Institute for Integrated Energy Systems (IESVic)

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The Institute for Integrated Energy Systems at the University of Victoria (IESVic) promotes feasible paths to sustainable energy systems by developing new technologies and perspectives to overcome barriers to the widespread adoption of sustainable energy. Founded in 1989, IESVic conducts original research to develop key technologies for sustainable energy systems and actively promotes the development of sensible, clean energy alternatives.

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IESVic's mission is to chart feasible paths to sustainable energy.

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Development and validation of an active magnetic regenerator refrigeration cycle simulation
(2006-08-10T17:35:10Z) Dikeos, John; Rowe, Andrew
An alternative cycle proposed for refrigeration and gas liquefaction is active magnetic regenerator (AMR) refrigeration. This technology relies on solid materials exhibiting the magnetocaloric effect, a nearly reversible temperature change induced by a magnetic field change. AMR refrigeration devices have the potential to be more efficient than those using conventional refrigeration techniques but, for this to be realized, optimum materials, regenerator design, and cycle parameters must be determined. This work focuses on the development and validation of a transient one-dimensional finite element model of an AMR test apparatus. The results of the model are validated by comparison to room temperature experiments for varying hot heat sink temperature, system pressure, and applied heat load. To demonstrate its applicability, the model is then used to predict the performance of AMRs in situations that are either time-consuming to test experimentally or not physically possible with the current test apparatus.
Computational modeling and optimization of proton exchange membrane fuel cells
(2007-11-13T22:40:51Z) Secanell Gallart, Marc; Djilali, Ned; Suleman, Afzal
Improvements in performance, reliability and durability as well as reductions in production costs, remain critical prerequisites for the commercialization of proton exchange membrane fuel cells. In this thesis, a computational framework for fuel cell analysis and optimization is presented as an innovative alternative to the time consuming trial-and-error process currently used for fuel cell design. The framework is based on a two-dimensional through-the-channel isothermal, isobaric and single phase membrane electrode assembly (MEA) model. The model input parameters are the manufacturing parameters used to build the MEA: platinum loading, platinum to carbon ratio, electrolyte content and gas diffusion layer porosity. The governing equations of the fuel cell model are solved using Netwon's algorithm and an adaptive finite element method in order to achieve quadratic convergence and a mesh independent solution respectively. The analysis module is used to solve two optimization problems: i) maximize performance; and, ii) maximize performance while minimizing the production cost of the MEA. To solve these problems a gradient-based optimization algorithm is used in conjunction with analytical sensitivities. The presented computational framework is the first attempt in the literature to combine highly efficient analysis and optimization methods to perform optimization in order to tackle large-scale problems. The framework presented is capable of solving a complete MEA optimization problem with state-of-the-art electrode models in approximately 30 minutes. The optimization results show that it is possible to achieve Pt-specific power density for the optimized MEAs of 0.422 $g_{Pt}/kW$. This value is extremely close to the target of 0.4 $g_{Pt}/kW$ for large-scale implementation and demonstrate the potential of using numerical optimization for fuel cell design.
Microfluidic fuel cells
(2007-11-21T21:50:57Z) Kjeang, Erik; Sinton, David; Djilali, Ned
Microfluidic fuel cell architectures are presented in this thesis. This work represents the mechanical and microfluidic portion of a microfluidic biofuel cell project. While the microfluidic fuel cells developed here are targeted to eventual integration with biocatalysts, the contributions of this thesis have more general applicability. The cell architectures are developed and evaluated based on conventional non-biological electrocatalysts. The fuel cells employ co-laminar flow of fuel and oxidant streams that do not require a membrane for physical separation, and comprise carbon or gold electrodes compatible with most enzyme immobilization schemes developed to date. The demonstrated microfluidic fuel cell architectures include the following: a single cell with planar gold electrodes and a grooved channel architecture that accommodates gaseous product evolution while preventing crossover effects; a single cell with planar carbon electrodes based on graphite rods; a three-dimensional hexagonal array cell based on multiple graphite rod electrodes with unique scale-up opportunities; a single cell with porous carbon electrodes that provides enhanced power output mainly attributed to the increased active area; a single cell with flow-through porous carbon electrodes that provides improved performance and overall energy conversion efficiency; and a single cell with flow-through porous gold electrodes with similar capabilities and reduced ohmic resistance. As compared to previous results, the microfluidic fuel cells developed in this work show improved fuel cell performance (both in terms of power density and efficiency). In addition, this dissertation includes the development of an integrated electrochemical velocimetry approach for microfluidic devices, and a computational modeling study of strategic enzyme patterning for microfluidic biofuel cells with consecutive reactions.
