MultiScanner: Enabling Simultaneous Detection of Multiple Liquids With mmWave Radar Based on a Composite Reflection Model

Traditional liquid detection approaches are often time-intensive and invasive, typically requiring the opening of containers for examination. While recent initiatives have proposed several innovative solutions, including camera-based and vibration sensor-based techniques, these approaches still face limitations in terms of convenience. The development of radio frequency (RF) technology, particularly millimeter-wave (mmWave) radar, offers a promising solution for non-invasive and contactless liquid detection. In particular, during the past few years, a number of radar-based sensing systems have been developed to detect or identify liquids. However, little work has been done on the simultaneous detection of multiple liquids. To fill this gap, we design a novel composite reflection model, which overcomes the detection challenges due to composite interference and environmental reflections, by utilizing the consistency and uniqueness of the reflection signals from multiple liquid targets. Based on the proposed model, we develop a system named MultiScanner, which is able to detect different types of liquids in multi-target scenarios, exhibiting high location independence without the need for extensive data training. Extensive experiments validate the effectiveness of MultiScanner, achieving up to 95.91% accuracy in detecting 10 hazardous-normal liquid combinations in 2-target scenarios. Moreover, even in more complex 5-target scenarios, an detection accuracy of 86.49% can be obtained. To the best of our knowledge, this is the first study that uses RF signals for multi-liquid detection.