Acoustic Time Delay Research Articles

Surface Acoustic Microwave Photonic Filters on Etchless Lithium Niobate Integrated Platform

AbstractLithium niobate on insulator emerges as a promising platform for integrated microwave photonics because of its capability of ultralow‐loss guidance and high‐efficiency modulation of light. Chip‐level integration of microwave filters is important for signal processing in the 5G/6G wireless communication. Here, by employing bound states in the continuum for low‐loss waveguiding, high‐performance microwave photonic filters are realized on an etchless lithium niobate integrated platform. These microwave photonic filters consist of a high‐quality photonic microcavity modulated by piezoelectrically excited surface acoustic waves. Acoustic time delays from 21 to 106 ns and passbands with bandwidth as narrow as 0.89 MHz are achieved in the fabricated filters operating at gigahertz frequencies. This demonstration may open up new applications on the lithium niobate integrated platform, such as optical communication, signal processing, and beam steering.

Study on acoustic time delay localization in boiler tube arrays considering effective sound velocity

Based on the study of sound propagation characteristics and acoustic radiation in periodic tube arrays, we found that the wave front differed from the no-tube arrays at the same frequency. The phenomenon indicated that there was different sound velocity in tube arrays. This research considered tube arrays as an effective medium for sound and studied the effective sound velocity at different frequencies in tube arrays. The numeral calculations and experiments shown similar conclusions that the sound velocity was slower than in no-tube arrays one. Acoustic velocity directly affects the accuracy of time delay localization method, and the time delay localization method in acoustic isotropic media is mature. The velocity of low frequency sound wave is isotropic in the arrays, we investigate the variation of sound velocity theoretically and experimentally. The sound demonstrates anisotropy at high frequency region, the effective sound velocity is related to the band gap in the tube arrays. The research has been found that the same frequency has different sound velocity values in different directions. In different directions of tube arrays, the effective sound velocity is used to conduct an one-dimensional acoustic source location experiment. This study can provide an innovative concept and method for leakage location in boiler tube arrays.

Underwater Acoustic Time Delay Estimation Based on Envelope Differences of Correlation Functions.

This paper proposes underwater acoustic time delay estimation based on the envelope differences of correlation functions (EDCF), which mitigates the delay estimation errors introduced by the amplitude fluctuations of the correlation function envelopes in the traditional correlation methods (CM). The performance of the proposed delay estimation method under different time values was analyzed, and the optimal difference time values are given. To overcome the influences of digital signal sampling intervals on time delay estimation, a digital time delay estimation approach with low complexity and high accuracy is proposed. The performance of the proposed time delay estimation was analyzed in underwater multipath channels. Finally, the accuracy of the delay estimation using this proposed method was demonstrated by experiments.

Estimation of the Acoustic Time Delay of Arrival by Adaptive Eigenvalue Decomposition with a Proportionate Step-Size Control and Direct-Path Constraint

Estimation of the Acoustic Time Delay of Arrival by Adaptive Eigenvalue Decomposition with a Proportionate Step-Size Control and Direct-Path Constraint

Scholte Wave at Air–Metal Interface Generated by a PulsedDisc-Like Source

The normal displacement and pressure of Scholte and Leaky Rayleighwaves at air–metal interface generated by a pulsed disc-like source aresimulated theoretically by the Cagniard–de Hoop method and studied bylaser ultrasound technique experimentally. It is found that the Scholtewave detected by a photorefractive interferometer is mainly contributedby the surface pressure and the Leaky Rayleigh wave is dominated by thesurface displacement. It is also proven that the pulse width of theseinterface waves is mainly determined by the acoustic time delay on thegenerating source size under our experimental conditions.

Acoustic time delay estimation and sensor network self-localization: Experimental results

Experimental results are presented on propagation, coherence, and time-delay estimation (TDE) from a microphone array in an outdoor aeroacoustic environment. The primary goal is to understand the achievable accuracy of acoustic TDE using low-cost, commercial off-the-shelf (COTS) speakers and microphones. In addition, through the use of modulated pseudo-noise sequences, the experiment seeks to provide an empirical understanding of the effects of center frequency, bandwidth, and signal duration on TDE effectiveness and compares this to the theoretical expectations established by the Weiss-Weinstein lower bound. Finally, sensor network self-localization is performed using a maximum likelihood estimator and the time-delay estimates. Experimental network localization error is presented as a function of the acoustic calibration signal parameters.

RELATIONSHIP BETWEEN OSCILLATION FREQUENCY AND GEOMETRY OF OSCILLATING LPA FLOW SENSOR

The oscillating LPA (Laminar Proportional Amplififier) flow sensor having bilateral feedback loops is available for the measurement of small volume flow. Pattern of LPA and feedback loops were sculpted on a flat plane. The relationship between the oscillating frequency and the geometry of the oscillating LPA flow sensors were measured. As the result of experiments, it was appeared that the oscillating frequency of the oscillating LPA flow sensor closely connected with the geometry and the sizes of the sensor, and the signal transport time through the feedback loop was about a half of the acoustic time delay, and it was proved that the signal transport time on the supply jet from the supply nozzle to the splitter were occupied about 60% of the oscillating frequency. It was demonstrated that the range ability of the oscillating LPA flow sensor could be extended by arranging the pattern of LPA and feedback loops in the same plane.

The influence of transducer transfer functions and acoustic time delays on the implementation of the LMS algorithm in active noise control systems

Forms of the LMS algorithm have been implemented recently in active noise control systems. Parallel to this, many studies of the convergence properties of the LMS algorithm have been conducted in the field of adaptive signal processing. However, these results cannot be applied directly to active noise control systems as the acoustic time delay and electro/acoustic transfer functions, inherent in an an active noise control system, require modification of the results. In this paper, the effect of the time delay and transfer functions on the convergence properties of the LMS algorithm for a single actuator, single error sensor active noise control system is examined. The results obtained provide some insights into efficient implementation of the algorithm.