Forces on bars in high-consistency mill-scale refiners
(2007-12-24T22:39:36Z) Olender, Dustin James; Wild, Peter
Refiners are used in the pulp and paper industry to separate wood chips into individual fibres and to develop the morphology of fibres to be suitable for the type and grade of paper to be produced. Within a refiner are discs, at least one of which rotates at high speed and all of which are lined with radial patterns of bars on their opposing surfaces. As the chips and fibres are accelerated through the refiner, compressive and shear forces are applied to them by the bars as the opposed discs cross each other. Experiments have shown that the contact mechanics of bar-crossings are a significant factor in the development of fibre properties. To investigate the contact mechanics in operating refiners, a prototype piezoelectric-based sensor was developed to measure the forces applied by the bars. This work re-designs the prototype sensor to function at the mill-scale, and validates the design in two trials. Performance during these trials is presented along with an in-depth analysis of the recorded data. Arrays of force sensors were installed in two single-disc refiners: a pilot-scale machine operating as a primary stage, and a mill-scale machine operating as a rejects stage. In the rejects refiner, mean forces were highest at the periphery of the refining zone, while in the primary stage, mean forces were higher at the sensor closest to the refiner axis. Higher coefficients of friction were measured in the primary stage refiner, which also showed less active bar-crossings. Distributions of peak force values were generated for a range of standard operating conditions. Primary stage refining showed near decreasing exponential distributions, while rejects refining showed skewed normal distributions. These results indicate a fundamental difference in the behavior of these refiners, which is explained in terms of the processing stage of the wood fibre and scale of the refiner. Past laboratory experiments in a single-bar refiner have shown that pulp consistency can greatly affect the contact mechanics of bar-crossing impacts. The effect was observed as a positive correlation between the coefficient of friction and the mass fraction of fibre in the stock, known as the consistency. In the present work, a similar correlation was found in the primary stage refiner, but only in the sensor closest to the refiner axis. No significant changes in the coefficient of friction were observed in the rejects refiner; however, only a small range of consistencies was tested. These initial findings suggest relationships found in past laboratory tests may translate to larger-scale equipment. The clashing of plates during refining accelerates bar wear, and delays production. An investigation of the ability of the sensor to predict plate clash was conducted. The force sensors consistently provided advanced warning of a clash event, many seconds before the accelerometer-based plate protection system currently in use by the mill. A sensitivity study showed that the new system was able to outperform the accelerometer system over a range of detection settings, and that the accelerometer could not be tuned to match the performance of the new system.
The extractable power from tidal streams, including a case study for Haida Gwaii
(2008-01-07T00:47:10Z) Blanchfield, Justin; Rowe, Andrew; Wild, Peter
Interest is growing worldwide among utility companies and governments of maritime countries in assessing the power potential of tidal streams. While the latest assessment for Canadian coastlines estimates a resource of approximately 42 GW, these results are based on the average kinetic energy flux through the channel. It has been shown, however, that this method cannot be used to obtain the maximum extractable power for electricity generation. This work presents an updated theory for the extractable power from a channel linking a bay to the open ocean. A mathematical model is developed for one-dimensional, non-steady flow through a channel of varying cross-section. Flow acceleration, bottom drag, and exit separation effects are included in the momentum balance. The model is applied to Masset Sound and Masset Inlet in Haida Gwaii, a remote island region, to determine the extractable power and its associated impacts to the tidal amplitude and volume flow rate through the channel.
Modeling and simulation of hybrid electric vehicles
(2008-01-14T22:36:14Z) Zhou, Yuliang Leon; Dong, Zuomin
With increasing oil price and mounting environment concerns, cleaner and sustainable energy solutions have been demanded. At present transportation constitutes a large portion of the energy consumed and pollution created. In this work, two hybrid vehicle powertrain technologies were studied, a fuel cell - battery hybrid and two internal combustion engine - battery/ultracapacitor hybrids. Powertrain performance models were built to simulate the performance of these new designs, and to assess the feasibility of a fuel cell hybrid power backup system for a special type of vehicles, elevators in high-rise buildings, using the ADvanced VehIcle SimulatOR (ADVISOR) first. The model was then applied to evaluate the two-mode hybrid powertrain for more common vehicles - commercial trucks, showing potential fuel consumption reduction. To improve modeling accuracy, a new and more flexible tool for modeling multi-physics systems, Modelica/Dymola, was used to carry out the modeling and analysis of next generation hybrid electric vehicles, exploring the potentials of new hybrid powertrain architectures and energy storage system designs. The study forms the foundation for further research and developments.
