher degrees of automation. With special focus on short and strongly damped oscillations, an optimization procedure is proposed that fine-tunes the reconstructed dynamical models with respect to model simplicity and error reduction. This framework is analyzed with particular focus on the amount of information available to the reconstruction, noise contamination and nonlinearities contained in the time series input. Using the example of a mechanical oscillator, we illustrate how the optimized reconstruction method can be used to identify a suitable model and how to extract features from uni-variate and multivariate time series recordings in an engineering-compliant environment. Moreover, the determined minimal models allow for identifying the qualitative nature of the underlying dynamical systems as well as testing for the degree and strength of nonlinearity. The reconstructed differential equations would then be potentially available for classical numerical studies, such as bifurcation analysis. These results represent a physically interpretable enhancement of data-driven modeling approaches in structural dynamics.

Binaural rendering of Ambisonic signals by head-related impulse response time alignment and a diffuseness constraint.

Binaural rendering of Ambisonic signals is of great interest in the fields of virtual reality, immersive media, and virtual acoustics. Typically, the spatial order of head-related impulse responses (HRIRs) is considerably higher than the order of the Ambisonic signals. The resulting order reduction of the HRIRs has a detrimental effect on the binaurally rendered signals, and perceptual evaluations indicate limited externalization, localization accuracy, and altered timbre. In this contribution, a binaural renderer, which is computed using a frequency-dependent time alignment of HRIRs followed by a minimization of the squared error subject to a diffuse-field covariance matrix constraint, is presented. The frequency-dependent time alignment retains the interaural time difference (at low frequencies) and results in a HRIR set with lower spatial complexity, while the constrained optimization controls the diffuse-field behavior. Technical evaluations in terms of sound coloration, interaural level differences, diffuse-field response, and interaural coherence, as well as findings from formal listening experiments show a significant improvement of the proposed method compared to state-of-the-art methods.

Study on acoustic improvements by sound-absorbing panels and acoustical quality assessment of teleconference systems

With the development of information and communications technology, conferences and remote education using teleconference systems have become common. When a teleconference system is used, the sound heard in a receiving room includes the acoustic characteristics of both the utterance and receiving rooms, in addition to the characteristics of the transmission via the teleconference system and Internet. Even today, when the digital technology is widely used, quality problems related to sound transmission remain; in particular, the influence of the reverberation of the conference room causes deterioration of the sound quality. Studies aiming to improve the quality of the signal transmission have been conducted; however, there are no acoustic countermeasure methods considering the acoustic characteristics of the two rooms connected by a teleconference system and performing the sound quality evaluation. In this study, focusing on a teleconference system sharing video and audio between two separate rooms, we evaluated the improvement in the sound transmission performance due to the addition of sound absorption to the conference room by examining the correspondence between the subjective assessment results and acoustical physical indexes. Additionally, the acoustical physical indexes that allow evaluating the quality of the sound transmitted via the teleconference system were also examined by comparing with the result of a subjective assessment. Intelligibility tests were conducted, listening difficulty ratings were evaluated, and the impulse response, STI, Clarity (C50), and reverberation time were measured in an actual teleconference system. We observed that, before the addition of sound absorption, the sound was difficult to listen to due to the acoustic characteristics of both of the utterance and receiving rooms. However, by suppressing reverberation in both the utterance and receiving rooms by using sound-absorbing panels, the difficulties in listening was improved. By examination of the correspondence between the subjective assessment results and acoustical physical indexes, we proved that STI and Clarity (C50) are highly correlated with intelligibility. On the other hand, reverberation time was found to be uncorrelated with the intelligibility of the rooms of teleconference systems.

Optimization of Pinned Photodiode Pixels for High-Speed Time of Flight Applications

We discuss optimizations of pinned photodiode (PPD) pixels for indirect time of flight sensors. We focus on the transfer-gate and dumping gate regions optimization, on the PPD dimension and shape to assure fast lateral charge transfer and on the epitaxial layer thickness for a good tradeoff between fast vertical charge transfer and high quantum efficiency at near infrared region. The overall performance of the pixel is quantified by the demodulation contrast of the pixel at specific frequencies. The operation frequency of the device is determined by the required ambiguity range of the application and the required distance noise. In order to reach a reasonable distance noise, the pixel needs to allow modulation frequencies up to 100 MHz. In this paper, we present TCAD simulation and experimental data on demodulation contrast, impulse response time, and quantum efficiency of $10 \times 10\,\,\mu \text{m}$ pixels. We introduce a setup for impulse response measurement and we compare this to the demodulation contrast. We also discuss the optimization of the dump gate and dump diffusion. With the best pixel we measured a quantum efficiency of about 45% at 850 nm, a demodulation contrast of 47% at 80 MHz, and an impulse response time < 5 ns.

