Risos Alex, Long Nicholas, Gouws Gideon
Robinson Research Institute, Victoria University of Wellington, Lower Hutt 5010, New Zealand.
School of Engineering and Computer Science, Victoria University of Wellington, Wellington 6012, New Zealand.
Rev Sci Instrum. 2017 Oct;88(10):105105. doi: 10.1063/1.5005857.
A measurement of the complex permittivity, ε, of a liquid can give valuable information about the molecular polarizability and dielectric losses. This can be obtained by means of an impedance measurement using a parallel plate test cell. However, highly accurate and precise measurements are challenging, in particular when measuring as a function of temperature. Thermal expansion affects the geometry of a test cell and thus the measured capacitance from which ε is calculated. In this paper, a broadband four-terminal dielectric test cell is presented that is insensitive to temperature fluctuations. This was achieved by means of a cell geometry exploiting the thermal expansion coefficient of different materials. Experimental measurements on the manufactured cell yielded a stable capacitance of 35.322 ± 0.001 pF across 20 °C-90 °C. The capacitance stayed within ±0.01 pF over multiple experimental cycles of cleaning and assembly. A finite element modeling showed a theoretical accuracy in measuring ε better than 99.995%. The measured ε values for a number of standard liquids showed an agreement of 99.7% compared to literature values.
测量液体的复介电常数ε可以提供有关分子极化率和介电损耗的有价值信息。这可以通过使用平行板测试单元进行阻抗测量来获得。然而，进行高精度和精确测量具有挑战性，特别是在测量作为温度函数时。热膨胀会影响测试单元的几何形状，从而影响用于计算ε的测量电容。本文提出了一种对温度波动不敏感的宽带四端介电测试单元。这是通过利用不同材料的热膨胀系数的单元几何形状实现的。对制造的测试单元进行的实验测量在20°C至90°C范围内产生了稳定的电容35.322±0.001 pF。在多次清洁和组装的实验循环中，电容保持在±0.01 pF以内。有限元建模表明，测量ε的理论精度优于99.995%。与文献值相比，多种标准液体的测量ε值显示一致性为99.7%。
