Nebuya S, Noshiro M, Brown B H, Smallwood R H, Milnes P
Department of Clinical Engineering, School of Allied Health Sciences, Kitasato University, Kanagawa, Japan.
Med Biol Eng Comput. 2002 Nov;40(6):647-9. doi: 10.1007/BF02345303.
Accurate electrical transfer impedance measurement at the high frequencies (> 1 MHz) required to characterise blood and intracellular structures is very difficult, owing to stray capacitances between lead wires. To solve this problem, an optically isolated measurement system has been developed using a phase-locked-loop technique for synchronisation between current injection (drive) and voltage measurement (receive) circuits. The synchronisation error between drive and receive circuits was less than 1 ns. The accuracy and reproducibility of the developed system was examined using a tissue equivalent Cole model consisting of two resistors and one capacitor. The absolute value Z and phase shift theta in impedance of the Cole model was measured at 1.25 MHz by both an LCR meter and the isolated measurement system. The difference between the values measured by the isolated measurement system and those measured by the LCR meter was less than 0.27omega (2.9%) in Z and 0.79 degree in theta. The standard deviation was less than 0.09 omega in Z and 0.60 degree in theta.
要表征血液和细胞内结构，需要在高于1MHz的高频下进行精确的电转移阻抗测量，但由于导线之间的杂散电容，这一测量非常困难。为了解决这个问题，已经开发了一种光隔离测量系统，该系统使用锁相环技术来实现电流注入（驱动）和电压测量（接收）电路之间的同步。驱动和接收电路之间的同步误差小于1纳秒。使用由两个电阻器和一个电容器组成的组织等效科尔模型，对所开发系统的准确性和可重复性进行了检验。通过LCR表和隔离测量系统，在1.25MHz下测量了科尔模型阻抗的绝对值Z和相移θ。隔离测量系统测量的值与LCR表测量的值之间的差异在Z方面小于0.27Ω（2.9%），在θ方面小于0.79度。Z的标准偏差小于0.09Ω，θ的标准偏差小于0.60度。