Experimental study of water droplet flows in a model PEM fuel cell gas microchannel
(2008-01-17T23:38:01Z) Minor, Grant; Djilali, Ned; Oshkai, Peter
Liquid water formation and flooding in PEM fuel cell gas distribution channels can significantly degrade fuel cell performance by causing substantial pressure drop in the channels and by inhibiting the transport of reactants to the reaction sites at the catalyst layer. A better understanding of the mechanisms of discrete water droplet transport by air flow in such small channels may be developed through the application of quantitative flow visualization techniques. This improved knowledge could contribute to improved gas channel design and higher fuel cell efficiencies. An experimental investigation was undertaken to gain better understanding of the relationships between air velocity in the channel, secondary rotational flows inside a droplet, droplet deformation, and threshold shear, drag, and pressure forces required for droplet removal. Micro-digital-particle-image-velocimetry (micro-DPIV) techniques were used to provide quantitative visualizations of the flow inside the liquid phase for the case of air flow around a droplet adhered to the wall of a 1 mm x 3 mm rectangular gas channel model. The sidewall against which the droplet was adhered was composed of PTFE treated carbon paper to simulate the porous GDL surface of a fuel cell gas channel. Visualization of droplet shape, internal flow patterns and Velocity measurements at the central cross-sectional plane of symmetry in the droplet were obtained for different air flow rates. A variety of rotational secondary flow patterns within the droplet were observed. The nature of these flows depended primarily on the air flow rate. The peak velocities of these secondary flow fields were observed to be around two orders of magnitude below the calculated channel-averaged driving air velocities. The resulting flow fields show in particular that the velocity at the air-droplet interface is finite. The experimental data collected from this study may be used for validation of numerical simulations of such droplet flows. Further study of such flow scenarios using the techniques developed in this experiment, including the general optical distortion correction algorithm developed as part of this work, may provide insight into an improved force balance model for a droplet exposed to an air flow in a gas channel.
Non-equilibrium evaporation and condensation : modeled with irreversible thermodynamics, kinetic theory, and statistical rate theory
(2008-04-10T05:59:03Z) Bond, Maurice.; Struchtrup, Henning
The purpose of this work is to demonstrate the usability of irreversible thermodynamics and kinetic theory in describing slow steady state evaporation and condensation, analyze the statistical rate theory (SRT) approach, and investigate the physical phenomena involved. Recently large interface temperature jumps have been observed during steady state evaporation and condensation experiments; the vapor interface temperature was greater than the liquid interface temperature for condensation and evaporation. To predict the temperature jump, the SRT mass flux was introduced as an alternative to the established approaches of irreversible thermodynamics and kinetic theory of gases. Simple one dimensional planar and spherical models were developed for slow evaporation and condensation based on the experiments. We considered pure liquid water evaporation and condensation to, and from its own vapor. Expressions for the mass and energy fluxes across the interface were found using irreversible thermodynamics, kinetic theory, and SRT. The SRT theory does not have an energy flux expression, as a substitute we use the irreversible thermodynamics energy flux in the SRT model. The equations were then solved to yield the mass and energy fluxes, and the liquid and vapor temperature profiles. We find the interface temperature jump is dependant on the energy flux expression. The irreversible thermodynamics energy flux closely predicts the measured temperature jump and direction. Kinetic theory models do not predict the jump, however with incorporation of a velocity dependant condensation coefficient, kinetic theory can predict the correct temperature jump direction, and vapor interface temperature. All the models predict mass fluxes that agree with the measured data. We suggest the temperature jump direction is established based on the direction of the vapor conductive energy flux, and not the direction of the mass flux (condensation or evaporation). We conclude that irreversible thermodynamics, kinetic theoiy, and SRT can all be used to model steady state evaporation and condensation.
