Echo Delay Research Articles

Population registration of echo flow in the big brown bat's auditory midbrain.

Echolocating big brown bats (Eptesicus fuscus) perceive their surroundings by broadcasting frequency-modulated (FM) ultrasonic pulses and processing returning echoes. Bats echolocate in acoustically cluttered environments containing multiple objects, where each broadcast is followed by multiple echoes at varying time delays. The bat must decipher this complex echo cascade to form a coherent picture of the entire acoustic scene. Neurons in the bat's inferior colliculus (IC) are selective for specific acoustic features of echoes and time delays between broadcasts and echoes. Because of this selectivity, different subpopulations of neurons are activated as the bat flies through its environment, while the physical scene itself remains unchanging. We asked how a neural representation based on variable single-neuron responses could underlie a cohesive perceptual representation of a complex scene. We recorded local field potentials from the IC of big brown bats to examine population coding of echo cascades similar to what the bat might encounter when flying alongside vegetation. We found that the temporal patterning of a simulated broadcast followed by an echo cascade is faithfully reproduced in the population response at multiple stimulus amplitudes and echo delays. Local field potentials to broadcasts and echo cascades undergo amplitude-latency trading consistent with single-neuron data but rarely show paradoxical latency shifts. Population responses to the entire echo cascade move as a unit coherently in time as broadcast-echo cascade delay changes, suggesting that these responses serve as an index for the formation of a cohesive perceptual representation of an acoustic scene.NEW & NOTEWORTHY Echolocating bats navigate through cluttered environments that return cascades of echoes in response to the bat's broadcasts. We show that local field potentials from the big brown bat's auditory midbrain have consistent responses to a simulated echo cascade varying across echo delays and stimulus amplitudes, despite different underlying individual neuronal selectivities. These results suggest that population activity in the midbrain can build a cohesive percept of an auditory scene by aggregating activity over neuronal subpopulations.

Numerical Simulation of Metal Defect Detection Based on Laser Ultrasound

The noncontact and wide-band characteristics of the ultrasonic signal excited by the laser make it widely used in nondestructive detection. In this paper, the finite element method is used to simulate multiple ultrasonic signal modes and the responses of them to metal defects. The simulation shows that the changes of excited Rayleigh-wave (RW) and shear-wave (SW) can be used to research the surface crack and internal defect of the sample respectively. By analyzing the reflected wave of RW and SW at the inspection point, the effects of surface crack and internal defect on the ultrasonic signals of the two modes are quantitatively compared. The results show that the time delay of the Rayleigh echo has a linear relationship to the width and transverse position of the crack, and the peak-valley difference of Rayleigh echo at the inspection point and the crack depth can also be fitted linearly. In addition, the Y component displacement of the bottom reflected SW also decays with the change of the internal defect. This simulation model provides a theoretical basis for further experimental verification basis.

Evaluation of the Rotating-Frame Relaxation (T1ρ) Filter and Its Application in Metabolomics as an Alternative to the Transverse Relaxation (T2) Filter.

Nuclear magnetic resonance (NMR)-based metabolomic studies commonly involve the use of T2 filter pulse sequences to eliminate or attenuate the broad signals from large molecules and improve spectral resolution. In this paper, we demonstrate that the T1ρ filter-based pulse sequence represents an interesting alternative because it allows the stability and the reproducibility needed for statistical analysis. The integrity of the samples and the stability of the instruments were assessed for different filter durations and amplitudes. We showed that the T1ρ filter pulse sequence did not induce sample overheating for a filter duration of up to 500 ms. The reproducibility was evaluated and compared with the T2 filter in serum and liver samples. The implementation is relatively simple and provides the same statistical and analytical results as those obtained with the standard filters. Regarding tissues analysis, because the duration of the filter is the same as that of the spin-lock, the synchronization of the echo delays with the magic angle spinning (MAS) rate is no longer necessary as for T2 filter-based sequences. The results presented in this article aim at establishing a new protocol to improve metabolomic studies and pave the way for future developments on T1ρ alternative filters, in liquid and HR-MAS NMR experiments.

