Measurement of the acoustic reflectivity of sirenia (Florida manatees) at 171 kHz

The Florida manatee (Trichechus manatus latirostris) is an endangered sirenian. At present, its adult population (approximately 2200) seems stable, but tenuous. Manatee-boat collisions are a significant proportion (approximately 25%) of mortalities. Here, the potential use of active sonar for detecting manatees by quantifying sonic reflectivity is explored. In order to estimate reflectivity two methods were used. One method measured live reflections from captive animals using a carefully calibrated acoustic and co-registered optical system. The other method consisted of the analysis of animal tissue in order to obtain estimates of the sound speed and density and to predict reflectivity. The impedance measurement predicts that for a lateral view, the tissue reflectivity is close to 0.13, with a critical grazing angle of 28 degrees. Data measured from live animals indicate that substantial reflections can be recorded, however in many instances observed "empirical target strengths" were less than an experimentally dependent -48-dB threshold. Conclusions favor the hypothesis that the animals reflect substantial amounts of sound; however, the reflections can often be specular, and therefore impractical for observation by a manatee detection sonar operating at 171 kHz.     

Ultrasonic flow measurement and wall acoustic impedance effects

An examination of the influence of wall acoustic impedance effects on sound propagation in flowing liquids confined by cylindrical walls is presented. Special focus is given to the importance of the wall acoustic impedance value for ultrasonic flow meter performance. The mathematical model presented allows any radially-dependent axial flow profile to be examined in the linear flow acoustics regime where fluid flow speed is much smaller than the fluid sound speed everywhere in the fluid medium.     

Low-frequency sound transmission through a gas-liquid interface

Typically, sound speed in gases is smaller and mass density is much smaller than in liquids, resulting in a very strong acoustic impedance contrast at a gas-liquid interface. Sound transmission through a boundary with a strong impedance contrast is normally very weak. This paper studies the power output of localized sound sources and acoustic power fluxes through a plane gas-liquid interface in a layered medium. It is shown that, for low-frequency sound, a phenomenon of anomalous transparency can occur where most of the acoustic power generated by a source in a liquid half-space can be radiated into a gas half-space. The main physical mechanism responsible for anomalous transparency is found to be an acoustic power transfer by inhomogeneous (evanescent) waves in the plane-wave decomposition of the acoustic field in the liquid. The effects of a liquid's stratification and of guided sound propagation in the liquid on the anomalous transparency of the gas-liquid interface are considered. Geophysical and biological implications of anomalous transparency of water-air interface to infrasound are indicated.     

A revisit to imperfect acoustic cloak of multi-layered shell structures considering sound speed and impedance matching

An imperfect multi-layered acoustic cloak is proposed for a two-dimensional cloaking zone based on feasible material properties. In this model, the matching of sound speed and acoustic impedance has been investigated, and the effects of material and geometric properties on the imperfect cloak have been studied for better design of the imperfect cloak. The imperfect cloak could be improved using appropriate changes in the design parameters. By increasing the thickness of the high density layer and with some changes in the sound speeds between the high density and the low density layers, the imperfect cloaking model showed better cloaking performance than Cummer–Schurig cloak. Also, present results show that the sound speed matching is more important for acoustic cloaking than the impedance matching. These results can be applied as a practical design guide for two-dimensional cloaks using multilayered structures composed of naturally existing materials.     

Acousto-mechanical and thermal properties of clotted blood

The efficacy of ultrasound-assisted thrombolysis as an adjunct treatment of ischemic stroke is being widely investigated. To determine the role of ultrasound hyperthermia in the process of blood clot disruption, the acousto-mechanical and thermal properties of clotted blood were measured in vitro, namely, density, speed of sound, frequency-dependent attenuation, specific heat, and thermal conductivity. The amplitude coefficient of attenuation of the clots was determined for 120 kHz, 1.0 MHz, and 3.5 MHz ultrasound at room temperature (20 +/- 2 degrees C). The attenuation coefficient ranged from 0.10 to 0.30 Np/cm in porcine clots and from 0.09 to 0.23 Np/cm in human clots. The experimentally determined values of specific heat and thermal conductivity for porcine clotted blood are (3.2 +/- 0.5) x 10(3) J/kg x K and 0.55 +/- 0.13 W/m x K, respectively, and for human clotted blood are (3.5 +/- 0.8) x 10(3) J/kg x K and 0.59 +/- 0.11 W/m x K, respectively. Measurements of the acousto-mechanical and thermal properties of clotted blood can be helpful in theoretical modeling of ultrasound hyperthermia in ultrasound-assisted thrombolysis and other high-intensity focused ultrasound applications.     

