Acoustic radiation force-induced longitudinal shear wave for ultrasound-based viscoelastic evaluation

Acoustic radiation force (ARF) is widely used to induce shear waves for evaluating the mechanical properties of biological tissues. Two shear waves can be generated when exciting with ARF: a transverse shear wave, also simply called shear wave (SW), and a longitudinal shear wave (LSW). Shear waves (SWs) have been broadly used to assess the mechanical properties. Some articles have reported that the LSW can be used to evaluate mechanical properties locally. However, existing LSW studies are mainly focused on the group velocity evaluation using optical coherence tomography (OCT). Here, we report that a LSW generated with ARF can be used to probe viscoelastic properties, including shear modulus and viscosity, using ultrasound. We took advantage of the surface boundary effect to reflect the LSW, named RLSW, to address the energy deficiency of LSW induced by ARF. We systematically evaluated the experiments with tissue-mimicking viscoelastic phantoms and validated by numerical simulations. Phase velocity and dispersion comparison between the results induced by a RLSW and a SW exhibit good agreement in both the numerical simulations and experimental results. The Kelvin-Voigt (KV) model was used to determine the shear modulus and viscosity. RLSW shows great potential to evaluate localized viscoelastic properties, which could benefit various biomedical applications such as evaluating the viscoelasticity of heterogeneous materials or microscopic lesions of tissues.

Ultrasonic depolymerization of Li2O-Na2O-SiO2 type silicate melt

Under the application of ultrasound, the organic polymers can be degraded for the reason of breakage of C-C or C-N bond induced by the cavitation effect, similar to organic polymers, the silicate melts are also one typical polymer connected with Si-O bonds. To verify the prediction of the depolymerization of silicate melt, the ultrasound was applied to one kind of silicate melt for the first time via a special designed experimental system. Results showed that, under the applying of the ultrasound, the Si-O (bridged O) bonds in the structure units of the silicate melt can be broken, which decreases the polymerization degree and the viscosity. Under the higher power of applied ultrasound, the polymerization degree and viscosity of the silicate melt further decrease. Unlike some organic polymers, once stopping applying ultrasound, the broken lower polymerized units reconnect to form higher polymerized units gradually, the degree of the polymerization and the viscosity reverse to its nature state of the silicate melts. According to these results, the potential applications in the steel continuous casting process and electrolytic aluminum process are predicted.