Date of Award

12-2020

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Daewon Kim

First Committee Member

Dr. Marwan Al-Haik

Second Committee Member

Dr. Eduardo Rojas

Abstract

Over the last couple of decades, smart transducers based on piezoelectric materials have been used as sensors in a wide range of structural health monitoring applications. Among them, a Surface Acoustic Wave sensor (SAW) offers an overwhelming advantage over other commercial sensing technologies due to its passive, small size, fast response time, cost-effectiveness, and wireless capabilities. Development of SAW sensors allows investigation of their potential not only for measuring less-time dependent parameters, such as pressure and temperature, but also dynamic parameters like mechanical strains. The objective of this study is to develop a passive flexible SAW sensor with optimized piezoelectric properties that can detect and measure mechanical strains occurred in aerospace structures. This research consists of two phases. First, a flexible thin SAW substrate fabrication using hot-press made of polyvinylidene fluoride (PVDF) as a polymer matrix, with lead zirconate titanate (PZT), calcium copper titanate (CCTO), and carbon nanotubes (CNTs) as micro and nanofillers’ structural, thermal and electrical properties are investigated. Piezoelectric property measurements are carried out for different filler combinations to optimize the suitable materials, examining flexibility and favorable characteristics. Electromechanical properties are enhanced through a noncontact corona poling technique, resulting in effective electrical coupling. Second, the two-port interdigital transducers (IDTs) deposition made of conductive paste onto the fabricated substrate through additive manufacturing is studied. Design parameters of SAW IDTs are optimized using a second-order transmission matrix approach. An RF input signal excites IDTs and generates Rayleigh waves that propagate through the delay line. By analyzing the changes in wave characteristics, such as frequency shift and phase response, the developed passive strain sensor can measure mechanical strains.

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