Acoustic foam

Tufcote, Faced acoustical foams, E-A-R Specialty Composites... 

Another space related topic is the reduction of noise impacts on pay-loads through active noise control using technologies such as an acoustic foam with embedded PVDF material, distributed active vibration absorbers (DAVA) made from acoustic foam hnked to a metallic plate and in a latest version even added by a very small electrodjmamic shaker that allows to cover lower frequencies [103]. This sandwich of acoustic foam, PVDF and electrodynamic shakers is then used as an active coating on the fairings of space vehicles. 

Faraday cage with acoustic foam insulation (9)... 

Electric, acoustic, and vibration isolation is essential for high-resolution current measurements and positional control. All instruments are mounted on vibration isolation tables (8 in Figure 19.2d), within a Faraday cage (custom made) with acoustic foam to reduce vibrations (9 in Figure 19.2d). Cameras or an optical microscope (not shown) can be used to aid positioning of the probe. 

Fig. 11.6 a The graph showing sound absorption efficiency of foam with and without nanofibre from low to high frequency, b The commercially available acoustic foam office furniture with Phonix ... 

M.Y. Serry Ahmed C. B. Park, N. Atalla. Control of Production and Morphology for Production of Novel LDPE Acoustical Foams. J of Cellular Polymers, V.25, 5, 277. 

Miscellaneous Properties. The acoustical properties of polymers are altered considerably by their fabrication into a ceUular stmcture. Sound transmission is altered only slightly because it depends predominandy on the density of the barrier (in this case, the polymer phase). CeUular polymers by themselves are, therefore, very poor materials for reducing sound transmission. They are, however, quite effective in absorbing sound waves of certain frequencies (150) materials with open ceUs on the surface are particulady effective. The combination of other advantageous physical properties with fair acoustical properties has led to the use of several different types of plastic foams in sound-absorbing constmctions (215,216). The sound absorption of a number of ceUular polymers has been reported (21,150,215,217). 

CeUular urea—formaldehyde and phenoHc resin foams have been used to some extent in interior sound-absorbing panels and, in Europe, expanded polystyrene has been used in the design of sound-absorbing doors (233). In general, cost, dammabUity, and cleaning difficulties have prevented significant penetration of the acoustical tile market. The low percent of redection of sound waves from plastic foam surfaces has led to their use in anechoic chambers (216). 

Other fibrous and porous materials used for sound-absorbing treatments include wood, cellulose, and metal fibers foamed gypsum or Pordand cement combined with other materials and sintered metals. Wood fibers can be combined with binders and dame-retardent chemicals. Metal fibers and sintered metals can be manufactured with finely controlled physical properties. They usually are made for appHcations involving severe chemical or physical environments, although some sintered metal materials have found their way into architectural appHcations. Prior to concerns regarding its carcinogenic properties, asbestos fiber had been used extensively in spray-on acoustical treatments. 

Generation Spontaneous generation of gas bubbles within a homogeneous liquid is theoreticaUy impossible (Bikerman, Foams Theoiy and Industrial Applications, Reinhold, New York, 1953, p. 10). The appearance of a bubble requires a gas nucleus as avoid in the liquid. The nucleus may be in the form of a small bubble or of a solid carrying adsorbed gas, examples of the latter being dust particles, boiling chips, and a solid wall. A void can result from cavitation, mechan-ic ly or acoustically induced. Blander and Katz [AlChE J., 21, 833 (1975)] have thoroughly reviewed bubble nucleation in liquids. 

Foam or sandwich penal lonulatlon CNor. suit, polyethylene roofing Sheet covering ter acoustic tie... 

STM is the basement rather than the top floor of a building. The microscope is placed in a little faraday cage, lined with foam rubber, for damping acoustic waves. 

Surface acoustic waves (SAWs), acoustic wave sensors and, 22 270 Surface-active agent(s), 12 33. See also Surfactant entries cmc values of, 24 121t general classification of, 24 144-153 nonionic, 10 665 organic esters as, 10 519 Surface-active molecules, 12 1 foaming and, 12 3... 

An application of ultrasound that is becoming increasingly popular in the food industry is the determination of creaming and sedimentation profiles in emulsions and suspensions (Basaran et al., 1998). Acoustic techniques can also assess nondestructively the texture of aerated food products such as crackers and wafers. Air cells, which are critical to consumer appreciation of baked product quality, are readily probed due to their inherent compressibility (Elmehdi et al., 2003). Kulmyrzaev et al. (2000) developed an ultrasonic reflectance spectrometer to relate ultrasonic reflectance spectra to bubble characteristics of aerated foods. Experiments were carried out using foams with different bubble concentration and the results showed that ultrasonic reflectance spectrometry is sensitive to changes in bubble size and concentration of aerated foods. 

Foamed plastics can be classified in different ways, for instance by their nature (flexible vs. rigid), chemical composition of the matrix, density, cell size, cell structure (open-celled vs. closed-celled), processing method, and dimensions. It is the aimed combination of these properties that determines the final application of the cellular polymer. As an example, open-celled ultra-low density foams are highly desirable for acoustical insulation, while rigid foams with closed-cells and elevated densities are preferred as load-carrying core materials in composite materials. 

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