Transport phenomena in polymer electrolyte membranes
(2008-04-10T05:59:06Z) Fimrite, Jeffrey Anders.; Struchtrup, Henning; Djilali, Nedjib
A techno-economic analysis of decentralized electrolytic hydrogen production for fuel cell vehicles
(2008-04-10T05:59:09Z) Prince-Richard, Sébastien.; Djilali, Nedjib
Modelling catalyst layers in PEM fuel cells : effects of transport limitations and non-uniform platinum loading
(2008-04-10T06:00:32Z) Schwarz, David Hans.; Djilali, Nedjib
Investigation of a U-shaped fuel cell flow channel with particle image velocimetry (PIV)
(2008-04-10T06:00:36Z) Martin, Jonathan Jackie.; Djilali, Nedjib; Oshkai, Peter
Flow through an experimental model of a U-shaped flow channel is used to investigate the hydrodynamic phenomena that occur within serpentine reactant transport channels of fuel cells. Achieving effective mixing within these channels is crucial for the proper operation of the fuel cell and proper understanding and characterization of the underlying fluid dynamics is required. Particle image velocimetry (PIV) is used to investigate the three-dimensional structure of the flow by analyzing the velocity and associated vorticity field over two perpendicular channel cross-sections. A range of Reynolds numbers, 109 I Re I 872, corresponding to flow rates encountered in a fuel cell operating at low to medium current densities is investigated. The effect of the flow rate is characterized in terms of the instantaneous and time-averaged representations of the velocity vectors, out-of-plane vorticity and the velocity streamlines. At the lowest Reynolds numbers, the flow is steady and is characterized by high vorticity regions associated with shear layers separating from the sharp convex comers of the U-bend and reattaching on downstream surfaces. The flow also exhibits the classical secondary Dean flow pattern with two symmetric circulation zones. Transition takes place in the range 381 I Re I 436 as the two recirculation zones, which originally develop in the U-bend region, merge into one separation region. This transition is accompanied by the generation of additional vortices in the secondary flow plane. The relationship between the flow in both planes and the transition is examined along with properties of the instability including RMS, Reynolds stress, and the oscillation frequency. The quantitative flow visualization results obtained presented here should be useful in guiding numerical models of fuel cells, and indicate that the commonly used assumption of steady laminar flow should be revisited, and alternative models developed.
Modelling and design optimization of low speed fuel cell hybrid electric vehicles
(2008-04-10T06:02:16Z) Guenther, Matthew Blair.; Dong, Zuomin
Microscale gas flow : a comparison of Grad's 13 moment equations and other continuum approaches
(2008-04-10T06:03:40Z) Thatcher, Toby; Struchtrup, Henning
Advances in manufacturing techniques over the last decade have made it possible to make electrical devices with dimensions as small as 90 nanometers [I]. Using similar techniques, devices that perform moving mechanical tasks less than 100 pm are being manufactured in quantity [2] [3], e.g., pumps, turbines, valves and nozzles. These devices are incorporated into microelectromechanical systems (MEMS) that can be potentially used in devices such as medical and chemical sensors, and fuel cells. The gas and fluid flows in devices of this size exhibit behavior that can not be described by the classical Navier-Stokes and Fourier equations of continuum mechanics. This happens when flows become rarefied such that the mean free path (distance between two subsequent particle collisions) is not negligible compared to the characteristic length scale. The rarefaction of a fluid flow is also seen in the upper atmosphere for larger length scales, e.g., for re-entry for space craft and some supersonic jet aircraft. Currently, when one looks to model fluid flow and heat transfer in a rarefied flow there are two predominantly accepted choices. Either one uses jump and slip boundary conditions with the Navier-Stokes and Fourier (NSF) equations, or a statistical particle model such as direct simulation Monte-Carlo (DSMC) [4] and the Boltzmann equation. DSMC is computationally intensive for complex flows and the NSF solutions are only valid for low degrees of rarefaction. As an alternative to these methods we have used Grad's 13 moment expansion of the Boltzmann equation [5]. For its implementation, a set of boundary conditions and three numerical methods for the solution have been devised. The model is applied to the solution of 2-D micro Couette flow with heat transfer. Results are compared to those obtained from the Navier-Stokes-Fourier equations, reduced Burnett equations, Regularized 13 moment equations and DSMC simulations.
