Real-Time Remote Monitoring of Temperature and Humidity Within a Proton Exchange Membrane Fuel Cell Using Flexible Sensors

This study developed portable, non-invasive flexible humidity and temperature microsensors and an in situ wireless sensing system for a proton exchange membrane fuel cell (PEMFC). The system integrated three parts: a flexible capacitive humidity microsensor, a flexible resistive temperature microsensor, and a radio frequency (RF) module for signal transmission. The results show that the capacitive humidity microsensor has a high sensitivity of 0.83 pF%RH−1 and the resistive temperature microsensor also exhibits a high sensitivity of 2.94 × 10−3 °C−1. The established RF module transmits the signals from the two microsensors. The transmission distance can reach 4 m and the response time is less than 0.25 s. The performance measurements demonstrate that the maximum power density of the fuel cell with and without these microsensors are 14.76 mW·cm−2 and 15.90 mW·cm−2, with only 7.17% power loss

In-situ Monitoring of Internal Local Temperature and Voltage of Proton Exchange Membrane Fuel Cells

The distribution of temperature and voltage of a fuel cell are key factors that influence performance. Conventional sensors are normally large, and are also useful only for making external measurements of fuel cells. Centimeter-scale sensors for making invasive measurements are frequently unable to accurately measure the interior changes of a fuel cell. This work focuses mainly on fabricating flexible multi-functional microsensors (for temperature and voltage) to measure variations in the local temperature and voltage of proton exchange membrane fuel cells (PEMFC) that are based on micro-electro-mechanical systems (MEMS). The power density at 0.5 V without a sensor is 450 mW/cm2, and that with a sensor is 426 mW/cm2. Since the reaction area of a fuel cell with a sensor is approximately 12% smaller than that without a sensor, but the performance of the former is only 5% worse

The State of the Art in Fuel Cell Condition Monitoring and Maintenance

Fuel cell vehicles are considered to be a viable solution to problems such as carbon emissions and fuel shortages for road transport. Proton Exchange Membrane (PEM) Fuel Cells are mainly used in this purpose because they can run at low temperatures and have a simple structure. Yet to make this technology commercially viable, there are still many hurdles to overcome. Apart from the high cost of fuel cell systems, high maintenance costs and short lifecycle are two main issues need to be addressed. The main purpose of this paper is to review the issues affecting the reliability and lifespan of fuel cells and present the state of the art in fuel cell condition monitoring and maintenance. The Structure of PEM fuel cell is introduced and examples of its application in a variety of applications are presented. The fault modes including membrane flooding/drying, fuel/gas starvation, physical defects of membrane, and catalyst poisoning are listed and assessed for their impact. Then the relationship between causes, faults, symptoms and long term implications of fault conditions are summarized. Finally the state of the art in PEM fuel cell condition monitoring and maintenance is reviewed and conclusions are drawn regarding suggested maintenance strategies and the optimal structure for an integrated, cost effective condition monitoring and maintenance management system

Real time measurement of oxygen by integrating a clark sensor with low cost printed circuit board technology and solid electrolyte membrane

A prototype of a miniaturized Clark type electrochemical oxygen sensor integrated with a 3D printed in vitro cell culturing platform is designed and developed for the purpose of monitoring the cellular oxygen consumption by the solution flowing through the cultured cells on the platform. Oxygen respiration indicates a cell's metabolic activity, so by measuring a chemical's oxygen content as it passes through a cell chamber, we can measure that chemical's potential effectiveness. This miniature micro sensor is designed and fabricated on a printed circuit board for the first time and integrated with a solid electrolyte membrane and 3D printed cell culturing platform to ensure robustness, low manufacturing cost and good electrical conductivity for sensing. Hence the sensor is aimed at enabling the pharmaceutical industry to rapidly test chemical products on animal and cancer cells; and has been designed to be low cost and suitable for mass production. The presented oxygen sensor configuration consists of two identical series of working, reference and counter microelectrodes. The solid polymer electrolyte membrane, Nafion (perfluorosulfunic acid membrane, DuPont Company) removed requirement for extra humidification and increased the shelf life of the sensor. The sensitivity of the oxygen sensor was tested in different oxygen concentration in gas and liquid states and was calibrated with measurements from a Portable Multi-Gas analyzer and a dissolved oxygen analyzer. The prototype can detect the small changes in oxygen concentration in the range of 0 to 5 μA current and has a response time of less than 5 seconds

