Development of a wireless passive capacitively coupled contactless conductivity detection (WPC4D) for fluidic flow detection utilizing 3D printing and PCB technologies

Abstract A modified capacitive-coupled contactless conductivity sensor is proposed and developed for microfluidic flow detection based on the passive wireless inductor-capacitor (LC) technique. The device utilizes rapid prototyping including PolyJet 3D printing and PCB technologies to fabricate the microchannel and the readout inductor through which the conductivity of the fluidic flow is analyzed and foreign objects identified. The system employs an LC resonance circuit to monitor the shift in frequency and the change in the reflection coefficient, thereby estimating the conductivity of the fluidic flow and the appearance of objects. The operating principles were characterized by numerical calculations. The performance was validated by experimental measurements. The results show that the higher the electrical conductivity (i.e. the higher concentration) of the NaCl solution passing through the sensing area, the lower the resonance frequency. The resonance frequency due to the passage of NaCl solution with concentrations of 0.1, 0.5, and 1 M were 225.24, 218.93, and 215.67 MHz, respectively. The influence of the distance between the inductors on the resonance frequency of different solution conductivities has also been studied. The sensor system has high potential in various biomedical and chemical applications, particularly in point-of-care applications where sensor chips can be easily incorporated.