8 research outputs found
Metahouse: noise-insulating chamber based on periodic structures
Noise pollution remains a challenging problem requiring the development of
novel systems for noise insulation. Extensive work in the field of acoustic
metamaterials has led to occurrence of various ventilated structures which,
however, are usually demonstrated for rather narrow regions of the audible
spectrum. In this work, we further extend the idea of metamaterial-based
systems developing a concept of a metahouse chamber representing a ventilated
structure for broadband noise insulation. Broad stop bands originate from
strong coupling between pairs of Helmholtz resonators constituting the
structure. We demonstrate numerically and experimentally the averaged
transmission -43 dB within the spectral range from 1500 to 16500 Hz. The
sparseness of the structure together with the possibility to use optically
transparent materials suggest that the chamber may be also characterized by
partial optical transparency depending on the mutual position of structural
elements. The obtained results are promising for development of novel
noise-insulating structures advancing urban science
Ultra-broadband Noise-Insulating Periodic Structures Made of Coupled Helmholtz Resonators
Acoustic metamaterials and phononic crystals represent a promising platform
for the development of noise-insulating systems characterized by a low weight
and small thickness. Nevertheless, the operational spectral range of these
structures is usually quite narrow, limiting their application as substitutions
of conventional noise-insulating systems. In this work, the problem is tackled
by demonstration of several ways for the improvement of noise-insulating
properties of the periodic structures based on coupled Helmholtz resonators. It
is shown that tuning of local coupling between the resonators leads to the
formation of ultra-broad stop-bands in the transmission spectra. This property
is linked to band structures of the equivalent infinitely periodic systems and
is discussed in terms of band-gap engineering. The local coupling strength is
varied via several means, including introduction of the so-called chirped
structures and lossy resonators with porous inserts. The stop-band engineering
procedure is supported by genetic algorithm optimization and the numerical
calculations are verified by experimental measurements
Thermal analysis for optimization of the optical duct of the ITER core CXRS diagnostics
The First Mirror (M1), as part of the ITER core CXRS diagnostics, is responsible for acquisition and transportation of the optical signal from the plasma to the corresponding spectrometer. The M1 is the most vulnerable component of this system working in severe conditions caused by its location in the direct view of the plasma. Based on the numerical analysis an optimized arrangement of baffles was found for the optical channel. It is shown that such measures like the deeper M1 positioning in the shielding, duct configuration and baffles implementation made it possible to reduce heat loads on the M1 by a factor of about 102–103