Ultrasensitive Edible Oil Sensor Based on Spiral SLSP Combined With Stepped Structure

This article presents a microwave sensor for detecting edible oils based on a spiral spoof localized surface plasmon (SLSP) resonator combined with a stepped structure. The stepped structure is able to concentrate the electric field in the middle substrate, while the spiral SLSP has the exceptional ability to collect the electric field with dimensions only a few tens of wavelengths. The electrical properties of the stepped structure and the spiral SLSP resonator are investigated. The effective permittivity of the proposed sensor is captured, and the circuit model is developed to explain its operating principle. The sensor demonstrates an ultrahigh sensitivity in detecting low-permittivity liquids, making it suitable for detecting oily substances. Experimental results confirm the sensor's ability to distinguish between different types of edible oils and detect adulterated edible oils. In addition, the proposed sensor offers the benefits of portability, low cost, and high sensitivity, which make it equally competent for industrial oils detection.