利用生物体的电阻抗值分析生物体特性，是一种简单、实用的方法。特别在人体成分的研究中，测量人体的生物电阻抗值可以得到脂肪含量等与人体健康状况密切相关的有用信息。常用的复阻抗谱图分析法一般需要测量到十兆或者上百兆频率的电阻抗值，如此高的测量频率使得仪器很难向小型化、便携化的方向发展，仪器的高成本也使得电阻抗测量的方法难以在家庭日常健康监测中推广。针对这一问题，本文对人体成分的电阻抗测量方法进行了研究。通过对人体电阻抗模型的数学推导，重点分析和研究了在较低频率范围下进行人体电阻抗测量、进而获取人体成分信息的方法。根据电阻抗测量的特点要求，设计并实现了一套针对人体电阻抗低频率范围测量的电路系统。该电路系统使用电流激励、测量响应电压的四电极测量方式，配合由高共模抑制比的仪表放大器组成的响应信号采集电路，有效降低了人体电阻抗测量中电极与皮肤的接触电阻带来的干扰影响。由于使用了直接数字频率合成器和数字信号处理器的技术，该电路可以在一定频率范围内进行扫频测量，并通过离散傅里叶变换直接得到被测量阻抗的阻抗模和相角的信息。对上述电路测量系统进行了电阻电容网络测量和人体电阻抗测量的实验。结果表明，电路系统可以实现对人体电阻抗的有效测量，并进而获取人体成分的信息。较低的测量频率和高的系统集成度大大降低了本测量系统的设计周期和生产成本，为发展小型化、便携化的生物电阻抗分析仪器提供了可能。结合具体应用需求，研究和实现了带存储功能的便携式人体生物电阻抗测量仪器和进行人体成分记录分析的计算机软件。此外，针对人体皮肤水分测量需求，实现了人体皮肤电阻抗测量测量系统，研制出了低成本、便携式的人体皮肤水分测量仪。

Bioimpedance measurement is a useful and easy to implement analysis method to obtain physical characteristics of living organisms, especially in the analysis of human body composition, bioimpedance measurement gives a method to obtain the Total Body Water(TBW) or body fat value. The technique Bioelectrical Impedance Spectroscopy(BIS) needs to measure the impedance in a wide frequency, sometimes as high as ten millions Hz. This critical requirement prevents bioimpedance measurement instrument from being widely used in personal health monitoring.To overcome the wide frequency measurement requirement, the Cole model of human body bioimpedance is discussed and a method to obtain body fat while measuring bioimpedance in a much lower frequency is presented. A prototype of bioimpedance measurement electrical system is designed. With the help of four-electrodes measurement mode, high Common-Mode Rejection Ratio(CMRR) instrument op-amp circuit and the technique of Digital Direct Frequency Synthesis(DDS) and Digital Signal Processing(DSP), the presented system can give the complex impedance results in a frequency-sweep measurement with acceptable error while there is high contact resistance.Experiment shows that the presented low-frequency bioimpedance measurement system can measure the body bioimpedance and help to obtain the fat value in body composition analysis. Furthermore, the technique of measurement results storage in portable instrument is investigated and a human health analysis PC software is designed. The bioimpedance measurement is also applied to the human skin moisture analysis, and a low-cost portable skin moisture monitor is designed and presented.