Joint Estimation of Target Parameters and System Deviations in MIMO Radar With Widely Separated Antennas on Moving Platforms

A multiple-input multiple-output (MIMO) radarwith widely separated antennas on moving platforms suffers from the effects of platform deviations on the target parameter estimation since the trajectories of the moving platforms are sensitive to environmental factors, such as strong wind. This article addresses the joint estimation of multiple target positions and velocities as well as radar system deviations to minimize the impact of platform deviations. The proposed algorithm can also be regarded as a self-calibration technique. First, the grid search dimensions for parameter estimation are reduced via a generalized maximum likelihood (GML) algorithm. Second, the adaptive gradient (AdaGrad) method is used to implement the GML estimation for multitarget echo delays and Doppler shifts. Finally, to address the nonlinear estimation problem of interest, the iterative least squares method is used to estimate the multiple target positions and velocities as well as radar system deviations based on the estimated delays and Doppler shifts. Prior information, such as target positions or the probability distribution of the echo coefficient, is not needed in the proposed method. The parameter identifiability is also derived in this article. Numerical simulations show that compared to a method without the estimation of system deviations, the proposed method is more efficient with respect to the derived Cramér–Rao bound.

Precision-Improved Pulsed Laser Ranging by Multidelayed Echo Signals Triggering

We propose a pulsed laser ranging method based on a multiecho delay trigger, which improves the precision of pulsed laser ranging. A signal delay unit is used to accurately delay the pulse-echo signal. In a fixed time window, the echo delay pulse triggers the laser transmitter to generate pulsed laser light; meanwhile, the counter records several echo pulses received, and then, the actual distance can be calculated. In terms of improving the ranging precision, this method overcomes the essential of higher time resolution time-to-digital converter (TDC) chip in traditional time-of-flight (TOF) pulsed laser ranging. The method can be realized by using a field-programmable logic gate array (FPGA) chip, a delay unit, and a set of laser transmitters and receivers, which makes the system structure simple and low cost. Experimental results show that this method can achieve more accurate distance measurement and significantly reduced error, to the best of our knowledge, which improves the pulsed laser ranging from centimeter- to millimeter-order precisions. We believe that this method has a promising application prospect in the field of high-precision pulsed laser ranging of fixed targets.

Echoes from corpuscular black holes

In the corpuscular picture of black hole there exists no geometric notion of horizon which, instead, only emerges in the semi-classical limit. Therefore, it is very natural to ask—what happens if we send a signal towards a corpuscular black hole? We show that quantum effects at the horizon scale imply the existence of a surface located at an effective radius R=Rs(1+ϵ) slightly larger than the Schwarzschild radius Rs, where ϵ=1/N and N is the number of gravitons composing the system. Consequently, the reflectivity of the object can be non-zero and, indeed, we find that incoming waves with energies comparable to the Hawking temperature can have a probability of backscattering of order one. Thus, modes can be trapped between the two potential barriers located at the photon sphere and at the surface of a corpuscular black hole, and periodic echoes can be produced. The time delay of echoes turns out to be of the same order of the scrambling time, i.e., in units of Planck length it reads √N log N. We also show that the ϵ-parameter, or in other words the compactness, of a corpuscular black hole coincides with the quantum coupling that measures the interaction strength among gravitons, and discuss the physical implications of this remarkable feature.

Robust transmit waveform and receive filter design in the presence of eclipsing loss and signal-dependent interference

Eclipsing is the designation for the attendant loss that occurs for return echoes that arrive when the receiver is turned off during the transmission of a long pulse. Assuming unknown knowledge about the target echo delay (TED), this paper presents a robust design approach to jointly optimize the transmit sequence and receive filter for the detection of radar targets in the presence of return echo eclipsing loss and signal-dependent interference.The worst-case signal-to-interference-plus-noise-ratio (SINR) at the output of the filter is considered as the performance measure of the system. The robust design problem is formulated as a non-convex max-min optimization problem to robustify the system SINR with respect to the unknown target eclipsing loss condition. In addition to an energy constraint, an upper bound to the peak-to-average-power ratio (PAR) is imposed on the transmit sequence. The original non-convex optimization problem is solved using relaxation methods and an iterative optimization process alternating between two sequential semi-definite programming (SDP) problems. Then, the randomization methods are utilized to synthesize the transmit sequence and the corresponding filter sharing the robust response. Finally, the effectiveness of the proposed procedure is demonstrated through experimental results, underlining the performance enhancement offered by a robust joint design.

