Boris Stoeber


Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Compact volumetric see-through near-eye display (2023)

No abstract available.

Lubricated rolling over a pool (2022)

The focus of this research is the rolling of a cylinder over a pool of viscous fluid. This process has many industrial applications such as roll coating, lubrication of bearings, and rail transport (the primary motivator of this research). The problem is studied for Newtonian and shear-thinning fluids. The speed, width and loading of the cylinder are varied as are the initial depth and length of the viscous pool. Depending on the operating conditions, the cylinder will either ride on a lubrication film or remain in solid contact with the underlying substrate (although in the wheel/rail interface, there could also be a mixed or boundary lubrication regime). For the former situation, a lubrication theory is provided to predict the pressure underneath the cylinder and the film thickness deposited on the substrate. To account for the flux of fluid escaping towards the cylinder edges (3D effects), an approximation of the lubrication theory is used that includes an adjustable parameter. Once this single parameter is calibrated against experiment, the theory predicts peak lubrication pressures, gap sizes and film thicknesses to within about ten percent. The printer's instability arises during the splitting process, patterning the residual fluid films on the substrate and cylinder. If the pool length is less than the cylinder circumference, the fluid adhering to the cylinder is rotated back into contact with the substrate, and when there is sufficient adhered fluid a lubrication film forms that can again be modelled by the theory. Conversely, if there is insufficient adhered fluid, no contiguous lubrication film is formed; instead the pattern from the printer's instability "prints" from the cylinder to the substrate. A field experiment was conducted to understand the initial pickup of the liquid by the train wheel and subsequent carrydown along the track. Due to the high wheel-rail contact pressure, the liquid failed to form a lubrication layer (not the preferred outcome) and was squeezed out laterally, adhering to the edges of the wheel contact band. This edge liquid, however, provides tribological benefits on the curved track due to movement of the contact band as the train rounds a curve.

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Paper drying - experimental studies on the influence of dryer fabric (2018)

This research is an experimental investigation on paper drying that primarily focuses on the effects of the dryer fabric on the drying process of paper. A novel method for moisture content measurement is presented. The working principle of this method is the strong correlation between the optical transparency of paper and its moisture content due to the refractive index matching role of water in wet paper. Spectrographic and microscopic measurement techniques were employed to characterize the relation of moisture content and relative transparency of paper. As optical access to the paper is restricted by the dryer fabric, the optical transparency of paper should be measured only with one-sided optical access. To achieve this goal, a novel technique of transmittance measurement is developed that is able to determine the transparency of thin film objects (i.e. paper) with only one-sided optical access. Employing a fluorescence imaging method, this optical configuration eliminates the spurious effect of reflection of the incident light by filtering the excitation wavelength before reaching the optical detector.To study the paper drying process in a multi-cylinder dryer, an experimental setup is designed to simulate realistic conditions of a typical paper dryer while providing optical access for the measurement system. Ten commercially available fabric types manufactured by weaving synthetic filaments are used in the investigations. It is shown that the fabric structure affects the drying progression and the drying time significantly. The contact area and three-dimensional arrangement of the filaments have the greatest impact on the drying process. To study through air drying (TAD), another experimental apparatus is designed to perform drying under controlled conditions of air temperature and mass-flowrate. Four commercially available TAD fabrics with different structural designs and characteristics are used in the investigations. It is shown that the geometry of the contact spots of the fabrics has a significant impact on the drying time at high drying intensities. Comparing the spatial maps of moisture content with the paper grammage distribution reveals that there is a correlation between the local grammage and the local moisture in a paper sheet during the drying process.

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Controlled spreading of complex droplets (2017)

The current thesis investigates the controlled spreading of droplets of complex fluids. This thesis makes four primary scientific contributions. Firstly, we provide detailed theoretical analysis on spreading of yield stress fluids. We employ lubrication theory, asymptotic solutions, and numerical simulations to explain the dynamics and final static shape of a viscoplastic droplet on a solid horizontal surface. We show that the final radius of the droplet becomes smaller with increasing the yield stress. Secondly, we provide experimental data to verify our theoretical solutions. In our experiments, we first provide a method to eliminate the apparent slip of the yield stress fluid. The method uses a chemical modification of glass surfaces to generate permanent positive charges, resulting in a no-slip boundary condition. We directly observe the slip and no-slip of the Carbopol droplets, using a visualization method based on confocal microscopy. We then perform shadowgraphy experiments to measure the final radius of the droplets under different conditions such as extruding and impacting droplets. We compare the theoretical and experimental results and discuss the similarities and differences. Briefly, the asymptotic solutions overestimates the experimental results (most likely due to the assumption of a shallow layer), while numerical solutions are much closer to the experimental outcomes. Thirdly, we provide a comprehensive rheological characterization of a particular thermo-responsive fluid, Pluronic F127. We show that the aqueous solution of the polymer undergoes a sol(Newtonian)-gel(yield stress) transition upon heating. We further characterize the properties of the gel in detail. Finally, we show one can thermally trigger a thermo-responsive droplet to externally control the final shape of the droplet on a surface. In short, the final radius of the droplet can be controlled by heating the surface; for a given concentration, the larger the surface temperature, the smaller the final shape of a droplet. In the same part of the thesis, we introduce a novel experimental method based on optical coherence tomography to identify the solidified region inside a droplet.

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Skin mechanics, intradermal delivery and biosensing with hollow metallic microneedles (2017)

