Modeling, Design, Packaging and Experimental Analysis of Liquid-Phase Shear-Horizontal Surface Acoustic Wave

Recent advances in microbiology, computational capabilities, and microelectromechanical-system fabrication techniques permit modeling, design, and fabrication of low-cost, miniature, sensitive and selective liquid-phase sensors and labon- a-chip systems. Such devices are expected to replace expensive, time-consuming, and bulky laboratory-based testing equipment. Potential applications for devices include: fluid characterization for material science and industry; chemical analysis in medicine and pharmacology; study of biological processes; food analysis; chemical kinetics analysis; and environmental monitoring. When combined with liquid-phase packaging, sensors based on surface-acoustic-wave (SAW) technology are considered strong candidates. For this reason such devices are focused on in this work; emphasis placed on device modeling and packaging for liquid-phase operation. Regarding modeling, topics considered include mode excitation efficiency of transducers; mode sensitivity based on guiding structure materials/geometries; and use of new piezoelectric materials. On packaging, topics considered include package interfacing with SAW devices, and minimization of packaging effects on device performance. In this work novel numerical models are theoretically developed and implemented to study propagation and transduction characteristics of sensor designs using wave/constitutive equations, Green’s functions, and boundary/finite element methods. Using developed simulation tools that consider finite-thickness of all device electrodes, transduction efficiency for SAW transducers with neighboring uniform or periodic guiding electrodes is reported for the first time. Results indicate finite electrode thickness strongly affects efficiency. Using dense electrodes, efficiency is shown to approach 92% and 100% for uniform and periodic electrode guiding, respectively; yielding improved sensor detection limits. A numerical sensitivity analysis is presented targeting viscosity using uniform-electrode and shear-horizontal mode configurations on potassium-niobate, langasite, and quartz substrates. Optimum configurations are determined yielding maximum sensitivity. Results show mode propagation-loss and sensitivity to viscosity are correlated by a factor independent of substrate material. The analysis is useful for designing devices meeting sensitivity and signal level requirements. A novel, rapid and precise microfluidic chamber alignment/bonding method was developed for SAW platforms. The package is shown to have little effect on device performance and permits simple macrofluidic interfacing. Lastly, prototypes were designed, fabricated, and tested for viscosity and biosensor applications; results show ability to detect as low as 1% glycerol in water and surface-bound DNA crosslinking

Characterising room temperature ionic liquids with acoustic wave devices

Data for the physical properties of Room Temperature Ionic Liquids (RTILs) as a function of chemical composition is limited due to the expense and difficulty of producing large volumes of pure samples for characterization. RTILs comprise solely of ions and are liquid at room temperature. These are becoming of increasing interest for an extensive range of applications. This thesis looks at developing small scale characterization processes to find low cost and efficient methods for processing smaller sample volumes. Quartz crystal impedance analysis has been used to assess whether room temperature ionic liquids behave in a Newtonian manner to determine the values of their square root viscosity-density product using small volumes. Values are compared to traditional viscometer and densitometer measurements. A range of harmonics were studied for a 5 MHz fundamental crystal. The frequency shift of the third harmonic was found to provide the closest agreement between the two measurement methods with a limit seen at a square root viscosity-density product value of approximately 18 kg m??2 s??0:5. Further characterisation of the liquid was performed to separate values of density and viscosity using dual Quartz Crystal Microbalance (QCM) with fabricated surface features on one QCM; this required a total sample volume of only 240 L. Values were corroborated with standard measurement techniques demonstrating good agreement. A QCM was then incorporated into a microfluidic glass chip system to measure the square root of the viscosity-density product of RTILs

THE ACOUSTIC WAVE SENSOR AND SOFT LITHOGRAPHY TECHNOLOGIES FOR CELL BIOLOGICAL STUDIES

Recently, cell-based biosensors have attracted many attentions because of their potential applications in fundamental biological research, drug development, and other fields. Acoustic wave biosensors offer powerful tools to probe cell behaviors and properties in a non-invasive, simple, and quantitative manner. Current studies on cell-based acoustic wave sensors are focused on experimental investigation of thickness shear mode (TSM) sensors for monitoring cell attachment and spreading. There are no theoretical models for cell-based TSM biosensors. No studies on other cell biological applications of TSM sensors or on surface acoustic wave cell-based biosensors have been performed. The reliability and sensitivity of current cell-based biosensors are low. Improving them requires studies on engineering cells and understanding the effects of cell morphology on cell function.The overall objective of this dissertation is to develop acoustic wave sensor systems for cell biological studies and to determine the effects of cell shape on cell function. Our study includes three parts: (1) Development of cell-based TSM sensor system; (2) Studies of Love mode devices as cell-based biosensors; (3) Studies of the effects of cell shape on cell function. In the first part, a theoretical model was developed, changes in cell adhesion were monitored and cell viscoelasticity was characterized by TSM sensor systems. The TSM sensor systems were demonstrated to provide a non-invasive, simple, and reliable method to monitor cell adhesion and characterize cell viscoelasticity. In the second part, a theoretical model was developed to determine signal changes in Love mode sensors due to cells attaching on their surface. Experimental results validated the model. In the third part, cell shape was patterned to different aspect ratios. Elongated tendon cells were found to express higher collagen type I than shorter cells. Changes in cell shape induced alterations in cytoskeleton, focal adhesions, and traction forces in cells, which may collectively prompt the observed differential collagen type I expression in cells with different shapes. Overall, our research expanded the applications of acoustic wave cell-based biosensors. Studies on cell shape control and the effects of cell shape on cell function will be useful for increasing the sensitivity of cell-based biosensors in future research

Acoustic Wave Biosensors for Biomechanical and Biological Characterization of Cells

During past decades, interest in development of cell-based biosensors has increased considerably. In this study, two kinds of acoustic wave sensors are adopted as the cell-based biosensors to investigate the biomechanical and biological behaviors of cells, the quartz thickness shear mode (TSM) resonator and Love wave sensor. For the first part, the quartz TSM resonator is applied to detect the structural and mechanical properties of tendon stem/progenitor cells (TSCs), which are one kind of newly discovered adult cells in tendons, and the platelets from blood. Through the TSM resonator, the related viscoelastic properties of cells are extracted, which could indicate the state of cells in different physiological conditions. The TSM resonator sensor is utilized to characterize the aging-related viscoelasticity differences between the aging and young TSCs, and also to monitor the dynamic activation process of platelets. For the second part, a 36˚ YX-LiTaO3 Love wave sensor with a parylene-C wave guiding layer is proposed as a cell-based biosensor. A theoretical model is derived, to describe the Love wave propagation in the wave guiding layer, the adherent cell layer, and penetration into the liquid medium. The Love wave sensor is used to monitor the adhesion process of cells. Compared with TSM resonator, the response of Love wave sensor to the cell adhesion is primarily induced by the formation of bonds between cells and the substrate. The numerical results indicate that the adherent cell layer of various storage or loss shear modulus in certain range can cause evident, characteristic variations in propagation velocity and propagation loss, revealing the potential of Love wave sensors in providing useful quantitative measures on cellular mechanical properties. In addition, a Love wave sensor with a phononic wave guiding layer is introduced for non-operation signal filtering and sensor sensitivity improvement. Both two kinds of acoustic wave sensors present their own advantages as the cell-based biosensors, indicating advisable techniques for investigating cell biology in general and certain physiological processes in particular

Semen quality detection using acoustic wave sensors

Artificial insemination (AI) is a widely used part of the modern agricultural industry, with the number of animals inseminated globally being measured in the millions per anum. Crucial to the success of AI is that the sperm sample used is of a high Quality. Two factors which determine the quality of the sample are the number of sperm present and their motility. There are numerous methods used to analyse the quality of a sperm sample, but these are generally laboratory based, expensive and in need of a skilled operator to perform the analysis. It would, therefore be useful to have a simple and inexpensive system which could be used outside the laboratory, immediately prior to the insemination of the animal. Presented in this thesis is work developing a time of flight (ToF) technique which makes use of a quartz crystal microbalance (QCM), operating at 5 MHz, as the sensing element. Data is shown developing a device where a 50 μl sample of boar sperm is added to a liquid filled swim channel, which the sperm are allowed to self-propel down and attach to the surface of a QCM at the end. The attachment of the sperm to the surface causes a measurable frequency decrease in the QCM, aproximately 50 Hz. An average effective mass measurement was made using a QCM and gave a value of 8 ± 5 pg per sperm, which was used in conjunction with the frequency change to determine the number rate of sperm reaching the QCM

Investigation of multilayered surface acoustic wave devices for gas sensing applications : employing piezoelectric intermediate and nanocrystalline metal oxide sensitive layers

In this thesis, the author proposes and develops novel multilayered Surface Acoustic Wave (SAW) devices with unique attributes for gas sensing applications. The design, simulation, fabrication and gas sensing performance of three multilayered SAW structures has been undertaken. The investigated structures are based on two substrates having high electromechanical coupling coefficient: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3), with a piezoelectric zinc oxide (ZnO) intermediate layer. Sensitivity towards target gas analytes is provided by thin film indium oxide (InOx) or tungsten trioxide (WO3). The high performance of the gas sensors is achieved by adjusting the intermediate ZnO layer thickness. Sensitivity calculations, undertaken with perturbation theory illustrate how the intermediate ZnO layer can be employed to modify the velocity-permittivity product of the supported SAW modes, resulting in highly sensitive conductometric SAW gas sensors. The work contained within this thesis addresses a broad spectrum of issues relating to multilayered SAW gas sensors. Topics include finite-element modelling, perturbation theory, micro-fabrication, metal oxide deposition, material characterisation and experiential evaluation of the layered SAW sensors towards nitrogen dioxide (NO2), hydrogen (H2) and ethanol gas phase analytes. The development of two-dimensional (2D) and three dimensional (3D) finite-element models provides a deep insight and understanding of acoustic wave propagation in layered anisotropic media, whilst also illustrating that the entire surface of the device can and should be used as the active sensing area. Additionally, the unique and distinctive surface morphology of the layered structures are examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline structure and orientation of the ZnO and WO3 layers are also examined by X-ray Diffraction Spectroscopy (XRD). The novel multilayered SAW structures a re shown to be highly sensitive, capable of sensing NO2 and ethanol concentration levels in the parts-per-billion and parts-per-million range, respectively, and H2 concentrations below 1.00% in air. The addition of platinum or gold catalyst activator layers on the WO3 sensitive layer is shown to improve sensitivity and dynamic performance, with response magnitudes up to 50 times larger than bare WO3. The gas sensing performance of the investigated structures provide strong evidence that high sensitivity can be achieved utilising multilayered SAW structures for conductometric gas sensing applications

Surface Acoustic Wave (SAW) Sensors: Physics, Materials, and Applications

Surface acoustic waves (SAWs) are the guided waves that propagate along the top surface of a material with wave vectors orthogonal to the normal direction to the surface. Based on these waves, SAW sensors are conceptualized by employing piezoelectric crystals where the guided elastodynamic waves are generated through an electromechanical coupling. Electromechanical coupling in both active and passive modes is achieved by integrating interdigitated electrode transducers (IDT) with the piezoelectric crystals. Innovative meta-designs of the periodic IDTs define the functionality and application of SAW sensors. This review article presents the physics of guided surface acoustic waves and the piezoelectric materials used for designing SAW sensors. Then, how the piezoelectric materials and cuts could alter the functionality of the sensors is explained. The article summarizes a few key configurations of the electrodes and respective guidelines for generating different guided wave patterns such that new applications can be foreseen. Finally, the article explores the applications of SAW sensors and their progress in the fields of biomedical, microfluidics, chemical, and mechano-biological applications along with their crucial roles and potential plans for improvements in the long-term future in the field of science and technology

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/ designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.The authors acknowledge support from the Innovative electronic Manufacturing Research Centre (IeMRC) through the EPSRC funded flagship project SMART MICROSYSTEMS (FS/01/02/10), Knowledge Transfer Partnership No KTP010548, EPSRC project EP/L026899/1, EP/F063865/1; EP/F06294X/1, EP/P018998/1, the Royal Society-Research Grant (RG090609) and Newton Mobility Grant (IE161019) through Royal Society and NFSC, the Scottish Sensing Systems Centre (S3C), Royal Society of Edinburgh, Carnegie Trust Funding, Royal Academy of Engineering-Research Exchange with China and India, UK Fluidic Network and Special Interest Group-Acoustofluidics, the EPSRC Engineering Instrument Pool. We also acknowledge the National Natural Science Foundation of China (Nos. 61274037, 51302173), the Zhejiang Province Natural Science Fund (No. Z11101168), the Fundamental Research Funds for the Central Universities (No. 2014QNA5002), EP/D03826X/1, EP/ C536630/1, GR/T24524/01, GR/S30573/01, GR/R36718/01, GR/L82090/01, BBSRC/E11140. ZXT acknowledges the supports from the National Natural Science Foundation of China (61178018) and the NSAF Joint Foundation of China (U1630126 and U1230124) and Ph.D. Funding Support Program of Education Ministry of China (20110185110007) and the NSAF Joint Foundation of China (Grant No. U1330103) and the National Natural Science Foundation of China (No. 11304209). NTN acknowledges support from Australian Research Council project LP150100153. This work was partially supported by the European Commission through the 6th FP MOBILIS and 7th FP RaptaDiag project HEALTH-304814 and by the COST Action IC1208 and by the Ministerio de Economía y Competitividad del Gobierno de España through projects MAT2010-18933 and MAT2013-45957R