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Surface acoustic wave sensors have the advantage of fast response, low-cost, and wireless interfacing capability and they have been used in the medical analysis, material characterization, and other application fields that immerse the device under a liquid environment. The theoretical analysis of the single guided layer shear horizontal acoustic wave based on the perturbation theory has seen developments that span the past 20 years. However, multiple guided layer systems under a liquid environment have not been thoroughly analyzed by existing theoretical models. A dispersion equation previously derived from a system of three rigidly coupled elastic mass layers is extended and developed in this study with multiple guided layers to analyze how the liquid layer’s properties affect the device’s sensitivity. The combination of the multiple layers to optimize the sensitivity of an acoustic wave sensor is investigated in this study. The Maxwell model of viscoelasticity is applied to represent the liquid layer. A thorough analysis of the complex velocity due to the variations of the liquid layer’s properties and thickness is derived and discussed to optimize multilayer Surface acoustic wave (SAW) sensor design. Numerical simulation of the sensitivity with a liquid layer on top of two guided layers is investigated in this study as well. The parametric investigation was conducted by varying the thicknesses for the liquid layer and the guided layers. The effect of the liquid layer viscosity on the sensitivity of the design is also presented in this study. The two guided layer device can achieve higher sensitivity than the single guided layer counterpart in a liquid environment by optimizing the second guided layer thickness. This perturbation analysis is valuable for Love wave sensor optimization to detect the liquid biological samples and analytes.

Traditionally, the measurement of turbulence has been conducted using hot-wire anemometry. This thesis presents the implementation of a constant voltage hot-wire anemometer for use with the Boundary Layer Data System (BLDS). A hot-wire calibration apparatus has been developed that is capable of operation inside a vacuum chamber and flow speeds up to 50 m/s. Hot-wires operated with a constant-voltage anemometer (CVA) were calibrated at absolute static pressures down to 26 kPa. A thermal/electrical model for a hot-wire and the CVA circuit successfully predicted the measured CVA output voltage trend at reduced pressure environments; however, better results were obtained when the Nusselt number was increased. A calibration approach that required only one measured flow speed was developed to allow autonomous calibrations of a CVA hot-wire. The single-point calibration approach was evaluated through comparison with the experimental data from the vacuum chamber over a range of 14-50 m/s and at pressures from 26 to 100 kPa. The thermal-electrical model was used to make predictions of CVA output voltage and the corresponding flow speed for conditions that could not be replicated within a laboratory. The first set of predictions were made for conditions from 7.5 to 100 kPa, at a constant temperature of 25⁰C, within a flight speed range of 40 to 150 m/s. Single-point calibrations were developed from these predictions. Additionally, the thermal-electrical model was used to predict hot-wire response for a change in temperature of ± 25⁰C at 26 kPa and the single-point calibration developed for the pressure range 7.5 to 100 kPa was tested for its ability to adjust. The temperature variation at a single pressure of 26 kPa proved that the single-point function was capable of adapting to off-standard temperatures with the largest deviations of +/-7% in the midrange velocities. With a temperature drop, the deviations were below 5%. The second set of thermal-electrical predictions involved conditions for altitude from 0 to 18 km at flow speeds from 40 to 150 m/s. A single-point calibration was developed for altitude conditions. Furthermore, to test the single-point calibration the thermal-electrical model was used to predict hot-re response for a temperature variation of ± 25⁰C at 18 km. The single-point calibration developed for altitude proved that it was capable of adjusting to a temperature variation of ± 25⁰C with maximum deviations of about 5% at mid-range velocities. It is proposed that the single-point calibration approach could be employed for CVA measurements with the Boundary Layer Data System (BLDS) to allow hot-wire data to be acquired autonomously during flight tests.

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