无源线圈在电磁感应溶液测量中的增强效应

Enhancement effect of a passive coil in electromagnetic induction solution measurement

将一只由线圈与电容元件共同组成的无源线圈放置于探测线圈与待测电解质溶液组成的测量系统中，借助无源线圈与两者之间的电磁感应耦合，可在谐振频率点附近提高测量系统的探测性能。以塑料容器内0—5％质量分数浓度的NaCl溶液为探测目标，对无源线圈置于目标溶液前侧及背侧两种情况下的阻抗谱进行了实验分析。结果表明，相同探测距离下，介入无源线圈的测量系统对电解质溶液的浓度表现出更高的灵敏度。当目标溶液位于探测线圈敏感距离之外时，介入无源线圈后依然可实现有效的溶液浓度测量。无源线圈的这种增强效应可提升电磁感应系统的有效探测距离，实现电解质溶液或生物组织等低电导率物质的远距离非接触测量。

A passive coil is composed of a coil and a capacitance element. It is placed in the electromagnetic induction electrolyte solution measurement system, which is made up of a readout coil and the electrolyte solution under test. Because of the electromagnetic coupling between the passive coil and the other two, the measurement performance can be improved around the resonant frequency. Sodium chloride solution with 0% - 5% mass fraction concentration in a plastic container is adopted as the target to be detected. In cases of that the passive coil is placed at front side and backside of the target solutions respectively, the impedance spectrums are experimentally analyzed. The results indicate that, the measurement system with a passive coil performs higher sensitivity to the solution concentration at the same detection distance. When the target solution is placed beyond the sensing range of the readout coil, the solution concentration can be also effectively measured with the aid of passive coil. Such an enhancement effect of the passive coil can efficiently promote the detection range of the electromagnetic induction system, and therefore longer range non-contact measurement could be implemented for lower conductivity targets, such as electrolyte solutions or biological tissues.