采用方波脉冲信号作为激励获取导电介质的电阻抗信息时,方波信号频谱中高次谐波的幅值衰减一直是难以克服的问题。对一阶阻容型传感系统添加电感或电容元件构成二阶谐振单元,在激励信号的上、下沿处会出现自由衰减振荡信号,可使激励信号频谱在谐振单元的谐振频率附近得到增强。通过测量方波下降沿处自由衰减振荡信号第一个波峰的峰值电压,即可得到谐振单元中等效电阻的测量值。实验结果表明: 这种检测方式只需要数字电路产生固定频率的方波激励信号,即可实现30 kHz~1 MHz范围内的电阻测量,可用于电解质溶液、水、人体皮肤等介质电导率的有线及无线测量。

When a square wave pulsed signal is adopted as excitation to obtain electrical impedance information for a conductive medium, the amplitude decay of the higher harmonics in square wave spectrum can have a significant effect. Adding an inductor or capacitor to a first-order resistant-capacitive-type sensing system creates a second-order resonant element that creates a freely damped oscillating signal at both the rising and falling edges of the excitation. The excitation amplitude near the resonant frequency is, therefore, enhanced. The equivalent resistance in the resonant element can be obtained by measuring the first positive peak voltage of the freely damped signal at the falling edge of the pulse. Tests indicate that resistance measurements for frequencies from 30 kHz to 1 MHz can be implemented only by a fixed frequency square wave excitation signal generated by a digital circuit. This method can be used for conductivity measurements of conductive media, such as electrolyte solutions, water and human skin, using both wired and wireless transmitters.