Alanen E, Lahtinen T, Nuutinen J
Department of Oncology, Kuopio University Hospital, Finland.
IEEE Trans Biomed Eng. 1998 Oct;45(10):1241-8. doi: 10.1109/10.720202.
An open-ended coaxial probe designed to measure layered biological media is analyzed with a new method. The probe is considered as an electrostatic circuit element whose capacitance is solved using a stationary functional. The fundamental transverse electric and magnetic field (TEM)-mode and the series of evanescent wavemodes in the coaxial cable are used as basis functions. The field outside the probe is solved using a Hankel transform. The capacitance is calculated for homogeneous materials and two-layer structures and the results are compared with values measured with a phantom model. The method can be easily extended for structures with an arbitrary number of layers. A practical approximation for two-layer cases, originally developed to take into account the effect of subcutaneous fat in skin measurements, is presented and its validity for different combinations of dielectric constants and the thickness of the first layer is demonstrated. The static approximation limits the frequency range, but it covers biological measurements up to 500 MHz. The developed method is accurate and easy to adopt in practice.
采用一种新方法对用于测量分层生物介质的开放式同轴探头进行了分析。该探头被视为一个静电电路元件，其电容通过一个定常泛函求解。同轴电缆中的基本横向电磁（TEM）模式和一系列消逝波模式用作基函数。探头外部的场通过汉克尔变换求解。计算了均匀材料和双层结构的电容，并将结果与用模型体测量的值进行了比较。该方法可轻松扩展到任意层数的结构。提出了一种最初为考虑皮肤测量中皮下脂肪的影响而开发的双层情况的实用近似方法，并证明了其对于不同介电常数组合和第一层厚度的有效性。静态近似限制了频率范围，但它涵盖了高达500 MHz的生物测量。所开发的方法准确且易于在实际中采用。