Density and sound speed of two gelatinous zooplankton: ctenophore (Mnemiopsis leidyi) and lion's mane jellyfish (Cyanea capillata)

The density and sound speed of two coastal, gelatinous zooplankton, Mnemiopsis leidyi (a ctenophore) and Cyanea capillata (lion's mane jellyfish), were measured. These parameters are important inputs to acoustic scattering models. Two different methods were used to measure the density of individual animals: one used a balance and graduated cylinder to determine the mass and displacement volume of the animal, the other varied the density of the solution the animal was immersed in. When the same animal was measured using both methods, density values were within 1% of each other. A travel-time difference method was used to measure the sound speed within the animals. The densities of both zooplankton slightly decreased as the animals increased in length, mass, and volume. The ratio of animal density and sound speed to the surrounding seawater (g and h, respectively) are reported for both animals. For Mnemiopsis leidyi ranging in length from 1 to 5 cm, the mean value (+/-standard deviation) of g and h were 1.009 (+/-0.004) and 1.007 (+/-0.001). For Cyanea capillata ranging in bell diameter from 2 to 11 cm, the mean value (+/-standard deviation) of g and single value of h were 1.009 (+/-0.004) and 1.0004.     

超声波多次回波反射法测量油料密度技术研究*

该文通过同时测量油料的声阻抗和声速来测量油料的密度。通过对超声波在不锈钢壁内的多次反射回波信号作快速傅里叶变换,取各次回波信号中心频率下的幅值在对数坐标系下作数据拟合,由拟合曲线斜率并结合多次反射理论求得油料的声阻抗;测量由聚苯乙烯壁面反射回来的二次回波信号计算油料的声速。实验中将温度控制在20?C,测量了8种油料的声阻抗和声速,进而求出8种油料的密度。实验结果表明8种油料密度测量结果的最大误差为1.2%。该方法适合油料密度在线、快速、准确测量。     

Calculation of B/A for n-alkane liquids using the Tait equation

The B/A parameter of acoustic nonlinearity was calculated for a series of n-alkane liquids using the Tait PVT equation of state supplemented with specific heat data. The calculations of sound speed, sound speed derivatives, the two components of B/A, and the value of B/A itself were compared with experimental data taken from the literature and with earlier calculations using a different equation of state. In addition, a comparison of the results with Ballou's rule (linear relation of B/A and reciprocal sound speed) was made. It is concluded that B/A can be calculated from the Tait equation of state with about the same accuracy as direct measurements of sound speed versus pressure and temperature, though the the temperature derivatives of the sound speed are calculated with much lower accuracy than pressure derivatives. The calculations made using the Tait equation are about the same accuracy as calculations made using our equation of state. Also, Ballou's rule does not hold for these liquids.     

Enhancement of gas phase heat transfer by acoustic field application

This study discusses a possibility for enhancement of heat transfer between solids and ambient gas by application of powerful acoustic fields. Experiments are carried out by using preheated Pt wires (length 0.1-0.15 m, diameter 50 and 100 micro m) positioned at the velocity antinode of a standing wave (frequency range 216-1031 Hz) or in the path of a travelling wave (frequency range 6.9-17.2 kHz). A number of experiments were conducted under conditions of gas flowing across the wire surface. Effects of sound frequency, sound strength, gas flow velocity and wire preheating temperature on the Nusselt number are examined with and without sound application. The gas phase heat transfer rate is enhanced with acoustic field strength. Higher temperatures result in a vigorous radiation from the wire surface and attenuate the effect of sound. The larger the gas flow velocity, the smaller is the effect of sound wave on heat transfer enhancement.     

