Wang Yong, Xu Zhonggui, Wang Yinshen, Xie Jin
The State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou 310027, China.
Sensors (Basel). 2017 Aug 7;17(8):1813. doi: 10.3390/s17081813.
In this paper, we report attenuation characteristics of aluminum nitride (AIN) film-based surface acoustic waves (SAWs) in liquids and their potential as liquid ethanol sensors. An AIN film-based SAW resonator was fabricated for liquid sensing application. The fabricated SAW device had a Rayleigh wave mode at a resonant frequency of 147.1 MHz and a low temperature coefficient of frequency (TCF) of -21.7 ppm/K. The signal attenuation in the transmission line of the SAW device was presented when ethanol (ETH) droplets and deionized water (DIW) with different concentrations and volume (0.2-1 µL) were dropped on the sensing area respectively. The attenuation of SAW as a function of time and liquid position was investigated. Residues left on the wave propagation path resulted in a frequency shift of the SAW device after liquid evaporation. For ETH, there was a 49 kHz frequency shift caused by a large amount of residues, while the frequency shift of DIW was not distinct, on account of a clean surface. The linear relationship between evaporation rate and ethanol concentration was demonstrated. The evaporation rate of ethanol droplets showed good consistency, and the evaporation time variation was less than 5% at each concentration level. Therefore, the proposed SAW device had great potentials to determine ethanol concentrations based on evaporation rate.
在本文中，我们报道了基于氮化铝（AIN）薄膜的表面声波（SAW）在液体中的衰减特性及其作为液体乙醇传感器的潜力。制备了一种基于AIN薄膜的SAW谐振器用于液体传感应用。所制备的SAW器件在147.1 MHz的谐振频率下具有瑞利波模式，频率温度系数（TCF）为-21.7 ppm/K。当分别将不同浓度和体积（0.2 - 1 μL）的乙醇（ETH）液滴和去离子水（DIW）滴在传感区域时，展示了SAW器件传输线中的信号衰减。研究了SAW衰减随时间和液体位置的变化。液体蒸发后，波传播路径上留下的残留物导致SAW器件出现频率偏移。对于ETH，大量残留物导致频率偏移49 kHz，而由于表面干净，DIW的频率偏移不明显。证明了蒸发速率与乙醇浓度之间的线性关系。乙醇液滴的蒸发速率表现出良好的一致性，在每个浓度水平下蒸发时间变化小于5%。因此，所提出的SAW器件具有基于蒸发速率测定乙醇浓度的巨大潜力。
