Abstract
Sensitivity is one of the most important parameters to put in the foreground in all sensing applications. Its increase is therefore an ongoing challenge, particularly for surface acoustic wave (SAW) sensors. Herein, finite element method (FEM) simulation using COMSOL Multiphysics software is first used to simulate the physical and electrical properties of SAW delay line. Results indicate that 2D configuration permits to accurately obtain all pertinent parameters, as in 3D simulation, with very substantial time saving. A good agreement between calculation and experiment, in terms of transfer functions (S21 spectra), was also shown to evaluate the dependence of the SAW sensors sensitivity on the operating frequency; 2D simulations have been conducted on 104 MHz and 208 MHz delay lines, coated with a polyisobutylene (PIB) as sensitive layer to dichloromethane (DCM). A fourfold increase in sensitivity was obtained by doubling frequency. Both sensors were then realized and tested as chem-sensors to detect zinc ions in liquid media. 9-{[4-({[4-(9anthrylmethoxy)phenyl]sulfanyl} methyl)]methyl] anthracene (TDP-AN) was selected as the sensing layer. Results show a comparable response curves for both designed sensors, in terms of limit of detection and dissociation constants Kd values. On the other hand, experimental sensitivity values were of the order of [7.0 ± 2.8] × 108 [°/M] and [16.0 ± 7.6] × 108 [°/M] for 104 MHz and 208 MHz sensors, respectively, confirming that the sensitivity increases with frequency.
Highlights
Surface acoustic wave (SAW) devices are investigated in a large variety of applications including signal processing [1], mobile and wireless communication [2,3], modulators [4] and RF filters [5]
The interest of MATLAB is to rapidly simulate the mathematical behavior of a SAW device in terms of transfer function. This can be done by considering an elementary equivalent electrical circuit, in which the operating frequency is related to the surface acoustic wave propagation
MATLAB software is used as simulation tool to get access to the frequency response (S21 spectrum) of SAW delay line, with reasonable calculation time
Summary
Surface acoustic wave (SAW) devices are investigated in a large variety of applications including signal processing [1], mobile and wireless communication [2,3], modulators [4] and RF filters [5].In the last decades, they have been more and more used as chemical and biological sensors due to their fast response [6], low cost [7], high sensitivity [8,9,10,11,12,13], low limit of detection [14,15] and real-time monitoring [16]. To design and optimize SAW sensors with time and money saving, several simulation methods were developed: delta function model [17], equivalent circuit model [18], P-matrix model [19], coupled mode theory [20], and CST (Computer Simulation Technology) software [21]. These methods are very complex and are mainly used in telecommunication applications such as filters and resonators. Finite Element Method (FEM) simulation was investigated and has proven to be the most suitable method for metrological characterization of SAW devices prior to their fabrication in a clean room [22,23,24,25,26].
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