Anisotropic response of surface circulation to wind forcing, as inferred from high‐frequency radar currents in the southeastern Bay of Biscay

AbstractThe short‐term (less than 20 days) response of surface circulation to wind has been determined in waters of the southeastern Bay of Biscay, using wind impulse response (time domain) and transfer (frequency domain) functions relating high‐frequency radar currents and reanalysis winds. The response of surface currents is amplified at the near‐inertial frequency and the low‐frequency and it varies spatially. The analysis indicates that the response of the ocean to the wind is slightly anisotropic, likely due to pressure gradients and friction induced by the bottom and coastline boundaries in this region. Thus, the transfer function at the near‐inertial frequency decreases onshore due to the coastline inhibition of circularly polarized near‐inertial motion. In contrast, the low‐frequency transfer function is enhanced toward the coast as a result of the geostrophic balance between the cross‐shore pressure gradient and the Coriolis forces. The transfer functions also vary with season. In summer, the current response to wind is expected to be stronger but shallower due to stratification; in winter, the larger mixed layer depth results in a weaker but deeper response. The results obtained are consistent with the theoretical description of wind‐driven circulation and can be used to develop a statistical model with a broad range of applications including accurate oceanic forecasting and understanding of the coupled atmosphere‐ocean influence on marine ecosystems.

Automatic evaluation of the fundamental frequency variations and related damping factor of reinforced concrete framed structures using the Short Time Impulse Response Function (STIRF)

Structural Health Monitoring (SHM) aims to improve knowledge of the safety and maintainability of civil structures and infrastructures. This paper presents an innovative strategy for automatic evaluation of the variable fundamental frequency and related damping factors of nonlinear structures during strong motion phases. In fact, most of methods for damage detection are based on the assessment of the variations related to dynamic parameters characterizing the monitored structure. In this case, a crucial aspect is a correct estimation of both structural eigenfrequencies and related damping factor also during the nonlinear behavior of a monitored structure. In this paper, nonlinear interferometric analyses combined with the Fourier Transform (FT) are proposed to evaluate the Short-Time Impulse Response Function (STIRF) able to characterize frequencies and damping variations of a monitored structure. Two application of the STIRF are proposed on both numerical and experimental models.

Response Time Measurements in Short-Wave Infrared HgCdTe e-APDs

The impulse response time has been measured as a function of reverse bias, gain, and temperature in backside-illuminated short-wave infrared HgCdTe avalanche photodiodes (APDs) with variable junction geometry. The APD geometry was altered using HgCdTe substrates of variable thickness and by variation of device fabrication parameters. This approach allowed study of the drift–diffusion dynamics of the electrons before entering the junction and the electron and hole dynamics during the junction transition in APDs with different carrier collection distances and junction widths. The response time was typically limited by a double exponential decay, which is attributed to contributions from the impedance mismatch between the interconnection circuit and the 50-Ω radiofrequency probe, and a delayed diffusion response from carriers generated far from the junction. These contributions limited the maximum bandwidth of the diodes to about 600 MHz, independently of gain and temperature. The hot carrier velocities are estimated by fitting the measured response with numerical calculations, taking into account contributions from a direct drift–multiplication response and a delayed diffusion response. This analysis shows that the hot carrier dynamics is close to independent of temperature and that the electron drift velocity saturates at the gain onset to a value of 1 × 107 cm/s, decreasing upon a further increase of the electric field E to a value of about 3 × 106 cm/s at E = 100 kV/cm. The hole velocity shows a slow variation from 3 × 106 cm/s at low electric fields to 1.5 × 106 cm/s at high electric fields.

Spatial Dynamic Wideband Modeling of the MIMO Satellite-to-Earth Channel

A novel MIMO (multiple input multiple output) satellite channel model that allows the generation of associated channel impulse response (CIR) time series depending on the movement profile of a land mobile terminal is presented in this paper. Based on high precise wideband measurements in L-band the model reproduces the correlated shadowing and multipath conditions in rich detail. The model includes time and space variant echo signals appearing and disappearing in dependence on the receive antenna position and movement, and the actual azimuths and elevations to the various signal sources. Attenuation and path delays relative to the hypothetical line of sight (LOS) ensure usability for ranging purposes. Parameters for car and pedestrian applications in urban and suburban environments are provided. The channel characteristics are determined independently of the transmitted signal. Therefore the usability, for example, for GPS and GALILEO, as well as wideband communication services from hovering platforms, is given.