Cell-Free Artificial Photosynthesis System

The objective of this research is to create a cell-free artificial platform for harvesting light energy and transforming the energy to organic compounds. In order to achieve this objective, we took the approach of mimicking the photosynthetic processes of a plant leaf and integrating them into a compact system using microfabrication technology. Photosynthesis consists of two parts: light reaction and dark reaction. During the light reaction, light energy is transformed to chemical energy in ATP that is a biological energy source, while during the dark reaction. Carbon dioxide is absorbed and used to synthesize organic compounds such as glucose and fructose. Many scientists had tried to realize artificial photosynthesis for energy harvesting for decades. However, most of the previous systems were simply based on light reaction and produced less desirable energy sources, such as explosive hydrogen gas and unstable electricity. Other works had been reported that combined both light and dark reactions to produce useful organic compounds, but they were all based on utilizing living cells that were difficult to maintain and were not reusable. We developed a cell-free artificial platform conducting both light and dark reactions. To the best of our knowledge, such a device had not been reported so far. This device was able to harvest light energy and transform the energy to organic compounds, mimicking a plant leaf. We envision integrating the "artificial leaves" to create a compact energy harvesting system with a promising efficiency. In order to create an artificial photosynthesis device, we had come up with four specific parts as follows. Part 1: Light reaction was realized in a microfluidic platform that consists of two fluid chambers separated by a planar membrane with embedded proteins that convert light energy into ATP. Four different materials were investigated as potential membrane materials and the optimal (most stable) material was identified through impedance spectroscopy. Since these membrane materials were very soft, it was challenging to integrate them in a microfluidic platform. Diverse support materials and fabrication techniques were investigated to identify the optimal fabrication process. Once the best membrane material was identified and a microfluidic platform was constructed, we would have light-converting proteins embedded in the membrane followed by the evaluation its light reaction performance. Part 2: Dark reaction was realized in another microfluidic platform porous PDMS cubes as gas-liquid interface media. We used porous PDMS as a gas-liquid interface between microfluidic channels to create a "one-way" diffusion path for carbon dioxide. The CO2 transport was evaluated based on pH change and successful CO2 transport would produce precursors (C3 compounds) for glucose production. Part 3: Glucose synthesis and storage unit was developed by mimicking sponge mesophyll found in a leaf (dicotyledons leaf). Chitosan porous structures with interconnected pores were used for this purpose and they were fabricated by lyophilization after casting or 3D printing. Part 4: The circuits for an integrated light reaction platform was designed and simulated. The digital encode/decode of microchip array was simulated. A high-resolution, low-speed analog-to-digital converter was also designed and simulated for ion channel monitoring purpose. While carrying out this research, the following scientific contributions were also made. First, electrochemical property database of planar membranes made of different biomaterials were established. Second, a novel gas-liquid interface was developed for microfluidic platforms using porous PDMS and its performance was thoroughly investigated by on-chip pH measurement. Third, during the study on 3D printing of chitosan porous structure, a mathematical model was established for identifying optimal operational parameters for printing non-Newtonian fluids with a pneumatic printer. This research brought together expertise in advanced manufacturing (MEMS and additive manufacturing), biochemistry and biomaterials, and system control and integration. We envisioned integrating the "artificial leaves" to create a compact energy harvesting system with high efficiency.Ph.D., Mechanical Engineering and Mechanics -- Drexel University, 201

Real-time measurement of tumour hypoxia using an implantable microfabricated oxygen sensor

