基于片上共面波导传输线型微流体介电特性检测若干关键问题的研究

Dielectric properties measurement is one of the foundational and hot research topics all along, especially in the biological matter, in which measuring dielectric property changes has been developed for bioanalysis and used as an effective approach to investigate the biological process, such as protein thermal unfolding and refolding, etc. Measuring the change of the transmission and reflection parameters (including amplitude and phase) to obtain the dielectric property (permittivity for example) is the basic principle of those traditional measurements. However the sensitivities of these approaches are relatively limited due to the strong background signals, especially when the change of the material under test (MUT) property is very weak, the tiny change of the transmission parameter is very hard to capture. Therefore, based on the transmission line characteristics, this project proposes that, based on the on-chip coplanar waveguide (CPW), consider directly place the MUT into the gap between signal line and ground line of CPW with finite metal thickness, in which the strongest field distribution located, thus making a substantial increase in the sensitivity of the microfluid dielectric parameters measurement, also, it can control the volume of the MUT precisely and the external PDMS walls or microfluid channel is not required. Accordingly, this project further proposes that by using of a cancellation type of permittivity variation observation measurement system based on two CPWs, the sensitivity will be further increased in which the weak signal changes will be extracted directly. Theoretically this idea is entirely possible to obtain the solution of extract the weak signal changes detect problems of the microfluid dielectric parameters.

在生物科学实验研究中，蛋白质热变性，复折叠和细胞等微流体介质参数瞬时变化信息获取非常重要。传统研究思路是直接测量微带线上微波信号传输或反射量的变化来获得被测介质介电参数变化信息。一个无法克服的障碍是背景信号过强限制了其工作灵敏度，尤其是当材料介电常数的微小变化所导致的信号微弱变化更是难以检测。基于片上共面波导传输线特性理论分析，本项目申请提出将被测微流体置于有限厚度共面波导信号线与地线之间槽内，由于微流体直接置于共面波导场强分布最强处，极大增强了对传输线传输特性的扰动，使得大幅提高微流体介质参数测试灵敏度成为可能；同时具有无需搭建封闭外墙或流体通道和可调节被测微流体用量的优点。据此，本项目进一步提出，利用两路传输信号相抵消这一弱信号强变化机制来进一步提高测试动态范围，该思路从理论上来说完全有可能在本质上获得一种传统微流体介电参数测试中弱小变化信号处理难题解决方案。

在生物科学实验研究中，蛋白质热变性，复折叠和细胞等微流体介质参数瞬时变化信息获取非常重要。基于片上共面波导传输线特性理论分析，本项目申请提出将被测微流体置于有限厚度共面波导信号线与地线之间槽内，由于微流体直接置于共面波导场强分布最强处，极大增强了对传输线传输特性的扰动，使得大幅提高微流体介质参数测试灵敏度成为可能。据此，本项目进一步提出，利用两路传输信号相抵消这一弱信号强变化机制来进一步提高测试动态范围，从本质上获得一种传统微流体介电参数测试中弱小变化信号处理难题解决方案。. 首先，本项目采用保角变换数学手段获得限金属厚度共面波导传输线参数，给出理论公式；并利用三维电磁仿真软件进行对比验证理论模型。其次，本项目研究了基于共面波导的单通道微流体介质介电常数的测量方案，本项目所提的基于有限金属厚度测量介电常数的方式与理论值有较好的一致性，特别是在金属厚度与槽宽可比拟的情况下，误差均在10%以内。最后，本项目完成了双通道微流体介电常数变化测试方案的设计与测试，该装置以共面波导作为信号传输线，由两个威尔金森功分器和两条路径相差半个波长的传输线构成，仿真结果表明在工作频率5 GHz附近处抵消点S21达到−92.15dB。在模型中加入不同介电常数和电导率的模拟材料进行仿真，当待测材料与参考材料的参数差异越大时，抵消点频率与S21变化越大，仿真结果符合理论预期。测试过程中，为了减小加工误差对抵消效果的影响，本项目提出了一种可校准的高灵敏度射频传感器装置。该传感器基于抵消型原理，并通过加装可调谐腔体，能够有效地对传感器上下支路的衰减和电长度进行微调，从而有效地提高了传感器的灵敏度和准确度，实验结果表明校准后的传感器能有效地将无水乙醇和正丙醇的输出S21的变化量提升7.05dB及10.26dB。同时该传感器由于加入了可校准结构，对于不同的参考物能进行不同的校准，也使得该传感器变得更通用。