An experimental technique is demonstrated for acoustically levitating aqueous foam drops and exciting their spheroidal modes. This allows fundamental studies of foam-drop dynamics that provide an alternative means of estimating the viscoelastic properties of the foam. One unique advantage of the technique is the lack of interactions between the foam and container surfaces, which must be accounted for in other techniques. Results are presented in which a foam drop with gas volume fraction $\phi =0.77\mathrm{}$ is levitated at 30 kHz and excited into its first quadrupole resonance at $63\pm 3\hspace{0.5em}\mathrm{Hz}.$ By modeling the drop as an elastic sphere, the shear modulus of the foam was estimated at $75\pm 3\hspace{0.5em}\mathrm{Pa}.$

A road is considered safe when it provides adequate friction between the tire and pavement surface interaction to avoid accidents. The current manual methods of evaluating surface friction of roads are not only dangerous for the inspectors and motorists on the road but are very time-consuming and subject to the inspector’s judgment. This paper confirms the possibility of monitoring pavement macrotexture from acoustic measurements underneath the body of a moving vehicle. Currently, macrotexture is quantified by a mean texture depth (MTD) index. In the present work, MTD is estimated from the sound generated by the tire-pavement interaction in a moving vehicle. To establish this approach, experiments were performed at the National Center for Asphalt Technology (NCAT), Auburn, Alabama. Signal processing techniques were used to identify a frequency band that led to an accurate correlation between integrated acoustic pressure and MTD collected by NCAT. This frequency band depends on the speed of the veh...

Surface waves are commonly used for vibration-based nondestructive testing for infrastructure. Spectral Analysis of Surface Waves (SASW) has been used to detect subsurface properties for geologic inspections. Recently, efforts were made to scale down these subsurface detection approaches to see how they perform on small-scale structures such as concrete slabs and pavements. Additional efforts have been made to replace the traditional surface-mounted transducers with non-contact acoustic transducers. Though some success has been achieved, most of these new approaches are inefficient because they require point-to-point measurements or off-line signal analysis. This article introduces a Mobile Acoustic Subsurface Sensing system as MASS, which is an improved surface wave based implementation for measuring the subsurface profile of roadways. The compact MASS system is a 3-wheeled cart outfitted with an electromagnetic impact source, distance register, non-contact acoustic sensors and data acquisition/ processing equipment. The key advantage of the MASS system is the capability to collect measurements continuously at walking speed in an automatic way. The fast scan and real-time analysis advantages are based upon the non-contact acoustic sensing and fast air-coupled surface wave analysis program. This integration of hardware and software makes the MASS system an efficient mobile prototype for the field test.

If the acoustic reflection coefficient is minimum phase, then the causality condition can be used to reconstruct its phase from its magnitude. Such reconstructions are useful when environmental conditions obscure the phase, which is vital to understanding the dynamics of the reflecting object. However, the reconstructions are usually impossible because one cannot be sure that the reflection coefficient is minimum phase. The present work addresses this difficulty by formulating a time-domain description of the minimum phase condition and by identifying classes of submerged objects that always create minimum phase reflection coefficients. Numerical examples are used to confirm the analytical findings and to illustrate their applicability to objects that reflect sound with a wide range of magnitudes.