激光声信号的频谱特性

构建了激光声实验测量系统,利用脉冲激光聚焦击穿水介质产生声信号,由水听器将声信号转换成电信号并送入数字存储示波器。分析了激光声信号的时频域数学模型,实验研究了激光声信号的频域能量分布,以及激光器重复频率和激光声信号频谱特性的关系。结果表明:激光声信号能量主要集中在200 kHz内,其中100~200 kHz内的能量所占比例约50%。激光声信号的幅频响应极大值点可以受到激光器重复频率的控制。     

Characteristics of biosonar signals from the northern bottlenose whale, Hyperoodon ampullatus

The biosonar pulses from free-ranging northern bottlenose whales (Hyperoodon ampullatus) were recorded with a linear hydrophone array. Signals fulfilling criteria for being recorded close to the acoustic axis of the animal (a total of 10 clicks) had a frequency upsweep from 20 to 55 kHz and durations of 207 to 377 μs (measured as the time interval containing 95% of the signal energy). The source level of these signals, denoted pulses, was 175-202 dB re 1 μPa rms at 1 m. The pulses had a directionality index of at least 18 dB. Interpulse intervals ranged from 73 to 949 ms (N?=?856). Signals of higher repetition rates had interclick intervals of 5.8-13.1 ms (two sequences, made up of 59 and 410 clicks, respectively). These signals, denoted clicks, had a shorter duration (43-200 μs) and did not have the frequency upsweep characterizing the pulses of low repetition rates. The data show that the northern bottlenose whale emits signals similar to three other species of beaked whale. These signals are distinct from the three other types of biosonar signals of toothed whales. It remains unclear why the signals show this grouping, and what consequences it has on echolocation performance.     

Cavitation threshold measurements for microsecond length pulses of ultrasound

The acoustic cavitation threshold of an aqueous solution has been measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these quantities. The fluid tested was a 0.1M KOH-H3BO3 buffer solution with pH 10.9, which contained luminol, was saturated with argon, and filtered to 25 mu. The presence of cavitation was detected by a photomultiplier tube that required the emission of visible light that was both larger in magnitude and longer in duration than a preset criterion. It was observed that the cavitation threshold of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition frequency is increased, and when the pulse repetition frequency is fixed and the pulse width is increased. Acoustic cavitation thresholds measured in aqueous solutions are significantly less than those acoustic pressures associated with instruments that are currently in widespread use in medicine.     

Evidence of high-frequency acoustic emissions from the white-beaked dolphin (Lagenorhynchus albirostris)

Recordings of the signals from a school of white-beaked dolphins show that the frequency of their acoustic emissions extends to at least 305 kHz. These signals were detected by a sector scanning sonar used as a passive listening device of high bearing and time resolution. The records contain three types of signal, one of high intensity, one of a variable high repetition rate, and another showing a time-varying effect. Acoustic signals radiated by dolphins have been recorded and studied over a long period of time by many investigators. The purpose of this letter is to report evidence that acoustic emissions from white-beaked dolphins have significant energy at frequencies around 305 kHz, about one octave higher than previously observed. The observations discussed here were made aboard the fisheries research vessel CLIONE in the Wellbank flat area of the southern North Sea on 13 June 1970 between 1040 and 1110 h. When the dolphin signals were observed, the transmitter of the sector-scanning sonar in use was turned off, and the system was utilized as a passive listening device of high bearing and time resolution.     

Reverberation of rapid and slow trills: implications for signal adaptations to long-range communication

Many acoustic signals in animals include trills, i.e., rapid repetitions of similar elements. Elements within these trills usually are frequency modulated and are degraded by reverberation during long-range transmission. Reverberation primarily affects consecutive elements with the same frequency characteristics and thus imposes a major constraint in the evolution of design and perception of long-range signals containing trills. Here transmission of frequency-unmodulated trills with different element repetition rates was studied. Trills were generated at different frequencies to assess frequency dependence of reverberation and then broadcast under three acoustic conditions--an open field and to assess seasonal changes in transmission properties, a deciduous forest before and after foliage had emerged. Reverberation was quantified at different positions within trills. The results show strong effects of vegetation density (season), transmission distance, frequency, element repetition rate, and element position within the trill on effects of reverberation. The experiments indicate that fast trills transmit less well than slow trills and thus are less effective in long-range communication. They show in particular that selection on trills should not act only on element repetition rate within trills but also on the trill duration as effects of reverberation increased with trill duration.     

