This work describes the design and testing of a wireless implantable bladder pressure sensor suitable for chronic implantation in humans. The sensor was designed to fulfill the unmet need for a chronic bladder pressure sensing device in urological fields such as urodynamics for diagnosis and neuromodulation for bladder control. Neuromodulation would particularly benefit from a wireless bladder pressure sensor providing real-time pressure feedback to an implanted stimulator, resulting in greater bladder capacity while using less power. The pressure sensing system consists of an implantable microsystem, an external RF receiver, and a wireless battery charger. The implant is small enough to be cystoscopically implanted within the bladder wall, where it is securely held and shielded from the urine stream, protecting both the device and the patient. The implantable microsystem consists of a custom application-specific integrated circuit (ASIC), pressure transducer, rechargeable battery, and wireless telemetry and recharging antennas. Because the battery capacity is extremely limited, the ASIC was designed using an ultra-low-power methodology in which power is dynamically allocated to instrumentation and telemetry circuits by a power management unit. A low-power regulator and clock oscillator set the minimum current draw at 7.5 µA and instrumentation circuitry is operated at low duty cycles to transmit 100-Hz pressure samples while consuming 74 µA. An adaptive transmission activity detector determines the minimum telemetry rate to limit broadcast of unimportant samples. Measured results indicated that the power management circuits produced an average system current of 16 µA while reducing the number of transmitted samples by more than 95% with typical bladder pressure signals. The wireless telemetry range of the system was measured to be 35 cm with a bit-error-rate of 10-3, and the battery was wirelessly recharged at distances up to 20 cm. A novel biocompatible (open full item for complete abstract)

Power management is considered to be an important aspect in designing battery operated Tire Pressure Monitoring Systems (TPMS) as it helps to prolong the lifespan of the battery. There are several methods that can be used to design a low power tire-pressure and service monitoring system. One of the most common methods for power reduction is the duty cycle method. This thesis suggests an idea of implementing the TPMS in combination with a separate Radio Frequency Identification (RFID) circuit, especially a very low power (active or passive) RFID whose sole purpose is to detect the interrogating signal. This RFID circuit which can operate at a typical frequency of 125 kHz is used to turn ON a higher power transmitter which is initially in SLEEP state and soon after entering the active state performs the communication, updating, etc. Once the desired task is completed, the high power transmitter returns to SLEEP state or is turned off until the next interrogation.The implementation of SLEEP mode to minimize power consumption is discussed in detail and the currents consumed by the microcontroller in SLEEP and ACTIVE modes are measured and recorded. The microcontroller in SLEEP mode consumed a current of 17μA which reduced the overall average current consumed by the microcontroller and the pressure sensor. Furthermore, this method promises an improvement in the battery life and the calculations showing this improvement are discussed with the example of an AA battery with 2800mAh battery life.

In recent years, flexible and stretchable sensors have been a subject of intensive research to replace the traditional sensors made up of metal and semiconductors. This thesis has been conducted with the objective of exploring the possible applications of Graphene/PVDF nanocomposite in various kinds of flexible sensors as a potential sensing material. Initially, graphene/PVDF nanocomposite was synthesized by the solution-phase mixing method. A thin film of 20-22 μm was coated on a glass substrate to investigate the characteristics of the composite by using XRD and SEM techniques. This nanocomposite was best suited for piezoresistive-based sensors where the sensor senses the external stimuli and outputs the response in terms of change in electrical properties such as resistance, voltage, or current. The synthesized graphene/PVDF nanocomposite was coated on different kinds of substrates to make three different kinds of flexible sensors. They are airflow sensor, knittle pressure sensor, and accelerometer. The airflow sensor was designed and fabricated by applying a thin film of nanocomposite on the polyethylene (PE) substrate and placed inside a PVC pipe at an angle to the central axis of the pipe. The response of the sensor was tested by passing air at various speeds and recorded in terms of resistance change. The linearity and repeatability of the curves were observed. Temperature dependence on electrical conductivity was studied by heating and cooling the sample between room temperature and below the melting point of PVDF. Further, the sensing characteristics were simulated using COMSOL Multiphysics software, and the modeled data were compared with the experimental result. Another application of our in-house fabrication with the use of the nanocomposite is a knittle pressure sensor. The primary purpose of developing knittle pressure is to monitor health by either attaching to the skin or using it inside the health monitoring device. The use of fabric substrate a (open full item for complete abstract)