Microneedles (MNs) have gained significant attention over the past decade in drug delivery and biosensing due to their minimally-invasive and less painful nature of use compared to intramuscular/subcutaneous injections, and significant biological benefits. Several fundamental processes enabling MN functionality have not been completely understood, including mechanical interaction between MNs and skin for targeted depth penetration; and precise quantification of fluid delivery in the skin. This thesis presents novel materials, and methodologies for evaluating MN interactions with skin, and investigates the performance of hollow MNs in both intradermal fluid drug delivery and biosensing.A micromechanical comparison between human skin and porcine skin was performed using to determine their mechanical behavior affecting MN insertions. Stratum corneum (SC) of human skin was significantly stiffer (117 ± 42 MPa) than porcine skin (81 ± 32 MPa), requiring higher force of MN insertion to rupture the SC in human skin (107 ± 17 mN) than porcine skin (96 ± 23 mN). An artificial mechanical skin model was developed layer-by-layer to simulate tough human skin (MN insertion force 162 ± 11 mN) and to study the dynamics of MN insertion. Key factors that affected MN insertions into skin, including velocity of impact and total energy delivered to the skin, were identified. ID fluid delivery by hollow MNs was assessed using a novel method involving the low-activity radiotracer technetium-99m pertechnetate (⁹⁹mTcO₄₋). Its delivery allowed accurate quantification of fluid delivered into the skin, back-flowed to the skin surface, and total fluid ejected from the syringes via ID devices with sub-nanoliter resolution. Hollow MNs performed more accurate ID injections than conventional needles (93% vs. 69-87% of fluid per 0.1 mL injection volume).A MN-optofluidic biosensing platform capable of eliminating blood sampling was developed with MNs that can access dermal interstitial fluid that contains numerous drugs at concentrations comparable to blood. The MN lumen was functionalized to collect, trap and detect drugs in 0.6 nL of sample. The optofluidic components provided specific high-sensitivity absorbance measurements for drug binding using enzyme-linked assays. Streptavidin-horseradish peroxidase (LoD = 60.2 nM) and vancomycin (LoD = 84 nM) binding validated this point of care system.

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ZnO-based thermoelectrics : modelling, electrochemical thick film growth, and characterization (2016)

The thermoelectric performance of electrodeposited, aluminum doped zinc oxide was assessed. In this work, wurtzite ZnO was first modelled using Mueller-Plathe to compare the effectiveness of different nanostructured configurations on reducing thermal conductivity. A new analysis technique, Local Vibrational Density of States Equilibrium Molecular Dynamics (LVDOS-EMD), was created to study localized lattice vibrations around nanostructural features of silicon and ZnO, and was used to predict thermal properties in materials of similar composition 17× faster than conventional thermal modelling methods. A 30% void density was determined to yield the best reduction in thermal conductivity by volume of voids in bulk Al:ZnO with a computed thermal conductivity of 0.77 W m-¹ K-¹ at room temperature, 3× below the threshold achieved through established experimental means with high electrical conductivity Al:ZnO. Thick film, electrodeposited Al:ZnO was grown using a nitrate system. Experiments on solution pH using various counter electrodes demonstrated that inert electrodes caused acidification of the growth solution, limiting film thickness. Chloride contamination from commonly used Ag/AgCl reference electrodes was also determined to affect thick film opacity, morphology, crystallinity, and electrical properties. Aluminum integration and activation was explored by adding Al(NO₃)₃ to the growth solution during film synthesis, yielding aluminum integration molar ratios of up to 1.72% (Al.₀₃₄Zn.₉₆₆₀). Partially doped films in excess of 95 µm thick, 4× the thickness reported elsewhere, were electrochemically grown and characterized. Sub-micron voids were integrated into the films using sacrificial material and annealing. A new electrochemical chromium etching methodology was developed and successfully used to free 20 films from their growth substrates for thermoelectric characterization. A new, reusable thermoelectric test apparatus for thin film thermoelectric testing was designed, implemented, calibrated, and successfully deployed to characterize ZnO and Al:ZnO thin films grown 79 – 95 µm in thickness. Extremely low thermal conductivity of 11 mW m-¹ K-¹ at room temperature was demonstrated concurrently with a Seebeck coefficient of -88 µV K-¹. Polycrystallinity and poor dopant activation yielded a low electrical conductivity of 0.75 mS/cm and corresponding low room temperature ZT of 1.3×10-⁵ for the Al:ZnO films.

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Flow physics during the drying of a thin polymer solution film near the contact line (2015)

The drying process of a thin polymer solution film has been studied inside a micro-liter cavity near the contact line. Confocal microscopy along with particle image velocimetry and laser induced fluorescence are used for the real time measurement of velocity and concentration fields during the drying process. In addition to the capillary flow and the Marangoni flow, the velocity field also reveals the possible existence of a single vortex and multiple vortices inside the creeping flow induced by evaporation. These vortices appear soon after the beginning of the evaporation process, their size shrinks over time, and they disappear before the end of the evaporation process. This thesis includes a study of the effect of rheological and geometrical parameters on the presence, size and endurance of these vortices. Significant concentration heterogeneity is observed across the film during the drying process, in particular near the contact line. The concentration at the solution-air interface is higher compared to the bulk, and it increases towards the contact line and also over time. A skin layer starts forming as soon as the surface concentration reaches the glass transition concentration after which the evaporation rate starts decreasing. The drying film undergoes a similar concentration evolution during the evaporation process, regardless of the cavity depth and the initial polymer concentration; although, minor differences can be recognized that are associated with the flow recirculations that delay the concentration increase inside the vortex. Finally, a theory is developed based on experimental data which explains the existence and behavior of viscous vortices near the bottom wall of the cavity. The competition between the capillary flow and the Marangoni flow results in flow separation on the bottom wall which leads to such vortices. This study provides better understanding of the drying process of thin polymer solution films near the contact line. Furthermore, viscous flow separation adds to the current understanding of flow physics during the drying process, in addition to the well-known evaporation induced capillary transport and the Marangoni effect.

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Particle Transport in Microfluidic Environments: Particle Adsorption at the Polydimethylsiloxane-Water Interface and the Effects of Flow Field and Image Processing on the Measurement Depth in Micro Particle Image Velocimetry (2015)

This thesis investigates several research questions associated with the transport of microscopic particles in microfluidic environments. This includes an investigation of the motion and deposition of micron sized polystyrene particles at the planar polydimethylsiloxane–water interface. Particle tracking shows that particles near the substrate can be immobilized to different degrees. Careful analysis of the more weakly immobilized particles reveals that there is a buildup of a particle accumulation layer near the substrate in which particle motion parallel to the substrate is hindered by non-hydrodynamic effects. The presence of lateral surface interaction forces resulting from charge heterogeneity of the PDMS substrate is found to be the most plausible explanation for the hindered particle transport across the substrate. The two other problems are concerned with micro particle image velocimetry (μPIV), which is a particle transport-based optical method for the characterization of flow fields in microfluidic devices. One limitation μPIV is the finite measurement depth associated with the optical setup, which can lead to bias errors in the measured flow-velocity. Analytical and numerical models are developed that describe the effect of common image pre-processing filters on the measurement depth in μPIV. Further, previous models are revisited that describe the effect of flow velocity gradients on the measurement depth in μPIV.