Sparse Blind Deconvolution Method for Wall Parameters Estimation

The information of wall parameters is very important for the imaging performance of through-the-wall radar imaging (TWRI). The existing estimation methods usually require the calibration procedure to ensure the accuracy of the estimated wall parameters. To avoid the time-consuming calibration procedure, a sparse blind deconvolution method for wall parameters estimation is proposed in this letter. The proposed method uses the time-delay-only estimation (TDOE) strategy with the hybrid bistatic–monostatic measurement configuration to retrieve the unknown thickness, relative permittivity, and conductivity of the wall. In the estimation process, the sparse blind deconvolution algorithm is developed to retrieve the time delays of echoes reflected from the wall. The proposed sparse blind deconvolution method can precisely extract the time delays of echoes in the time domain without the calibration procedure to obtain the shape of the transmitted pulse and the frequency response of the antennas. The estimation results from the full-wave synthetic data have shown that the proposed method can also improve the estimation accuracy of the wall parameters.

The precedence effect: Is it the same for interaural time and interaural level differences?

Until recently, it was believed that the precedence effect operated for both interaural time and interaural level differences (ITDs and ILDs). Stecker and Brown (2010) demonstrated the absence of precedence effects for ILDs under conditions producing strong effects for ITDs. In order to provide a quantitative measure of the precedence effect, echo weights were measured using a correlational analysis as a function of echo delay for both ITDs and ILDs in 14 individuals for judgments based on binaural cues presented by the echo pulse. Stimuli were pairs of 3000-Hz 4-ms Gaussian pulses presented with echo delays between 4 and 96 ms. Echo weights at short echo delays (4 ms) were significantly higher for ILDs (M = 0.445) than ITDs (M = 0.196). Additional data were collected for conditions in which an ITD followed an ILD versus an ILD followed an ITD. Performance was far superior at short echo delays for ILDs following ITDs, with the leading ITD barely exerting any influence on subsequent processing of ILDs. We speculate that the mechanism by which ILDs are extracted (integration of sound pressure over time) makes later non-zero ILDs informative whereas later arriving ITDs provide little information about the location of sound sources.

Robust Transceiver Design in the Presence of Eclipsing Loss for Spectrally Dense Environments

Radar system design for the detection of targets with unknown actual range in spectrally crowded environments is a challenge due to increasing demands for spectrum and the possibly experienced echo eclipsing. Assuming unknown target echo delay, this article deals with robust joint design of the radar code and receive filter bank guaranteeing spectral compatibility with the surrounding electromagnetic radiators. The average signal-to-interference-plus-noise ratio (SINR) at the output of the filter bank is considered as the performance measure to optimize under both similarity and spectral compatibility constraints on the radar code. Through an appropriate reformulation of the resulting nonconvex optimization problem, we devise an alternate optimization algorithm, which sequentially improves the average SINR and converges to a point fulfilling the Karush-Kuhn-Tucker (KKT) conditions of the design problem. Each iteration of the algorithm involves both a convex and a hidden convex optimization problem, which can be solved via the rank-1 decomposition procedure. Finally, the performance is assessed by studying the tradeoff among the SINR, spectral shape, and autocorrelation. Numerical results reveal that the new method has better flexibility and robustness compared to several counterparts, which are presented in open literature.

