Experiments in the study of transient aerodynamics typically require pressure measurements with a high spatial and temporal resolution. Existing commercial pressure transducers are expensive and they provide a spatial resolution only on the order of millimetres. The full bandwidth of commercial devices (which extends to around 200 kHz) can only be utilised by exposing the transducer to the flow environment with very little thermal or mechanical protection. If insufficient protection is provided, the expensive commercial devices are likely to be damaged. Inexpensive pressure sensors based on extrinsic Fabry-Perot fibre optic interferometry are capable of measurement with a high spatial and temporal resolution. Thermal protection or isolation for these sensors is still required, but they can be exposed directly to the flow if the sensors are disposable (low cost). Excessive thermal or mechanical protection is not required for these sensors because the damaging heat transfer and particle impacts that may occur in transient aerodynamic facilities generally occur after the useful test flow. In this dissertation, a variety of construction techniques for diaphragm-based Fabry-Perot fibre optic pressure sensors were investigated and the advantages and disadvantages of all techniques are compared. The results indicate that using a zirconia ferrule as the substrate, a liquid adhesive as the bonding layer, and a polished copper foil as the diaphragm provide the best results. It is demonstrated that a spatial resolution on the order of 0.1 mm and a bandwidth to more than 100 kHz can be achieved with such constructions. A variety of problems such as hysteresis, response irregularity, low visibility and sensor non-repeatability were observed. By using a thinner bonding layer, a larger bonding area, longer cavity length, increased calibration period, and applying load cycling to the diaphragm, the hysteresis was minimized. Sensor response irregularity was also minimized using a polished diaphragm. Visibility increased to about 90% using active control of the cavity length during the construction process. Non-repeatability was found to be a consequence of adhesive viscoelasticity and this effect was minimized using a thin layer of adhesive to bond the diaphragm to the substrate. Due to the effects of adhesive viscoelasticity, the pressure sensors indicate an error of up to 10% of mean value for the reflected shock pressure. This error could not be further reduced in the current sensors configuration. Some new configurations are proposed to decrease the effect of sensor non-repeatability. The effect of pretensioning the diaphragm was investigated analytically but the results do not indicate any considerable advantage for the levels of pretension likely to be achieved in practice. However, the results do indicate that pretension effects caused by an environmental temperature change can damage the sensor during storage. The effect of the initial diaphragm deflection on the sensor performance and temperature sensitivity was modelled and the results show that an initial diaphragm deflection can improve the sensor performance. The effect of the thermal isolation layer on the sensor performance was also investigated and the results show that for a shock tube diaphragm bursting pressure ratio up to 5.7, heat transfer does not contribute to sensor errors for the first millisecond after shock reflection. However, it was found that the use of a thin layer of low viscosity grease can protect the sensor for about 20 ms while only decreasing its natural frequency by typically 17%. The grease layer was also found to decrease the settling time of a low damping ratio sensor by 40%. The sensor was successfully employed to identify an acoustic disturbance in a shock tube.

A railroad yard in Oneida, Tennessee was contaminated with creosote in the 1950s and 1960s through cross tie treatment. The problem was discovered in 1990 and phytoremediation in combination with an interception trench was chosen as the remediation strategy. Hybrid poplar trees (1,036) were planted in 1997 within 0.7 acres. The goals of the phytoremediation system are to prevent migration of the contaminant off the site and clean up the contaminant in-situ. This study is focused on quantifying the rate of evapotranspiration of the phytoremediation system and then determining the effect on groundwater flow. This will be accomplished by quantifying evapotranspiration using a water budget, applying White's Equation, comparing groundwater recession curves, creating a groundwater flow model, and examining water table elevations obtained at the site. Calculations of water use by the poplar trees in early September 1999 ranged from 0.62 to 1.34 gal/day/tree. The volume of evapotranspiration calculated for the trees during 1999 is 140,292 gallons. Total evapotranspiration determined by the water budget for 1998 is 1,570,064 gallons. Evaluation of the water level data over a period of several years shows significant lowering of the water table (fluctuations of up to four feet) during the summer and fall months due to evapotranspiration. Although calculated evapotranspiration rates are not as high as seen in the literature, continued monitoring of the site should show large increases in evapotranspiration rates in the future as the poplar trees mature. / Master of Science

