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Nov 2003

Volume 114, Issue 5, pp. 2507-2968

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Detection of object resonances by vibro-acoustography and numerical vibrational mode identification

Farid G. Mitri, Philippe Trompette, and Jean-Yves Chapelon

J. Acoust. Soc. Am. Volume 114, Issue 5, pp. 2648-2653 (2003); (6 pages) | Cited 6 times

Online Publication Date: 29 Oct 2003

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Chalk sphere and cylinder resonance frequencies related to compressional and bending modes were detected in water, using vibro-acoustography, a relatively new imaging technique. The variable (radiation) force of low-frequency excitation, produced by intersecting two primary focused ultrasound waves with slightly different frequencies, forces the object to vibrate. The low-frequency acoustic emission field, resulting from object vibration, was detected by a hydrophone. By fixing the object at the focus of the ultrasound beam and sweeping the frequency of one of the primary beams within a chosen bandwidth, it was possible to detect some of the resonance frequencies (those related to compressional and bending modes) via variations in acoustic emission amplitude. Experimental results showed excellent agreement with finite element calculations. This method can be used to characterize the presence of heterogeneities in various media, in the field of materials science or biology. © 2003 Acoustical Society of America.
Show PACS
43.25.Qp Radiation pressure
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance

The selection of layer thicknesses to control acoustic radiation force profiles in layered resonators

Martyn Hill

J. Acoust. Soc. Am. Volume 114, Issue 5, pp. 2654-2661 (2003); (8 pages) | Cited 4 times

Online Publication Date: 29 Oct 2003

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Ultrasonic standing waves can be used to generate radiation forces on particles within a fluid. A number of authors have derived detailed representations of these forces but these are most commonly applied using an approximation to the energy distribution based upon an idealized standing wave within a mode based upon rigid boundaries. An electro-acoustic model of the acoustic energy distribution within a standing wave with arbitrary thickness boundaries has been expanded to model the radiation force on an example particle within the acoustic field. This is used to examine the force profile on a particle at resonances other than those predicted with rigid boundaries, and with pressure nodes at different positions. A simple analytical method for predicting modal conditions for combinations of frequencies and layer thickness characteristics is presented, which predicts that resonances can exist that will produce a pressure node at arbitrary positions in the fluid layer of such a system. This can be used to design resonators that will drive particles to positions other than the center of the fluid layer, including the fluid/solid boundary of the layer, with significant potential applications in sensing systems. Further, the model also predicts conditions for multiple subwavelength resonances within the fluid layer of a single resonator, each resonance having different nodal planes for particle concentration. © 2003 Acoustical Society of America.
Show PACS
43.25.Qp Radiation pressure
43.20.Ks Standing waves, resonance, normal modes

The ultrasonic weak short-pulse responses of microbubbles based on a two-frequency approximation

Chung-Yuo Wu and Jenho Tsao

J. Acoust. Soc. Am. Volume 114, Issue 5, pp. 2662-2671 (2003); (10 pages)

Online Publication Date: 29 Oct 2003

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The ultrasonic short-pulse responses of microbubbles are of interest in cavitation, transient responses, and contrast imaging. We extend the two-frequency analytic solutions of Newhouse and Shankar [J. Acoust. Soc. Am. 75, 1473–1477 (1984)] to approximate the short-pulse responses of microbubbles in a low-amplitude field. Based on their results, there is an expected component near dc in the spectrum of bubble echoes excited by a short pulse. Here this component is named the low-frequency response, and its theoretical properties are verified experimentally. Including the fundamental and second-harmonic components, the weak short-pulse responses of microbubbles include three types of response. Our work has determined the constraint conditions under which this approximated solution can be used to analyze these short-pulse responses. This paper also provides the amplitude and spectral properties of these responses. The low-frequency response has a special bandwidth-dependent property and has potential applications in imaging and bubble sizing. © 2003 Acoustical Society of America.
Show PACS
43.25.Yw Nonlinear acoustics of bubbly liquids
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
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