How frequency hopping suppresses pulse-echo ambiguity in bat biosonar

Big brown bats transmit wideband FM biosonar sounds that sweep from 55 to 25 kHz (first harmonic, FM1) and from 110 to 50 kHz (second harmonic, FM2). FM1 is required to perceive echo delay for target ranging; FM2 contributes only if corresponding FM1 frequencies are present. We show that echoes need only the lowest FM1 broadcast frequencies of 25 to 30 kHz for delay perception. If these frequencies are removed, no delay is perceived. Bats begin echo processing at the lowest frequencies and accumulate perceptual acuity over successively higher frequencies, but they cannot proceed without the low-frequency starting point in their broadcasts. This reveals a solution to pulse-echo ambiguity, a serious problem for radar or sonar. In dense, extended biosonar scenes, bats have to emit sounds rapidly to avoid collisions with near objects. But if a new broadcast is emitted when echoes of the previous broadcast still are arriving, echoes from both broadcasts intermingle, creating ambiguity about which echo corresponds to which broadcast. Frequency hopping by several kilohertz from one broadcast to the next can segregate overlapping narrowband echo streams, but wideband FM echoes ordinarily do not segregate because their spectra still overlap. By starting echo processing at the lowest frequencies in frequency-hopped broadcasts, echoes of the higher hopped broadcast are prevented from being accepted by lower hopped broadcasts, and ambiguity is avoided. The bat-inspired spectrogram correlation and transformation (SCAT) model also begins at the lowest frequencies; echoes that lack them are eliminated from processing of delay and no longer cause ambiguity.

Dolphin echo-delay resolution measured with a jittered-echo paradigm.

Biosonar echo delay resolution was investigated in four bottlenose dolphins (Tursiops truncatus) using a "jittered" echo paradigm, where dolphins discriminated between electronic echoes with fixed delay and those whose delay alternated (jittered) on successive presentations. The dolphins performed an echo-change detection task and produced a conditioned acoustic response when detecting a change from non-jittering echoes to jittering echoes. Jitter delay values ranged from 0 to 20 μs. A passive listening task was also conducted, where dolphins listened to simulated echoes and produced a conditioned acoustic response when signals changed from non-jittering to jittering. Results of the biosonar task showed a mean jitter delay threshold of 1.3 μs and secondary peaks in error functions suggestive of the click autocorrelation function. When echoes were jittered in polarity and delay, error functions shifted by approximately 5 μs and all dolphins discriminated echoes that jittered only in polarity. Results were qualitatively similar to those from big brown bats (Eptesicus fuscus) and indicate that the dolphin biosonar range estimator is sensitive to echo phase information. Results of the passive listening task suggested that the dolphins could not passively detect changes in timing and polarity of simulated echoes.

Identification of the acoustic signal models of audio exchange systems under conditions of interference and acoustic feedback

In this paper questions of building models of information exchange systems with discrete and distributed delay and with delayed feedback by methods of the theory of linear functional differential equations are investigated. When solving the said equations, it is necessary to consider restrictions caused by the uncertainties in the system under modeling, such as the absence of the exact data on the parameters of the model elements, their natural spread and temporal variations, thus requiring the solution of an identification problem. The models with continuous aftereffect introduced in this work take a fuller account of reflected signal characteristics in closed space, which increases the reliability of modeling results in comparison with the known differential models. At the same time, there is a problem of finding functions that characterize the value distribution of the echo delay. In this work, these functions (kernels) are approximated by a number of exponents, which simplifies the equations and allows the assumption that the aftereffect can be concentrated on both final and infinite intervals. The echo components caused by closed-space resonances are modeled by transfer functions of the corresponding linear links. In numerical modeling, a single-channel model represented by a second-order resonance link and a pulse-shaped kernel described by a sum of two decreasing exponents is considered. The analysis of stability of the models of systems with delayed feedback is conducted by a frequency method. In the paper an approach to estimating the correlation and spectral functions of signals and noise components based on the parametric representation of the latter is considered. The paper also considers issues relating to the practical significance of the research results.

