The solubility data of carbon dioxide (CO2) in a series of ionic liquids (ILs): 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]+[BF4]−), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]+[BF4]−), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIM]+[Tf2N]−), and their binary mixtures (i.e., [EMIM]+[BF4]− + [OMIM]+[Tf2N]− and [BMIM]+[BF4]− + [OMIM]+[Tf2N]−) at temperatures (313.2 and 333.2) K and pressures up to 6 MPa were measured by a high-pressure view-cell technique. The mixed ILs tested were (0, 20, 50, 80, and 100) wt % [EMIM]+[BF4]− (or [BMIM]+[BF4]−) in [OMIM]+[Tf2N]−. The solubility data of CO2 in pure ILs were correlated with the Peng–Robinson equation of state (PR EOS), whereas the solubility data of CO2 in mixed ILs can be well predicted based on the mole fraction average of [EMIM]+[BF4]− (or [BMIM]+[BF4]−) and [OMIM]+[Tf2N]− over the solubility of CO2 in pure ILs. It was found that the solubility of CO2 in pure or mixed ILs increases with increasing pressure at all temperatures but decreases with increasing temperature. The Henry’s constants follow the order of [BMIM]+[BF4]− + [OMIM]+[Tf2N]− > [EMIM]+[BF4]− + [OMIM]+[Tf2N]− at the same content of [OMIM]+[Tf2N]−. The use of mixed ILs provides the opportunity to tune the solubility and selectivity for capturing CO2 at high pressures. It is the first work for us to present the solubility data of CO2 in binary mixtures of ILs at high pressures for physical absorption.

In this paper, we propose a physical model for the analysis of transverse modes in surface acoustic wave (SAW) devices. It is mostly equivalent to the scalar potential (SP) theory, but sufficiently flexible to include various effects such as anisotropy, coupling between multiple modes, etc. First, fundamentals of the proposed model are established and procedures for determining the model parameters are given in detailed. Then the model is implemented in the partial differential equation mode of the commercial finite element analysis software COMSOL. The analysis is carried out for an infinitely long interdigital transducer on the 128°YX-LiNbO3 substrate. As a demonstration, it is shown how the energy leakage changes with the frequency and the device design.

In this paper, we propose the use of the hierarchical cascading technique (HCT) for the finite element method (FEM) analysis of bulk acoustic wave (BAW) devices. First, the implementation of this technique is presented for the FEM analysis of BAW devices. It is shown that the traveling-wave excitation sources proposed by the authors are fully compatible with the HCT. Furthermore, a HCT-based absorbing mechanism is also proposed to replace the perfectly matched layer (PML). Finally, it is demonstrated how the technique is much more efficient in terms of memory consumption and execution time than the full FEM analysis.

In this paper, we investigate the impact of the coupling with shear horizontal (SH) surface acoustic wave (SAW) on the propagation of Rayleigh SAW in periodic grating structures on 128°YX-LiNbO3. First, the frequency dispersion behavior with longitudinal and lateral wavenumbers of Rayleigh SAW is calculated using the finite element method (FEM) software COMSOL. It is shown that the coupling causes (1) the satellite stopband and (2) variation of the anisotropy factor. It is also shown these phenomena remain even when the electromechanical coupling factor of SH SAW is zero. Then, the extended thin plate model which can take coupling between two SAWs into account, is applied to simulate the result of FEM. Good agreement between these results indicated that the mechanical coupling is responsible for these two phenomena. Finally, including electrical excitation and detection, the model is applied to the infinitely long interdigital transducer (IDT) structure and the calculated result is compared with that obtained by the three-dimensional FEM. The excellent agreement of both results confirms the effectiveness of the extended thin plate model.

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In this paper, we propose the use of the “longitudinal resonance condition” for the characterization of the two-dimensional propagation of surface acoustic waves (SAWs) in periodic grating structures, and also show a procedure for extracting parameters required in the behavior model from the full-wave analysis. The condition is given by β xp = π, where p is the grating period and β x is the wavenumber of the grating mode in the longitudinal direction (x). This is based on the fact that in conventional SAW resonators, acoustic resonances including transverse ones occur when β x is real but the longitudinal resonance condition is mostly satisfied. The longitudinal resonance condition is applied to a simple model, and the wavenumber β y in the lateral direction (y) is expressed as a simple function of the angular frequency ω. The full-wave analysis is applied for SAWs propagating in an infinite grating on a 128°YX-LiNbO3 substrate, and the anisotropy parameter γ is extracted by the fitting with the derived equation. The fitted result agrees well with the original numerical result. It is also indicated that γ estimated by this technique is significantly different from the value estimated without taking the effects of the grating structure into account.

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