Exploring thermal discomfort amongst lower-limb prosthesis wearers

Amongst lower-limb prosthesis wearers, thermal discomfort is a common problem with an estimated prevalence of more than 50%. Overheating does not just create discomfort to the user, but it has been linked to excessive sweating, skin damage caused by a moist environment and friction. Due to impermeable prosthetic components and a warm moist environment, minor skin damage can result in skin infections that can lead to prosthesis cessation, increased social anxiety, isolation and depression. Despite the seriousness of thermal discomfort, few studies explore the issue, with research predominantly constrained to controlled laboratory scenarios, with only one out of laboratory study. In this thesis, studies investigate how thermal discomfort arises and what are the consequences of thermal discomfort for lower-limb prosthesis wearers. Research studies are designed around the principles of presenting lived experiences of the phenomenon and conducting research in the context of participants' real-life activities. A design exploration chapter investigates modifying liner materials and design to create a passive solution to thermal discomfort. However, this approach was found to be ineffective and unfeasible. Study 1 presents a qualitative study which investigates the user experience of a prosthesis, thermal discomfort and related consequences. Study 2 explores limb temperature of male amputees inside and outside the laboratory, with the latter also collecting perceived thermal comfort (PTC) data. Finally, Study 3 investigates thermal discomfort in the real-world and tracks limb temperature, ambient conditions, activities, and experience sampling of PTC. While there were no apparent relationships presented in sensor data, qualitative data revealed that in situations where prosthesis wearers perceived a lack of control, thermal discomfort seemed to be worse. When combined, the studies create two knowledge contributions. Firstly, the research provides a methodological contribution showing how to conduct mixed-methods research to obtain rich insights into complex prosthesis phenomena. Secondly, the research highlights the need to appreciate psychological and contextual factors when researching prosthesis wearer thermal comfort. The research contributions are also converted into an implication for prosthesis design. The concept of 'regaining control' to psychologically mitigate thermal discomfort could be incorporated into technologies by using 'on-demand' thermal discomfort relief, rather than 'always-on' solutions, as have been created in the past

Millimetre-wave power sensor design

This study is to maintain and extend the power standards at National Physical Laboratory (NPL) in the United Kingdom. The calibration service of microwave power sensors at high frequencies is endangered because a limited number of traceable waveguide power sensors is available at 50 GHz and above. In this thesis, the technologies of sensing microwave power in waveguides are reviewed, and the bolometric power sensor is investigated further, as its principle is suitable for the traceability requirement at NPL. The conventional design technique of bolometric sensor based on transmission line theory is generalised and two power sensor designs are introduced. The X-band sensor was fabricated, measured at the University of Birmingham and calibrated at NPL. Excellent linearity and high effective efficiency of the design was obtained. The high frequency power sensor designs based on the proposed technique can be scalable to 300 GHz and above, and a W-band sensor is introduced as an example. In order to add more flexibility in selecting frequency and bandwidth, a novel design of microwave power sensor with integrated filter function is described. An analytical power sensor synthesis technique using coupling matrix is presented for the first time. An X-band power sensor with integrated third order Chebyshev filter function was designed and manufactured. Experiential measurements in Birmingham and NPL are in good agreement with simulation and theoretical expectation

System Integration & Programming of EHD 3D printer

This project is the base for Electro Hydro Dynamics (EHD) & Air Focusing Flow (AFF) 3D printer. Electro Hydo Dynamics (EHD) is the study of dynamics of electrically charged fluids and motions of ionized particles or molecules and their interactions with electric fields and the surrounding fluid. In order to study and work on EHD, this is the first phase. Before going to 3D printing or Manufacturing of the components, it's better to test the machine and evaluate its performance in a virtual environment. First, we took food printer and converted into a simple 3D printer. Then we took a high precision Semprex KL-series table to work on the EHD. With our project outlined, we had to choose a design, source the parts, build the printer, and get the printer to work with NI's software and hardware which has not yet been done before. The nozzle and base both are not stationary. The base lies on the XY-axis while the nozzle is fixed on the Z-axis. The LabVIEW has to be designed so that it can integrate MACH3 as well as Slicer with an integration of temperature and pressure control. For this project we are using NI LabVIEW 2016, which is the latest version.M.S., Mechanical Engineering and Mechanics -- Drexel University, 201

