Boris Stoeber

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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. 

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record

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.

View record