Waveguide Iris Sensor with Thermal Modulation for Non-Intrusive Flow Rate Measurements

This paper proposes a novel waveguide iris sensor with thermal modulation for non-intrusive flow rate measurement of uniform liquids. The thermal modulation was performed by changing a liquid's exposure time to a constant heat source. Different flow rates change the heat exposure time, generating a temperature gradient in the liquid. The temperature gradient changes the dielectric properties of the liquid in the medium between two iris pairs. The changes in the dielectric properties impact the impedance matching at the boundary of irises and the waveguide, consequently changing the| S
11
| (dB) parameters measured at the input of the guide. Experimental results show that the sensor successfully detects the flow rates of water (uniform liquid) in 30–250 mL/hr range by tracking the notch value of the| S
11
| (dB). The maximum sensitivity of| S
11
|'s notch value was 0.25 dB for 25 % variation in the flow rate.