Refractive indices of uniaxially stretched poly(ethylene terephthalate) films with 9–10% crystallinity were determined at microwave frequencies. An empirical formula nMW=0.0508+1.0681 nOPT was derived, with a correlation coefficient of 0.998, where nMW and nOPT denote the refractive indices at 4.0 GHz and 5.09×1014 Hz (589 nm wavelength), respectively. The coefficient of 1.0681 between nMW and nOPT was smaller than that of 1.3561 in the previously determined empirical formula for biaxially stretched poly(ethylene terephthalate) films with 35% crystallinity. Such a difference in the coefficient may be ascribed to the difference in crystallinity between two kinds of films. It was found that nMW decreased when the frequency increased from 4.0 GHz to 12.2 GHz but was distinctly higher than nOPT and appeared to approach nOPT.
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Osaki, S. Refractive Index of Uniaxially Stretched Poly(ethylene terephthalate) Film at Microwave Frequencies. Polym J 28, 131–133 (1996). https://doi.org/10.1295/polymj.28.131
- Refractive Index
- Poly(ethylene terephthalate)
- Visible Ray
- Frequency Dependence
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