Microstrip-Line Sensor for the Estimation of the Fluid Level Inside a Closed Metal Pipe

Abstract

A transmission-line type fluid-level sensor with a low-cost connected oscillator and detector is proposed. The designed sensor is a physical sensor applicating microwave technology and is a simple fluidlevel sensor that relies on radio frequency (RF) signal-attenuation changes based on the fluid's height. The proposed sensor can provide real-time measurements of fluid height inside an opaque metal pipe by inserting a microstrip line into the pipe, with a simple oscillator and detector module connected at each end. The fluid level inside the metal pipe can be accurately determined with a portable multimeter, eliminating the need for the complex calibration process typically associated with conventional RF-based measurement instruments. The transmission line for the proposed sensor is designed to operate within a dynamic range of -15 dB in a 50-mm diameter metal pipe used for fluid transportation. This system accommodates microstrip line with superstrate and a superstrate-to-substrate thickness ratio of 0.236 to satisfy dynamic range and the linear insertion loss trend. A prototype sensor tested with purified water achieves a dynamic range of 13.1 dB and shows linearity between insertion loss and fluid height at 3.9 GHz.