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Effect of Substrate Cooling and Droplet Shape and Composition on the Droplet Evaporation and the Deposition of Particles (2014)

Sessile droplets are liquid droplets resting on a flat substrate. During the evaporation of small sessile droplets, the contact line of the droplet undergoes two different stages: pinned stage with fixed contact area and de-pinned stage with fixed contact angle. An evaporation with a pinned contact line produces a flow inside the droplet toward the contact line. This flow carries particles and deposits them near the contact line. This causes the commonly observed “coffee-ring” phenomenon. This thesis provides a study of the evaporation process and the evaporation-induced flow of sessile droplet and brings insights into the deposition of particles from colloidal suspensions. Here we first study the evaporation of small sessile droplets and discuss the importance of the thermal conductivity of the substrate on the evaporation process. We show how current evaporation models produce a significant error for droplet sizes below 500 μm. Furthermore, we study the evaporation of line droplets with finite sizes and discuss the complex behavior of the contact lines during evaporation. We apply an energy formulation and show that the contact line starts receding from the two ends of line droplets with a contact angle above the receding contact angle of spherical droplets. And then we show the evaporation-induced flow inside the line droplets. Finally, we discuss the behavior of the contact line under the presence of surfactant and discuss the Marangoni flow effects on the deposition of the particles. We show that the thermal Marangoni effect affects the amount of the particles deposited near the contact line, where a lower substrate temperature corresponds to a larger amount of particles depositing near the contact line.

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Fabrication of out-of-plane microneedles for drug delivery and biosensing (2014)

Hollow microneedles can be used to painlessly inject drugs or extract dermal interstitial fluid for biosensing. However, their fabrication so far has been associated with costly and time-consuming steps restricting their batch production as a viable option. This thesis presents novel methods for fabricating inexpensive hollow microneedles, and investigates new methods of characterizing the drug delivery and interstitial fluid sampling using microneedles. First, a method is presented for fabrication of hollow polymer microneedle arrays. Microneedles are formed during a solvent casting process, which leaves a polymer layer around pillars in a pre-fabricated mold. Arrays of microneedles with lengths up to 250 µm have been fabricated. The strength of the microneedles was evaluated to ensure reliable skin penetration and their suitability for drug delivery was demonstrated by injection of fluorescent beads into a skin sample. A second fabrication method is presented for making metallic microneedles with high aspect ratios. Solvent casting was used to coat a mold with a conductive polymer composite layer, which was then used as a seed layer in a metal electrodeposition process to form 500 µm tall microneedles. Some fabrication process steps were characterized and the strength of the microneedles was evaluated. Their usefulness for drug delivery was also demonstrated by injection of fluorescent microspheres into animal skin. Designing effective microneedles requires understanding the drug diffusion process in skin. Here, a novel method is used to characterize diffusion of a chemotherapeutic drug injected with microneedles into skin. Using confocal microscopy, the concentration distribution of the drug was measured over time and then compared to an analytical diffusion model to obtain the drug’s diffusion coefficient. Using this method, different skin storage conditions were evaluated. It was concluded that using previously frozen skin should be avoided for transdermal drug delivery studies. Finally, using the proposed processes, hollow and solid microneedles were fabricated for sampling interstitial fluid for biosensing applications. Minimal removal of the interstitial fluid was achieved with a solid microneedle design as well as a hollow metallic microneedle array attached to a vacuum probe, while no trace of the fluid was observed when using hollow polymer microneedles.

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Vibration-based Electromagnetic Energy Harvesters for MEMS Application (2011)

This thesis investigates vibration-based electromagnetic energy harvesters (EMEHs) for application in low power autonomous sensors. It makes contributions pertaining to the development of a low cost fabrication technology, analytical modeling, simulations and characterization of EMEHs under harmonic and random vibrations. A novel, low cost, one mask fabrication technology devised in this thesis is used to develop a copper foil-type linear EMEH, and a polydimethylsiloxane (PDMS) membrane type nonlinear EMEH. The voltage and power generated by these harvesters are comparable to existing EMEHs which use more involved fabrication processes. In the membrane type EMEH the inclusion of a more flexible PDMS membrane design reduces the harvester resonant frequency and makes it suitable for extracting energy from low level vibration environments. For acceleration levels greater than 0.1 g, this harvester exhibits a nonlinear behaviour. At higher levels of narrow band random excitations, the device therefore exhibits broadening of the load voltage spectrum in comparison to the response under relatively low levels of narrow band random excitations.Analytical models for linear EMEHs with non-uniform magnetic field for harmonic vibrations are developed. A simple analytical model based on Faraday’s law and uniform gradient of the normal component of the magnetic flux density is developed for EMEHs where the entire coil experiences approximately the same gradient of the normal component of the magnetic flux density. However, for EMEHs where the entire coil is not exposed to the same magnetic flux gradient a more robust model, based on the off-center analytical solution of the magnetic flux density is devised. The simulation results of the developed models are in good agreement with the experimental observations.Analytical models for linear and nonlinear EMEHs under random vibrations are derived. The models are parameterized such that they are applicable to all architectures of EMEHs and can be utilized for designing and performance estimation of EMEHs. Nonlinear harvesters with spring nonlinearity and with combined spring and damping nonlinearity are modeled using the statistical linearization method. The developed models are useful in investigating the effects of the mechanical nonlinearity on the performance and bandwidth of the harvesters under random vibrations.

