On new applications and sensitivity enhancement of cantilever-based sensing systems

• Main Author: Bradley, Calvin Rhett
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2008
• Subjects: Mechanical engineering
• ISBN: 0549520155; 9780549520153

Cantilever-based Sensing Systems (CSS) have become a focal area for research with the rise of micro- and nanotechnology. History has led us to use cantilever beams as one of the foremost sensing devices for small scale applications, beginning with the atomic force microscopy, and then being expanded into numerous sensor devices. The CSS include such applications as accelerometers, thermal and chemical sensors which are expanding into the applications of mass sensing and material characterization. Soon, this technology may be used in "lab on chip" biosensing applications. This study covers the experimentation into new CSS applications and sensitivity enhancement. In order to do this, an overview of CSS is presented. The history of cantilever is covered from its humble beginnings to the recent explosion of interest. Next, working principles, operational modes and microfabrication of the CSS are briefly overviewed. Experimentation into novel CSS applications for material characterization of a thermally sensitive polymer is discussed first. To accomplish this, an array of cantilevers is used to isolate effect of the polymer. The results show that static mode CSS using optical transduction can be effectively used to sense polymers lower critical solution temperature via measuring the beam deflection caused by surface stress due to the polymer instead of repeated traditional surface hydrophobicity tests. In the next part of the thesis, a new CSS design is fabricated and used for mass detection. This new design utilizes stress measurements of an integrated strain gauge with reference cantilever. The new design allows for the measurement of the frequency shift while compensating for environmental effects. The CSS design is characterized and tested utilizing the addition of Au nanoparticles as functional added mass. The final section of this study focuses on an exciting new CSS sensitivity enhancement technique. This new technique utilizes a delayed feedback to create stable limit cycles. The amplitude of these limit cycles is shown to be highly sensitive to changes in tip mass added or attached to the cantilever. The theory is presented and verified utilizing macroscale experimentation. Both theoretical and experimental results demonstrate a two-orders-of magnitude sensitivity enhancement over traditional frequency shift methods.