Development and Optimization of 3D Phononic-Fluidic Sensors for Liquid Analysis

Measurement of volumetric properties of liquids in small volumes is a challenge due to the limitations of classical ultrasonic and resonant sensors, specifically low sensitivity and only probing surface layers of an analyte. A phononic-fluidic sensor is an alternative approach, which provides a direct access to the volumetric properties of liquids such as, for example, speed of sound. However, many factors and design parameters such as unit cell topology, cavity width and dimensions influence on the performance of a sensor. This work presents a systematic design study of a 3D phononic-fluidic sensor based on a cubic unit cell with spherical void. This study aims to establish a fabrication process of a sensor element and to build a measurement setup, which is capable to control positions of the sensor element and the transducers. Moreover, this study includes creation of an advanced finite element model of the sensor, which takes into account its finite geometry, measured material parameters of the sensor material, vibration pattern of the transducers and fabrication tolerances. As a result, computed and measured transmission spectra are in a very good agreement. Furthermore, the effect of viscothermal boundary losses has been evaluated for two sensor materials: acrylic plastic and steel. The systematic design study creates the basis of the second part of this thesis: numerical optimization of a phononic-fluidic sensor. In this part, the method of shape optimization was applied to create the design of a sensor with the aim to increase the Q-factor of acoustic resonance peaks. Moreover, the suitable formulation of thefigure of merit has been suggested and different parametrization techniques have been tested. Finally, the computed transmission spectrum through the optimized design with periodic boundary conditions shows the Q-factor is increased by 107.4%. Transmission measurements demonstrate the Q-factor growth by 75%. In addition, the method of topology was utilized to design the material layout around the cavity resonator. The advanced two-step figure of merit has been formulated and implemented. Furthermore, our implementation consists of a gray scale suppressor to obtain a perfect black-white design and takes into account fabrication tolerances. The computed transmission spectrum through the optimized design presents the Q-factor increase by 3.7 times.