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High-dynamic Range Projection Using a Steerable MEMS Mirror Array (2010)

This thesis describes a novel way to improve the contrast and peak brightness of conventional projectors by directing the light from the lamp away from the dark parts of the image towards the light parts before it reaches the projector's primary image modulator. AMicroelectromechanical Systems (MEMS) micromirror array is inserted into the optical path between the lamp and the image-forming element. Each element of the array can be tip/tilted to divert portions of the light from the lamp. By directing these mirrors on an image-dependent basis, we can make the dark parts of the image darker and the bright parts brighter. In effect, this method will produce a low resolution approximation of the image on the image-forming element. The micromirror array will allow the projector to adapt its light source to the image being projected in order to maximize peakbrightness, contrast and efficiency.Employing such an mechanism within a projector's display chain requires contributions to a number of different fields related to displays. Tradeoffs between the distance on the screen that a light spot from a mirror (mobile light, or ML) could be moved, and its spatial extent were established. Micromirrors suitable for this application were designed, simulated and fabricated. A novel way of optimizing the tradeoffs between tilt angle, mirror size, and mirror resonance frequency by splitting the mirrors into smaller functionalsubsections was employed. We developed several algorithms that determine favourable placement of the mobile lights from each of themicromirrors in the array, in order to best improve the image. From simulations, the projector average brightness could be increased by a factor of 1.4 if micromirrors were available that could be tilted to 3.5 degrees with the addition of this technology, without changing the projector lamp. If the requirement for perfect image reconstruction is relaxed, the improvement factor increases to 2.5. A prototype was system was developed that allows for fast control of mirror elements, and the positive effect of employing adaptive lightdistribution in this manner was demonstrated.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Characterization of filter membranes with application to red blood cell removal (2023)

Removing red blood cells (RBCs) from blood to general RBC poor plasma is a common practice during blood tests, which improves the accuracy of biomarker detection in plasma. Membrane filtration is a promising technique that utilizes a filter membrane to retain undesired blood cells while letting plasma pass through. Compared to the conventional method of centrifugation, membrane filtration features high portability and low cost due to the simple mechanism it is based on. As the most critical component in membrane filtration, filter membrane can significantly affect the quality of the generated plasma and the efficiency of the overall process. In this thesis, we conduct filtration with four commercial membranes with different properties and compare the performance parameters relevant in RBC filtration. We firstly characterize the permeability of the four membranes by passing water through them, investigating the membranes’ flow-induced permeability change. Microspheres with a mean diameter of 2.9 µm are then used to mimic the effective filtration size of human RBCs to investigate and compare the performance of the membranes for filtration. We notice that the filtration efficiency depends on the volume of fluid to be filtered and the operational condition of filtration. To test the membrane’s suitability for blood filtration, the four membranes are tested with human blood or its components. Coagulation factors are our target biomarker to be analyzed in the generated plasma. The biomarker depletion on the membranes is measured by passing plasma through the membranes. RBC lysis and leakage under different driving pressures are also evaluated by conducting filtration of RBC-plasma mixture and diluted human whole blood. With a filtration pressure up to 9 kPa, the tested polycarbonate (PC) membrane with track-etched pores shows the most promising filtrate quality with low hemolysis and leakage ratio. The tested polysulfone (PS) membrane with a gradient structure, on the other hand, can preserve more biomarkers in the fluid. The selection of the membrane should also consider other factors such as the biomarker detection method utilized.

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Optical measurement of paper moisture content with application in paper pressing (2023)

The measurement of moisture content (MC) distribution in the paper is important as it affects the overall quality of the paper. It is common practice to measure the moisture content distribution at the end of the forming section of the paper machine, in order to control the papermachine headbox slice gap distribution. However, there exists no equivalent measurement technique to measure the moisture distribution downstream of the press section in real-time.This thesis presents a novel non-contact method for measuring moisture content. The method is based on the high light absorptivity of liquid water in the 1400-1500 nm wavelength range. By using a short-wave infrared (SWIR) camera and an infrared LED to illuminate the paper, the relationship between moisture content and relative intensity RI was investigated for four different samples (Whatman paper, NBSK, NBHK, tissue paper), where RI corresponds to the measured light intensity due to wet paper normalized by the intensity due to dry paper. The results show that for all samples, RI decreases as moisture content increases, and it is possible to measure the spatial moisture content distribution using this relationship. The value of this measurement technique was demonstrated by using it to measure the moisture distribution in the paper during a simulated pressing operation.

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Optimization of piezoelectric and mechanical performance of piezoelectric paper composites for MEMS applications (2023)

Paper, one of the oldest and greatest inventions, has and continues to play a significant role in many applications of day-to-day life. Recently, paper-based substrates have attracted significant attention in the realm of smart materials and electronics due to a growing desire for environmentally sustainable platforms, inexpensive flexible devices, and the opportunity to incorporate functional materials within the matrix. The possibility to integrate novel nanomaterials within the production methods of the paper industry is of current interest to enhance and to add new functionalities to conventional cellulose-fiber-based paper. Paper has been used as a substrate for flexible devices for several years now. However, the methods for preparing such paper-based devices are typically too complex for integration with large-scale paper manufacturing processes. This research proposes a simple process for manufacturing nanoparticle-incorporated paper-based piezoelectric composites with tailorable mechanical properties which is compatible with the conventional papermaking processes. This method utilizes a layer-by-layer process to electrostatically bind BaTiO3 particles (~300 nm diameter) to microfibrillated wood pulp with a significant particle loading of up to 72% yielding a high piezoelectric coefficient (d33) of up to 57.8 pC/N post corona poling. Such piezoelectric paper composites have potential in microelectromechanical systems (MEMS) and are used as a simple accelerometer and tactile sensor to demonstrate their efficacy in inertial sensing and touch applications. This work is part of a larger scope to develop a device which uses the functionalized paper as sensing strips for real-time particulate matter (PM) monitoring. In particular, PM2.5 (PM smaller than 2.5 μm) is targeted for detection as it is one of the main causes of air pollution related health issues, subsequently contributing to billions of dollars spent annually.

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Poling of barium titanate nanoparticles-incorporated piezoelectric paper substrates (2023)

Paper manufacturing is a strategic industry for Canada. However, rapidly changing markets, weak prices, increasing transportation costs, frequent wildfires, and recent mill closures have significantly impacted the pulp and paper industry. According to Canadian Industry Statistics, in British Columbia alone, the gross domestic product contribution from pulp and paper industry has declined by more than 25% from 2018 to 2020. Developing paper-based composites for specialized applications such as transducers will open new markets for pulp and paper industry. Incorporating piezoelectric particles in paper matrices leads to composites that can be employed as piezoelectric transducers whilst retaining the intrinsic properties of paper such as porosity and flexibility. Yet, to impart piezoelectric properties, these composites need to be electrically poled. This research project focuses on corona poling of 300 nm barium titanate nanoparticles incorporated paper based piezoelectric composites manufactured using unrefined and refined Northern Bleached Softwood Kraft (NBSK) pulp. The highest piezoelectric charge constant of 37.2 pC/N (comparable to commercially available polymers such as PVdF) was obtained for the composite manufactured using 300 kWh/t refined NBSK pulp with a barium titanate mass loading of 69.3 wt.%. This was attributed to increased surface roughness of fibers and enhanced stress transfer within the compact paper matrix formed due to refining, and enhanced polarization paths due to nanoparticle clusters within the paper composite. Best poling conditions were identified based on the studies on the effects of grid voltage in the corona triad, poling temperature, and poling time on the piezoelectric response. The observed decay in piezoelectric response of the composite over time was attributed to the dielectric contrast in constituent materials in the composite, hindrance to domain motion due to particle size, and depolarization fields caused by space charges. Findings of this work can be transferred to develop practical applications of barium titanate nanoparticles-incorporated paper-based piezoelectric composites such as tactile sensors, accelerometers, and smart packaging systems.