Acoustic-structural interaction is the key to understand a wide range of engineering problems such as membrane-based dynamic pressure sensors, hearing devices for sound source localization, and acoustic absorbers for noise reduction. Despite tremendous developments in the last decades, there is still a fundamental size limitation in these areas. In the case of dynamic pressure sensors, sensitivity usually suffers for miniature sensors; the available acoustic directional cues proportionally decrease with size, which adversely affects the localization performance; thick panels are required to achieve superior sound attenuation, particularly for low-frequency sound. It is the motivation of this dissertation research to address the abovementioned size limitation that involves acoustic-structural interaction. The overall goal of this dissertation work is to achieve an enhanced understanding of the acoustic-structural interaction between diaphragms and air cavity and to apply this understanding to develop high-performance miniature acoustic sensors and noise reduction metamaterials. First, a finite element method (FEM) model and large-scale device are developed to understand how the interaction between the diaphragm and its backing air cavity affects the equivalent mass, stiffness, and damping of air-backed diaphragms. The numerical and experimental study shows that the complex interaction cannot be captured by the commonly used lump model. Then, air-backed graphene diaphragms are used to develop fiber optic sensors with sub-millimeters footprint and high sensitivity. Two different configurations are designed to enhance the sensor sensitivity limited by the backing air cavity. One is to increase the mechanical sensitivity by using a larger backing volume, the other is to increase the optical sensitivity by using silver-graphene composite diaphragm. Next, acoustic metamaterials with air-coupled diaphragms as unit cells are developed to achieve perfect acoustic absorption with thickness much smaller than the sound wavelength, which cannot be realized using natural materials. Finally, an expanded configuration of two diaphragms coupled by an air-filled tunnel is experimentally developed to mimic the hearing system of small vertebrates. The goal is to amplify the small directional cues available to the small animals so that a high angular resolution can be achieved. This dissertation provides a quantitative and mechanistic explanation for the interaction between the diaphragms and the sealed air cavity. It offers several frameworks for the development of miniature pressures, directional sensors, and thin sound absorbers. / Mechanical Engineering

Detecting heart and respiratory rates is an essential means of providing emergency medical care. Current methods of detecting such signals include the widely used electrocardiography (ECG) method. Other more manual methods of heart and respiratory rate estimation require a practitioner to constantly observe the patient. These methods are time consuming and detract valuable time from emergency medical care. This thesis presents a novel, hands off, heart and respiratory monitor (HARMONI). It uses pressure transducers and medical tubing placed on a person's chest. The tubing is plugged off at one end, and then attached to a pressure transducer at the other end. The transducer sees spikes in voltage whenever the pressure inside the tubing changes. Heart and respiratory rates both cause expansion in the chest, increasing the pressure in the tubing, and causing the transducer to see a change in voltage. The method was first validated, and then tested in a simulated environment. Finally, the device was transformed in to a full system prototype. Human tests were conducted to correlate the signal with that of an industry standard ECG device. This thesis explains how heart and respiratory rates can be derived using signal processing techniques and a simple non-invasive sensor. This device is a rapidly deployable tool that has the potential to save lives specifically in mass casualty situations. It would be a force multiplier, allowing a single responder to monitor multiple casualties, saving time and lives. / Master of Science

Este trabalho apresenta a modelagem da parte dinâmica de dois transdutores de pressão tipo piezorresistivo. Geralmente processos de calibração dinâmica usam bancadas sofisticadas, mas neste trabalho procurou-se um processo simples e de baixo custo. A metodologia baseou-se em aumentar lentamente a pressão, fornecida por um sistema hidráulico básico, até que ocorresse a explosão de um diafragma e, com isso, obteve-se um degrau de pressão, supostamente ideal. Considerado como sistemas lineares, com a resposta obtida verificou-se qual a ordem e o tipo de sistema correspondente à resposta do transdutor. Através dos dados experimentais determinou-se os parâmetros dinâmicos do modelo matemático. Foram obtidos modelos matemáticos lineares de segunda ordem de cada transdutor. As respostas dos modelos mostram ter uma concordância satisfatória quando comparadas aos dados experimentais. / This work presents a dynamic modeling method for two hydraulic piezoresistive pressure transducers. Usually the dynamic calibration processes apply sophisticated devices, but in this work a simple and low cost process was searched. The methodology was based on increasing the pressure slowly, supplied by a basic hydraulic system, up to a diaphragm explosion, assumed as an ideal step pressure variation. Considered as linear systems, the responses obtained were verified and compared with a second order linear system. Using the experimental data, the dynamic parameters of the mathematical model were determined for each of the two transducers. The theoretical responses of the models showed to have a satisfactory agreement when compared with the experimental data.