Thin-film pressure sensors have received widespread attention in recent times due to its ease of manufacture, characterization, and fatigue strength. Commercial fabrication of these sensors is inexpensive and compatible with the current manufacturing technologies. It has been found that the sensitivity of the flexible pressure sensor depends on the sensing pressure, the microstructural dispersion of nanoparticles, and the compatibility of the binder and the nanoparticles. The binder/particle dispersion should be such that it facilitates the formation of a greater number of conduction paths with a slight change in sensing pressure. The objective of this thesis includes the fabrication and characterization of a thin-film pressure sensor using different novel materials. The first material to be investigated was ZnO. ZnO thin-film materials that have received a great deal of attention due to its unique properties of being a semiconductor with wide bandgap and piezoelectric effect. The sensor characteristic of ZnO was compared with barium-titanate (BaTiO3) Gallium arsenic (GaAs) and Polyvinylidene fluoride (PVDF). The second material to be investigated was aluminum-doped zinc oxide (AZO). AZO has attracted a great deal of attention in many applications because of its nontoxicity, abundancy, and lower cost than other materials such as indium tin oxide (ITO). The AZO films were deposited on polyethylene (PE) substrates by a radiofrequency (rf) magnetron sputtering method. The piezoresistive sensor was tested for different pressures in vacuum and gage pressure conditions. The response characteristics indicated that resistance increased with the bending of the AZO layer in both compressive and tensile operation modes. The sensor characteristics exhibited that the AZO piezoresistive sensor can be used to measure ambient pressure quantitatively. This investigation indicated that AZO can be used as an alternative material for the fabrication of pressure sensors. Lastly (open full item for complete abstract)

Soft and stretchable electronics will play an important role in the areas of robotics, prosthetics, wearables, and energy harvesting devices. The emergence of smart technologies is spurring the development of a wider range of applications for stretchable and conformable pressure sensors. Concomitant with the material research on soft sensors, the fabrication method is also gaining major progress. The manufacturing and design flexibility offered by additive manufacturing (AM) may enable the fabrication of sensors that are superior to those fabricated by conventional manufacturing techniques. AM could realize applications of the sensors which are difficult to achieve via a conventional method. In this work, a flexible and stretchable pressure sensor has been proposed. A pressure-sensitive membrane was fabricated through the polymerization of an ionic liquid (IL)-prepolymer blend. Stretchable conductive strips or electrodes were fabricated using a carbon nanotube (CNT)/polymer composite. The IL-based pressure-sensitive layer was sandwiched between CNT–based stretchable electrodes and encapsulated within stretchable top and bottom insulating layers. The multi-layer multi-material sensor was first fabricated through a screen-printing and molding process for evaluation and characterization purposes. Sensor performance was investigated for different degrees of crosslinking and polymerization, concentrations of IL, and thicknesses of the IL/polymer layer. The experimental results showed that these variables affect the sensitivity of the sensor. Next, various forces were applied to a screen-printed sensor to determine the reliability, sensitivity, and dynamic range. The proposed IL-based sensor displayed superior performance with high sensitivity and reliability. The sensor was also investigated for temperature dependence and shelf life. Different applications of the screen-printed sensor were explored such as sensor embedded tire and sensor embedded insole. While the s (open full item for complete abstract)

Pressure and temperature are parameters essential for brain monitoring. Currently, the intracranial pressure (ICP) and intracranial temperature (ICT) are measured by the separate sensors/catheters in clinic. Although integrated ICP and ICT sensors with low cost and minimal damage to brain is highly favored, the integration of the sensors involves complicate assembly and packaging process, and also increases the diameter of micro-catheters. Researches have been done to develop integrated pressure and temperature sensors on the same platform, especially on flexible substrate, to minimize the damage to brain caused by the device implantation. However, the developed sensors are either merely prove-of-concept or difficult to be manufactured due to the complicate and costly process. This work proposes and explores novel approaches to develop the integrated flexible ICP and ICT sensors with low cost and simple process. High quality polysilicon thin film was directly grown on flexible substrate as the sensing material for both ICP and ICT sensors with simple, fast, and low cost aluminum induced crystallization (AIC) process. A continuous P-type polysilicon film with the crystals' average size of 49 nm was developed and shown. Based on the polysilicon thin film, a flexible thermistor array was designed, developed and characterized. It achieved good in vitro performance with a sensitivity of -0.0031/°C, response time of 1.5 s, resolution of 0.1 °C, thermal hysteresis less than 0.1°C, and long term stability with drift less than 0.3 °C for 3 days in water. In vivo tests of the polysilicon thermistor showed a low noise level of 0.025±0.03 °C and the expected transient temperature increase associated with cortical spreading depolarization. In addition, polysilicon based flexible pressure sensor was developed for ICP measurement. The gauge factor of polysilicon thin film was characterized with a value of 10.316. The dimensions of the flexible piezoresistive pressure (open full item for complete abstract)

