Joel B. Lonzaga

Liquid jet response to internal modulated ultrasonic radiation pressure and stimulated drop production.

Experimental evidence shows that a liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. Ultrasound applied to the jet supply liquid can propagate within the jet when the acoustic frequency is near to or above the cutoff frequency. Modulated radiation pressure is used to stimulate large amplitude deformations and the breakup of the jet into drops. The jet response to the modulated internal ultrasonic radiation pressure was monitored along the jet using (a) an optical extinction method and (b) images captured by a video camera. The jet profile oscillates at the frequency of the radiation pressure modulation and where the response is small, the amplitude was found to increase in proportion to the square of the acoustic pressure amplitude as previously demonstrated for oscillating drops [P.L. Marston and R.E. Apfel, J. Acoust. Soc. Am. 67, 27-37 (1980)]. Small amplitude deformations initially grow approximately exponentially with axial distance along the jet. Though aspects of the perturbation growth can be approximated from Rayleighs analysis of the capillary instability, some detailed features of the observed jet response to modulated ultrasound are unexplained neglecting the effects of gravity.

Uniformly valid solution for acoustic propagation in weakly tapered circular waveguides: liquid jet example.

The propagation of ultrasound down laminar liquid jets has potential applications to the stimulation of liquid drop production [J. B. Lonzaga, C. F. Osterhoudt, D. B. Thiessen, and P. L. Marston, J. Acoust. Soc. Am. 121, 3323-3330 (2007)] as well as to the coupling of ultrasound to objects through contact with a jet. In normal gravity, a jet issuing from a nozzle becomes tapered as the jet accelerates downward. A uniformly valid solution for the acoustic propagation in a weakly tapered, liquid jet waveguide in air with a turning point is derived using Langers transformation and the method of multiple scales. The loss of energy from transmission into the air and from thermal viscous absorption is neglected. A solvability condition is used to obtain the leading-order correction due to the taper of the waveguide. This asymptotic solution is validated using finite-element numerical calculations. The ultrasonic wave amplitude is enhanced in the region of the jet close to the cutoff of the excited mode.

Time reversal for localization of sources of infrasound signals in a windy stratified atmosphere

Time reversal is used for localizing sources of recorded infrasound signals propagating in a windy, stratified atmosphere. Due to the convective effect of the background flow, the back-azimuths of the recorded signals can be substantially different from the source back-azimuth, posing a significant difficulty in source localization. The back-propagated signals are characterized by negative group velocities from which the source back-azimuth and source-to-receiver (STR) distance can be estimated using the apparent back-azimuths and trace velocities of the signals. The method is applied to several distinct infrasound arrivals recorded by two arrays in the Netherlands. The infrasound signals were generated by the Buncefield oil depot explosion in the U.K. in December 2005. Analyses show that the method can be used to substantially enhance estimates of the source back-azimuth and the STR distance. In one of the arrays, for instance, the deviations between the measured back-azimuths of the signals and the known source back-azimuth are quite large (-1° to -7°), whereas the deviations between the predicted and known source back-azimuths are small with an absolute mean value of <1°. Furthermore, the predicted STR distance is off only by <5% of the known STR distance.

A theoretical relation between the celerity and trace velocity of infrasonic phases

This paper presents a relationship between the celerity and trace velocity of infrasound signals propagating in a stratified, windy atmosphere. Despite their importance, known celerity values have only been determined empirically. An infrasonic phase (I-phase) diagram is developed which is useful in identifying different I-phases. Such an I-phase diagram allows for the prediction of the range of values of the celerity and trace velocity for each I-phase. The phase diagram can easily be extended to underwater acoustic and acoustic-gravity waves. An I-phase diagram is compared with data obtained from a ground-truth event where qualitative agreement is obtained.

Manipulation of fluid objects using acoustic radiation pressure: Beyond drops and bubbles and retrospection

Some standard applications of acoustic radiation pressure include the manipulation of drops and bubbles for the study of interfacial dynamics and light scattering. After a review, this presentation summarizes recent applications including radiation pressure effects on small flames and liquid cylinders [Wei et al., J. Acoust. Soc. Am. 116, 201–208 (2004)]. The dependence of the radiation pressure on the acoustic frequency has important consequences including liquid cylinder stabilization. While the radiation pressure is normally associated with sound propagation in the outer gas or liquid, our recent experiments also show that interfacial responses to modulated radiation pressure can be significant when the sound is applied internally to the manipulated object. For example, a liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. When modulated ultrasound is applied to the jet supply liquid with the ultrasonic carrier frequency near‐to or above the ...