Introduction. To test the effects of torsion torques on intradiscal pressure and disc height in human lumbar specimens. Methods. Six human lumbar cadaveric functional spine units (FSU) were loaded in the neutral position with 600 N compression. Nucleus pressure measurements were obtained at 0 Nm, 0.5 Nm, 1.0 Nm and 2 Nm torsion torque. Posterior elements were removed and pressure measurements were repeated at the same torsion torques for the disc body unit (DBU). The pressure in the nucleus was measured by pulling a pressure probe through the disc along a straight path in the midsagittal plane. Results. There was no statistically significant difference of nucleus pressure or intervertebral disc height with different torsion torques among or between the FSU's and DBU's. However, a disc height increase ranging from 0.13 mm to 0.16 mm occurred with the insertion of a 1.85 mm diameter cannula. Conclusions. Small torsion torques showed no significant difference in intradiscal pressures or disc heights. Disc height increases were seen with the insertion of the cannula that could lead to methods of disc height restoration.

The effects of microbubbles injection in the boundary layer of a turbulent channel flow are investigated. Electrolysis demonstrated to be an effective method to produce microbubbles with an average diameter of 30 ??m and allowed the placement of microbubbles at desired locations within the boundary layer. Measurement of velocity fluctuations and the instantaneous wall shear stress were carried out in a channel flow facility. The wall shear stress is an important parameter that can help with the characterization of the boundary layer. This parameter can be obtained indirectly by the measurement of the flow pressure at the wall. The wall shear stress in the channel was measured by means of three different independent methods: measurement of the pressure gradient by a differential pressure transducer, Particle Image Velocimetry (PIV), and an optical wall shear stress sensor. The three methods showed reasonable agreement of the wall shear stress values for single-phase flow. However, differences as skin friction reductions were observed when the microbubbles were injected. Several measurements of wall-pressure were taken at various Reynolds numbers that ranged from 300 up to 6154. No significant drag reduction was observed for flows in the laminar range; however, a drag reduction of about 16% was detected for turbulent Reynolds numbers. The wall-pressure measurements were shown to be a powerful tool for the measurement of drag reduction, which could help with the design of systems capable of controlling the skin friction based on feedback given by the wall-pressure signal. The proposed measurement system designed in this work has capabilities for application in such diverse fields as multiphase flows, drag reduction, stratified flows, heat transfer among others. The synchronization between independent systems and apparatus has the potential to bring insight about the complicated phenomena involved in the nature of fluid flows.

Este trabalho apresenta a modelagem da parte dinâmica de dois transdutores de pressão tipo piezorresistivo. Geralmente processos de calibração dinâmica usam bancadas sofisticadas, mas neste trabalho procurou-se um processo simples e de baixo custo. A metodologia baseou-se em aumentar lentamente a pressão, fornecida por um sistema hidráulico básico, até que ocorresse a explosão de um diafragma e, com isso, obteve-se um degrau de pressão, supostamente ideal. Considerado como sistemas lineares, com a resposta obtida verificou-se qual a ordem e o tipo de sistema correspondente à resposta do transdutor. Através dos dados experimentais determinou-se os parâmetros dinâmicos do modelo matemático. Foram obtidos modelos matemáticos lineares de segunda ordem de cada transdutor. As respostas dos modelos mostram ter uma concordância satisfatória quando comparadas aos dados experimentais. / This work presents a dynamic modeling method for two hydraulic piezoresistive pressure transducers. Usually the dynamic calibration processes apply sophisticated devices, but in this work a simple and low cost process was searched. The methodology was based on increasing the pressure slowly, supplied by a basic hydraulic system, up to a diaphragm explosion, assumed as an ideal step pressure variation. Considered as linear systems, the responses obtained were verified and compared with a second order linear system. Using the experimental data, the dynamic parameters of the mathematical model were determined for each of the two transducers. The theoretical responses of the models showed to have a satisfactory agreement when compared with the experimental data.

