Sensors Research Laboratory
University of Warwick
Tel: 02476 574494
High Frequency SH-SAW Microsensors for Liquid Phase Analysis
This project aims to develop a novel, low-cost, robust, durable, micropower microsystem for rapid liquid characterisation, a so-called Electronic Tongue (E-Tongue). The system is to be based on shear-horizontal surface acoustic wave (SH-SAW) microsensors and envisaged applications are within the food and beverage industries, environmental monitoring and biomedical field.
The E-Tongue consists of a LiTaO3 substrate upon which thin-film interdigital transducers (IDTs) and/or reflectors are fabricated. Various high frequency (433MHz, 869MHz and 2.4GHz) sensor configurations have been considered, all employing the same basic sensing principle based on the interaction between the liquid under test and the shear horizontal polarized wave mode. The way the liquid perturbs the acoustic waves and hence changes the wave phase velocity and attenuation can help in identifying and analyzing the liquid samples.
Preliminary results have oriented the research towards two major areas of study, one centred on the actual taste sensor (E-Tongue) and the other focused on the development of a voltage modulated SH-SAW biosensor.
The E-Tongue SH-SAW devices (delay lines and resonators) operate without the need for analyte-specific coatings. Tests have been performed on aqueous solutions with different tastants representing not only the four basic tastes of saltiness, sweetness, sourness, and bitterness but also of umami and metallic tastes. Results (Fig. 1) show research good discrimination between the six different taste samples confirming the high-frequency SH-SAW microsensors potential of acquiring qualitative and to certain extend qualitative information.
Fig. SEQ Figure \* ARABIC 1: E-Tongue taste results
The second main direction within this SH-SAW sensors research consists of a voltage modulated device. The principle of operation of this sensing system is illustrated in Fig. 2: a liquid sample is passed into a micro reservoir, high voltage is applied to the metal electrode thus forcing charged bioparticles to stick to the piezoelectric substrate while the measurement takes place. Bioparticles of different dielectric constant can also be attracted, but with an ac field. The sensor comprises a voltage modulated shorted 433 MHz delay-line device together with a reference free delay-line (Fig. 3) and a parylene coated SU8 liquid reservoir with an embedded microparticle filter (Fig. 4).
The voltage can be setaccording to the properties of the bioparticles, e.g. charge/size, dielectric constant. Initially the SAW sensors will have no bio-chemical layers but a functionalized biocoating can be added for more specific protein-based biological applications. An experimental set-up is currently being developed for the voltage modulated sensor for bioliquids and estimated that this novel sensor configuration will bring a significant enhancement of sensor sensitivity.