Learning Ratio Mask with Cascaded Deep Neural Networks for Echo Cancellation in Laser Monitoring Signals

Laser monitoring has received more and more attention in many application fields thanks to its essential advantages. The analysis shows that the target speech in the laser monitoring signals is often interfered by the echoes, resulting in a decline in speech intelligibility and quality, which in turn affects the identification of useful information. The cancellation of echoes in laser monitoring signals is not a trivial task. In this article, we formulate it as a simple but effective additive echo noise model and propose a cascade deep neural networks (C-DNNs) as the mapping function from the acoustic feature of noisy speech to the ratio mask of clean signal. To validate the feasibility and effectiveness of the proposed method, we investigated the effect of echo intensity, echo delay, and training target on the performance. We also compared the proposed C-DNNs to some traditional and newly emerging DNN-based supervised learning methods. Extensive experiments demonstrated the proposed method can greatly improve the speech intelligibility and speech quality of the echo-cancelled signals and outperform the comparison methods.

Mirror symmetric broadband homodecoupled perfect echo spectroscopy

A new experiment for recording phase sensitive ω1-broadband homodecoupled TOCSY spectra is presented. The method is an extension of the already existing perfect echo (PE) filter, proposed to sample t1 chemical shift under sustained homodecoupling. The modification is made by attaching a time reversed perfect echo filter to a regular perfect echo scheme. Thus it becomes possible to acquire for longer t1 acquisition times without compromising the quality of homodecoupling. The mirror symmetric double perfect echo is implemented into the evolution period of a TOCSY experiment. A spin lock pulse purges undesired dispersive antiphase components at the end of the central t1 evolution period. Pure absorptive lineshapes with reduced proton spin multiplicities are obtained. The approach can be used in conjunction with real or constant time chemical shift evolution. In case of compounds with reduced T2 relaxation time, the real time approach is advisable, where the echo delays are an extension of the t1 evolution period. In this way, an unnecessary loss due to T2 relaxation is avoided. Using the pulse sequence in constant time mode at high t1max values gives ω1-homodecoupled TOCSY spectra without a significant dependence of the transfer amplitude on J. All experiments were carried out using non uniform sampling to decrease the measurement time. Experimental setup, advantages and limitations are discussed.

A Virtual Switching Model for Improvement of Call Quality in Integrated Communication System

Poor voice quality in VoIP models during communication has been a common occurrence which VoIP users experience, this can be frustrating when users cannot communicate efficiently. Most people find it difficult to think straight when they make calls and there is an echo. In addition to this frustration, the caller’s money, time, effort, energy is all wasted without compensation of any kind. Users are also frustrated by not receiving, transmitting or misunderstanding voice messages correctly. Given the need for voice quality in calls, it is of no importance when there is no proper communication. This study aims to reduce the threat of bad calls and improve the quality of voice calls. Nonetheless, we need to raise the filter duration to a high value in some real telecom’s environments with long echo delays. But, because of high computational complexity, it is not efficient in efficiency. In this study, we suggest a solution that uses a computational formula to compensate long echo, delay, packet loss, jitter and noise. The model designed was developed using MATLAB 2019b. This approach demonstrated productivity in terms of both voice quality and system speed.

Weak-Field Limit of a Kaluza-Klein Model with a Nonlinear Perfect Fluid

The main purpose of our paper is to construct a viable Kaluza-Klein model satisfying the observable constraints. To this end, we investigate the six-dimensional model with spherical compactification of the internal space. Background matter is considered in the form of a perfect fluid with non-linear equations of state both in the external/our and internal spaces and the model is set to include an additional bare cosmological constant $\Lambda_6$. In the weak-field approximation, the background is perturbed by pressureless gravitating mass that is a static point-like particle. The non-linearity of the equations of state of a perfect fluid makes it possible to solve simultaneously a number of problems. The demand that the parameterized post-Newtonian parameter $\gamma$ be equal to 1 in this configuration, first, ensures compatibility with gravitational tests in the Solar system (deflection of light and time delay of radar echoes) at the same level of accuracy as General Relativity. Second, it translates into the absence of internal space variations so that the gravitational potential coincides exactly with the Newtonian one, securing the absence of the fifth force. Third, the gravitating mass remains pressurless in the external space as in the standard approach to non-relativistic astrophysical objects and meanwhile, acquires effective tension in the internal space.

