Ultra-sensitive flow rate sensor based on Vernier effect and carbon nanotubes-doped PDMS

An ultrasensitive flow rate sensor is proposed and demonstrated, which leverages two cascaded Fabry–Perot interferometers (FPIs) to generate the Vernier effect. The single-mode fiber (SMF) fused with hollow-core fiber (HCF) forms the base of the two FPIs. Polydimethylsiloxane (PDMS) doped with carbon nanotubes (CNTs) is used to partially fill the HCF of one of the FPIs, which is used as the sensing FPI. The CNTs within the PDMS absorb the laser and then generate heat, which will cause the thermal expansion of the PDMS. At a certain flow rate, the microfluidic flow dissipates the heat until thermal equilibrium is achieved. The cavity length of the sensing FPI varies with the thermal equilibrium temperature. Then, the flow rate of the microfluid in the channel can be determined by monitoring the envelope shift of the Vernier spectrum. The proposed sensor exhibits a flow rate sensitivity of 36.5 nm/(µL/s), which demonstrates exceptional sensitivity, high stability and ultra-compactness, and then shows great potential for application in microfluidics.