Comparison of fundamental frequency and perturbation measurements among three analysis systems

The need for standardization of procedures in approaches to voice measurement has been recently emphasized. The purpose of this study was to determine the extent to which the acoustic perturbation measurements from three different analysis systems agree when standardized recording and analysis procedures are used. High-quality acoustic voice recordings from 20 patients were analyzed. The results showed that, although fundamental frequency measurements were in strong agreement among the three systems tested, frequency and amplitude perturbation measurements were not in agreement. The underlying approaches to perturbation measurement appeared to be sufficiently different to produce different results. An argument is made for a standardized set of acoustic signals representing normal, dysphonic, and synthesized voices with known characteristics to facilitate testing of new acoustic analysis systems and confirm measurement accuracy and sensitivity.     

Illusory continuity of tonal and infratonal periodic sounds

Temporal induction can restore masked or obliterated portions of signals so that tones may seem continuous when alternated with sounds having appropriate spectral composition and intensity. The upper intensity limits for the induction of tones (pulsation thresholds) are related to masking functions and have been used to define the characteristics of frequency domain (place) analysis of tones. The present study has found that induction also occurs for infratonal periodic sounds that require a time domain analysis for perception of acoustic repetition. Limits for temporal induction were determined for iterated frozen noise segments from 10-2000 Hz alternated with a louder on-line noise. Masked thresholds were also obtained for the pulsed signals presented along with continuous noise, and it was found that the relation between induction limits and masking changed with frequency. The results obtained for induction and masking are discussed in terms of general principles governing restoration of obliterated sounds.     

Low frequency acoustic signals associated with rock falls,thunderstorms, and wind turbulences in field environment

This paper characterized the observed low frequency acoustic signals generated by rock falls, thunderstorm, and wind turbulence in large rocky landslide. A digital infrasonic recording system was deployed on site to capture real-time low frequency acoustic signals associated with rock falls. An advanced non-stationary signal analysis method, i.e. Empirical Mode Decomposition (EMD), was applied to get insight to the characteristics of the low frequency acoustic signals induced by the hazards. Joint time–frequency distribution spectra technique was used to detect distinctive features of the events. The study shows that the low frequency acoustic signals can be excited by rock falls, thunderstorm and wind turbulence in the field environment, but the signal varies in both time domain and frequency domain with different patterns depending on the physical processes. The results demonstrated that the EMD-based signal processing technique is capable of extracting distinctive features to differentiate acoustic signals in real environment.     

Effect of combined source (F0) and filter (formant) variation on red deer hind responses to male roars

Studying female response to variation in single acoustic components has provided important insights into how sexual selection operates on male acoustic signals. However, since vocal signals are typically composed of independent components, it is important to account for possible interactions between the studied parameter and other relevant acoustic features of vocal signals. Here, two key components of the male red deer roar, the fundamental frequency and the formant frequencies (an acoustic cue to body size), are independently manipulated in order to examine female response to calls characterized by different combinations of these acoustic components. The results revealed that red deer hinds showed greater overall attention and had lower response latencies to playbacks of roars where lower formants simulated larger males. Furthermore, female response to male roars simulating different size callers was unaffected by the fundamental frequency of the male roar when it was varied within the natural range. Finally, the fundamental frequency of the male roar had no significant separate effect on any of the female behavioral response categories. Taken together these findings indicate that directional intersexual selection pressures have contributed to the evolution of the highly mobile and descended larynx of red deer stags and suggest that the fundamental frequency of the male roar does not affect female perception of size-related formant information.     

Modulated resonant versus pulsed resonant photoacoustics in trace gas detection

Modulated resonant photoacoustics is a sensitive technique widely used for trace gas sensing. Generally, a continuous-wave laser is modulated at a frequency corresponding to an acoustic resonance of a photoacoustic cell. Another mode of operation—which we propose to call the pulsed resonant mode—consists in matching the frequency repetition rate of a pulsed laser to an acoustic resonance of the cell. We present a theoretical model to compare the performance of these two configurations. For a given average power of the incoming light inside the cell, the pulsed resonant mode of operation (nanosecond pulses or shorter) produces π/2 times higher photoacoustic signals than the modulated resonant scheme (the latter is optimized for a 50% duty cycle). This result agrees with experiments during which both cases were investigated at 532 nm using the same photoacoustic cell containing trace concentrations of NO₂.     

Evidence for a behavioral significance of saccular acoustic sensitivity in humans

In this article the results are reported of an experiment to provide direct evidence for a perceptual and behavioral significance of human saccular acoustic sensitivity. Ten human subjects were stimulated monaurally with 100-ms trains of 10-ms tone pulses with pulse repetition rate of 40 Hz, and were required to rate the pleasantness of the stimuli on a nine-point scale. The design included three within-subject factors: carrier frequency (two levels, 200 and 4,000 Hz), intensity [13 levels from 55 to 115 dB(A) in 5-dB steps] and ear (left and right). For intensities above 90 dB myogenic vestibular evoked potentials (MVEP) were also obtained from the ipsilateral sternocleidomastoid muscle from which it was possible to obtain thresholds by linear regression of MVEP amplitudes against intensity. A further between-subjects factor was added which assessed subjects' attitude to vestibular sensations. The results indicate that across subjects there is a general trend of decreasing pleasantness with increasing intensity, but for the 200-Hz condition there is a significant positive departure from monotonicity in pleasantness (p<0.05) above the mean saccular threshold. However, when split by the between-subjects factor, the positive departure was only evident for those subjects who have a positive attitude to vestibular sensations (p < 0.01). Implications of these results for human responses to loud sound and the possible evolutionary significance of saccular acoustic sensitivity are discussed.     

A selective two microphone acoustic intensity method

A multiple input, two output model is proposed which enables the two microphone acoustic intensity method to decompose the intensity vector into contributions from individual sources, even when they are coupled and in close proximity within the measurement surface. By treating characteristic signals from each source as the inputs, and the sound pressure signals from the two closely spaced microphones as the outputs, the model's frequency response functions are developed from a least squares approximation. The cross spectrum between the two microphones can then be expressed as a function of the input signal spectra and the model's frequency response functions. By manipulating the model terms the selective cross spectrum associated with the radiation from each individual source can then be estimated. The selective cross spectrum is then processed via standard methods to obtain the acoustic intensity vector from each source. A series of laboratory experiments is summarized which demonstrates that the technique can accurately decompose the acoustic intensity vector from highly coherent sources (γ₁₂² > 0·9) buried in background noise in a semireverberant environment, to within 1 dB of the directly measured intensities.     

2D Periodic Structure for Acoustic and Electromagnetic Radiation

The propagation of microwaves in the frequency range from 8.5 to 12GHz and acoustic radiation in the frequency range from 8.5 to 14 kHz in the same 2D periodic crystal formed by cylindrical spiral coils has been investigated. The frequency ranges in which the effective refractive index n_ef of the crystal is close to zero are found. In these ranges, microwaves are collimated and concentrated in a narrow lobe with an FWHM of about 9?. Focusing of divergent microwave and acoustic beams by a flat periodic structure has been observed in the frequency range where the effective refractive index of this structure is negative.     

Communicative pulsed signals of beluga whales in the reproductive gathering off Solovetskii Island in the White Sea

Results of the perceptive and acoustic analysis of communicative pulsed signals recorded in a reproductive gathering of beluga whales off Solovetskii Island in the white sea are presented. The mean signal duration varies from 0.04 to 1.52 s for various signal types, the pulse repetition rate on the average ranges from 13 to 1300 (possibly, 2700) impulses per second, and the mean peak frequency falls within 0.2 to 11.3 kHz. A high degree of similarity between the communicative pulsed signals produced by beluga whales from different populations is revealed.     

Repetition rate and signal level effects on neuronal responses to brief tone pulses in cat auditory cortex

This study describes the effects on the spike count, spike timing, and entrainment of cat auditory cortex neurons of parametric variations in the repetition rate and amplitude of a brief, characteristic frequency tone pulse. Data were obtained from single neurons in barbiturate-anesthetized cats to which signals were presented monaurally to the ear contralateral to the recording electrode. All neurons showed low-pass sensitivity to tone repetition rate. In cells with a monotonic rate response, the effect of an increasing stimulus level was to elevate the response rate and to extend performance to higher repetition rates. In nonmonotonic cells, cutoff frequencies (for repetition rate) varied with overall spike count. Latent periods increased with increases in repetition rate. This effect developed over the first few stimulus trials at any given repetition rate. Spike entrainment to the tone pulses varied with both repetition rate and signal level. Increases in signal level improved entrainment for responses to stimuli presented at low repetition rates, but entrainment at high repetition rates always saturated at significantly imperfect levels.     

Rhythm analysis of orthogonal signals from human walking

In physical terms, periodic movements of a human body resulting from walking produce a pulse sequence with repetition time T(1) (instant cadence frequency, 1/T(1)) and duration time T(2). Footstep forces generate periodic T(1) broadband seismic and sound signals due to the dynamic forces between the foot and the ground/floor with duration time T(2), which is equal to the time interval for a single footstep from heel strike to toe slap and weight transfer. In a human gait study (for normal speeds of walking), T(1) was detected as 0.5-0.69 s and double limb support takes up about 12% of the gait cycle (2T(1)), so T(2) is greater than 0.12-0.17 s. Short range (of about 50 m) signatures for 30 humans were recorded simultaneously by four orthogonal sensor types at two locations. The sensor types were active Doppler sonar/radar and passive seismic/acoustics. Analysis of signals from these four sensors collected for walking humans showed temporal synchronization and stability of the cadence frequencies, and the cadence frequency from each sensor was equivalent. The time delay between signals from these sensors due to the differences in speeds of propagation for seismic, sound, and electromagnetic waves allows calculation of the distance from a walker to the sensor suite.     

Mode-locked laser pulse trains with subfemtosecond timing jitter synchronized to an optical reference oscillator

We independently phase lock the repetition rates of two femtosecond lasers at their approximately 456, 000th harmonic to a common optical oscillator. The timing jitter of each individual laser relative to the optical reference is only 0.45 fs in a 100-Hz bandwidth. Our method takes advantage of the tremendous leverage that is possible when stability is transferred from the optical to the microwave domain. The low timing jitter is commensurate with the independently measured fractional frequency instability in the repetition rates of < or = 2.3 x 10(-15) in 1-s averaging time, limited by the measurement system. The microwave signals at 1 GHz that are extracted by photodetection of the pulse trains have a 10-times-greater instability, confirming the presence of excess noise in the photodetection.     

Suitability of minidisc (MD) recordingsfor voice perturbation analysis

A new digital recording format, Minidisc (MD), shows promise for high-quality voice recordings. It is available in a portable size and uses magneto-optical recording techniques on a miniature compact disc. The disc can be recorded an unlimited number of times with essentially the same playback life span; however, the digital recording technique uses a data compression algorithm that may interfere with acoustic voice perturbation analysis. This study investigated what effects this compression may have and whether the MD format is viable for use in this application.The MD format was evaluated by traditional synthetic test signals used onrecording devices. In addition, human phonation recorded on Digital Audio Tape (DAT) was used as the input to the MD. The output of the MD was then compared to the original DAT recording. The two signals were analyzed for long- and short-term perturbation measures, and their waveforms were visually inspected. The results indicated that the MD format performed as well as the DAT format in all areas of standard tests, with the exception of signal-to-noise (S/N) ratio. S/N ratio for the MD was approximately 10 dB less than for the DAT under normal operating conditions; however, in comparing perturbation measures on normal human vowels, there were no significant differences between the two formats, i.e., no distortions in voice perturbation were introduced by the MD record/playback process.     

超高速撞击声发射信号在载人航天器加筋结构的传播特性实验研究

为研究超高速撞击声发射信号经过载人航天器加筋结构后的传播规律,分别在平板结构和加筋结构上模拟高速撞击实验,利用传感器阵列采集高速撞击产生的声发射信号。结合小波和傅里叶分析方法从板波模态、频域以及时域三方面分析加筋结构对声发射信号传播特性的影响,并研究成坑和穿孔损伤模式下声发射信号的传播规律。结果表明:加筋板中的信号高频部分比平板中高频部分能量少,筋体对信号高频部分有滤波效果。加筋结构受高速撞击产生穿孔损伤时,S0模态声波的能量增多。研究成果可为载人航天器结构的高速撞击感知与定位技术提供有利参考。      

A semi-automatic processing technique for elastic-wave laboratory data

This paper addresses the problem of determining the onset of transient signals such as seismograms, acoustic emissions or ultrasonic signals. Usual manual techniques of onset-time picking are time consuming when numerous measurements are available. This may occur when dealing with (i) anisotropic rocks requiring many elastic wave velocities measurements in the laboratory, (ii) 4-D seismic field data or (iii) laboratory acoustic emissions data. We present a semi-automatic processing technique devoted to the study of case (i). It is based on ultrasonic signal analysis by wavelet transform and an onset-time picking procedure combining Akaike Information Criterion and cross-correlation method. The first step consists in extracting, from the whole experimentally recorded signal, the frequency component corresponding to the perturbation induced by a typical ultrasonic transducer in the laboratory. The second step is dedicated to the onset-time picking of the phase arrival in the extracted signal. The use of this processing technique based on mathematical arguments reduces human subjectivity. Main outcomes are: (i) increase of signal-to-noise ratio; (ii) measurement of elastic wave velocities at prescribed central frequency; (iii) drastic increase of efficiency in wave data processing; and (iv) increase in reliability (repeatability) of wave data acquisition.