Perforated membrane-type acoustic metamaterials

This letter introduces a modified design of membrane-type acoustic metamaterials (MAMs) with a ring mass and a perforation so that an airflow through the membrane is enabled. Simplified analytical investigations of the perforated MAM (PMAM) indicate that the perforation introduces a second anti-resonance, where the effective surface mass density of the PMAM is much higher than the static value. The theoretical results are validated using impedance tube measurements, indicating good agreement between the theoretical predictions and the measured data. The anti-resonances yield high low-frequency sound transmission loss values with peak values over 25 dB higher than the corresponding mass-law.</p

In situ differential scanning calorimetry analysis of dissolution and precipitation kinetics in Mg–Y–RE alloy WE43

Further development of our differential scanning calorimetry (DSC) method for the analysis of solid-solid phase transformations now also allows for its application in the kinetic analysis of age hardening in Mg alloys. As a result, the state-of-the-art for DSC on Mg alloys has been improved with respect to the accessible temperature range, zero-level accuracy and dynamic range. DSC analysis was performed on the example of Mg wrought alloy WE43. Heating DSC experiments on the initial condition T4 and even direct continuous cooling DSC analysis on the kinetics of quench induced precipitation during cooling from solution treatment were possible, covering a dynamic range of 0.01–3 K/s. The DSC findings are discussed with respect to literature knowledge and scanning electron microscopy analysis of the defined heat treatment states. Keywords: Precipitation, Dissolution, Kinetics, DSC, Magnesium alloy, WE43, SEM, Quench induced precipitation, Continuous coolin