Thermal characteristics of the 12-gigahertz, 200-watt output stage tube for the communications technology satellite

A description of the methods used to measure component temperatures and heat-rejection rates in a simulated space environment on output stage tubes (OST's) developed for the Communications Technology Satellite is presented along with summaries of experimentally determined values. The OST's were operated over the entire anticipated operating drive range, from the dc beam (zero drive) condition to the 6-db overdrive condition. The baseplate temperature was varied from -10 to 58 C with emphasis placed on the testing done at 45 C, the normal anticipated operating temperature. The heat-rejection rate of the OST baseplate ranged from 7.6 W at the dc beam condition to 184.5 W at the 6-db overdrive condition; the heat-rejection rate of the multistage depressed collector (MDC) cover ranged from 192.2 to 155.9 W for the same conditions. The maximum OST temperature measured on the MDC cover was 227 C during a dc beam test. The minimum temperature measured, also on the MDC cover, was -67.5 C at the end of an extended simulated eclipse test period. No effects were observed on the OST thermal characteristics due to vibration testing or temperature-reversal cycle testing

Low-power silicon planar micro-calorimeter employing nanostructured catalyst

This thesis describes the development of silicon planar micro-calorimetric gas sensors employing a nanostructured palladium (Pd) catalyst. Present commercial, bead-type calorimetric sensors have been manufactured for nearly forty years and are used in many applications, such as mining, water treatment and emergency services, with an estimated European market value of €221M by 2004. However, recent advances in both silicon micro-machining and nano materials have created the technologies necessary to transform the present labour-intensive fabrication process in to a new low-cost batch production. In addition, a reduction in power consumption, improved sensitivity and increased poisoning resistance of the sensor can also be achieved. Here, two generations of micro-calorimeter have been designed and fabricated comprising a silicon membrane structured micro-hotplate that can reach up to a temperature of 870'C without failure and an ultra-high surface area nanoporous Pd catalyst (about 20 m2/g), typically 25 run thick, deposited electrochemically on top of a gold electrode above the micro-heater. The exothermic reaction caused by the target gas (e.g. methane) interacting with the Pd catalyst results in an increase in the temperature and so resistance of the micro-heater. A Wheatstone bridge interface circuit is normally used to detect and measure the fractional resistance change. Full 3-D thermo-mechanical simulations have been performed employing experimental data in order to establish a simulation database for future developments. The differences between simulated and experimental results were found to be as low as 4.6%. The response of the sensors has been characterised in both continuous powering mode and pulse modulation powering mode. Device power consumption is only 50mW at 500'C in continuous mode, which is up to 100mW lower than that for commercial sensors. Typical response times of 2ms have been measured and so further power saving can be achieved when the sensors are operated in a pulse mode, e.g. 50% duty-cycle at 10Hz. Hence, an overall power saving of 75% could be achieved compared to commercial product. Infrared thermography revealed that a centre hot spot, commonly found with meander style micro-heaters, has been eliminated by the new drive-wheel micro-heater design. The sensitivity of the sensors has also been improved, up to a factor of 4 at 500'C ((60 mV/mm2)/%CH4), by the nanoporous catalyst and by heating it more isothermally. Furthermore, improvements have also been found on the poisoning resistance. Therefore, the potential commercialisation of the micro-calorimeter is very promising

Measurement of electrical properties of electrode materials for the bakelite Resistive Plate Chambers

Single gap (gas gap 2 mm) bakelite Resistive Plate Chamber (RPC) modules of various sizes from 10 cm \times 10 cm to 1 m \times 1 m have been fabricated, characterized and optimized for efficiency and time resolution. Thin layers of different grades of silicone compound are applied to the inner electrode surfaces to make them smooth and also to reduce the surface resistivity. In the silicone coated RPCs an efficiency > 90% and time resolution \sim 2 ns (FWHM) have been obtained for both the streamer and the avalanche mode of operation. Before fabrication of detectors the electrical properties such as bulk resistivity and surface resistivity of the electrode materials are measured carefully. Effectiveness of different silicone coating in modifying the surface resistivity was evaluated by an instrument developed for monitoring the I-V curve of a high resistive surface. The results indicate definite correlation of the detector efficiency for the atmospheric muons and the RPC noise rates with the surface resistivity and its variation with the applied bias voltage. It was also found that the surface resistivity varies for different grades of silicone material applied as coating, and the results are found to be consistent with the detector efficiency and noise rate measurements done with these RPCs.Comment: 9 Pages, 6 figure