Pressure ulcers are a dangerous injury resulting from extensive pressure being applied to the body over a prolonged period of time resulting in a lack of blood flow reaching the affected site. If the pressure is not relieved in a timely manner, the lack of nutrients causes the tissue in the surrounding area to eventually die and decompose creating an open sore that could become infected. Pressure ulcers usually form over areas of the skin where a boney prominence is closest to the skin, such as the hips or ankle bones, so subjects who lose a leg and depend on a prosthetic are at constant risk of developing them due to the residual leg bone left by the surgery. In addition to this, muscle mass is reduced in subjects with a lower limb amputation due to lack of use which brings the bone even closer to the surface of the skin. If a lower limb amputee does form a pressure ulcer, they can no longer rely on their prosthetic for mobility and are reduced to using crutches, a wheelchair, or are bedridden until the wound heals. This thesis presents a low cost, high mobility prototype microcontroller-based pressure sensor that is capable of detecting normal and shear forces with the possibility of said sensor being integrated into a lower limb prosthetic to detect problem areas of high pressure in real time. This information can then alert the user to a potential problem with their prosthetic allowing them to take proactive measures to prevent a pressure ulcer from forming. The proposed device incorporates an off-the-shelf microcontroller that serves as the control unit along with flexible analog piezoresistive sensors. Using the built-in analog-to-digital module and serial peripheral interface, the device is capable of measuring and storing approximately 1,000 data points per second and detecting pressures in the range of 60mmHg to 798mmHg.

In this dissertation, the development of a packaged silicon carbide (SiC) based MEMS capacitive pressure sensor system that is designed to monitor the pressure of a conventional gas turbofan engine is described. The electronic circuit of the pressure sensor system is based on a Clapp-type oscillator that includes a 6H-SiC MESFET, a SiCN MEMS-based capacitive pressure sensor, titanate MIM capacitors, wirewound inductors, and thick film resistors. The capacitive pressure sensor is incorporated in the LC tank circuit of the oscillator so that a pressure-induced change in capacitance causes a change in the resonant frequency of the oscillator. The MESFET is used to induce oscillation. Individual passive components were evaluated at high temperature to assess their utility in an integrated system. Both wireless and wired variants of the pressure sensor systems for use at high temperature were developed. In developing the final packaged device, several prototype designs of the Clapp-type oscillator circuit that incorporate wireless capability were explored. Prototype circuits with slot-ring and chip antennas operating between 700 MHz and 1 GHz exhibited a maximum operating temperature of 250¿C, limited by the low gain of the MESFET at these frequencies. Prototype circuits operating at 30 and 90 MHz that utilize large spiral inductors in the Clapp oscillator as the radiating element extended stable operation to 470°C. Several wireless pressure sensor prototypes based on the Clapp oscillator circuit were developed. A prototype incorporating a polysilicon capacitive pressure sensor and a spiral inductor exhibited stable operation up to 300°C. A second prototype that used a SiCN capacitive pressure sensor functioned at temperatures up to 400°C. A third prototype based on the 2nd prototype but incorporating a compact, directional chip antenna had a maximum operating temperature of 300ºC, limited by the antenna. Based on size restrictions, the packaged system u (open full item for complete abstract)

