Specular reflection contributions to dynamic radiation forces on highly reflecting spheres (L).

Specular reflection contributions to dynamic radiation forces were recently mentioned for highly reflecting spheres to facilitate comparison with forces on cylinders [Marston, Daniel, Fortuner, Kirsteins, and Abawi, J. Acoust. Soc. Am. 149, 3042-3051 (2021)]. Both shapes of reflectors were taken to be illuminated by short-wavelength plane wave double-sideband suppressed-carrier ultrasound. Here, the geometric method of evaluating dynamic forces on spheres is illustrated along with an analysis of the phase of the modulated radiation force. Comparison with partial wave series solutions supports the relevance of the specular reflection analysis for insight into forces on highly reflecting objects in water.

Specular-reflection contributions to static and dynamic radiation forces on circular cylinders.

Interest in the response of highly reflecting objects in water to modulated acoustical radiation forces makes it appropriate to consider contributions to such forces from perfectly reflecting objects to provide insight into radiation forces. The acoustic illumination can have wavelengths much smaller than the object's size, and objects of interest may have complicated shapes. Here, the specular contribution to the oscillating radiation force on an infinite circular cylinder at normal incidence is considered for double-sideband-suppressed carrier-modulated acoustic illumination. The oscillatory magnitude of the specular force decreases monotonically with increasing modulation frequency, and the phase of the oscillating force depends on the relative phase of the sidebands. The phase dependence on the modulation frequency can be reduced with the appropriate selection of a sideband relative-phase parameter. That is a consequence of the significance of rays that are incident on the cylinder having small impact parameters that are nearly backscattered. For one choice of a relative sideband phase, a prior partial wave series (PWS) solution is available, which supports the specular analysis when the PWS is evaluated for a rigid cylinder. The importance of specular contributions for aluminum cylinders in water is noted. A specular analysis for an analogous spherical reflector is also summarized.

Maxwell stress excitation of wire vibrations at difference and sum frequencies of electric currents in separate circuits.

Oscillating electric currents through a wire under tension can excite transverse vibrational modes of the wire when a perpendicular static magnetic field is present and the frequency of the current is close to the natural frequency of the mode of interest. The excitation of the mode is associated with temporally oscillating Maxwell stresses on the wire, often also known as oscillating Lorentz forces. That excitation process is sometimes demonstrated in educational contexts. The investigation here concerns situations where a temporally oscillating magnetic field generated by oscillating electric currents in a cylindrical coil replaces the imposed perpendicular static magnetic field. The frequencies of the currents in the wire and in the coil are related to the frequency of the oscillating stress. In this experiment, this effect is documented for sum-frequency excitation (with input frequencies in the range of half that of the excited lowest vibrational mode of the wire) and the difference-frequency excitation (with input frequencies an order-of-magnitude larger than the mode frequency). This coupling may be useful when it is desirable to use only high-frequency currents. The experiment uses tone-burst stress excitation and a differential photodiode for detecting transverse low-amplitude wire oscillations. Signal envelopes decayed exponentially after the tone-burst.

A Pilot Study to Assess Clinical Utility and User Experience of Professional Continuous Glucose Monitoring Among People With Type 2 Diabetes.

IN BRIEF Glucose variability is a potential independent risk factor of poor clinical outcome among people with diabetes, with adequate measurement technically difficult and cumbersome. For this study, a novel 14-day continuous sensor was used to assess glucose variability among people with type 2 diabetes (T2D). The aim was to characterize glucose profiles for up to 2 weeks in T2D and to survey device utilization in a standard clinical setting and its potential to collect clinically meaningful data.

Bessel beam expansion of linear focused ultrasound.

Previous work on scattering by Bessel beams shows that expansion of incident sound fields in term of these beams has application to scattering [P. L. Marston, J. Acoust. Soc. Am. 122, 247-252 (2007)]. In this work, an expression for the expansion coefficients of propagating, axisymmetric, sound fields are derived. In this paper, this expression is applied to a linear focused axisymmetric sound field and is expanded in terms of Bessel beam components. This is done for focused beams radiated from a spherical cap source. A physical optics model is applied to sound propagation close to the source to facilitate the calculation of the Bessel beam expansion coefficients. This type of model is useful for focused scattering [P. L. Marston and D. S. Langley, J. Acoust. Soc. Am. 73, 1464-1475 (1983)]. Once the expansion coefficients are found, the sound field can be evaluated by superposition. The model agrees approximately with Chen, Schwarz, and Parker [J. Acoust. Soc. Am. 94, 2979-2991 (1993)] and O'Neil [J. Acoust. Soc. Am. 21, 516-526 (1949)] on axis and with direct integration of a Kirchhoff integral both on and off axis. This type of expansion will have applications to scattering problems.

Observation and modeling of acoustic scattering from a rubber spherical shell.

Acoustic backscattering from a rubber spherical shell in water is observed to contain a delayed enhancement, demonstrated to be associated with a waveguide path along the shell. This path is somewhat analogous to that of the Lamb wave observed on metallic shells. Rubber is a unique material because of its subsonic sound speed relative to water, and because shear coupling is often small enough to be neglected in typical models, making it fluid-like. This makes rubber a material of interest for coating and cloaking underwater devices and vehicles. Both fluid and elastic rubber partial wave series models are tested, using experimentally measured longitudinal and shear speeds, attenuation, and rubber density. A finite element model for the shell is also developed. Comparison of the models and experiments highlights the importance of the waveguide path to the overall scattering. Estimates for the group and phase velocities of the lowest order propagating mode in the shell are determined through waveguide normal mode analysis and Sommerfeld-Watson theory, and are shown to give good agreement with experiments in predicting the time of arrival of the waveguide path.