Investigation on Electrical Properties of Solid Polymer Sheets (HDPE AND LDPE) at Audio Frequency Range

Two different groups of solid polymer sheets: low density polyethylene (LDPE) sample of thickness 0.006 cm and 0.007 cm along with high density polyethylene (HDPE) sample of the thickness of 0.009 cm, 0.010 cm were taken in this work. The measurement of electrical properties such as dielectric constant, ε' and dielectric loss, ε'' for LDPE and HDPE polymer sheets have been measured using a dielectric cell. The dielectric cell has been fabricated which consists of two circular parallel plates of pure stainless steel each of 5 cm diameter and 2 mm thickness. An impedance bridge (GRA 650A) was used for measurement of capacitance, C, and dissipation factor, D in the audio frequency (AF) range, 100 Hz to 10 kHz. Different samples were loaded in between the two plates of the cell and the capacitance as well as the dissipation factor were estimated from the dial readings of the bridge. Effect of frequency variation on ε', ε'', relaxation time, τ , dissipation factor, tanδ and ac conductivity, σ were also discussed at audio frequency range. The complex permittivity, ε*, related to free dipole oscillating in an alternating field and loss tangent, tanδ were calculated. The frequency-dependent conductivity, dielectric behavior, and electrical modulus, both real (M') and imaginary (M") parts of LDPE and HDPE have been studied in this work. The values of the real part of the electrical modulus (M') did not equal to zero at low frequencies and it is expected that the electrode polarization may develop in both sheets. These findings reveal an increased coupling among the local dipolar motions in a short-range order localized motion. The analysis of real (ε') and imaginary (ε'') parts of dielectric permittivity and that electrical modulus real (M') and imaginary (M") parts signify poly dispersive nature of relaxation time as observed in Cole-Cole plots.

Monitoring of brightness temperature fluctuation of water in SHF range

Цель исследования - в мониторинге флуктуаций Т воды в процессе ее испарения при температуре t = 42°С, критической для человека, с помощью СВЧ-радиометрии. Методика: проводился мониторинг изменения яркостной температуры Т воды в СВЧ-диапазоне частот 3,8-4,2 ГГц в процессе ее испарения при температуре в измерительной конусной полипропиленовой кювете t = 42°С. Измерения яркостной температуры проводились при помощи радиотермометра. Результаты. Обнаружено появление скачка яркостной температуры Т при температуре в измерительной конусной полипропиленовой кювете = 42°С. Скачок Т характеризовался фронтом нарастания яркостной температуры в этом диапазоне частот в диапазоне ~4°С с градиентом ~0,05°С/мин - 15°С/мин в зависимости от условий организации процесса испарения и резким спадом в течение 10 с, после чего наблюдалась следующая серия менее интенсивных флуктуаций. При этом температура воды оставалась постоянной. Заключение. Выявлены существенные изменения яркостной температуры воды в СВЧ-диапазоне при ее испарении при температуре воды в конусной измерительной кювете t = 42°С, наблюдается флуктуация в виде скачка Т порядка DТ ~4°C в исследуемой области температуры флуктуаций. При этом термодинамическая температура практически не изменяется. Наблюдаемые эффекты должны учитываться при разработке диагностических систем патологического состояния человека и при создании аналитических устройств. The purpose of the research consisted in detection of fluctuation of brightness temperature (T) of water in the area of the temperature Т = 42°С (that is critical for human) during its evaporation by SHF radiometry. Methods: Monitoring of the changes in brightness temperature of water in superhigh frequency (SHF) range (3.8-4.2 GHz) near the phase transition temperature of water Т = 42°С during its evaporation in the cone dielectric cell. The brightness temperature measurements were carried out using radiometer. Results: Fluctuation with maximum of brightness temperature was detected in 3.8-4.2 GHz frequency range near at the temperature of water Т = 42°С. It was characteristic for these T fluctuations that brightness temperature rise time in this range of frequencies in ~4°С temperature range with 0.05-15°С/min gradient and a sharp decrease during 10 s connected with measuring vapor conditions. Then nonintensive fluctuation series was observed. At that, the environment temperature remained constant. Conclusion: The significant increasing in brightness temperature of water during its evaporation in SHF range near the temperature of Т ~42°С were detected. It was shown that for water, Т pull with the amplitude DТ ~4°C are observed. At the same time, thermodynamic temperature virtually does not change. The observed effects can be used in the development of the systems for diadnostics of pathologies in human and analytical system.

A Low Temperature Dielectric Cell and the Permittivity of Hexagonal Ice to 2 K

The limiting high frequency permittivity ε∞ of hexagonal ice, measured using a coaxial three terminal dielectric cell designed to minimize errors arising from differential thermal contraction, varies from 3.093 ± 0.003 at 2 K to 3.15 ± 0.02 at 200 K. The result is discussed in relation to the translational lattice vibrations and a comparison is made with other ices.