Low Absorption Capability Research Articles

Interface feature via key factor on adhesion of CrN multilayer and alloy substrate

CrN multilayer coatings were deposited on 316L stainless steel, which has a high modulus, and TC4 titanium alloy, which exhibits the opposite properties, to reveal adhesion mechanisms and deformation behavior of the coating/substrate systems. Because of the different microstructures, the coatings’ morphologies varied from single polygon on the 316L to polygon and rectangle-mixed shapes on the TC4. On 316L, the cracks initiated from the Cr/CrN interfaces and propagated into the CrN layer, which stopped within it. On TC4, the cracks propagated through the CrN layer. The coherent nanocrystal interfaces in CrN/Cr/316L exhibited orderly bending, revealing the presence of strong interfacial bonds. The undeformed interfaces in CrN/Cr/TC4 indicated incompatible deformation and weak bonds. This was consistent with the fact that on TC4, the Cr/CrN interface tensile stress was high, at 123.1 GPa, while it was lower on 316L, at 99.3 GPa. The Wp/We ratio of CrN/TC4, namely 1.94, was lower than that of CrN/316L, namely 2.61. This indicated that CrN/316L had a high energy-absorption ability because of compatible plastic deformation. The failure mechanism observed between the coating/TC4 was attributed to the differences in their moduli, which led to incompatible deformation, high interfacial tensile stress, and low absorption capability for external work.

Enhancement of bass frequency absorption in fabric-based absorbers

Variable Acoustics has become an important topic in the acoustic design of multi-purpose venues but also in classical concert halls and opera houses. Varying the reverberation time in the middle and high frequencies can easily be achieved by using fabric-based absorbers like curtains or roll banners. When using fabric-based absorbers, the proportionally low absorption capability in the bass frequencies below 400 Hz can be challenging when planning a multi-purpose facility. A full range variable system would provide a great tool to consultants and architects. Double layer roll banner systems with a highly absorbing fabric are mostly installed freely hanging in front of the wall. Research shows a significant enhancement of the bass frequency absorption if the fabric is installed in an enclosed housing. This paper will examine the fundamental problem of low bass absorption capability but will also show the measurement data and technical solution for the described problem.

Investigation and correction for the calibration error of using two-microphone impedance tube method on low absorption materials

The two-microphone impedance tube method has been widely used for determining the sound absorption coefficients of materials. In this method, a calibration procedure is performed to correct the amplitude and phase mismatch of the two microphones, through repeated measurement of a specimen with the two channels interchanged. Both ASTM E1050-12 and ISO 10534-2 suggest the use of a highly absorptive material as the calibration specimen and the calibration, once complete, is valid for all successive measurements. When following the Standards, however, test materials of low absorption capability exhibited a pattern of peaks and dips in the absorption coefficient curve at certain frequencies, which are obviously not a part of the material’s own behavior. This paper will discuss the cause of these peaks and dips and also suggest a simple solution to the issue. Using the new method, one is able to obtain smooth absorption coefficient curves for low absorption test materials just as expected.

Water sorption-desorption test and moisture accumulation test for functional assessment of atopic skin in children.

Sorption-desorption and moisture accumulation tests are simple and quick methods for the in vivo functional analysis of stratum corneum hydration kinetics. The aim of this study was to evaluate the hydration dynamics of the uninvolved and affected skin of children with atopic dermatitis and to compare them with the skin of healthy children. The study investigated 45 children. The dynamic tests were performed using the corneometer CM820. Numerical parameters were calculated. With the sorption-desorption test, eczematous skin showed lower water accumulation during the sorption phase, whereas water was released more slowly during the desorption phase. With the moisture accumulation test, increases in water accumulation velocity and in water accumulation were observed in atopic children. Dynamic tests showed that the stratum corneum of unaffected atopic skin was less hydrated but more easily hydratable than normal skin. Conversely, despite a lower absorption capability, eczematous skin showed a greater avidity to retain water. New functional parameters (water-sorption capacity and accumulated water decay) are proposed to describe more precisely the hydration kinetics of eczematous skin.