Dielectric Behaviour of Methyl Palmitate in the Microwave Region

Abstract

THE variation of the dielectric constant and loss of methyl palmitate at room temperature over the frequency range 50 c./s. to 3 × 10¹⁰ c./s. was first reported by Dryden and Willis Jackson¹. The evidence provided for resonance absorption in the frequency range centred on 10¹⁰ c./s. led us to investigate the absorption at room temperature and at as many frequencies as practicable in the microwave region. All measurements except those at 10¹⁰ c./s. were made in a coaxial line using the standing-wave method of Roberts and von Hippel². At 10¹⁰ c./s. the same method was used in a rectangular wave-guide carrying the H₀₁ mode. The accuracy of this method is greatest when the specimen length is an odd number of quarter wave-lengths. Therefore at all frequencies the measurements were done with specimen lengths complying as nearly as possible with this condition. Cast specimens were first used, but were found to give inconsistent results. This was thought to be due to the non-uniform nature of the material prepared in this way, the average densities being much less than the crystal density of 1.007 gm./c.c. calculated from the spacing obtained by Malkin³. Specimens pressed from powder were found to have densities of 0.985 ± 0.005 gm./c.c. and have, therefore, been used throughout the investigation.