Mathematical modelling of fuel cells for portable devices
(2008-04-10T06:04:28Z) Litster, Shawn Edward.; Djilali, Nedjib
Algorithm development for electrochemical impedance spectroscopy diagnostics in PEM fuel cells
(2008-04-10T06:05:02Z) Latham, Ruth Anne.; Harrington, David A.
Integration and dynamics of a renewable regenerative hydrogen fuel cell system
(2008-04-25T00:08:28Z) Bergen, Alvin P; Djilali, Ned; Wild, Peter
This thesis explores the integration and dynamics of residential scale renewable-regenerative energy systems which employ hydrogen for energy buffering. The development of the Integrated Renewable Energy Experiment (IRENE) test-bed is presented. IRENE is a laboratory-scale distributed energy system with a modular structure which can be readily re-configured to test newly developed components for generic regenerative systems. Key aspects include renewable energy conversion, electrolysis, hydrogen and electricity storage, and fuel cells. A special design feature of this test bed is the ability to accept dynamic inputs from and provide dynamic loads to real devices as well as from simulated energy sources/sinks. The integration issues encountered while developing IRENE and innovative solutions devised to overcome these barriers are discussed. Renewable energy systems that employ a regenerative approach to enable intermittent energy sources to service time varying loads rely on the efficient transfer of energy through the storage media. Experiments were conducted to evaluate the performance of the hydrogen energy buffer under a range of dynamic operating conditions. Results indicate that the operating characteristics of the electrolyser under transient conditions limit the production of hydrogen from excess renewable input power. These characteristics must be considered when designing or modeling a renewable-regenerative system. Strategies to mitigate performance degradation due to interruptions in the renewable power supply are discussed. Experiments were conducted to determine the response of the IRENE system to operating conditions that are representative of a residential scale, solar based, renewable-regenerative system. A control algorithm, employing bus voltage constraints and device current limitations, was developed to guide system operation. Results for a two week operating period that indicate that the system response is very dynamic but repeatable are presented. The overall system energy balance reveals that the energy input from the renewable source was sufficient to meet the demand load and generate a net surplus of hydrogen. The energy loss associated with the various system components as well as a breakdown of the unused renewable energy input is presented. In general, the research indicates that the technical challenges associated with hydrogen energy buffing can be overcome, but the round trip efficiency for the current technologies is low at only 22 percent.
Liquid water transport in fuel cell gas diffusion layers
(2008-04-26T00:43:17Z) Bazylak, Aimy Ming Jii; Djilali, Ned; Sinton, David; Liu, Zhong-Sheng (Simon)
Liquid water management has a major impact on the performance and durability of the polymer electrolyte membrane fuel cell (PEMFC). The gas diffusion layer (GDL) of a PEMFC provides pathways for mass, heat, and electronic transport to and from the catalyst layers and bipolar plates. When the GDL becomes flooded with liquid water, the PEMFC undergoes mass transport losses that can lead to decreased performance and durability. The work presented in this thesis includes contributions that provide insight into liquid water transport behaviour in and on the surface of the GDL, as well as insight into how future GDLs could be designed to enhance water management. The effects of compression on liquid water transport in the GDL and on the microstructure of the GDL are presented. It was found that compressed regions of the GDL provided preferential locations for water breakthrough, while scanning electron microscopy (SEM) imaging revealed irreversible damage to the GDL due to compression at typical fuel cell assembly pressures. The dynamic behaviour of droplet emergence and detachment in a simulated gas flow channel are also presented. It was found that on an initially dry and hydrophobic GDL, small droplets emerged and detached quickly from the GDL surface. However, over time, this water transport regime transitioned into that of slug formation and channel flooding. It was observed that after being exposed to a saturated environment, the GDL surface became increasingly prone to droplet pinning, which ultimately hindered droplet detachment and encouraged slug formation. A pore network model featuring invasion percolation with trapping was employed to evaluate the breakthrough pattern predictions of designed porous media. These designed pore networks consisted of randomized porous media with applied diagonal and radial gradients. Experimental microfluidic pore networks provided validation for the designed networks. Diagonal biasing provided a means of directing water transport in the pore network, while radially biased networks provided the additional feature of reducing the overall network saturation. Since directed water transport and reduced saturation are both beneficial for the PEMFC GDL, it was proposed that biasing of this nature could be applied to improved GDL designs. Lastly, recommendations for future extensions of this research are proposed at the end of this thesis.