A thermistor based sensor for flow measurement in water

There is limited experimental data describing the mixing processes and coherent velocity structures near the surface of the ocean. These play an important part in the interactions between the atmosphere and the ocean and thus affect the climate of the earth. A robust, low cost thermistor based sensor suitable for use in the detection and quantification of velocity structures has been designed and developed. The flow sensor, a thermal anemometer, consists of a self-heated thermistor that is maintained at constant temperature using a feedback control circuit. The thermistor is exposed to the moving fluid and the heat transfer from it is a function of the velocity of the fluid. The sensor has been interfaced with a PC to facilitate data acquisition. A tow tank calibration and testing facility also interfaced to a PC was developed. The sensor is compensated for changes in ambient fluid temperature, which is a major problem for all thermal anemometers that operate in water. The calibration relation that is normally used for thermistor anemometers has been improved upon and gives better results than any found in the literature. In order to provide electrical isolation from the water the sensor was protected with an insulating coating. The effect of coating thickness and the type of coating used on sensor performance was investigated. It was found that a polymer coating resulted in a sensor that did not show any appreciable drift due to sensor contamination over a number of months. This is a significant improvement over glass coated hot film sensors, which are widely used for velocity measurements in water and previously developed thermistor based sensors. The effect of various control circuit parameters on the frequency response of the sensor was determined and these parameters were tuned to give maximum frequency response A procedure for easily replacing broken/damaged sensors in the field was also developed

A Physical Unclonable Function derived from the power distribution system of an integrated circuit

Hardware support for security mechanisms such as authentication, cryptographic protocols, digital rights management and hardware metering depend heavily on the security of embedded secret keys. The current practice of embedding these keys as digital data in the Integrated Circuit (IC) weakens security because the keys can be learned through attacks. Physical Unclonable Functions (PUFs) are a recently- proposed alternative to storing digital keys on the IC. A PUF leverages the inherent manufacturing variations of an IC to define a random function. However, poor performance under PUF quality criteria such as the level of randomness and reproducibility in the responses have detracted from their adoption and widespread use. In this dissertation, I propose several ways to define a novel PUF using the Power Distribution System (PDS) of an IC. First, I describe the hardware primitive and test setup that is required to obtain the PUF responses. Then, I evaluate the analog PUF responses from silicon against standard PUF quality metrics in order to qualify the strengths and weaknesses of the proposed PUF. I show that the analog PUFs ex- hibit very high levels of randomness and reproducibility, but are sensitive to changes in temperature. Next, I propose extensions to our PUF that enable an exponential number of Challenge/Response Pairs (CRPs) with respect to the number of hardware resources, as well as yielding a marginal increase in the level of randomness. I also use these same analog measurements from silicon to simulate an integrated implementation of the PUF that takes a digital challenge and returns a digital response. I show that the integrated architecture also exhibits high levels of randomness and reproducibility, and is also resistant to changes in temperature. Future work includes designing and building a new IC that implements a more powerful hardware primitive that will improve both the number and accuracy of the measurements, as well as additional hardware that will allow the challenge and response generation to be performed on-chip

Applying of mechanical failure criteria of brittle material to the design of high temperature heat exchanger

Previous studies have suggested using a ceramic high temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur iodine thermochemical cycle. The decomposer was manufactured using fused ceramic layers that allow the creation of channels with dimensions below one millimeter. The heat exchanger is expected to operate in the range of 950°C. Thermal stresses are however induced in the heat exchanger ceramic components. In this study, proper failure criteria are selected to evaluate the safety level of the ceramic components. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer, stresses and chemical reactions in the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. The temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis. Results of this research can be used as a basis for the investigation of the optimal design of the decomposer that can provide a maximum chemical decomposition performance while maintaining stresses within design limits. The stress results are used to calculate the probability of failure based on Weibull failure criteria and the factor of safety based on Coulomb-Mohr failure criteria; A parametric study of a straight channel sulfuric acid decomposer is made. Several different geometries of the decomposer channels which include straightforward, ribbed, hexagonal, and diamond forms are investigated. The influence of the mass flow rate and of the area of chemical reaction on the chemical decomposition performance for the decomposer are also explored. The analysis includes the steady state operating conditions and the transient operating conditions. The research considers stresses that are induced during transient scenarios, in particular, the cases of startup and shutdown. The analysis includes also the Bayonet design of heat exchanger as silicon carbide integrated decomposer (SID) which produces sulfuric acid decomposition product - sulfur dioxide. The product can be used within the sulfur iodine thermochemical cycle portion of the hydrogen production process. A two-dimensional axisymmetric geometry of the bayonet heat exchanger is created using GAMBIT software. A computational model is developed to investigate fluid flow, heat transfer and chemical reactions in the porous medium of the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. Temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis