Optical MEMS sensors for wall-shear stress measurements

Ph. D. Thesis.This research reports on the development and experimental characterisation of optical sensors based on Micro-Electro-Mechanical-Systems (MEMS) technologies for walls hear stress quantification in turbulent boundary-layer flows. The MEMS sensors are developed to measure the instantaneous wall-shear stress directly via a miniature flush-mounted floating element, which is on the order of hundreds of microns square. The floating element is suspended flush to the wall by up to four specially designed micro-springs. As the flow passes over the wall, the sensor’s floating element moves, allowing direct measurement of the local forces exerted by the flow on the wall. A new optical transduction scheme based on the Moiré fringe pattern is developed alongside with an optical pathway to measure the instantaneous wall-shear stress using a single photodetector. Using this new optical technique consists of a lens array and fibre optics that provides the ability to detect the wall-shear stress using different sensing element sizes, leads to miniaturisation of sensors. Utilising the lens array, the focused light spot size is controlled, providing the opportunity of scanning the Moiré fringe pattern area on the sensors with different sensing element sizes. The microfabrication process of the devices are carried out by using a four mask bulk Silicon-on-Insulator (SOI) process and a BF33 wafer, where each device is placed at the center of a 5 mm × 5mm chip. Two generations of sensor packaging are developed to accommodate the sensors’ dies as well as the sensors’ optoelectronics, whilst the floating element is flush-mounted to the surface. The MEMS sensors calibration is carried out in a laminar flow rig over a wall-shear stress range of 0 to 5.32 Pa, where the results indicate a sensitivity range of 38 to 740 nm/Pa, an accuracy range of 1.4 to 2.36% and a repeatability range of 0.68 to 1.96%. The value of the of minimum detectable wall-shear stress for the developed MEMS wall-shear stress sensors varies in a range of 17 to 593 µPa, resulting in a minimum and maximum dynamic range value of 79 dB and 109 dB, respectively. The results from the dynamic characterisation indicate a resonant frequency range of 1 to 8.3 kHz. In a series of wind tunnel experiments over a range of Reτ = 560 to 1320, the instantaneous wall-shear stress within the turbulent boundary-layer flow is measured simultaneously by the MEMS sensors and an by either hot-wire anemometry or laser Doppler velocimetry using the near-wall velocity gradient technique. Excellent agreement is observed in the time series and statistics across these three independant measurement techniques.Faculty of Science, Agriculture and Engineering (SAgE), Newcastle Universit

Smart Materials and Devices for Energy Harvesting

This book is devoted to energy harvesting from smart materials and devices. It focusses on the latest available techniques recently published by researchers all over the world. Energy Harvesting allows otherwise wasted environmental energy to be converted into electric energy, such as vibrations, wind and solar energy. It is a common experience that the limiting factor for wearable electronics, such as smartphones or wearable bands, or for wireless sensors in harsh environments, is the finite energy stored in onboard batteries. Therefore, the answer to the battery “charge or change” issue is energy harvesting because it converts the energy in the precise location where it is needed. In order to achieve this, suitable smart materials are needed, such as piezoelectrics or magnetostrictives. Moreover, energy harvesting may also be exploited for other crucial applications, such as for the powering of implantable medical/sensing devices for humans and animals. Therefore, energy harvesting from smart materials will become increasingly important in the future. This book provides a broad perspective on this topic for researchers and readers with both physics and engineering backgrounds

A Monolithic Spiral Coil Acoustic Transduction Sensor for Chemical and Biological Analytes

Acoustic wave sensor platforms typically consist of piezoelectric materials in which bulk or surface acoustic waves are excited by metallic transducers deposited on the sensing surface of the platform. This type of transduction has limitations. In particular the transducer may limit the type of sensing film that can be used or analyte that can be measured and limit the frequency of operation of the sensor. In this work a novel method of exciting high frequency bulk acoustic waves in piezoelectric sensor platforms has been explored. This technique consists of applying time varying electromagnetic fields to the sensor platform using an antenna in order to excite high order harmonic acoustic waves. This configuration is known as a Monolithic Spiral Coil Acoustic Transduction (MSCAT) device. This technique offers benefits such as a bare sensing surface that allows for the detection of both mechanical and electrical property changes in the film or analyte and is capable of operating at high frequencies by exciting high order harmonics (\u3e 99th harmonic) in the substrate. The antenna configurations have been experimentally and theoretically examined and an understanding of how these electric fields excite the acoustic waves in the substrate has been developed. Finally, the MSCAT sensor platform was used to detect real world chemical and biological analytes and found in many cases to be superior to other bulk acoustic wave sensor platforms

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

Investigation of sensing membranes for QCM devices in gas sensing applications

The standard Quartz Crystal Resonator (QCR) and network analysis based methods in conjunction with curve fitting were used to investigate the sensing capability and characterize the properties of phthalocyanine films on vapour exposure. The measurement of frequency shift and resistance change (mass loading and film damping), caused by adsorption of organic vapour namely, Benzene, Hexane, Ethanol and Toluene were investigated. Confirmation of film properties using supplementary methods such as AFM, Ellipsometry and UV-visible spectrometer was also performed to provide a full characterization of the sensing membranes. The extracted values of Δƒ and ΔR from subsequent fitting of the spectra to the BVD model are observed on vapour exposure. A frequency shift (Δƒ) and change in magnitude (as related to ΔR of the BVD equivalent circuit) indicate changes in the films viscoelastic properties for the increasing concentrations of tested vapours. The sensitivity of the coating has been estimated from the slope of fitted trend line and gives values below LEL thresholds (the Lower explosive limit) and IDLH thresholds (Immediately Dangerous to Life or Health) for the ZnPcs films. The experimental results of the study demonstrate selected sensing membranes are easily applied through spin coating techniques evident from definitive shifts in resonance. Additionally when exposed to the target vapours tested, the film(s) exhibit fast and consistent responses, consequently giving significant potential for gas/vapour sensing applications. Changes in the film parameters have also been observed through the measurement of the admittance spectra. Shifts in both frequency and resistance are observed on exposures which indicate mass loading and changes in film viscosity caused by ad/absorption of the vapour. Response times appear to be quick and full recovery is observed. From the tested vapours, toluene gives the most significant frequency shift exhibiting the highest sensitivity for this compound; this can be attributed to relatively high saturated vapour pressure as compared to the other analytes. In addition, the film parameters extracted from this work were used to estimate the shear modulus parameters. It was found the shear modulus of viscous material (coating film) extracted electrical equivalent circuit parameters are dependent on film properties, thickness and analyte ad/absorption. Consequently, the QCR sensor can act iv as a gravimetric and non gravimetric sensitive device for thin film depending on load and adsorption characteristics. In most instances the studied film behaviour demonstrates a rubbery regime that was indicated from increase in resistance for the coating film at series resonant frequency typically. Consequently the calculation of change in film mass from frequency shift (Sauerbrey equation) is inaccurate except for suitably thin rigid films. A range of Phthalocyanine sensing membranes have been successfully evaluated; selected variants (mainly ZnPc) have given promising results to their viability as gas sensing membrane to detect a range of organic solvents at vapour concentrations below their lower explosive level, It was found suitably sensitive with detection limits in the low parts-per million ranges for the selected analytes. Furthermore, a comparison of gas sensor responses for the selected materials is included, and consequently a particular type of substituent is proposed as a suitable sensor coating for Quartz Crystal Resonator (QCR) gas sensor applications. Other phthalocyanine materials initially chosen proved less successful; demonstrating limited responsiveness to analytes ad/absorption and giving inconsistent results over the tested concentration range. Factors range from non-homogenous film surfaces to the structure and consequent suitability of the synthesised film(s). Moreover, further research is suggested to fully characterize the complete adsorption process with wide range of phthalocyanine material and various organic analytes

Nanoplasmonic Sensors based on Periodic Arrays of Gold Nanoparticles

Nanoplasmonic sensors use the localized surface plasmon resonance (LSPR) of metal nanostructures to sense the refractive index change in a surface-bound layer caused by biomolecular interactions or changing chemical environment. In this thesis, four types of sensor configurations based on gold nanoparticle arrays are thoroughly investigated. The first configuration is a periodic array of gold nanoparticles excited by the evanescent field of an optical waveguide mode. Since light carried by a waveguide mode propagates along the same plane of the periodicities, the coupling of nanoparticles are strongly affected by the photonic crystal lattice. This configuration is investigated both in simulations and in experiments, focusing on the sensing aspects of various spectral features attributed to different types of LSPRs. In simulation, it was found that, the LSPR modes of the gold nanoparticle array excited by the waveguide modes demonstrated similar trends as the array being excited by normal transmission. However, under waveguide excitation, the coherent interactions of the periodic array are through the grating order carried by the waveguide mode. Selective suppression of LSPR and grating-induced mode were also found from the waveguide excitation, which extended the existing knowledge of the optical properties of the periodic array. Under waveguide excitation, both quadrupolar and dipolar resonance peaks are sensitive to the surface-bound layer, however, the grating-induced mode is not sensitive. Preliminary experiments were conducted on ion-exchanged channel waveguides on BK7 glass and the trends of the dipolar resonance peak has been proved. The second configuration is a biosensor based on gold nanodisk arrays under normal transmission. By varying the lattice constant, the refractive index resolution was found to depend on the lattice constant, as a result of the figure of merit and signal/noise ratio together. The best refractive index resolution achieved is better than 1.5x10-4 RIU, when lattice constant equals to 550 nm. The sensor structure was used in detecting the binding of antigen (human IgG) and antibody (anti-human IgG) and a limit of detection better than 1 ng/mL (equivalent to 8 pM) was achieved. The third configuration is a chemical sensor based on a gold nanocrescent array combined with hydrogel. Under changing chemical environment, the hydrogel thin film can swell or shrink, depending on the pH of the solution. The swelling or shrinking of hydrogel thin film changes the refractive index, which can be detected by the near-infrared LSPR peak shift of the gold nanocrescent array. The sensor was proved to function in the range 4.5 pH - 6.4 pH and the detection resolution is better than 0.045 pH. At the most sensitive point, pH = pKa = 5.45, the peak-shift sensitivity is 11.1 nm/pH and transmission-shift sensitivity is 1.16 /pH. The fourth configuration is periodic array of gold nanorings under normal transmission. The effects of coherent interactions on the sensing characteristics of periodic arrays of gold nanorings were investigated in detail. In simulations, it was found that, the sensitivity, figure of merit both significantly depend on the lattice constant. The structure with highest figure of merit was found to be the one with lattice constant smaller than and close to the resonant lattice constant. The periodic array can improve the figure of merit by more than 2.5 times, compared to a single nanoring, which demonstrates the great sensing capabilities of periodic arrays. The simulated trend was proved by the experiments of the gold nanoring arrays patterned on top of pyrex substrate. A method was also demonstrated on how to tune the sensor structure to function in a desired spectrum window, with high figure of merit and high signal/noise ratio, at the same time. The highest figure of merit achieved from experiment is around 5.1, which is among the highest in literature

Flow-enhanced detection of biological pathogens using piezoelectric microcantilever arrays

The piezoelectric microcantilever sensor (PEMS) is an all-electrical resonant oscillator biosensor system capable of in-situ and label-free detection. Immobilized receptors on the sensor surface enable real-time electrical measurement of the resonance frequency shift due to the binding of target antigens to the surface. With silane-based insulation methods and bifunctional linker antibody immobilization schemes, it is wellsuited for applications in sensitive, specific detection of biological pathogens with limits of detection on the order of relevant lethal infectious dosage concentrations. Initial PEMS implementation demonstrated biodetection of Bacillus anthracis (BA) spores at a concentration of just 36 total spores in 0.8 mL of liquid. While these results are exciting, concerns that cross reactivity between the antibody and closely related species of the target pathogens cast doubts on the usefulness of any antibody-based assays in terms of the specificity of pathogen detection.The goal of this dissertation is to develop the PEMS biosensor as a viable antibody-based assay for in-situ, label-free, water-borne pathogen detection with better limits of detection than current antibody-based methods as well as high sensitivity and specificity, by exploring array PEMS detection and specificity augmentation by engineered fluidics. In the detection of BA spores, controlled fluid flow experiments in an 8 mm wide flow channel at flow rates ranging from 0 to 14 mL/min led to a determination of optimal flow rates for discriminatory detection of BA spores among close cousins: B. cereus (BC), B. thuringiensis (BT) and B. subtilis (BS). It is shown that the detection signal of all such spores first increased with an increasing flow rate. The detection signals of BC, BT and BS eventually diminished with the increasing flow rate as the force of the flow overcame the interaction force of the BC, BT, and BS spores with the sensor surface. The optimal flow rate was determined to be 14 mL/min at which detection signals of BC, BT, and BS all fell to within the noise level of the sensor, while the detection BA was still nearly optimal. As a result, it was deduced that the interaction forces of BC, BT, and BS were about 100 pN.Design and implementation of array sensing systems enabled real-time simultaneous redundant biosensor assays and concurrent background determination by a reference PEMS. By virtue of this advance in PEMS technology, successful real-time detection of just 10 BA spores/mL was achieved and step-wise, single Cryptosporidium parvum (CP) oocyst detection at 0.1 oocysts/mL was accomplished with resonance frequency step-wise shifts of 290 Hz and signal to noise ratios greater than 5 per instance of oocyst detection. It was found that, in a 19 mm wide flow channel, optimal single oocyst detection efficiency was achieved at 2 mL/min, while optimal discrimination of CP from C. muris (CM) oocysts was achieved at 5 mL/min. At this flow rate the detection signal of CP was close to optimal with a signal to noise ratio of 5 per step-wise shift and that of CM was close to the noise level. The interaction forces of CP and CM oocysts with the biosensor surfaces were deduced to be 110 and 70 pN, respectively.Ph.D., Materials Science and Engineering -- Drexel University, 200

Thermally modulated solidly mounted resonators for air quality monitoring

The effect of air pollution on the environment and human health is a cause of major concern. Each year millions of deaths are attributed to poor air quality, and it is estimated that its economic cost runs into the trillions of pounds. Especially the pollutant particulate matter has been identified as one of the main contributors to poor health. Hence there is much activity that attempts to reduce the concentration of small particles in air. To better understand the effect of particulate matter on the world and for the effective mitigation of the problems it causes and exacerbates, it is necessary to acquire reliable air quality data. Readily available particle sensing equipment is thus required to expand existing air quality monitoring systems that can deliver meaningful results. To this end, a range of particle sensing technologies have been studied. Resonator particle sensors based on microelectromechanical systems are one promising example of this because of their potential to provide an affordable solution that can be mass manufactured and use very little power or space compared to many currently available particle monitoring devices. In this thesis a novel particle sensor based on a solidly mounted resonator with an integrated microheater that is compatible with a standard integrated circuit fabrication process is developed and tested experimentally. The main objective of this work is to demonstrate for the first time that temperature modulation applied to a solidly mounted resonator could increase its sensitivity to particles, while targeted particle deposition could increase the effective sensitivity of the system to aerosolised particles and that the application of both could thus help to make this type of sensor more suitable for real world air quality monitoring applications. The design of the sensor is based upon a complementary metal oxide semiconductor process that includes the deposition of a piezoelectric bulk acoustic wave resonator on top of the standard layer stack. It is verified in an extensive set of simulations and the fabricated sensor is subsequently characterised. In the characterisation study the resonator had a resonant frequency around 2 GHz and a Q factor of approximately 200. The device was found to be capable of handling temperatures induced through the application of an electric current to the integrated microheater of up to 598 K. Experimentally the device’s resonant frequency, S-parameter value and its temperature for different applied currents were found to be within approximately 6 % of the sensor simulations. A custom particle test rig was built to evaluate the sensors performance as a particle sensor. One of the main obstacles remaining with these types of sensors is the reliability of particle measurements, which is reduced by difficulties to achieve repeatable particle sampling. To resolve this issue a thermophoretic particle deposition channel was added to a commercial FBAR device and experimental tests were carried out that showed it could reduce the variation in measurement results between repeat tests from 71 % to 14 %. The novel solidly mounted resonator particle sensor device was tested inside the particle test rig and found to have a sensitivity to particle deposition of approximately 40 Hz/ng. Temperature modulation was applied to the sensor through the integrated microheater and this was found to increase the sensitivity of the device by a factor of almost five to 190 Hz/ng. It also reduced the sensor’s detection limit from approximately 100 ng to 50 ng. The thermophoretic microchannel was added and found to approximately double the sensitivity of the novel sensor to airborne particles through increased particle sampling efficiency. The novel thermally modulated SMR particle sensor was found to have significant potential for low-cost quality monitoring applications

CEPC Technical Design Report -- Accelerator (v2)

The Circular Electron Positron Collider (CEPC) is a large scientific project initiated and hosted by China, fostered through extensive collaboration with international partners. The complex comprises four accelerators: a 30 GeV Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to 180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar). The Linac and Damping Ring are situated on the surface, while the Booster and Collider are housed in a 100 km circumference underground tunnel, strategically accommodating future expansion with provisions for a Super Proton Proton Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab for two interaction points over a decade, producing 2.6 million Higgs bosons. Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs coupling at sub-percent levels, exceeding the precision expected from the HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design Report (CDR, 2018), comprehensively detailing the machine's layout and performance, physical design and analysis, technical systems design, R&D and prototyping efforts, and associated civil engineering aspects. Additionally, it includes a cost estimate and a preliminary construction timeline, establishing a framework for forthcoming engineering design phase and site selection procedures. Construction is anticipated to begin around 2027-2028, pending government approval, with an estimated duration of 8 years. The commencement of experiments could potentially initiate in the mid-2030s.Comment: 1106 page