Abstract This thesis describes the development of pressure sensor arrays and a range of methods suitable for the long-term measurement of heart rate and blood pressure determination using a cuff and a pressure sensor array on the radial artery. This study also reviews the historical background of noninvasive blood pressure measurement methods, summarizes the accuracies achieved and explains the requirements for common national and international standards of accuracy. Two prototype series of pressure transducer arrays based on electro-mechanical film (EMFi) were designed and tested. By offering high (∼TΩ) resistance, EMFi is an excellent material for low-current long-term measurement applications. About 50 transducer arrays were built using different configurations and electrode materials to sense low-frequency pressure pulsations on the radial artery in the wrist. In addition to uniform quality, essential requirements included an adequate linear response in the desired temperature range. Transducer sensitivity was tested as a function of temperature in the range of 25–45 °C at varying static and alternating pressures. The average sensitivity of the EMFi used in the transducers proved adequate (∼2.2 mV/mmHg and ∼7 mV/mmHg for normal and high sensitive films) for the intended purpose. The thesis also evaluates blood pressure measurements by the electronic palpation method (EP) and compares the achieved accuracy to that of the oscillometric method (OSC) using average intra-arterial (IA) blood pressure as a reference. All of these three measurements were made simultaneously for each person. In one test group, measurements were conducted on healthy volunteers in sitting and supine position during increasing and decreasing cuff pressure. Another group, comprising elderly cardiac patients, was measured only in the supine position during cuff inflation. The results showed that the EP method was approximately as accurate as the OSC method with the healthy subjects and slightly more accurate with the cardiac patient group. The advantage of the EP method is that also the wave shape and velocity of arterial pressure pulses is available for further analysis, including the assessment of arterial stiffness.

Background: Registering a true maximum bite force on the most commonly-used force transducers is problematic. It is often believed that this is related mainly to discomfort and the fear of breaking teeth. Objectives: The aim of the project was to compare the suitability of different bite force measuring transducers including ones which were designed to improve subject comfort. The transducers used were a traditional strain-gauge transducer with and without covering with ethylene vinyl acetate (EVA) sheets, and a newly-developed pressure transducer. Methods: Five separate studies were performed in this project. The experiments were carried out on human volunteer subjects (aged 24 to 41 years). They were all dentate with no missing anterior teeth and with no crowns on these teeth. The following procedures were used in some or all of the studies: measurement of MVBF, electrical stimulation of the masseter muscle, and EMG recording from two pairs of jaw closing muscles. Results: The highest MVBF values were recorded on the pressure transducer, mean (± S.D.) 464 N ± 224 N; followed by the strain-gauge transducer with EVA sheets, 243 ± 80 N; and last of all the strain-gauge transducer with silicone indices, 165 ± 35 N; or acrylic indices, 163 ± 82 N. Significantly higher maximum potential bite forces were predicted by twitch interpolation for the pressure transducer (730 ± 199 N) than for the strain-gauge transducer with EVA sheets, 354 ± 67 N (Paired t test, P < 0.05). Significantly higher EMGs of the masseter and anterior temporalis muscles were found to be associated with MVBFs on the pressure transducer than with MVBFs on the strain-gauge transducer with EVA sheets (Paired t test, P < 0.05). Conclusions: It is concluded that: a) the pressure transducer system and to a lesser extent the strain-gauge transducer covered with EVA sheets seemed to overcome the fear associated with biting on the hard surfaces of the strain-gauge transducer alone; b) the pressure transducer may have some multi-directional capabilities which allow for total bite forces, or at least larger parts of them, to be recorded than on a uni-directional strain-gauge transducer.