System for determination of ultrasonic wave speeds and their temperature dependence in liquids and in vitro tissues

An interferometric technique capable of accurately measuring wave speed in liquids is reported. The hardware is adapted from a design to measure nonlinear responses of biological tissues to pressure changes (pressure derivatives) and temperature changes (temperature derivatives). It is used with the highly sensitive variable frequency pulsed phase-locked loop (VFPPLL) instrument. The system uses well-understood and well-characterized components and systems. The apparatus covers a temperature range from below 5 degrees C to above 45 degrees C. The system with the high-sensitivity VFPPLL is capable of measurement of wave speed to an uncertainty of less than 0.1%, and changes in wave speed to better than 0.001%. The transducer is an undamped temperature-characterized PZT-5A 500-kHz plate, whose output is corrected for off-resonance operation and for diffraction effects. To test the accuracy of the technique, measurement of ultrasonic compressional wave speed in water at temperatures from 10 degrees C to 45 degrees C are reported, with an estimated uncertainty of 0.07% and a temperature uncertainty of 0.15 degrees C. The agreement between mean values and literature values is better than 0.05%.     

Measurement of the acoustic properties of a sound absorbing material at high temperatures

Measurements have been made of the acoustic properties of a typical mineral wool fibrous material at temperatures up to 500C. In addition to acoustic impedance and propagation constant the flow resistance of the material was measured over the same temperature range. With use of a modified form of the Delany-Bazley empirical formula good agreement was found between predicted and measured values of the acoustic impedance and propagation constant at various temperatures up to 500°C.     

1,1,1,2,3,3,3- 七氟丙烷的气相声速

析了气相声速与理想气体比定压热容的热力学关系,用超声变程干涉仪测定了1,1,1,2,3,3,3-七氟丙烷(HFC-227ea)的72组气相声速值,温度范围273-333 K,压力范围26-315 kPa,测量不确定度小于0.05%。根据这些实验数据,确定了HFC-227ea的理想气体比定压热容和声速第二维里系数,并分别拟合得到了与温度的函数,理想气体比定压热容的不确定度小于0.5%。使用方阱势能模型导出了HFC-227ea的第二维里系数,并与文献值进行了比较。     

Ultrasound beam shift induced by short-beaked common dolphin's(Delphinus delphis) tissues as an attenuating gradient material

To understand sound propagation and beam formation, the physical properties of soft tissues from the biosonar system of odontocetes should be explored. Based on the acoustic impedance distributions of biosonar systems, these processes have been examined via numerical simulations. In this study, the images of a short-beaked common dolphin(Delphinus delphis) were obtained via computed tomography. Then, the dolphin was dissected to extract tissue samples for additional examination. In addition to the speed of sound and density measurements, the acoustic attenuation coefficients of the biosonar system in the forehead were tested. The results revealed that the inner layer of the forehead was characterized using low sound speed, low density, and high attenuation. Acoustic fields and beam patterns were then evaluated by setting acoustic attenuation coefficients at different levels. Sounds propagating along the low-attenuation path had a lesser reduction in amplitude. Beam directivities in near and far fields suggested that changes in attenuation distribution would cause beam patterns to shift. These results indicated the complexity of a dolphin's sonar emission system and helped improve our understanding of sound energy attenuation via studies on the forehead of odontocetes.     

Temperature dependence of ultrasonic propagation speed and attenuation in excised canine liver tissue measured using transmitted and reflected pulses

Previous reported data from our laboratory demonstrated the temperature dependence of propagation speed and attenuation of canine tissue in vitro at discrete temperatures ranging from 25 to 95 degrees C. However, concerns were raised regarding heating the same tissue specimen over the entire temperature range, a process that may introduce irreversible and, presumably, cumulative tissue degradation. In this paper propagation speed and attenuation vs temperature are measured using multiple groups of samples, each group heated to a different temperature. Sample thicknesses are measured directly using a technique that uses both transmitted and reflected ultrasound pulses. Results obtained using 3 and 5 MHz center frequencies demonstrate a propagation speed elevation of around 20 m/s in the 22-60 degrees C range, and a decrease of 15 m/s in the 60-90 degrees C range, in agreement with previous results where the same specimens were subjected to the entire temperature range. However, sound speed results reported here are slightly higher than those reported previously, probably due to more accurate measurements of sample thickness in the present experiments. Results also demonstrate that while the propagation speed varies with temperature, it is not a function of tissue coagulation. In contrast, the attenuation coefficient depends on both tissue coagulation effects and temperature elevation.     

