Multilayer reflectivity

More advanced insulations are also under development. These insulations, sometimes called superinsulations, have R that exceed 20 fthh-°F/Btu-m. This can be accomplished with encapsulated fine powders in an evacuated space. Superinsulations have been used commercially in the walls of refrigerators and freezers. The encapsulating film, which is usually plastic film, metallized film, or a combination, provides a barrier to the inward diffusion of air and water that would result in loss of the vacuum. The effective life of such insulations depends on the effectiveness of the encapsulating material. A number of powders, including silica, milled perlite, and calcium silicate powder, have been used as filler in evacuated superinsulations. In general, the smaller the particle size, the more effective and durable the insulation packet. Evacuated multilayer reflective insulations have been used in space applications in past years. 

The interaction between a light wave and a surface plasmon in the ATR method can be investigated using the Fresnel multilayer reflection theory [18]. Herein, we shall present analysis of the reflectivity for the Kretschmann geometry of the ATR method. 

Montcalm, S. Bajt, P.B. Mirkarimi, E. Spiller, F.J. Weber, and J.A. Folta, Multilayer reflective coatings for extreme ultraviolet lithography, Proc. SPIE 3331, 42 51 (1998). 

Multilayer reflecting shields - Foil or aluminized plastic alternated with paper-thin glass or plastic-fiber sheets lowest conductivity, low density, and heat storage good stability minimum support structure. 

Engineering Aspects of Heat Transfer in Multilayer Reflective Insulation and Performance of NRC Insulation (5) 199 On the Evacuation of Plastic Foams to Reduce Their Thermal Conductivity (5) 273... 

Figure 21.6 Effect of a multilayer reflective coating on light propagation.

ENGINEERING ASPECTS OF HEAT TRANSFER IN MULTILAYER REFLECTIVE INSULATION AND PERFORMANCE OF NRC INSULATION... 

Our NRC insulation has an apparent heat transfer coefficient as low as 0.28 w/cm- K between room temperature and boiling liquid nitrogen, and is an insulating system using a special form of multilayer reflective shields in high vacuum. The apparent thermal conductivity is a function of the bulk density, as shown in Fig. 3, with a pronounced minimum between 2 and 3 Ib/ft. ... 

In this section, two illustrative numerical results, obtained by means of the described reconstruction algorithm, are presented. Input data are calculated in the frequency range of 26 to 38 GHz using matrix formulas [8], describing the reflection of a normally incident plane wave from the multilayered half-space. 

Fig. 13. Expected signal and noise levels for RE-TM alloys and Pt/Co multilayers (schematic). The total noise entering the SNR is the sum of the system noise, disk noise, and write noise. The system noise is electronic noise and photon shot noise and is comparable for disks with the same reflectivity.

Antireflective (AR) coatings are required on optics to reduce the reflective surface losses. Vitreous siHca coatings in the form of porous or multilayer films are used extensively in this appHcation. Antireflective coatings have been developed which employ coUoidal fused siHca sol—gel particles made from organometaUic materials (253). 

Equations la and lb are for a simple two-phase system such as the air-bulk solid interface. Real materials aren t so simple. They have natural oxides and surface roughness, and consist of deposited or grown multilayered structures in many cases. In these cases each layer and interface can be represented by a 2 x 2 matrix (for isotropic materials), and the overall reflection properties can be calculated by matrix multiplication. The resulting algebraic equations are too complex to invert, and a major consequence is that regression analysis must be used to determine the system s physical parameters. ... 

The reflectivity for this simple case can be extended readily to more complex situations where there are concentration gradients in single films or multilayers comprised of different components. Basically the reflectivity can be calculated from a simple recursion relationship that effectively reduces any gradients in composition to a histogram representing small changes in the concentration as a function of depth. Details on this can be found in the literature cited. ... 

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