Einzel-Interdigital Signalwandler als Oberflächenwellenimpedanzsensor
- Single Interdigital Transducer as Surface Acoustic Wave Impedance Sensor
Nguyen, Vu Hoa; Schnakenberg, Uwe (Thesis advisor); Knoch, Joachim (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020
Surface acoustic wave (SAW) devices are well known for sensor applications, especially for gravimetrical approaches. In conventional biosensing applications, chemically and biochemically evoked binding processes at surfaces are detected in liquid environments using delay line or resonator sensor configurations, preferably in combination with appropriate microfluidic devices. All configurations have in common that they analyze the transmission characteristic of the propagating SAW, in the form of amplitude, propagation velocity or frequency. SAW sensors have gained high interest due to their higher mass sensitivity in comparison to conventional quartz crystal microbalance (QMB) sensors and their versatile applicability compared to optical or electrical sensors. However, despite of numerous reported progresses in the research field, there is still a lack of commercialized outcomes based on SAW technology compared to the benchmark optical sensor solutions. In this thesis, a novel single IDT approach has been implemented in microfluidic devices and studied, where a single interdigital transducer (IDT) was simultaneously used for SAW generation and detection. Hence, not the transmission characteristic was used for detecting environmental influences, but the input impedance of the SAW sensor. Additionally, the whole sensor concept was simplified with respect to fabrication effort and chip size. Experiments with different fluid characteristics and three different mass adsorption approaches have been carried out to quantitatively determine the SAW sensor performance. The achieved results showed a comparable sensitivity in comparison with the conventional transmission approach. Furthermore, a portable measurement system based on the single IDT approach has been developed and characterized. The pivotal strength of the portable system is the use of cheap and commercially available RF-gain-phase meters and the simplification of a radio frequency problem to a quasi-static one. This thesis is contentwise divided into the following three parts. At first, the theory of SAW sensors, the state-of-the-art and the material and methods are summarized. In the next part, the experimental results are presented and the last part describes the implementation and characterization of the portable system.