04 Dec

Winter Symposium 2012/End of Semester Celebration

In two days we will be holding our second annual ASA symposium. This year we will hear interesting talks from the student body here at Georgia Tech. See the list below for this year’s speakers and presentation topics. Please make an effort to come and support your lab mates, students, or friends. Again we will also have a full spread of food as we wrap up another great semester. Feel free to bring friends to this event.

ASA Winter Symposium
Time: Thursday December 6th 4:30 -7p
Location: MRDC 4211

Presenter: Drew Loney
Title: Acoustic analysis of a horn-based ultrasonic ejector for viscous fluid atomization
Abstract: An analytical model of a horn-based ultrasonic atomizer is developed for investigating droplet generation from high viscosity fluids. The simulated device incorporates a piezoelectric transducer, a fluid reservoir, and a micromachined silicon array of acoustic liquid horn structures as ejection nozzles. When driven at resonant frequencies of the fluid cavity, a locally increased pressure gradient results at the horn aperture. Previous experimental work showed the capability of the atomizer to eject high viscosity fluids, overcoming a limitation traditionally associated with piezoelectric inkjets. This work focuses on the acoustics of the device, developing a quasi-one-dimensional, analytical model of the device which is validated with finite element analysis simulations. Emphasis is placed on accounting for viscous effects such as wave attenuation and viscous boundary layer losses. The effect of viscous attenuation on the pressure gradient magnitude at horn aperture – the parameter which defines the threshold for the fluid ejectability – is also investigated.

Presenter: Brendan Nichols
Title: Locating Sources with Vector-Sensor Beamforming
Abstract: Locating objects in an ocean environment is a key component in naval defense as well as marine mammal observation. Localization can be performed using beamforming, a technique which combines data from multiple sensors to estimate the position of a source. This technique can also be applied to vector sensors, which are capable of measuring both acoustic pressure and particle velocity. To determine the effects of sensor position and uncertainty on the localization accuracy, simulation code was implemented to test the beamforming method and its accuracy under various conditions.

Presenter: Shima Shahab
Title: Outgoing Waves from a Fully and Partially Submerged Cylindrical Pile
Abstract: Pile driving can produce underwater sound pressures exceeding 200 dB at ranges greater than 100 meters. Methods are needed to predict sound levels and develop appropriate mitigation techniques for potentially harmful sound exposures. A finite-difference time-domain (FDTD) formulation is presented to analyze sound produced from a large steel pile. Following an impact hammer strike, a stress wave travels down the pile wall and produces expansions and contractions in the radial direction, which couple with the surrounding fluids to create propagating sound waves. Results of correlations between radiated sound fields predicted by the FDTD model and acoustic field data are presented.

Presenter: Shane Lani
Title: Coherent processing of shipping noise for ocean monitoring
Abstract: Extracting coherent wavefronts between passive receivers using cross-correlations of ambient noise may provide a means for ocean monitoring without conventional active sources. Hence applying this technique to continuous ambient noise recordings provided by existing or future ocean observing systems may contribute to the development of long-term ocean monitoring applications such as passive acoustic thermometry. To this end, we investigated the emergence rate of coherent wavefronts over 6 days using low-frequency ambient noise (f < 1.5 kHz) recorded on two vertical line arrays-separated by 500m- deployed off San-Diego CA in ~200m deep water. The recorded ambient noise was dominated by nonstationary distributed shipping activity with the frequent occurrence of loud isolated ships. Noise data were first processed to mitigate the influence of these loud shipping events in order to primarily emphasize the more homogenous and continuous background ambient noise in the frequency band. Furthermore, the coherent noise field propagating between the VLAs was beamformed using spatio-temporal filters to enhance the emergence rate of specific coherent wavefronts. This presentation will discuss various strategies for the selection of these spatio-temporal filters (either data-derived or model-based) in order to improve the continuous tracking of these coherent wavefronts over 6 days.

Presenter: Katherine Woolfe
Title: Results of a scaled physical model to simulate impact pile driving
Abstract: To have a better understanding of the parameters involved in the structural acoustics modeling of pile driving, a scaled physical model has been created. By measuring the radial wall motion of the model and comparing this with the pressure measured by two separate hydrophone arrays, the effects of fluid loading upon wall motion can be observed in both the time and frequency domains. The intensity data obtained from this model can be used to analyze the transient energy exchange between the structure and the water, showing that energy radiated into the fluid re-enters the structure when the wall motion attenuates.

Presenter: Toby Xu
Title: Investigation of Dual Mode Side and Forward Looking IVUS Using a Dual Ring CMUT-on-CMOS Array
Abstract: Forward looking (FL) capability is desired in IVUS catheters to enable real time volumetric visualization of especially nearly or fully blocked arteries to guide interventions. The addition of side looking (SL) capability in the same catheter would be valuable to locate the device with respect to vessel walls and provide a conventional image to the clinicians. A single chip CMUT-on-CMOS array may provide both capabilities while enabling an extremely flexible catheter tip implementation. In this study, the combined side and forward viewing ability of the CMUT-on-CMOS IVUS array is investigated and initial experimental results are presented. To demonstrate SL imaging, we used a 20-MHz single chip dual-ring CMUT-on-CMOS array with 56 transmit and 48 receive elements fabricated on a 1.5-mm diameter 0.3-mm thick silicon donut. We placed four vertical wire targets close to the array plane and a front wire located above the same array. The frequency spectrums of the side and front targets have a center frequency of 12 MHz and 20 MHz, respectively. We also performed finite element method (FEM) simulations to obtain the frequency spectrums of the transient pressure signals at 0° and 90° which showed the same center frequencies. These results show promise for the viability of FLIVUS CMUT-on-CMOS device with dual mode side-forward looking imaging.