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Poroelastic behavior of skin tissue in response to pressure driven flow (2023)

Below its outermost layer, skin tissue is permeable to fluid flow. Further understanding of skin tissue’s permeability could help with innovations related to intradermal vaccine and drug delivery, the development of artificial skin grafts, and other biomedical technologies concerning skin tissue and its pathologies. This work investigates porcine skin tissue as a poroelastic medium, where pressure driving fluid flow induces tissue deformation, affecting its permeability. A custom-made experimental setup applied a pressure driven fluid flow across skin tissue’s epidermal and dermal layers, which were supported by a porous, rigid base. Simultaneously, an Optical Coherence Tomography (OCT) system captured images of a cross section of skin tissue as it experienced deformation caused by pressure induced flow. Digital Image Correlation (DIC) was used to analyze the OCT images, thus providing the deformation field of the skin tissue. The image analysis corrected for the change in the tissue’s refractive index, which occurred due to fluid flow-induced deformation and thus change in the tissue’s water content. Skin tissue was found to exhibit a non-linear relation between pressure driving and the resulting fluid flow rate, where further increased pressure led to increased flow rate by lesser extents. The skin tissue was observed to experience compressive strain closest to the supported base, with magnitudes increasing with increasing driving pressure, and the free surface experienced relatively little deformation. A 1D depth-wise assumption was made concerning the skin tissue’s response to the pressure driven flow, then Darcy’s law and a permeability-strain relation were used to validate the results with good similarity between observed and calculated flowrates. The permeability-strain relation was found to have material constants: k₀ (initial uniform permeability) of 9.6 ×10ˉ¹⁵ m² with a standard deviation of 0.7 ×10ˉ¹⁵ m² and m (extent of nonlinearity for the material’s permeability-volumetric strain relation) of 2.94 with a standard deviation of 0.09. Overall, this work provides a fundamental understanding to skin behaviour under pressurized driving fluid, which can be generalized to study or model other geometries of induced flow through skin tissue.

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A machine learning approach to classification of gas entrainment and impeller wear in centrifugal pumps (2021)

Centrifugal pumps are a fundamental part of fluid transport around the world. Consequently, they are also one of the world’s dominant energy consumers. The impacts of inefficient operation and undiagnosed wear are widely documented and can be disastrous environmentally, financially, and logistically. Though commercial tools and methods for monitoring pump performance are abundant, they are used infrequently in practice. This phenomenon derives from several factors, including monitoring systems’ poor scalability to function with large numbers of pumps, acquisition costs, the necessity for additional technical personnel, and stringent policies constraining process downtime.This thesis describes the development of an affordable, adaptable sensing method for classifying two conditions detrimental to centrifugal pump operation; gas entrainment and radial impeller wear. The method utilizes dynamic pressure measurements, collected at the pump discharge using a solitary, conventional pressure transducer. Decomposing these pressure fluctuations into a novel array of statistical features yields characteristic trends correlated to the target phenomena. These features are then used to train a series of machine learning algorithms, including multilayer perceptrons (MLP), support vector machines (SVM), and random forests, which are in turn used to characterize the target conditions using binary, multi-class, and regression methods. Dynamic pressure data for training and testing the classification algorithms is generated using simulated and experimental methods. The binary MLP model predicts gas entrainment exceeding a 2% void fraction of air with 90% accuracy, and radial wear exceeding 1.5% of the impeller diameter with 97% accuracy. The multi-class MLP classifies gas entrainment and radial impeller wear into severity classes spanning 1% increments with 62% and 82% success rates, respectively. The random forest regression model achieves a median prediction error of 0.44% for gas entrainment and 0.16% for impeller wear. The diagnostic system presented in this research is unique in that it is not conceived as a standalone tool for pump users, but rather a shared process to be trained and configured by the pump manufacturer, then implemented by the operators. In its envisioned application, the scope of the classified phenomena would be augmented by the manufacturer to capture a wide variety of pump performance characteristics.

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Concentration and mass deposition measurements in two-phase jet flow with applications to railroad friction management systems (2021)

This work presents initial results of a new method to apply friction modifier materials for railroad applications along with a novel particle concentration measurement method for two-phase flows. Until now, railroad friction management systems used liquid friction modifiers or solid sticks to apply the material to the top of the rail or to a moving train’s wheel to reduce the friction. We investigate in lab experiments a new method of applying solid lubricant powders such as molybdenum disulfide (MoS2) and graphite directly on top of the rail using electrostatic powder coating. To design and assess the performance of an applicator for spray or powder coating, it is useful to know the particle concentration in the particle jet. The concentration distribution data will aid in modifying the design of the applicator to achieve the desired deposition pattern. Current methods of concentration measurements such as laser Doppler anemometry (LDA)/phase Doppler anemometry (PDA) and planar nephelometry are excellent to provide accurate local measurements of concentration but are expensive and complicated to set up and operate. Our proposed measurement method is based on light extinction and is much easier to set up and use. This method is capable of providing particle concentration statistics for axisymmetric distributions. We show that the extinction efficiency measured with this method for a given particle agrees with known values (of somewhat less than two) for a non-ideal imaging setup. Furthermore, we demonstrate that the concentration distribution of a jet at the exit of a pipe nozzle as well as downstream is similar to that observed by previous researchers. We also present data on the deposition efficiency of electrostatic powder coating for railroad friction management systems under different test conditions. The results show that applying pure MoS2 or graphite achieves low deposition efficiencies and these materials should be surface treated with a non-conductive coating before being applied. We also discuss how the newly developed particle concentration measurement method can be used to design and monitor the performance of the new railroad friction modifier applicator.

