Identification of electrolyte solutions using a shear horizontal surface acoustic wave sensor with a liquid-flow system

A liquid-flow system with a shear horizontal surface acoustic wave (SH-SAW) sensor is developed to identify electrolytes in an aqueous solution without selective coatings. When the electrical properties of sample solution are the same, it is impossible to identify the differences by using steady-state values. The transient responses from the liquid-flow system, however, depend on the materials contained in a sample solution. Therefore, it is possible to determine the type of ion species in the solution from the transient responses. To identify and evaluate the sample solutions, the self-calibrating ratiometric method (SCRM) is proposed. Since the SCRM is based on the time differences between rise and fall responses, the influences of experimental conditions can be calibrated and thus ignored. The results indicate that the SCRM is an effective identification method based on the transient responses. Moreover, the mechanisms are discussed and it is found that the dispersion of an electrolyte based on the gravity effect and the evanescent piezoelectric potential are essential for the identification.