Hypoxia commonly occurs within tumours and is a major cause of radiotherapy resistance. Clinical outcomes could be improved by locating and selectively increasing the dose delivered to hypoxic regions. Here we describe a miniature implantable sensor for real-time monitoring of tissue oxygenation that could enable this novel treatment approach to be implemented. The sensor uses a solid-state electrochemical cell that was microfabricated at wafer level on a silicon substrate, and includes an integrated reference electrode and electrolyte membrane. It gave a linear response to oxygen concentration, and was unaffected by sterilisation and irradiation, but showed susceptibility to biofouling. Oxygen selectivity was also evaluated against various clinically relevant electroactive compounds. We investigated its robustness and functionality under realistic clinical conditions using a sheep model of lung cancer. The sensor remained functional following CT-guided tumour implantation, and was sufficiently sensitive to track acute changes in oxygenation within tumour tissue

Development and Application of Integrated Silicon-in-Plastic Microfabrication in Polymer Microfluidic Systems

Polymer-based microfluidic devices can offer a number of advantages over conventional devices, and have found many applications in chemical and biological analysis. In order to fully develop a lab-on-chip (LOC) device, the functional components, such as sensors and actuators, tend to be assembled to complete a functional device. But the integration of silicon chips into polymer-based microfluidic systems remains a virtually unexplored area. In this work, a novel silicon-in-plastic microfabrication technology is developed, which involves seamlessly integrating individual microfabricated silicon chips into a larger polymer substrate, where the silicon components provide functionality, and the plastic substrate provides system-level fluid handling. This technology employs low-cost polymer substrates and simple polymer processing techniques which are amenable to mass production. The fabrication and testing of two polymer microfluidic systems using the silicon-in-plastic technology are presented in this dissertation. The first integrated microsystem is a water-based chemical monitoring system based on microhotplate gas sensor and polymer microfluidics. The chemical monitoring system is designed to sample a water source, extract solvent present within the aqueous sample into the vapor phase, and direct the solvent vapor past the integrated gas sensor for analysis. Design, fabrication, and characterization of a prototype system are described, and results from illustrative measurements performed using methanol, toluene, and 1,2-dichloroethane in water are presented. The second one is an integrated UV absorbance detection system that uses silicon-in-plastic technology to seamlessly integrate bare photodiode chips into a polymer microfluidic system. Detection platforms fabricated using this approach exhibit excellent detection limits down to 1.5 x 10 8 M for bovine serum albumin (BSA) as a model protein. In addition to providing high sensitivity, sub-nanoliter detection volumes are enabled by the use of direct photodetector integration. The fabrication methodology is detailed, and system performance metrics including minimum detection limit, detection volume, dynamic range, and linearity are reported

Conceptual Study of Rotary-Wing Microrobotics

This thesis presents a novel rotary-wing micro-electro-mechanical systems (MEMS) robot design. Two MEMS wing designs were designed, fabricated and tested including one that possesses features conducive to insect level aerodynamics. Two methods for fabricating an angled wing were also attempted with photoresist and CrystalBond™ to create an angle of attack. One particular design consisted of the wing designs mounted on a gear which are driven by MEMS actuators. MEMS comb drive actuators were analyzed, simulated and tested as a feasible drive system. The comb drive resonators were also designed orthogonally which successfully rotated a gear without wings. With wings attached to the gear, orthogonal MEMS thermal actuators demonstrated wing rotation with limited success. Multi-disciplinary theoretical expressions were formulated to account for necessary mechanical force, allowable mass for lift, and electrical power requirements. The robot design did not achieve flight, but the small pieces presented in this research with minor modifications are promising for a potential complete robot design under 1 cm2 wingspan. The complete robot design would work best in a symmetrical quad-rotor configuration for simpler maneuverability and control. The military’s method to gather surveillance, reconnaissance and intelligence could be transformed given a MEMS rotary-wing robot’s diminutive size and multi-role capabilities

