Fabrication of microchannels for use in micro-boiling experiments

Increased power densities in VLSI chips have led to a need to develop cooling methods that can cope with the increased heat produced by such chips. Currently one of the more attractive methods to meet this goal is through the use of two phase flow of a fluid as changing phase of the material allows high heat transfer rates for a low temperature change. To bring this technology to commercialisation a greater understanding of the underlying physics involved at the microscale is required as there is much debate within literature as to what occurs during two phase flow heat transfer at these scales. The work conducted as part of this thesis is a step towards improving the understanding of the mechanisms involved with this process. This thesis describes the fabrication of a novel microchannel structure, which can be used to experimentally characterise two phase heat transfer as it occurs. The final process reported for these microchannels structures provides the basis of a technology for the fabrication of microchannels with increased sensor densities. Two types of microchannel devices have been fabricated for this project. The first device of these was an array of parallel microchannels formed by the reactive ion etching (RIE) of silicon, which was then bonded with Pyrex glass. These microchannels were simple in that sensors were not integrated for local measurement. However the production of these devices incorporated fabrication techniques such as anodic bonding and inductively coupled plasma RIE that were essential to the fabrication of more complex devices. The second device built was a single microchannel that contained an integrated heater and several temperature sensors. The use of wafer bonding enabled the device to take full advantage of both bulk and surface micromachining technology as the placement of the temperature sensors on the channel floor would not be possible with conventional bulk micromachining. The initial microchannel structures demonstrated that wafer bonding could be used to fabricate novel devices, but they highlighted the difficulty of achieving strong anodic bonds due to the presence of dielectric films throughout the fusion bonded wafer stack used in the channel fabrication. To improve the performance of the device the process was optimised through the use of insitu, non-destructive test structures. These structures enabled the uniformity and strength of the bonds to be optimised through visualisation over the whole wafer surface. The integrated sensors enabled temperature measurements to be taken along the channel with a sensitivity 3.60 ΩK-1 while the integrated heater has delivered a controllable and uniform heat flux of 264 kWm-2

Cluster Based Term Weighting Model for Web Document Clustering

The term weight is based on the frequency with which the term appears in that document. The term weighting scheme measures the importance of a term with respect to a document and a collection. A term with higher weight is more important than a term with lower weight. A document ranking model uses these term weights to find the rank of a document in a collection. We propose a cluster-based term weighting models based on the TF-IDF model. This term weighting model update the inter-cluster and intra-cluster frequency components uses the generated clusters as a reference in improving the retrieved relevant documents. These inter cluster and intra-cluster frequency components are used for weighting the importance of a term in addition to the term and document frequency components

Wireless Power Transfer Techniques for Implantable Medical Devices:A Review

Wireless power transfer (WPT) systems have become increasingly suitable solutions for the electrical powering of advanced multifunctional micro-electronic devices such as those found in current biomedical implants. The design and implementation of high power transfer efficiency WPT systems are, however, challenging. The size of the WPT system, the separation distance between the outside environment and location of the implanted medical device inside the body, the operating frequency and tissue safety due to power dissipation are key parameters to consider in the design of WPT systems. This article provides a systematic review of the wide range of WPT systems that have been investigated over the last two decades to improve overall system performance. The various strategies implemented to transfer wireless power in implantable medical devices (IMDs) were reviewed, which includes capacitive coupling, inductive coupling, magnetic resonance coupling and, more recently, acoustic and optical powering methods. The strengths and limitations of all these techniques are benchmarked against each other and particular emphasis is placed on comparing the implanted receiver size, the WPT distance, power transfer efficiency and tissue safety presented by the resulting systems. Necessary improvements and trends of each WPT techniques are also indicated per specific IMD

High Affinity Mannotetraose as an Alternative to Dextran in ConA Based Fluorescent Affinity Glucose Assay Due to Improved FRET Efficiency

Diabetes mellitus affects millions of people worldwide and requires that individuals tightly self-regulate their blood glucose levels to minimize the associated secondary complications. Continuous monitoring devices potentially offer patients a long-term means to tightly monitor their glucose levels. In recent years, fluorescent affinity sensors based on lectins (e.g., Concanavalin A (ConA)) have been implemented in such devices. Traditionally, these sensors pair the lectin with a multivalent ligand, like dextran, in order to develop a competitive binding assay that changes its fluorescent properties in response to the surrounding glucose concentrations. This work introduces a new type of fluorescent ligand for FRET-based assays in an attempt to improve the sensitivity of such assays. This ligand is rationally designed to present a core trimannose structure and a donor fluorophore in close proximity to one another. This design decreases the distance between the FRET donor and the FRET acceptors on ConA to maximize the FRET efficiency upon binding of the ligand to ConA. This work specifically compares the FRET efficiency and sensitivity of this new competing ligand with a traditional dextran ligand, showing that the new ligand has improved characteristics. This work also tested the long-term thermal stability of the assay based on this new competing ligand and displayed a MARD of less than 10% across the physiological range of glucose after 30 days incubation at 37 °C. Ultimately, this new type of fluorescent ligand has the potential to significantly improve the accuracy of continuous glucose monitoring devices based on the competitive binding sensing approach