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Design and fabrication method for a microneedle electrode with flexible backing for biosignals monitoring (2021)

The conventional wet electrode still poses many inconveniences when recording biosignals, as it requires an electrolytic gel that dries over time, and the skin often needs to be abraded when the electrode is applied to record high-quality signals. Therefore, the wet electrode placement process often needs the assistance of trained personnel. Alternative electrode designs have been investigated to overcome the challenges of the wet electrode but most of them are not able to record small amplitude signals or their fabrication methods are complex and expensive.This research thesis proposes a novel design and simple fabrication method for a dry microneedle electrode for biosignals monitoring. The electrode can record electroencephalogram and electrocardiogram signals from a human subject without electrolytic gel and it does not require skin preparation or abrasion. When applied to the skin of a human subject with an impact inserter, the electrode has a lower impedance at the skin-electrode interface yielding better signal recording compared to application by hand. The selection of the electrode materials provides microneedles stiff enough to cross the outmost layer of the skin, while the flexible backing of the electrode has been designed to improve the conformation of the electrode to the rounded shape of the body. The proposed fabrication method for the electrode is a simple mold casting process that enables batch production reducing the time spent in the cleanroom and the use of expensive machinery. 

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Experimental investigations of the effect of surface roughness on high-acceleration film splitting between two substrates (2021)

Thin liquid film separation is an important part of many industrial processes and is relevant to “rewet” that can occur in the press section of a papermachine. The separation ratio, the mass of the remaining liquid on one (“the moving”) substrate after separation to the total mass of the initial liquid film between two substrates, is of particular interest in this thesis because reducing rewet reduces the energy consumption in the dryer section of a paper machine significantly. The focus of this study is the experimental measurement of high-acceleration separation of Newtonian liquid films trapped between two substrates. The behavior of the liquid bridges between smooth separating substrates has been a subject of past studies at low separation rates. A distinction of this study is the investigation of high-acceleration separation of the thin liquid bridging the gap between rough as well as smooth substrates. An experimental apparatus has been designed and manufactured that can produce average separation accelerations of up to 325 m/s2, initial bridge heights starting from 10 µm, and average surface roughness values of up to 86 µm.When the distance between substrates increases, a viscous fingering region is observed along the perimeter of the wetted area where air fingers grow radially inward, while in the center region, cavitation bubbles can emerge and grow until the two substrates are sufficiently separated such that the liquid bridges between them break. The separation ratio is meaningfully affected by the surface roughness, viscosity, and acceleration, creating variations of up to 20% in the separation ratio. It is hypothesized that the separation ratio is affected by the relative amounts of the flow field that are subject to viscous fingering and liquid cavitation. Two distinct separation processes, residual layer formation and fibrillation, corresponding to the two flow regimes have been suggested to explain the difference in the measured separation ratios of different cases. A laser-induced fluorescence (LIF) measurement system has been developed to measure the thickness distribution of the liquid bridges during the separation process, and the results of the LIF measurements are consistent with the suggested hypothesis.

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A highly sensitive modular elastomer-based capacitive pressure sensor for respiration monitoring (2020)

Sleep Apnea (SA) is one of the most prevalent but yet underreported public health issues all around the world. The diagnosis of SA requires sleep monitoring or polysomnography (PSG), which is recording several bio-physiological signals during sleep, including respiration. The state of the art for respiration monitoring is measuring the nasal or oral airflow by means of a pressure sensor, placed on the chest of the patient and connected to a long nasal/oral cannula (tube) that is placed in front the nose/mouth. This long tube in many cases is a source of discomfort for the patient. In this work, an elastomer-based flexible capacitive pressure sensor is presented that mounts on the upper lip of the patient. The sensor structure has a novel modular design that gives freedom to make the sensor smaller or larger with the same relative sensitivity . The sensor is designed for the low pressure range from -50 to 100 Pa suitable for the intended application with a high absolute and relative sensitivity of 0.52 pF/Pa and 2.064 kPa-¹, respectively, and capability to withstand overpressure up to 2 kPa without permanent damage. The sensor prototype has low non-linearity and hysteresis errors of less than 12%FS a resolution of 1.7 Pa.

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Intradermal injections through hollow microneedles (2018)

Hollow microneedles are a promising alternative to conventional drug delivery techniques such as oral drug administration and hypodermic injections, and are used for delivering drugs and therapeutics into the skin. Although the benefits of intradermal drug delivery have been known for decades, our understanding of fluid absorption by skin tissue has been limited due to the difficulties in imaging a highly scattering biological material such as skin. In this thesis, we report the results from ex-vivo injection experiments into excised porcine skin tissue using hollow microneedles. We introduce the use of optical coherence tomography (OCT) for real-time imaging of skin tissue at the micro-scale during intradermal injections through hollow microneedles. We identify two modes of flow into the skin – microinjection, a region of high transient flow-rate, and microinfusion, a region of lower steady-state flow-rate. We relate the two modes of flow to tissue deformation. Using images from the OCT, we find that the skin tissue behaves like a deformable porous medium and absorbs fluid by locally expanding rather than rupturing to form a fluid filled cavity. We measure the strain distribution in a cross section of the tissue to quantify local tissue deformation using digital image correlation (DIC), and find that the amount of volumetric expansion of the tissue corresponds closely to the volume of fluid injected. Mechanically restricting the tissue expansion limits fluid absorption into the tissue, and allowing the tissue to expand leads to increased fluid absorption. Our experimental findings can provide physical insights for optimizing the delivery of drugs into the skin for different therapeutic applications, and for better modelling fluid flow into biological tissue.