Modelling, simulation, testing, and optimization of advanced hybrid vehicle powertrains
(2008-05-02T17:22:13Z) Wishart, Jeffrey; Dong, Zuomin
The internal combustion engine (ICE) vehicle has dominated the transportation market for nearly 100 years. Numerous concerns with continued use of fossil fuels arise, however, and these concerns have created an impetus to develop more efficient vehicles that release fewer emissions. There are several powertrain technologies that could supplant conventional ICEs as the dominant technology, most notably electric and hybrid powertrains. In order to achieve the levels of performance and cost of conventional powertrains, electric and hybrid powertrain designers must use design techniques and tools such as computer modelling, simulation and optimization. These tools facilitate development of a virtual prototype that allows the designer to rapidly see the effects of design modifications and precludes the need to manufacture multiple expensive physical prototypes. A comprehensive survey of the state of the art of commercialized hybrid vehicle powertrains is conducted, and the term multi-regime in ICE hybrid vehicle (ICEHV) modelling is introduced to describe designs that allow for multiple configurations and operating regimes. A dynamic mathematical model of a power-split architecture with two modes (or configurations) introduced by General Motors Corporation is developed and a steady-state version is programmed into the ADvanced VehIcle SimulatOR (ADVISOR) simulation software package. This ADVISOR model is applied to a commercial delivery vehicle, and the fuel consumption of the vehicle undergoing a variety of drive cycles is determined. The two-mode model is compared to the ADVISOR models for the Toyota Hybrid System (THS), parallel hybrid, and conventional powertrains in the same vehicle. The results show that for this vehicle type, the two-mode design achieves lower fuel consumption than the THS and conventional powertrains, and only slighter greater fuel consumption than the parallel hybrid design. There is also considerable potential for improvement in performance of the two-mode model through the development of an optimal power management strategy. In the medium- to long-term, the necessity for zero-emission vehicles may position fuel cell systems (FCSs) to be commercialized as on-board energy conversion devices. FCSs are currently inordinately expensive with power density and durability issues, among other design problems. Fuel cell hybrid vehicle (FCHV) designers must use the available design techniques intelligently to overcome the limitations and take advantage of the higher efficiency capabilities of the fuel cell. As the first step in creating a virtual prototype of a FCS, a semi-empirical model of the system is developed and further enhancements such as transient response modelling are proposed. An optimization of the operating parameters to maximize average net power and average exergetic efficiency is conducted, and the technique is applied to the FCS model for the prototype fuel cell hybrid scooter (FCHS). The optimizations demonstrate that significant improvements in performance can be achieved, and that optimizations with more design variables are warranted. Models of a conventional battery scooter (BS) and of the FCHS are developed in ADVISOR. Simulations are conducted which compare the performance of the two models. Subsequently, performance tests of the BS and FCHS are conducted using a chassis dynamometer. Despite problems with the prototype FCHS, the tests confirm the theoretical results: the FCHS model achieves higher performance in terms of acceleration and power, while the BS model operates more efficiently and requires less energy. This study provides better understanding on the emerging FCHV and ICEHV technologies; introduced new and improved models for FCHV and multi-regime hybrid powertrains; developed FCHV and ICEHV performance simulation and design optimization methods using the new computer models; explored the methods for validating the computer models using prototype BS and FCHS on a research dynamometer; identified areas of improvements of the new experiment methods; and formed the foundation for future research in related areas.
Development and application of in-fibre Bragg grating based biomedical pressure sensors
(2008-07-15T23:30:01Z) Dennison, Christopher Raymond Stuart; Wild, Peter
Two in-fibre Bragg grating based optical pressure sensors were developed to address the limitations of conventional solid-state electronic biomedical sensors. The first sensor, developed for intervertebral disc pressure measurements varying over several MPa, had a major diameter of only 400 μm and sensing area of 0.03 mm2. This sensor was validated in spine biomechanics studies and was shown to: give accurate and repeatable measurements, be compatible with the small (e.g. cervical) discs, and alter disc mechanics less than the current alternative sensor. This sensor is also the smallest, most mechanically compliant disc pressure sensor presented to date. The second FBG sensor was developed to measure sub-kPa pressure variations and had a major diameter and sensing area of only 200 μm and 0.02 mm2, respectively. This sensor achieves sub-kPa repeatability through a novel design that is approximately 100 times smaller than other FBG sensors presented with sub-kPa pressure repeatability.

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