Optical detection of the response of liquid jets to internal modulated ultrasonic radiation pressure

A liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. Ultrasound applied to the jet supply liquid can propagate down the jet when the carrier frequency is near‐to or above the cutoff frequency. The jet response to the internal acoustic radiation pressure of amplitude modulated ultrasound was monitored along the jet using an optical pseudo‐extinction method. The jet profile oscillates at the frequency of the radiation pressure modulation and, where the response is small, the amplitude was found to increase in proportion to the square of the acoustic pressure amplitude as previously demonstrated for oscillating drops [P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27–37 (1980)]. Small amplitude deformations initially grow approximately exponentially with axial distance along the jet. Modulated radiation pressure can be used to stimulate large amplitude deformations and the breakup of the jet into drops. [Work supported by NASA.]

On atmospheric updating, attenuation, and thermospheric phases in infrasonic wave-trains

Because of the dramatic increase in temperature in the thermosphere, thermospheric phases are ubiquitous, despite the fact that they are less often detected than are stratospheric phases. In the thermosphere, the density of the atmosphere is very low so that, as a propagation medium, the thermosphere is very non-linear and very attenuating. Atmospheric specifications of the lower thermosphere are not well constrained by data. This can lead to significant errors in modeling propagation along thermospheric paths. Methods for generating corrections to specifications of the thermosphere from infrasonic data are described. Further, using a non-linear ray theory model we find that non-linear effects in the thermosphere, in particular, period lengthening, mitigate against attenuation. Finally, we show that it is possible to use thermospheric returns to simultaneously update the atmospheric specifications while determining source yield.

On the interaction of infrasonic waves with internal gravity waves perturbations

Infrasonic waves propagate at long range through atmospheric ducts resulting from the stratification of atmospheric properties. These ducts are characterized by their spatio-temporal variability. Hence, infrasonic waves integrate atmospheric information along their propagation paths. In order to study infrasonic wave propagation, we resort to atmospheric specification combining Numerical Weather Prediction and climatological models. However, due to the lack of observations, these models fail to describe small scale variability such as perturbations associated to the presence of internal gravity waves. These waves play an important role in the atmospheric dynamic by transferring momentum to the mean flow at critical levels and at wave-breaking altitudes. In this study we intend to describe the interaction of infrasonic waves with internal gravity waves in order to understand the long-tail behavior observed in infrasound broadband signals. We developed a model for the propagation of internal waves used to generate realistic perturbations of the background atmospheric states. By using a linear full-wave model of infrasound propagation, our goal is to ultimately relate infrasound characteristics to internal waves properties.

Infrasound as a remote sensing technique for the upper atmosphere

Understanding and specification of the higher altitudes of the atmosphere with global overage over all local times is hampered by the challenges of obtaining direct measurements in the upper atmosphere. Methods to measure the properties of the atmosphere above the stratopause is an active area of scientific research. In this presentation, we revisit the use of infrasound as a passive remote sensing technique for the upper atmosphere. In the past, various studies focused on the sensitivity of infrasound to various upper atmospheric processes. It has been shown that the current state-of-the-art climatologies for the middle and upper atmosphere are not always in agreement with the acoustic data, suggesting a use of infrasound as a complementary remote sensing technique. Previously, we reported on the error in thermospheric celerities which was found to be in accord with the typical uncertainty in upper atmospheric winds and temperature. In this presentation, we report on the expected variation of the various...

Non-linear infrasound signal distortion and yield estimation from stratospheric and thermospheric arrivals

The propagation of sound through gases and fluids is intrinsically non-linear. The degree of non-linearity increases as the density of the propagation medium decreases. As a consequence, signals traveling through the upper atmosphere undergo severe non-linear distortion. This distortion takes two forms: waveform steepening and pulse stretching. These nonlinear effects are numerically investigated using non-linear ray theory. On one hand, waveform steepening is generally associated with stratospheric arrivals with sufficiently large amplitude for which the decreased density of the atmosphere causes shock fronts to form. On the other hand, pulse stretching is generally associated with thermospheric arrivals where severe attenuation prevents significant shock formation but severe non-linearity causes significant pulse stretching. Since non-linear effects increase with increasing signal amplitude, it is possible to use non-linear distortion to estimate signal source strength. Uncertainties in propagation path...