Development and Characterization of a Superresolution Ultrasonic Transducer.

Highly sensitive ultrasound probes are needed to expand the capabilities of biomedical ultrasound and industrial nondestructive testing (NDT). Pursuing better imaging quality, while keeping fabrication costs low, is an important trend in the current development of ultrasound imaging systems. In this article, we report the development and characterization of an ultrasonic transducer that (super)focuses ultrasonic waves beyond the so-called diffraction limit, that is, the beamwaist is roughly narrower than one wavelength.

Acoustic radiation force and torque on spheroidal particles in an ideal cylindrical chamber.

In this article, the acoustic radiation force and torque exerted on a small spheroidal particle immersed in a nonviscous fluid inside an ideal cylindrical chamber is theoretically investigated. The ideal chamber comprises a hard top and bottom (rigid boundary condition) and a soft or hard lateral wall. By assuming that the particle is much smaller than the acoustic wavelength, analytical expressions of the radiation force and torque caused by an acoustic wave of arbitrary shape are presented.

Acoustic spin transfer to a subwavelength spheroidal particle.

We demonstrate that the acoustic spin of a first-order Bessel beam can be transferred to a subwavelength (prolate) spheroidal particle at the beam axis in a viscous fluid. The induced radiation torque is proportional to the acoustic spin, which scales with the beam energy density. The analysis of the particle rotational dynamics in a Stokes flow regime reveals that its angular velocity varies linearly with the acoustic spin.

Acoustic radiation torque exerted on a subwavelength spheroidal particle by a traveling and standing plane wave.

The nonlinear interaction of ultrasonic waves with a nonspherical particle may give rise to the acoustic radiation torque on the particle. This phenomenon is investigated here considering a rigid prolate spheroidal particle of subwavelength dimensions that is much smaller than the wavelength. Using the partial wave expansion in spheroidal coordinates, the radiation torque of a traveling and standing plane wave with arbitrary orientation is exactly derived in the dipole approximation.

Acoustic radiation force due to incident plane-progressive waves on coated spheres.

The acoustic radiation force exerted by a traveling plane wave on a coated sphere was theoretically investigated. After carefully re-calculating the scattering coefficients of a model presented by Mitri [Eur. Phys.