Leonte, Irina Ionela (2008) High frequency acousto-electric microsensors for liquid analysis. PhD thesis, University of Warwick.

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Abstract

Liquid sensors are required for a multitude of applications in the food and beverage sectors, in the pharmaceutical industry or environmental monitoring. The focus of this work is on the development of high frequency shear horizontal surface acoustic wave (SH-SAW) sensors for liquid media identification and characterisation. Among the various types of surface acoustic wave modes propagating in solids, the SH-SAWs were found to be the most suitable for operation in liquids. Dual delay line and resonator sensor configurations were designed and fabricated on lithium tantalate (LiTa03) substrates; the design and the subsequent fabrication procedures of the sensors are described in detail. Furthermore, the electrical characterization of the sensors was carried out with a network analyser, and a comparative analysis was performed between sensors with different configurations. The interdigital transducers, used as the interface between the electrical and acoustic domains, presented good reflection coefficients and had near perfect matched impedances and return loss figures up to 45 dB. The insertion loss of the sensors varied with the surface conditions while it was improved by using total or partial metallization of the surface or employing grating structures on the propagation path. The SH-SAW devices were exposed to basic taste solutions and all the sensor configurations tested were able to discriminate them well. Measurements were done in both standard wired set-ups and a semi-wireless set-up, thus proving the sensor's capability for remote operation. Further investigations regarding the electronic tongue applicability of the SH-SAW sensors were conducted on a two port resonator device. The resonator was tested with six basic taste solutions, with taste solutions with varying concentrations, with binary mixtures of taste solutions and proved successful in identifying all test samples. A multivariate analysis was performed on the resonator data, and confirmed that the sensor's responses are influenced by the physical properties of the tested solutions. The multiple linear models derived are statistically significant and can explain high percentage of the data variability, offering a simplified alternative to the complex analytical models of the SH-SAW sensors. Also, a voltage modulated sensor system was proposed for smart assaying of biomaterials and its operation principle is described. The preliminary tests carried out showed a significant voltage effect on carbon nanoparticles. The voltage modulated system is proposed as an analytical microsystem for the screening of bacterial cells. All sensors in this project had no bio-chemical selective layer making them nonspecific, yet they create robust, durable and low-cost systems.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Chemical detectors, Acoustic surface wave devices, Liquids, Taste
Date:	15 April 2008
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Gardner, J. W. (Julian W.), 1958- ; Cole, Marina
Sponsors:	University of Warwick ; Universities UK ; Sir Arthur Shercliff Scholarship Fund
Extent:	xii, 242 leaves
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/3681

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