NASA Tech Briefs, January 2005

Topics covered include: Fiber-Optic Sensor Would Monitor Growth of Polymer Film; Sensors for Pointing Moving Instruments Toward Each Other; Pd/CeO2/SiC Chemical Sensors; Microparticle Flow Sensor; Scattering-Type Surface-Plasmon-Resonance Biosensors; Diode-Laser-Based Spectrometer for Sensing Gases; Improved Cathode Structure for a Direct Methanol Fuel Cell; X-Band, 17-Watt Solid-State Power Amplifier; Improved Anode for a Direct Methanol Fuel Cell; Tools for Designing and Analyzing Structures; Interactive Display of Scenes with Annotations; Solving Common Mathematical Problems; Tools for Basic Statistical Analysis; Program Calculates Forces in Bolted Structural Joints; Integrated Structural Analysis and Test Program; Molybdate Coatings for Protecting Aluminum Against Corrosion; Synthesizing Diamond from Liquid Feedstock; Modifying Silicates for Better Dispersion in Nanocomposites; Powder-Collection System for Ultrasonic/Sonic Drill/Corer; Semiautomated, Reproducible Batch Processing of Soy; Hydrogen Peroxide Enhances Removal of NOx from Flue Gases; Subsurface Ice Probe; Real-Time Simulation of Aeroheating of the Hyper-X Airplane; Using Laser-Induced Incandescence To Measure Soot in Exhaust; Method of Real-Time Principal-Component Analysis; Insect-Inspired Flight Control for Unmanned Aerial Vehicles; Domain Compilation for Embedded Real-Time Planning; Semantic Metrics for Analysis of Software; Simulation of Laser Cooling and Trapping in Engineering Applications; Large Fluvial Fans and Exploration for Hydrocarbons; Doping-Induced Interband Gain in InAs/AlSb Quantum Wells; Development of Software for a Lidar-Altimeter Processor; Upgrading the Space Shuttle Caution and Warning System; and Fractal Reference Signals in Pulse-Width Modulation

Rapid Prototyping of Microfluidic Devices:Realization of Magnetic Micropumps, Fuel Cells and Protein Preconcentrators

With the growing importance of miniaturized energy applications and the development of micro Total Analysis Systems (μTAS), we have realized microfluidic devices, namely, magnetic micropumps, microfluidic fuel cells and membrane-based protein preconcentrators, all having high application potential in future. The choice of rapid prototyping microfabrication technologies and the selection of affordable materials are important aspects, when thinking of commercialization. Thus, we have employed powder blasting, polymer molding and assembly technologies during devices fabrication throughout the thesis. The first type of microfluidic device that we present is a poly(methyl methacrylate) (PMMA) ball-valve micropump with two different designs of the electromagnetic actuator, as optimized by the finite element method. The integration of a permanent magnet in a flexible polydimethylsiloxane (PDMS) membrane, which is clamped into PMMA structure, is proposed for providing a large stroke of the pumping membrane, making the micropump bubble-tolerant and self-priming Focusing on low power consumption for μTAS integration, another type of magnetic micropump with active valves is realized. It consists of a microfluidic chamber structure in glass that is assembled with a PDMS sheet, which comprises two valving membranes and a central actuation membrane, having each an integrated permanent magnet that is peristaltically actuated by a rotating arc-shaped permanent magnets assembly. A lumped circuit model is developed to predict and describe the frequency-dependent flow rate behavior for this type of pump. Powder blasting and PDMS molding rapid prototyping technologies are employed for realization of these two types of micropumps. Fuel cells with fluid delivery and removal options, having chemical reaction sites and electrode structures that can be realized in a microfluidic format, have high potential for applications. Therefore, microfluidic direct methanol fuel cells with embedded ion- permselective medium are studied and such type of fuel cell is realized by integrating a narrow Nafion strip in a molded elastomeric structure. A mechanical clamping assembly technology enables leakage-free operation and stable performance. The characterization reveals its output power density, using H2O2-based oxidant, is among the high-performance direct methanol fuel cells in microscale. Re-using the technology of the fuel cell chip, with its particular ion-permselective Nafion membrane and assembly method, we also have developed a protein preconcentrator with high purification performance. Our device can preconcentrate negatively charged biomolecules located at the anodic compartment side of the Nafion strip within only a few minutes with a high preconcentration factor. Moreover, a complex microfluidic finite element model is proposed to study and understand the physics of the preconcentration effect. Finally, we conclude the thesis with an outlook on future developments based on our work of the project and on the assembly technologies for microfluidic device integration