Ultrasound capsule endoscopy:sounding out the future

Video capsule endoscopy (VCE) has been of immense benefit in the diagnosis and management of gastrointestinal (GI) disorders since its introduction in 2001. However, it suffers from a number of well recognized deficiencies. Amongst these is the limited capability of white light imaging, which is restricted to analysis of the mucosal surface. Current capsule endoscopes are dependent on visual manifestation of disease and limited in regards to transmural imaging and detection of deeper pathology. Ultrasound capsule endoscopy (USCE) has the potential to overcome surface only imaging and provide transmural scans of the GI tract. The integration of high frequency microultrasound (µUS) into capsule endoscopy would allow high resolution transmural images and provide a means of both qualitative and quantitative assessment of the bowel wall. Quantitative ultrasound (QUS) can provide data in an objective and measurable manner, potentially reducing lengthy interpretation times by incorporation into an automated diagnostic process. The research described here is focused on the development of USCE and other complementary diagnostic and therapeutic modalities. Presently investigations have entered a preclinical phase with laboratory investigations running concurrently

Integrated Front End Circuitry for Microultrasound Capsule Endoscopy

Video capsule endoscopy (VCE) was originally developed to address the limitation of conventional endoscopy in accessing the small bowel as a remote part of the gastrointestinal tract. To further enhance the diagnostic ability of VCE, microultrasound capsule endoscopy is under development for identification of disease at an earlier stage and visualisation of subsurface tissue features. This paper presents an evaluation of two approaches to improve signal to noise ratio (SNR) in rapid prototyped capsule endoscopes. First, noise reduction techniques are applied to the integrated front-end circuits in the prototype capsules. Secondly, multiple types of coded excitation transmission are tested and benchmarked with respect to non-coded transmission. Results are presented for both bench top phantom imaging and in vivo translational trial imaging

Sensors for foetal hypoxia and metabolic acidosis: a review

This article reviews existing clinical practices and sensor research undertaken to monitor fetal well-being during labour. Current clinical practices that include fetal heart rate monitoring and fetal scalp blood sampling are shown to be either inadequate or time-consuming. Monitoring of lactate in blood is identified as a potential alternative for intrapartum fetal monitoring due to its ability to distinguish between different types of acidosis. A literature review from a medical and technical perspective is presented to identify the current advancements in the field of lactate sensors for this application. It is concluded that a less invasive and a more continuous monitoring device is required to fulfill the clinical needs of intrapartum fetal monitoring. Potential specifications for such a system are also presented in this paper

Translational trial outcomes for capsule endoscopy test devices

Current clinical standards in the endoscopic diagnosis of gastrointestinal diseases are primarily based on the use of optical systems. Ultrasound has established diagnostic credibility in the form of endoscopic ultrasound (EUS), however it is limited to examination of the upper gastrointestinal tract (oesophagus, stomach and upper (proximal) small bowel). Access to the remainder of the small bowel is currently limited to optical capsule endoscopes and a limited number of other modalities as these capsules are restricted to visual examination of the surface or mucosa of the gut wall. Ultrasound capsule endoscopy has been proposed to integrate microultrasound imaging capabilities into the existing capsule format and extend examination capabilities beyond the mucosa. To establish the ability of high frequency ultrasound to resolve the histological structure of the gastrointestinal tract, ex vivo scans of pig and human tissue were performed. This was done using 25 and 34 MHz single element, physically focused composite transducers mechanically scanned along the tissue. Tethered prototype devices were then developed with 30 MHz physically focused polyvinylidene fluoride (PVDF) single element transducers embedded for use in initial translational trials in the small bowel of porcine subjects. B-scan images from the ex vivo model validation and the in vivo trials are presented

Optimised co-electrodeposition of Fe-Ga alloys for maximum magnetostriction effect

AbstractThe article reports the electrochemical deposition and characterisation of a 600nm thick Fe–Ga alloy film plated on a 20μm thick copper cantilever. The co-electrodeposition process was optimised for the production of Fe–Ga in the ratio of 81% Fe to 19% Ga, which is known to maximize the magnetostriction (MS) effect. The foil was cut into 1mm wide and 5mm long cantilevers and the deflection was measured with DC co-planar magnetic field intensities ranging from 0 to 60kA/m. The maximum strain coefficient λ was measured to be 96ppm for a field strength range 58kA/m. The field strain plot over exhibits a typical second order magnetically induced strain curve, as seen in other magnetostrictive materials

Optimization and characterisation of bonding of piezoelectric transducers using anisotropic conductive adhesive

Bonding technology using anisotropic conductive paste shows great promise to achieve the denser integration schemes that are required for the application of high resolution ultrasonic imaging. A design of experiments has been carried out to characterize and optimize a flip-chip bonding technology that utilizes a novel, magnetically aligned anisotropic conductive paste. This optimized process has the potential to implement more reliable and electrically conductive, fine pitch bonding for the production of high density ultrasound transducer arrays in needle devices