A Differential Liquid Level Sensors Using Transmission Line Loaded With Spoof Localized Surface Plasmons

Microwave detection based on resonant peak tracking is the basis of various types of microwave near-field sensors. In this article, a microwave near-field liquid level sensor based on an array of spoof localized surface plasmons (SLSPs) is proposed, which can be used to measure the liquid level in a nonmetallic container in real time. Two arrays of the same SLSPs are distributed on the two branches of the splitter/combiner microstrip sections and excited by it. When the horizontal liquid level rises, the corresponding resonant peaks are shifted, and when the liquid level is tilted, the symmetrical condition of the system will be broken, and the resonant peaks of the corresponding SLSPs will be split, two notches (i.e., frequency splitting) appear, and the resonant frequency will be changed. By analyzing the signal, the current liquid level situation and liquid level tilt angle can be judged. Taking an acrylic container as an example, simulations and experiments show that the sensor can measure the tilt angle with a max accuracy of up to 1°. Compared with other types of liquid level sensors, this sensor can penetrate the container for measurement and has the advantages of high accuracy, low cost, easy container integration, and can measure the liquid surface tilt angle.