Liquid sensor composed of one-dimensional sonic Helmholtz resonator array

In this work, we propose a one-dimensional (1D) Helmholtz resonator (HR) array that can be used to measure the molar ratio of a 1-propanol solution. This 1D HR array is made from aluminum and is immersed in the 1-propanol solution to measure its molar ratio. The transmission spectra of the 1D HR array show two dips, which are caused by the local resonance effect. Molar ratio sensing is achieved by monitoring the frequency shifts of these transmission dips. The experimental and theoretical results show that our structure has both high sensitivity and a high extinction ratio. The measured sensitivities of the high- and low-frequency modes are approximately 1757 and 428 kHz/molar ratio unit, respectively. The measured extinction ratio is approximately 20 dB. Additionally, we show that a Fabry–Pérot-like resonance results in a reduction in the extinction ratio. This phenomenon can be avoided by appropriate selection of the substrate thickness.