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A Magnetic Sensor to Measure Wear in Centrifugal Pumps (2016)

On average, centrifugal pumps consume between 25% and 60% of the total consumed electrical energy inside process plants. Erosion inside open-impeller centrifugal pumps leads to a reduction in pump efficiency and occasional plant downtime. This work demonstrates a new concept for an online instrument capable of monitoring wear with the objective of improving the maintenance scheduling of centrifugal pumps and the prevention of unexpected failure through a predictive maintenance system. A magnetic wear sensor is designed and fabricated that allows for wear measurement while the pump is in operation. This sensor can be installed on existing centrifugal pumps and does not require any pump modifications. Wear mostly occurs on the tip of the impeller blades reducing the thickness of the impeller which in turn increases the gap width between the impeller and the side plate inside the pump housing, from 0.65 mm (no wear) to 2.50 mm for maximum allowable wear on the pump used for prototyping. By using a magnetic circuit with the pump and its components, wear is estimated by measuring the change in the width of the varying gap between the impeller and the side plate. To assemble the magnetic circuit, a high-permeability clamping mechanism with a relative permeability of 10,000 is designed and fabricated along with a magnetic coil excited using a 1.0 V AC voltage signal at 70 Hz to drive flux through the circuit. As wear occurs, the total reluctance of the magnetic circuit increases causing the inductance of the coil to drop. The coil's inductance is also a function of the impeller's angular position. To estimate wear, data is collected at a sampling frequency of 500 kHz and then assessed in the frequency domain after fast Fourier transform (FFT). The amplitude of the FFT signal at the frequency correlated with the pump's rotational speed is then considered to estimate wear. For a data sampling time of one second the sensor has a signal to noise ratio of 17.8 dB with an average sensitivity of 0.022 mV/mm and a resolution of 0.38 mm.

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Droplet formation on demand at a microfluidic T-junction (2015)

Microfluidic aliquot dispensing technologies have been utilized in many chemical or biological high throughput assays to provide high-speed deposition of high-resolution droplets. Particularly, these aliquots can be used to dispense a controlled volume of liquid into multi-well plates in drug screening applications. However, existing platforms are often designed to print a limited set of materials where each material is handled by an independently actuated nozzle. A more convenient and scalable technology that could allow digital output of multiple materials on demand must be explored. Monodispered droplets can be formed continuously in a microfluidic T-junction when two input flows of immiscible fluids are maintained. However, it is difficult to form stable air separated aliquots in a simple T-junction configuration. Electrowetting-on-dielectric (EWOD) is commonly used to control individual droplets in a planar configuration. But it is not usually used in microfluidic channels. In this device, a new method for creating air separated aliquots on demand using EWOD at a microfluidic T-junction was demonstrated. Since air is the carrier fluid, these aliquots can be dispensed without further liquid processing. A device that consists of SU-8 channels with electrodes in alignment with the channels was designed and fabricated. A double wedged junction was incorporated at the dispersed channel to create a barrier pressure that allows the meniscus location to be controlled by the applied pressures. Droplets of approximately 15 nL can be generated by applying a voltage at the electrode at the junction. Liquid flow is stopped when the voltage is removed. This mechanism can be used as a digital valve to generate a sequence of aliquots of different materials for a multi-material printing platform.

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Electro-Hydrodynamic Micro Prism with Applications to Automultiscopic Displays (2015)

The recent trend in display technology is to provide the viewer with an artificial three- dimensional (3D) experience using lenses or aides, however the number of viewers and resolution of the display is limited. To remedy these problems, an array of prisms can be placed over the display redirecting the projected light at specific angles in a time-multiplexed fashion and at full resolution. The difficulty in this approach is that the angle of the prism needs to be adjustable with accurate and fast control.This thesis presents the theory, development, and analysis of a novel adjustable prism coined an electro-hydrodynamic micro prism (EHMP). An EHMP consists of an elongated conducive water droplet with pinned contact lines using hydrophobic surface patterning. By applying a voltage between the droplet and an offset electrode above it, the shape of the droplet is deformed into a triangular prism where the angle of the prism is dictated by the strength of the applied voltage.A numerical model of an EHMP was developed using finite element analysis and smoothed particle hydrodynamics to model the electro-hydrodynamics of the system. The numerical model was qualitatively verified using the collapsing square and oscillating droplet tests, and then used to predict an operating voltage range of 400 – 550 V for a 200 μm droplet, and that the leading edge of the electrode dictates the final deformation of the drop.To fabricate a prototype EHMP, a microcontact printing technique was developed to pattern polytetrafluoroethylene nanoparticles onto an indium tin oxide coated glass slide creating the hydrophobic patterning. A prototype 1 mm diameter prototype EHMP was fabricated and tested in the 1.5 – 2 kV range. It was found that there was minimal droplet deformation before failure due to electrospray formation. Though not useful for 3D displays, the results from these large-scale experiments experimentally validate the numerical model. Model simulations showed ideal EHMP deformations can occur under the right conditions, however its performance under current conditions is limited due to dielectric breakdown failure and a fill factor of only 0.66 thus proving not to be a practical solution to automultiscopic displays.

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Use of Compound Microlens Arrays as a Magnifier in Near-Eye Head-Up Displays (2015)

This thesis reports a new approach for making a very compact near-eye display (NED) using two microlens array (MLA) layers. The two MLAs will work in conjunction as a magnifying lens (MLA magnifier). The purpose of the MLA magnifier is to aid the eye accommodate on a display that is positioned within several centimeters from the eye, by generating a virtual image of the display at optical infinity. While there are recently developed techniques for similar purposes such as waveguides [17, 18], and retinal scanning methods [21], using a magnifying lens has been the most exploited avenue for generating a virtual image due to its rather simple, tried-and-true optical properties; near-eye display systems that incorporate a magnifying lens, whether it is a single piece or a compound, has been well-studied since the dawn of head-up displays. However, magnifying lens-based optics is inherently hard to make compact, because as the focal length becomes smaller, the thickness of the lens becomes larger. This thesis presents in detail the method for making a MLA magnifier that retains a thin profile of about 2 mm in thickness with a system focal length of about 6 mm. Thus the total thickness of the MLA magnifier system is around 8 mm (excluding the thickness of the display) in non-folded optics configuration, which is much more compact in comparison to other popular near-eye displays such as Google Glass or Recon Instrument’s Snow HUD goggles having folded optics.

