Microwave Resonance-Based Lab-on-a-Chip Local Pressure Sensing

An expandable microfluidic component is integrated with a microwave resonator to allow in situ monitoring of pressure/flow rate changes in a microfluidic system. The resonator is a modified H-slot, which is etched into the ground plane of a microstrip transmission line. The microfluidic component is a circular reservoir with a flexible cover and specially designed inlet and outlet channels. The circular reservoir is placed in the near field of the resonator. The expansion of the reservoir cover depends on the pressure of the fluid that flows through the device. This leads to a frequency shift of the resonance, which is monitored by measuring the transmission parameter of the microstrip line. The design and fabrication procedures are discussed, and prototypes are presented. Electromagnetic and fluid-dynamic simulations are performed to determine the optimal geometry parameters of the device to achieve improved sensitivity for different scenarios. The performance of the device is demonstrated by filling the reservoir with distilled water and monitoring the pressure as a function of the liquid inflow. A sensor with a chamber radius of 3 mm and a cover height of 1.76 mm allows for the measurement of pressures ranging from 0 to 2 bar.