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Radiation, Diffraction, and Scattering
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
One of the many issues of this chapter will be the treatment of diffraction effects. For simplicity, we deal with scalar theory for a fluid medium although the results can be directly extended to a solid medium. We start with radiation from a point source and then extend the discussion to radiation by a circular piston. This is a classic problem in ultrasonics and the results give general guidelines for the emission of ultrasonic waves from a piezoelectric transducer. Following that, an outline is provided for the scattering of ultrasonic waves by circular and cylindrical obstacles. Finally, the main issues involved in focused ultrasonic waves, acoustic radiation pressure and the Doppler shift, are addressed.
Modeling and simulation of single droplet drying in an acoustic levitator
Published in Drying Technology, 2023
Martin Doß, Nadja Ray, Eberhard Bänsch
In this section, we present our direct numerical model for the full drying process of an acoustically levitated droplet containing water, protein, and possibly some salt for pH regulation. The reader is also referred to our previous paper[25] where some aspects are carried out in more detail. Our main assumptions and conventions are the following: Neither gravity nor the acoustic radiation pressure affects the shape of the levitated droplet. Therefore, its spherical domain is given by where Rd denotes the time-dependent droplet radius. As illustrated in Figure 1, the protein molecules are compressed within the shrinking droplet until they form a rigid packed particle at the end of the first drying stage. This assumption requires the Péclet number
Theoretical formulism analyzing damping nature of the ferromagnetic shape memory alloy
Published in Mechanics of Advanced Materials and Structures, 2023
S. B. P. Abirami, M. Mahendran
Ni48Mn32Ga20 single crystal sample is placed in contact with the stack along the direction of wave propagation. Stress pulses outputted from the stack extend or contract the FSMA sample. At first, the driving electrical pulse forces the stack to rapidly charge up to 20 V and expand thus generating a compressive stress pulse in FSMA. Then while discharging the stack, it recoils slowly transmitting a tensile stress pulse. The expansion/contraction of the piezostack after each pulse is a few microns, whereas that of FSMA sample is a few tenths of a millimeter as they exhibit strains up to 50 or 100 times greater than those of piezoelectric material. By tuning the rise time of the electrical pulses, the stack is expanded quickly in microseconds but contracted more slowly in milliseconds to facilitate the generation of asymmetric acoustic pulses in FSMA. In asymmetric stress pulse, the magnitude of the compressive stress in FSMA is higher than the twinning-yield stress whereas that of tensile stress is below that. Asymmetric acoustic stress is a crucial feature to extend or contract the crystal one pulse at a time to induce twin boundary motion. There are other ways too, like using resonant waves with stress intensities high enough to induce twin boundary motion, or using the acoustic radiation pressure of a sound wave. The former method has the drawback of rapid heating of the stack causing phase transformation in FSMA sample, and the latter would require implausible levels of stress wave amplitudes on the order of 1 GPa [37, 42].