Measurement of electrical properties of electrode materials for the bakelite Resistive Plate Chambers

Single gap (gas gap 2 mm) bakelite Resistive Plate Chamber (RPC) modules of various sizes from 10 cm \times 10 cm to 1 m \times 1 m have been fabricated, characterized and optimized for efficiency and time resolution. Thin layers of different grades of silicone compound are applied to the inner electrode surfaces to make them smooth and also to reduce the surface resistivity. In the silicone coated RPCs an efficiency > 90% and time resolution \sim 2 ns (FWHM) have been obtained for both the streamer and the avalanche mode of operation. Before fabrication of detectors the electrical properties such as bulk resistivity and surface resistivity of the electrode materials are measured carefully. Effectiveness of different silicone coating in modifying the surface resistivity was evaluated by an instrument developed for monitoring the I-V curve of a high resistive surface. The results indicate definite correlation of the detector efficiency for the atmospheric muons and the RPC noise rates with the surface resistivity and its variation with the applied bias voltage. It was also found that the surface resistivity varies for different grades of silicone material applied as coating, and the results are found to be consistent with the detector efficiency and noise rate measurements done with these RPCs.Comment: 9 Pages, 6 figure

Thermal Microfluidic Devices; Design, Fabrication and Applications

This thesis investigates the thermal actuation and temperature measurement methods in microfluidic devices. We designed and fabricated microfluidic devices with various functionalities such as: bio sensing, particle counting, microscale calorimetry, and cellular temperature measurement. All of these functionalities use thermal measurement methods. When quantitative measurements are required, the label-free nature of thermal measurement methods, along with its simple readout, make it a powerful candidate for lab on a chip and bio sensing/detection applications. In this work, thermal measurement methods are used to characterize bio-samples, measure concentrations, study thermal responses, and even perform particle cytometry. However, thermal measurement methods are known for their low speed and low sensitivity characteristics, which are influenced by thermal properties of materials and structural design. On the microscale, we designed and fabricated microfluidic structures with modified thermal properties to achieve low response times and high sensitivity. To optimize our devices, we analyzed the thermal responses of the designed structures using a first order equivalent electrical circuit model. We then compared the results of the model to the fabricated device responses. To increase the functionality of our device, we used a number of temperature measurement techniques; thermal wave analysis, AC calorimetry, time of flight measurement, and the continuous recording of differential temperature. In this work, we fabricated an on-chip calorimeter with a 200 nL chamber volume and measured specific heat and thermal conductivity of water and glycerol. Also, we measured the thermal properties of the ionic liquids with the calorimeter. Moreover, we fabricated a calorimetric microfluidic biosensor to detect and measure the glucose levels of blood with concentrations of 0.05 to 0.3% wt/vol. We applied the same method to measure DNA concentration in buffer solution and a protein binding reaction. Also, we developed a method to count the number of particles passing through a micro channel while simultaneously measuring the size deference between particles by measuring changes in thermal conductivity. We fabricated a microfluidic platform to capture a single cell to measure the temperature of the cell in response to an external stimulation

Precision control of thermal transport in cryogenic single-crystal silicon devices

