Locating an acoustic point source scattered by a skull phantom via time reversal matched filtering

This paper examines the utilization of the time reversal matched filtering method to resolve the location of an acoustic point source beneath a skull phantom (variable thickness layer), without the removal of this layer. This acoustical process is examined experimentally in a water tank immersion system containing an acoustic source, a custom-made skull phantom, and a receiving transducer in a pitch-catch arrangement. The phantom is designed to approximately model the acoustic properties of an average human skull bone (minus the diploe layer), while the variable thickness of the phantom introduces a variable time delay to the acoustic wave, relative to its entry point on the phantom. This variable delay is measured and corrected for, and a matched filtering time reversed process is used to determine the location of the point source. The results of the experiment are examined for various positions of the acoustic source behind the phantom and compared to the reference cases with no phantom present. The average distance between these two cases is found to be 4.36 mm, and within the expected deviation in results due to not accounting for the effects of refraction.     

Linear dichroism, produced by thermo-electric alignment of silver nanoparticles on the surface of ion-exchanged glass

A heated Ag⁺-doped glass is subjected to an external constant uniform electric field (E_o > 250 V/cm) parallel to its surface. Absorption spectra studies by linear polarized light imply the induction of a linear dichroism in the samples, after the above-mentioned thermo-electrical process. It is found that the increase in the temperature (400 °C ≤ T ≤ 600 °C), results in the formation of neutral silver multimers and clusters on the samples. Dichroism is the result of simultaneous application of the steady uniform electric field and heating. That is, the process aligns the produced silver nanoparticles along the applied electric field (E_o) during the aggregation of silver nano-clusters via dipole-dipole interaction, leading to the formation of chain-like conductive structures.