Nelson S, Forbus W, Lawrence K
J Microw Power Electromagn Energy. 1994;29(2):81-93. doi: 10.1080/08327823.1994.11688235.
Permittivities, moisture contents, tissue densities, and total soluble solids data were determined for samples of twenty-three kinds of fresh fruits and vegetables at 23 degrees C. Permittivities were measured at 41 frequencies between 200 MHz and 20 GHz with an open-ended coaxial-line probe and a microwave network analyzer. Results of the permittivity measurements are presented graphically, and dielectric constant and loss factor values at six frequencies across the range are tabulated along with sample descriptions and moisture, density, and total soluble solids data. Although specific values differ, the dielectric constant decreases steadily with increasing frequency, dropping more rapidly at frequencies above 5 GHz. Values for the loss factor decrease as frequency increases above 200 MHz to a broad minimum in the 1- to 3-GHz region and then increase again as the frequency approaches 20 GHz. The dielectric behavior of the fruit and vegetable tissues appears to be influenced by ionic conductivity and bound water relaxations at the lower frequencies and by free water relaxation at the higher end of the frequency range.
在23摄氏度下，测定了23种新鲜水果和蔬菜样品的介电常数、含水量、组织密度和总可溶性固形物数据。使用开口同轴探头和微波网络分析仪在200兆赫兹至20吉赫兹之间的41个频率下测量介电常数。介电常数测量结果以图表形式呈现，并列出了该范围内六个频率下的介电常数和损耗因子值，以及样品描述、水分、密度和总可溶性固形物数据。尽管具体数值不同，但介电常数随频率增加而稳步下降，在5吉赫兹以上频率下降更快。损耗因子值在频率高于200兆赫兹时随着频率增加而降低，在1至3吉赫兹区域达到一个较宽的最小值，然后随着频率接近20吉赫兹再次增加。水果和蔬菜组织的介电行为似乎在较低频率下受离子电导率和结合水弛豫影响，在频率范围较高端受自由水弛豫影响。