This thesis presents the design, fabrication, and testing of novel MEMS pressure and temperature sensors fabricated on optical fiber end faces. A simple micromachining process compatible with MEMS was developed in fabricating sensors directly on optical fibers. The pressure sensor configuration involves anodic bonding of a piece of an extremely thin silicon wafer onto the fiber end face over a cavity etched in the central portion of the fiber end face. Final device diameter is thus the same as that of the optical fiber. The temperature sensor is based on anodically bonding a thin piece of silicon onto the fiber end face.The pressure sensors were fabricated on 400 um diameter fibers while temperature sensors were fabricated on both 200 and 400 um diameter fibers. Pressure measurements were made over the 14 to 80 psi range while temperature measurements were made over the 23 to 300 Celcius range. Pressure sensor sensitivities of 0.1 mV/psi and 0.2 mV/psi were obtained. The pressure sensors were designed with cavity diameter d=150 um, and cavity depth h=0.640 um. Diaphragm thickness for the two sensors were t=7.1, and t=3.4 um. Higher sensitivity was achieved by design of a sensor with the thinner diaphragm. A sensor array fabrication effort demonstrated that our micromachining process could be extended to simultaneous processing of an array of fibers. The temperature sensor was fabricated by bonding 3.1 um thick silicon onto the fiber end face. An oxidant-resistant encapsulation scheme for the temperature sensor was proposed, namely aluminum coated silicon nitride (Al/Si3N4). The uncoated side of silicon was bonded to a fiber end face using the anodic bonding method. The measured values of kf=(lambda)-1x(dlambda/dT) for capped and uncapped sensors were kf=(7.5±0.6)x10-5/Celcius, and kf=(7.2±0.1)x10-5/Celcius respectively. The measured kf value for the uncapped sensor is equal to that which was determined using the published material properties for crystalline silicon (open full item for complete abstract)

The object of this thesis is to develop a new packaging method to mount silicon micro pressure sensors into 1.67 mm diameter neonatal catheters to measure blood pressure. A new polymer flip-chip bonding method on a flexible Kapton film has been developed and applied to dual lumen neonatal catheters integrated with silicon micro pressure sensors. Flip chip bonding technique has inherent advantages of miniaturization, improved reliability and cost reduction. This polymer flip-chip bonding technique requires a low temperature process and improved tolerance of thermal stress which are very desirable for mounting micro sensors or micro actuators on lower-cost flexible polymer substrates for medical applications. The silicon micro pressure sensors, which are mounted on a flexible Kapton film with metal lines for neonatal catheter, have been fully characterized in both gas and liquid environments, indicating that the packaging was satisfactory rugged for catheter use.

Development of a low cost shock pressure sensor.

This study investigated the impact of high-stage events on riverbed scour and hydraulic conductivity (Kv). Seepage-meter measured riverbed Kv averaged 0.092 m/d. Slug-test measured Kv of the underlying sediment averaged 9.6 m/d. The low riverbed Kv is probably due to a gravel and cobble layer clogged with fine sediment (colmation layer). Kv of cores of transient material overlying the cobble layer averaged 5.3 m/d. Event-driven scour, measured with cross-sectional profiles, scour chains, and a load-cell pressure sensor, never exceeded 0.06 m, indicating that the colmation layer remained intact, despite even a 60-year event. A riverbed conceptual model of three distinct layers –transient sediment, an armor/colmation layer and a transitional bottom – had an overall Kv of 4.6 m/d. Sensitivity analysis of layer thicknesses indicated that a) the transient layer has negligible impact on the overall Kv and b) loss of the colmation layer, while not observed, could double the overall Kv.

This dissertation explores the development of a new stainless steel pressure sensor capable of sustaining harsh environments, including high pressures, high temperatures, and/or corrosive media. The proposed pressure sensor utilizes commercial off-the-shelf (COTS) components, adapts vacuum coupling radiation (VCR) tube fitting (Swagelok Co.) for sensor packaging, and combines micro- and conventional-machining techniques for sensor realization. Capacitive transduction is used to simplify the implementation, as well as take advantage of the high stability and low temperature drift associated with this transduction scheme. Two generations of stainless steel capacitive pressure sensors have been developed in this dissertation. The first-generation sensor is comprised of a stainless steel diaphragm die and a stainless steel backing plate, each electrically isolated with tetraethylorthosilicate (TEOS) silicon dioxide, and packaged by a set of COTS VCR tube fitting. The pressure sensor responses show four operating regions, including stabilizing, non-touch, transition, and touch mode regions. The fully packaged pressure sensor is characterized at high pressures of up to 10,340 kPa (1,500 psi) and at high temperatures of up to 300°C. Corrosive pressure media, including potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) solutions, are used to demonstrate the corrosive-media compatibility of the pressure sensor. After soaking in these corrosive media and several tens of pressure cycles over a month, the fully packaged pressure sensor continues to show stable and consistent operation. Because of the anomalous stabilizing region in these sensors, sensor-to-sensor variance is very poor (i.e., 62% in full-scale (FS)). The second-generation sensor is developed to address the shortcomings found in the first-generation pressure sensor. A hard tungsten carbide backing plate used to replace the stainless steel backing plate and a stainless steel press plate are used (open full item for complete abstract)