Phase transitions of nanoemulsions using ultrasound: experimental observations

The ultrasound-induced transformation of perfluorocarbon liquids to gases is of interest in the area of drug and gene delivery. In this study, three independent parameters (temperature, size, and perfluorocarbon species) were selected to investigate the effects of 476-kHz and 20-kHz ultrasound on nanoemulsion phase transition. Two levels of each factor (low and high) were considered at each frequency. The acoustic intensities at gas bubble formation and at the onset of inertial cavitation were recorded and subsequently correlated with the acoustic parameters. Experimental data showed that low frequencies are more effective in forming and collapsing a bubble. Additionally, as the size of the emulsion droplet increased, the intensity required for bubble formation decreased. As expected, perfluorohexane emulsions require greater intensity to form cavitating bubbles than perfluoropentane emulsions.     

Vocal tract resonances and the sound of the Australian didjeridu (yidaki) I. experiment

The didjeridu, or yidaki, is a simple tube about 1.5 m long, played with the lips, as in a tuba, but mostly producing just a tonal, rhythmic drone sound. The acoustic impedance spectra of performers' vocal tracts were measured while they played and compared with the radiated sound spectra. When the tongue is close to the hard palate, the vocal tract impedance has several maxima in the range 1-3 kHz. These maxima, if sufficiently large, produce minima in the spectral envelope of the sound because the corresponding frequency components of acoustic current in the flow entering the instrument are small. In the ranges between the impedance maxima, the lower impedance of the tract allows relatively large acoustic current components that correspond to strong formants in the radiated sound. Broad, weak formants can also be observed when groups of even or odd harmonics coincide with bore resonances. Schlieren photographs of the jet entering the instrument and high speed video images of the player's lips show that the lips are closed for about half of each cycle, thus generating high levels of upper harmonics of the lip frequency. Examples of the spectra of "circular breathing" and combined playing and vocalization are shown.     

High-performance optical code generation and recognition by use of a 511-chip, 640-Gchip/s phase-shifted superstructured fiber Bragg grating

The generation and recognition of a record-length 511-chip optical code is experimentally demonstrated by use of a superstructured fiber Bragg grating (SSFBG) with a chip rate of 640 Gchips/s. Very high reflectivity (92%) is achieved with high-quality correlation properties. The temperature deviation tolerance is approximately +/- 0.3 degrees C, which is within the package's temperature stability range (+/- 0.1 degrees C). Experimental results show good agreement with the theory. They indicate the SSFBG's potential for processing a long optical code with an ultrahigh chip rate, which could significantly improve the system's performance.     

Determination of physicochemical properties of diacylglycerol oil at high pressure by means of ultrasonic methods

The purpose of the paper is to address, using ultrasonic methods, the impact of temperature and pressure on the physicochemical properties of liquids on the example of diacylglycerol (DAG) oil. The paper presents measurements of sound velocity, density and volume of DAG oil sample in the pressure range from atmospheric pressure up to 0.6 GPa and at temperatures ranging from 20 to 50 °C.     

On the metrology of the speed of sound in liquids

Decentralization of the standards base in measuring the speed of sound in liquids by expressing the speed of sound in fractions of the speed of light in vacuum is considered. A method to take into account the diffraction effects by measuring the speed of sound in the case of a constant acoustic wavelength and binding the absolute speed of sound values to the calculated thermodynamic values obtained by the nonacoustical method when the adiabatic compressibility is equal to the isothermal one is proposed. Errors of the reproducibility of the unit of the speed of sound in water using the proposed method are estimated.     

Acoustic scattering from double-diffusive microstructure

Laboratory measurements of high-frequency broadband acoustic backscattering (200-600 kHz) from the diffusive regime of double-diffusive microstructure have been performed. This type of microstructure, which was characterized using direct microstructure and optical shadowgraph techniques, is identified by sharp density and sound speed interfaces separating well-mixed layers. Vertical acoustic backscattering measurements were performed for a range of physical parameters controlling the double-diffusive microstructure. The echoes have been analyzed in both the frequency domain, providing information on the spectral response of the scattering, and in the time domain, using pulse compression techniques. High levels of variability were observed, associated with interface oscillations and turbulent plumes, with many echoes showing significant spectral structure. Acoustic estimates of interface thickness (1-3 cm), obtained for the echoes with exactly two peaks in the compressed pulse output, were in good agreement with estimates based on direct microstructure and optical shadowgraph measurements. Predictions based on a one-dimensional weak-scattering model that includes the actual density and sound speed profiles agree reasonably with the measured scattering. A remote-sensing tool for mapping oceanic microstructure, such as high-frequency broadband acoustic scattering, could lead to a better understanding of the extent and evolution of double-diffusive layering, and to the importance of double diffusion to oceanic mixing.