Date of Award
Summer 2005
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Electrical and Computer Engineering
First Advisor
Josse, Fabien
Second Advisor
Yaz, Edwin
Third Advisor
Hossenlopp, Jeanne
Abstract
The last decade has been devoted to exploring the use of acoustic wave based sensors for the detection of harmful compounds in gas environments. The successful results of these investigations of acoustic wave based sensors have led us to consider other issues of application to this technology. It is in this perspective that, recently the use of the device in liquid environment is being investigated. The investigation involves direct contact of the device with a solution and this process is well known as liquid phase sensing application. Various types of acoustics waves have been studied for detection in liquid environments. They include TSM (thickness shear mode), SH-APM (shear horizontal acoustic plate mode), FPW (flexural plate wave), SH-SAW (shear horizontal surface acoustic wave). Only TSM and SH-SAW sensors are mostly used in liquid environments. TSM, due to its nature (bulk type wave) is less sensitive to surface perturbation. SH-SAW on the other side combines both the advantages of a typical SAW and a bulk wave. However, the wave propagates slightly deeper inside the substrate, which decreases its sensitivity to surface perturbation. Depositing a thin guiding layer on the device surface traps the acoustic energy to the surface and increase sensitivity. Polymer materials, silicon nitrite and silicon dielectric are used as waveguiding material. Easy deposition and low shear wave velocity make polymer materials the principal choice. PMMA (Poly methyl methacrylate) is one of the mostly used waveguiding materials despite its tendency to absorb water, and its relatively high acoustic loss. This thesis investigates the use of epoxy resin (SU-8) as a waveguiding material. The mechanical loading, which is assumed to be mass loading, is the sensing mechanism. The change in mechanical loading is measured through the frequency change, which is used to characterize the SH-SAW sensor sensitivity. A change in the viscoelastic properties of the polymer, which can place the sensor in non-gravimetric regime where the sensor response is no longer linear with the mass of the detected chemical analyte, was examined. The analysis of the frequency shift and the insertion loss indicates the existence of an optimum thickness of SU-8 where the sensitivity is high. Combinations of the SU-8 as waveguiding material and sensitive layer such as PIB are used to detect different concentrations of toluene in water. The sensor responses increase monotonically with increasing concentrations of the organic compounds. The sensor responses also show reversibility and reproducibility.
Recommended Citation
Houndegla, Arnaud, "The Use of SU-8 As Waveguide Material for Liquid Phase Sensor Applications" (2005). Master's Theses (1922-2009) Access restricted to Marquette Campus. 4806.
https://epublications.marquette.edu/theses/4806