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All-polymer flexural plate wave devices for sensing and actuation (2014)

Polymer based flexural plate wave (FPW) chemical sensors are unique among guided acoustic devices inthat they are comprised of components with similar elastic moduli. As a result, they can be very sensitiveto stiffness and stress variations in an applied sensing layer. This property may be leveraged to detect thepresence of an analyte or to interrogate the mechanical properties of the applied polymer. In this work,polyvinylidene fluoride (PVDF) based, polyethylene dioxythiophene polystyrene sulfonate (PEDOT:PSS)coated FPW devices are fabricated and tested with the purpose of developing an all-polymer VOC sensor.The sensors are coated in polyvinyl acetate (PVAc) and polystyrene (PS) sensing layers and exposed tovarying concentrations of toluene during testing. The PS coated sensors show a sensitivity of -80 cm²/g to -200 cm²/g while the PVAc coated devices demonstrate a sensitivity of -240 cm²/g to -490 cm²/g. A performance model is proposed which seeks to describe the sensing layer mechanical properties as a function of analyte vapour concentration in order to predict the sensor resonant frequency. The predictions of this model are compared with experimental results and design modifications are proposed. Along with this, soft material mechanical characterisation is investigated with the purpose of developing a tool for measuring composite resin properties during cure. Finally, it is proposed that these devices may be used to drive acoustic streaming in microfluidic systems. To test the concept, droplets of fluid are applied to thedevice substrates and acoustically driven flow rates are measured.

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All-polymer flexural plate wave sensors (2011)

A novel all-polymer flexural plate wave (FPW) sensor from a piezoelectric polyvinylidene fluoride (PVDF) thin-film with poly-(3,4-ethylenedioxythiophene) poly- (styrenesulfonate) (PEDOT:PSS) interdigital transducer (IDT) electrodes has been fabricated and characterized. PVDF films are made piezoelectric by stretching and poling. X-ray diffraction measurements confirm the transition of the PVDF into its piezoelectric β-phase. Inks of PEDOT:PSS, dimethyl sulfoxide and Triton X-100 are deposited on the PVDF films by inkjet printing to produce the IDT patterns. The sensor operates using fundamental frequency, f0, detection of Lamb waves propagating through the PVDF film. Upon the application of a time-varying voltage signal to the input IDT, acoustic waves are generated and measured using a laser Doppler vibrometer, as well as through an electric signal at the output IDT. The output signal is amplified, filtered and processed using an analog to digital converter, digital signal processor and a computer program. The measured fundamental frequencies range from 330 to 1600 kHz for devices with 18 and 125 micron thick PVDF substrates and 800 and 400 micron acoustic wavelengths. These values for fundamental frequency are well predicted by the device geometry using Lamb wave theory. The effect of mass-loading was characterized by inkjet printing layers of polyvinyl alcohol on the sensors and measuring the resulting frequency shift. The devices demonstrate a frequency shift, Δf , to mass loading, m, with a measured resonance frequency mass sensitivity of Δf/(mf0) = -55.9 cm²/g. Temperature sensitivity was measured to be 1870 Hz/ C. Sensors were also coated with a sensing layer of polyvinyl acetate and its response to toluene and acetone vapour concentrations was characterized.

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Transport and size-separation of airborne particles in a microchannel for continuous particle monitoring (2011)

Microfluidics research and development has emerged as a novel and promising tool for the development of sensors and actuators. However, one area in which microfluidics has been only minimally employed is in the handling of airborne particles, or aerosols. The real-time monitoring of aerosols is important for protecting human health and earth’s environment. The small size of microchannels, coupled with the opportunity to integrate sensing technologies, suggests them as a promising tool for the next generation of aerosol sensors. To that end, this thesis presents a microfluidics-based system for the size-separation of aerosols. Specifically, centrifugal force is exerted on each particle as it travels around a curved microchannel, resulting in the particle occupying a size-dependent lateral position in the channel. The behaviours of aerosols in a microchannel are examined, including the effects of flow focusing, the diffusion of airborne particles in a channel, and the centrifugal and viscous forces exerted on particles in a curved microchannel. Mathematical descriptions and computer simulations of these effects are developed to model these effects. Straight and curved microchannels were fabricated and each of these effects was measured experimentally, and compared to the models. Various combinations of airborne particles between 0.2 µm and 3.2 µm were successfully separated by size. A prototype optical particle detector was built and tested for its suitability as a candidate for integration with the microchannel particle separator. This represents the first approach in which aerosols have been separated by centrifugal forces in a microchannel, and one of very few approaches that have been used for any kind of size-based separation of airborne particles in microchannels. The small footprint and potential for integration offered by microsystem fabrication technology make it a desirable avenue of pursuit for the development of small, portable particulate monitors. The results presented here confirm that this approach to size-separation is a feasible option for a future microsystem based size-selective particulate monitor.

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Towards All-polymer Surface Acoustic Wave Chemical Sensors for Air Quality Monitoring (2010)

Volatile organic compounds (VOCs) are a precursor to the formation of ground-level ozone and airborne particulate matter, both of which are hazardous to human health. Currently in Canada, other air pollutants such as ozone and nitrous oxides are measured by an air quality monitoring network in real-time, while VOCs are collected in canisters and sent to a central laboratory for analysis. This is a time-consuming and non real-time method, and due to the spatial variability of air pollution, many points of measurement are needed. A distributed point sensor network could address the resolution and real-time challenges, but would impose an added operating expenditure burden on air quality monitoring agencies. Low-cost, yet sensitive chemical sensors could contribute to lowering operating expenditures of a network’s sensing units over the installed lifetime of the units. The objective of this work was to lay the groundwork for a sensing platform from which low-cost yet sensitive chemical sensors can be developed. The sensing platform is an all-polymer surface acoustic wave (SAW) device, and the materials selected for its fabrication are Polyvinylidene Fluoride (PVDF) for the sensor substrate and Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) for the interdigital transducer electrodes. In this work, an apparatus and a process for preparing piezoelectric PVDF film was developed. PVDF-based resonators were successfully demonstrated. In addition, repeatable processes for inkjet micropatterning highly electrically conductive PEDOT:PSS electrode tracks on PVDF were developed for three inkjet nozzle orifice sizes (20, 30, 40 µm). For tracks micropatterned using the same process, the electrical resistances have a standard deviation of 8.5% of the average. The electrical conductivity of micropatterned tracks is approximately 150 S/cm, or one-sixth of the manufacturer’s claimed bulk film conductivity. Using the 30 µm nozzle, the smallest electrode track width that can be micropatterned repeatably is 75 µm. A track width of 55 µm was achieved using the 20 µm nozzle.

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