Echolocating bats perceive natural-size targets as a unitary class using micro-spectral ripples in echoes.

Echolocating big brown bats emit frequency-modulated (FM) sounds covering ultrasonic frequencies in two harmonic sweeps (FM1 from 50-60 kHz sweeping down to 20-25 kHz, FM2 from 100-110 kHz sweeping down to 45 kHz). Using a complex interplay of acoustic cues, the bats perceive object distance from echo delay and object shape from echo spectra. Typical natural targets-flying insects-return discrete reflections, called glints, from prominent body parts (e.g., head, wings). Insect sizes are mostly 0.5 cm to about 3.5 cm, corresponding to reflected time separations of 30 to 210 μs. When closely spaced reflections overlap, they interfere to create a characteristic echo spectrum containing repetitive peaks and nulls. Time spacing of these glints (Δt) is transposed into spectral ripples at frequency intervals (Δf = 1/Δt) from about 30 kHz down to 5 kHz. The bat's perception of rippled echoes as a distinct class was tested in two-alternative forced-choice discrimination experiments with a standard stimulus of 100 μs glint separation (10 kHz ripples), in the middle of natural ripple separations (30 kHz to 5 kHz). Stimuli were electronically generated virtual targets with simulated 2-glint sizes from smaller than 0.5 cm to larger than 3.5 cm. Bats perceived insect-sized virtual objects (glint delays of 36-300 μs) as similar to the 100-μs standard, while smaller or larger virtual objects were perceived as not similar. Insect-sized echoes contained a pattern of microscale spectral ripples that stood apart from the coarser, macroscale spectral features of smaller objects or the temporally separate reflections of larger objects. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Multilayer film thickness measurement using ultrafast terahertz pulsed imaging

Terahertz (THz) rays have higher penetration depth compared to visible rays, and hence can be effectively used to measure a geometric thickness of soft samples with no damage. Measurement of such soft samples with contact methods is a challenge in terms of accuracy and speed. In this paper, a terahertz pulsed imaging(TPI) imaga 3000 system with reflection imaging module has been employed to measure the individual soft thickness of a multilayer structure made of adhesive soft polymer films with temporal method. Automatic scan of the sample has been carried out and the echoes at each interface are sampled and then detected. The complex refractive index (RI) of the sample has been measured with terahertz pulsed spectra (TPS) 3000 with transmission module. To avoid the incorrect thickness from the measured complex RI due to dispersion, propagation constants of the sample for a given mode and polarization have been extracted by solving the Helmholtz equation, numerically. From the detected delay of echoes and the calculated propagation constants, the geometric thickness of each layer is calculated. Further thickness of an onion leaf as a biological sample was measured based on the propagation constant. Results showed good accuracy with uncertainty budget of 7% of the THz wavelength used.

Bio-inspired generalizable-focusing wideband FM sonar

The bat’s inner ear and auditory brainstem register successive frequencies in FM sweeps of broadcasts and echoes with single spikes. Using the neural spectrogram of each broadcast as reference, spike latencies trace the FM sweeps for imaging echo delay by spectrogram correlation. If mutually-interfering glint reflections are present, the echo’s neural spectrogram has regularly-spaced ripples caused by amplitude-latency trading. Glint-delay estimates are generated by transforming the ripple pattern from frequency to time in real time using feedforward inhibition. Several glint delay estimates can coexist in focused target images before accumulation of nulls generates too many glint estimates and blurs the image. Echo lowpass filtering, characteristic of clutter, affects a wide swath of frequencies and changes the slope of the neural spectrogram, which evokes multiple nulls and causes image blurring that suppresses the clutter. Echo Doppler shifts also change the slope of the FM sweep, and the same mechanism is capable of blurring Doppler-shifted images so that troublesome ambiguity is suppressed. By internally adjusting the neural FM sweep of the broadcast reference, the images of echoes can be refocused onto any desired location not only in range, azimuth, and elevation, but also on the range-Doppler plane. [Work supported by ONR.]