Optimalizace parametrů dutinových rezonátorů s rezonanční membránou
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Obecným problémem dneška je vyřešení otázky všudypřítomného hluku, který je velmi obtížné pohlcovat v oblasti nízkých frekvencí zvukového vlnění. Neboť je z principu potřeba materiálu velké tloušťky. Pohltivá sendvičová řešení uvažovaná v této práci jsou založena na resonančním principu nanovlákenné membrány a úspěšně působí jako širokospektrální zvukově pohltivá řešení. Nanovlákenná vrstva zanedbatelné tloušťky, připravená z roztoku polymeru (např. PA6, PVA, PUR, aj.) metodou elektrostatického zvlákňování, je schopna rezonovat na vlastní frekvenci a tím pohlcovat kritické nižší zvukové frekvence. Tyto výjimečné vlastnosti jsou dány povahou nanovlákenných vrstev - zejména malým průměrem vláken, resp. velkým specifickým povrchem. To umožňuje vyšší viskózní ztráty. Optimální tuhost membrány pak díky nanovlákenné struktuře umožňuje snadnější rezonanci systému. Tak byly vyvinuty a optimalizovány akustické systémy ve formě nanovlákenné resonanční membrány tlumené pohltivým porózním materiálem, které pohlcují zvuk již od oblasti nízkých frekvencí a přitom zůstávají pohltivými pro frekvence vyšší. Resonanční membránou byly dále optimalizovány dutinové rezonátory a perforované panely. Byly navrženy optimální materiály a strukturní parametry jednotlivých akustických prvků. Ty byly poté vyrobeny a jejich pohltivost hodnocena metodou Dvoumikrofonové impedanční trubice. Na základě toho došlo k optimalizaci strukturních parametrů a byla vybrána nejvýhodnější uspořádání akustických systémů, která byla testována nejprve v laboratorním měřítku opět pomocí Dvou-mikrofonové impedanční trubice, poté nezávislou laboratoří v dozvukové místnosti a nakonec ještě podstoupila zkoušky hořlavosti. Ukázalo se, že akustické systémy s nanovlákennou vrstvou zvyšují hodnoty zvukové pohltivosti a posouvají ji do oblasti nízkých a středních kmitočtů. Oproti samotným akustickým systémům přitom dochází k výraznému snížení tloušťky pohltivého materiálu, přičemž zvuková pohltivost je vyšší či stejná.Zde optimalizovaná akustická řešení jsou novým technologickým směrem akustiky. Při nízké hmotnosti a minimální tloušťce (nižším odsazení od obkládaných stěn) nabízí účinný, esteticky zajímavý, funkčně modifikovatelný a ekonomicky výhodný způsob jak řešit prostorovou akustiku objektů nebo odhlučnění provozních elektromechanických zařízení.
One of the current issues is a solution of an omnipresent background noise, which is really difficult to absorb in the area of low frequencies of sound waves. The basic principle of sound absorption is the fact that the effectiveness of the sound absorbing material increases with its thickness. Absorbing sandwich-like solutions developed in this thesis are based on a resonant principle of a nanofibrous membrane and they function successfully as broadband sound absorbing solutions. The resonant nanofibrous layer of insignificant thickness was prepared from a solution of polymer (PA6, PVA, PUR, etc.) with the electrospinning method. Due to the possibility of resonating on its own resonant frequency the nanofibrous membrane is able to absorb critical lower sound frequencies. These unique properties come from the nature of nanofibrous layers small fibrous diameter, respectively enormous surface area of the layer. This makes it possible to reach higher viscous loss inside the material. Optimal rigidity of the membrane then makes an acoustic system possible to vibrate easier. Thus were developed and optimized acoustic structures in the form of the resonant nanofibrous membrane damped by the fiber web and sound absorbing porous bulk material which absorb sound already from a low-frequency range while they stay absorbing for higher frequencies. Helmholtz-based resonators cavity resonators and perforated panels, were also optimized with the resonant membrane. The optimal material types and structural characteristics of the each acoustic component have been proposed. Then the earlier designed solutions were made and their sound absorbing ability was estimated in an impedance tube. Structural characteristics were then optimized on the basis of obtained sound absorption coefficients from the impedance tube. The optimal adjustment of acoustics systems, which was tested by an independent reverberant chamber and underwent flammability tests at the same time, were chosen. It turned out the acoustic systems with the nanofibrous layer increase values of sound absorption and move it to the range of low and middle frequencies. While the thickness of those absorption materials is rapidly decreasing, sound absorption remains still the same or higher.The acoustic solutions presented in this thesis were optimized by adding a nanofibrous membrane. These structures are a new technological section of acoustics. They offer an efficient, aesthetically appealing, functionally modifiable and economically advantageous way how to deal with architectural acoustics or noise elimination of electromechanical operation devices, whereas they excel at low weight and minimal thickness (or air gaps).
One of the current issues is a solution of an omnipresent background noise, which is really difficult to absorb in the area of low frequencies of sound waves. The basic principle of sound absorption is the fact that the effectiveness of the sound absorbing material increases with its thickness. Absorbing sandwich-like solutions developed in this thesis are based on a resonant principle of a nanofibrous membrane and they function successfully as broadband sound absorbing solutions. The resonant nanofibrous layer of insignificant thickness was prepared from a solution of polymer (PA6, PVA, PUR, etc.) with the electrospinning method. Due to the possibility of resonating on its own resonant frequency the nanofibrous membrane is able to absorb critical lower sound frequencies. These unique properties come from the nature of nanofibrous layers small fibrous diameter, respectively enormous surface area of the layer. This makes it possible to reach higher viscous loss inside the material. Optimal rigidity of the membrane then makes an acoustic system possible to vibrate easier. Thus were developed and optimized acoustic structures in the form of the resonant nanofibrous membrane damped by the fiber web and sound absorbing porous bulk material which absorb sound already from a low-frequency range while they stay absorbing for higher frequencies. Helmholtz-based resonators cavity resonators and perforated panels, were also optimized with the resonant membrane. The optimal material types and structural characteristics of the each acoustic component have been proposed. Then the earlier designed solutions were made and their sound absorbing ability was estimated in an impedance tube. Structural characteristics were then optimized on the basis of obtained sound absorption coefficients from the impedance tube. The optimal adjustment of acoustics systems, which was tested by an independent reverberant chamber and underwent flammability tests at the same time, were chosen. It turned out the acoustic systems with the nanofibrous layer increase values of sound absorption and move it to the range of low and middle frequencies. While the thickness of those absorption materials is rapidly decreasing, sound absorption remains still the same or higher.The acoustic solutions presented in this thesis were optimized by adding a nanofibrous membrane. These structures are a new technological section of acoustics. They offer an efficient, aesthetically appealing, functionally modifiable and economically advantageous way how to deal with architectural acoustics or noise elimination of electromechanical operation devices, whereas they excel at low weight and minimal thickness (or air gaps).
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nanovlákenný, resonanční, akustický, nízké frekvence, širokospektrální, porózní, činitel zvukové pohltivosti, impedanční trubice, nanovrstva, membrána, perforace, Helmholtz, sendvič, nanofibrous, resonant, acoustic, low frequencies, broadband, porous, sound absorption coefficient, impedance tube, nanolayer, membrane, perforation, Helmholtz, sandwich