We report on the diffusive-ballistic thermal conductance of multi-moded single-crystal silicon beams measured below 1 K. It is shown that the phonon mean-free-path $\ell$ is a strong function of the surface roughness characteristics of the beams. This effect is enhanced in diffuse beams with lengths much larger than $\ell$, even when the surface is fairly smooth, 5-10 nm rms, and the peak thermal wavelength is 0.6 $\mu$m. Resonant phonon scattering has been observed in beams with a pitted surface morphology and characteristic pit depth of 30 nm. Hence, if the surface roughness is not adequately controlled, the thermal conductance can vary significantly for diffuse beams fabricated across a wafer. In contrast, when the beam length is of order $\ell$, the conductance is dominated by ballistic transport and is effectively set by the beam area. We have demonstrated a uniformity of $\pm$8% in fractional deviation for ballistic beams, and this deviation is largely set by the thermal conductance of diffuse beams that support the micro-electro-mechanical device and electrical leads. In addition, we have found no evidence for excess specific heat in single-crystal silicon membranes. This allows for the precise control of the device heat capacity with normal metal films. We discuss the results in the context of the design and fabrication of large-format arrays of far-infrared and millimeter wavelength cryogenic detectors

Building blocks of a silicon photonic integrated wavelength division multiplexing transmitter for detector instrumentation = Bausteine für einen integrierten siliziumphotonischen Wellenlängenmultiplexsender zur Detektorinstrumentierung

In dieser Arbeit werden Datenübertragungssysteme für die Detektorinstrumentierung und die Herausforderungen dieser einzigartigen Anwendung untersucht. Begrenzt durch die hohe Strahlungsintensität, den verfügbaren Platz, niedrige Temperaturen usw., liegt die Auslesebandbreite von Detektoren nach dem derzeitigen Stand der Technik im Bereich von einigen zehn Gb/s pro Faser. Angesichts des ständig wachsenden Datenvolumens ist die Verbesserung der Übertragungsbandbreite ein dringend zu lösendes Problem. Daher wird in dieser Arbeit ein universell einsetzbares Konzept für einen integrierten, siliziumphotonischen Sender auf Basis der Wellenlängenmultiplex-Technologie vorgeschlagen. Die angestrebte Übertragungsbandbreite in der ersten Version beträgt 40 Gb/s. Zwei Schlüsselbausteine des integrierten Senders, der Mach-Zehnder-Modulator und der Wellenlängen-Demultiplexer, werden im Detail untersucht. Eine Reihe von Modulatoren mit unterschiedlichen Längen und Ätztiefen werden entworfen, hergestellt und charakterisiert. Für den Entwurf des Demultiplexers wird eine angepasste Entwurfsmethode entwickelt, die mit zwei dedizierten Brennpunkten arbeitet. Ein neuer Entwurfsparameter wird in diese Methode eingeführt, um sie flexibler und leichter anwendbar zu machen. Die Auswirkung der Modifizierung des eingeführten Parameters wird anhand einer Reihe vergleichbarer Bauelemente untersucht. Alle Charakterisierungen bestätigen die Machbarkeit des vorgeschlagenen Konzepts

Microwave Driven Magnetic Plasma Accelerator Studies (CYCLOPS)

A microwave-driven cyclotron resonance plasma acceleration device was investigated using argon, krypton, xenon, and mercury as propellants. Limited ranges of propellant flow rate, input power, and magnetic field strength were used. Over-all efficiencies (including the 65% efficiency of the input polarizer) less than 10% were obtained for specific impulse values between 500 and 1500 sec. Power transfer efficiencies, however, approached 100% of the input power available in the right-hand component of the incident circularly polarized radiation. Beam diagnostics using Langmuir probes, cold gas mapping, r-f mapping and ion energy analyses were performed in conjunction with an engine operating in a pulsed mode. Measurements of transverse electron energies at the position of cyclotron resonant absorption yielded energy values more than an order of magnitude lower than anticipated. The measured electron energies were, however, consistent with the low values of average ion energy measured by retarding potential techniques. The low values of average ion energy were also consistent with the measured thrust values. It is hypothesized that ionization and radiation limit the electron kinetic energy to low-values thus limiting the energy which is finally transferred to the ion. Thermalization by electron-electron collision was also identified as an additional loss mechanism. The use of light alkali metals, which have relatively few low lying energy levels to excite, with the input power to mass ratio selected so as to limit the electron energies to less than the second ionization potential, is suggested. It is concluded, however, that the over-all efficiency for such propellants would be less than 40 per cent

Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies