Design of Autonomous Underwater Vehicle and Optimization of Hydrodynamic Properties and Control

Autonomous vehicles are becoming more and more prevalent in military, private industry and residential applications. Unfortunately, research currently being done in the area of autonomous underwater craft is often hindered by expense. It was desired to build a craft at WPI which could serve as an inexpensive test-bed for future research and implementation of control algorithms, etc. The vehicle\u27s construction required the design and manufacture of a number of components including water-jet stabilization thrusters, propeller driven main thrusters, a complete multi-hub electronic sensor and drive control system and individual sensors such as a tri-axial sonar unit as well as a capacitance based water-leak sensor. A Lexan heat forming process was also developed for hull construction

Microaccelerometer with mechanically-latched memory

A new mechanically-latching micromachined accelerometer is designed in this thesis based on the large deflection of a microcantilever beam. This surface micromachined device moves in the plane of the substrate surface. This device is surface micromachined with no backside etching needed. The interaction of the friction tether and the dimensions of the cantilever beam have been modeled and calculated. The design acceleration sensitivity range is from 100G to 1000G. The photomask set has been designed by using the Mentor Graphics system. The dimension of individual accelerometers ranges from 100 to 1000 micrometers in length to tens of micrometers in width. A special prototype mask containing 8 latched microaccelerometers has been designed with 3 levels and an overall dimension of 5*5 mm. Fabrication techniques for this accelerometer are described. This proposed cantilever beam is to be fabricated by low pressure chemical vapor deposition. A test station for creating a controlled acceleration has been designed and constructed. The test acceleration can be created in the range from 0 to 200G

The Use of a Capacitive Sensor Matrix to Determine the Grip Forces Applied to the Olive Hand Held Harvesters

The hand held olive harvesters increase the work productivity but they submit the operator’s hand arm system to high vibration level values and to relevant efforts to drive them through the tree branches. Many scientific works demonstrate that a correlation exists among the intensity of vibration, their direction and the grip force applied by the operators’ hands. It is not easy to measure these parameters, unless instruments which permit the measurement in an objective way are available. Aim of the work is to present the results of the application of a measurement instrument that allows to detach the operator’s hands grip force applied to drive the olive harvesting shaker. This device is done using a capacitive sensor matrix that can be wrapped around the machine handlebars. The matrix is thin (approximately 0.9 millimetres of thickness): for this reason its presence does not modify the operator’s behaviour and allows to obtain measures of the pressure dynamic contact distribution and its time history. In this way we have the grip forces applied by the operator’s hand over the machine handlebars. This matrix has been fixed over olive harvesting machine handlebars and the grip forces time histories have been recorded. The tests have been carried out in a laboratory simulating the olive harvesting operations by means of the arms movements towards to targets positioned at different heights. Obtained results permit to appreciate both the grip force time history and the spatial force application: with the spatial and temporal applied force values, more ergonomic solutions and implementations are possible for olive hand held harvesters

Acoustic Simulation and Characterization of Capacitive Micromachined Ultrasonic Transducers (CMUT)

Ultrasonic transducers are used in many fields of daily life, e.g. as parking aids or medical devices. To enable their usage also for mass applications small and low- cost transducers with high performance are required. Capacitive, micro-machined ultrasonic transducers (CMUT) offer the potential, for instance, to integrate compact ultrasonic sensor systems into mobile phones or as disposable transducer for diverse medical applications. This work is aimed at providing fundamentals for the future commercialization of CMUTs. It introduces novel methods for the acoustic simulation and characterization of CMUTs, which are still critical steps in the product development process. They allow an easy CMUT cell design for given application requirements. Based on a novel electromechanical model for CMUT elements, the device properties can be determined by impedance measurement already. Finally, an end-of-line test based on the electrical impedance of CMUTs demonstrates their potential for efficient mass production

Performance improvement of MEMS accelerometers in vibration based diagnosis

Vibration measurement and analysis has been an accepted method since decades to meet a number of objectives - machinery condition monitoring, dynamic qualification of any designed structural components, prediction of faults and structural aging-related problems, and several other structural dynamics studies and diagnosis. However, the requirement of the vibration measurement at number of locations in structures, machines and/or equipments makes the vibration measurement exorbitant if conventional piezoelectric accelerometers are used. Hence, there is a need for cheaper and reliable alternative for the conventional accelerometers. The Micro-Electro-Mechanical Systems (MEMS) accelerometers are one such cheap alternative. However, a significant deviation in the performance of the MEMS accelerometers has been observed in earlier research studies and also confirmed by this presented study when compared with well known conventional accelerometer. Therefore, two methods have been suggested to improve the performance of the existing MEMS accelerometers; one for correction in time domain and other in frequency domain. Both methods are based on the generation of a characteristic function (CF) for the MEMS accelerometer using well known reference accelerometer in laboratory tests. The procedures of both methods have been discussed and validations of these methods have been presented through experimental examples. In addition, a Finite Element (FE) model of a typical MEMS accelerometer has been developed and modal analysis has been carried out to understand the dynamics of capacitive type MEMS accelerometer and to identify the source of errors. It has been observed that the moving fingers behave like a cantilever beam while the fixed fingers showed rigid body motion. This cantilever type of motion seems to be causing non-parallel plates effect in the formed capacitors between moving and fixed fingers which results in errors in the vibration measurement. Hence, design modifications on finger shape have been suggested to remove the cantilever motion and results showed remarkable improvement. Moreover, the effect of using synchronous amplitude modulation and demodulation in the readout circuit has been studied. The experimental study showed that this circuit also introduces errors in amplitude and phase of the output signal compared with the input signal. Thus, in the new design of MEMS accelerometers, improvements in both mechanical design and electronic circuit are required.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Convergence of Parametric Resonance and Vibration Energy Harvesting

Energy harvesting is an emerging technology that derives electricity from the ambient environment in a decentralised and self-contained fashion. Applications include self-powered medical implants, wearable electronics and wireless sensors for structural health monitoring. Amongst the vast options of ambient sources, vibration energy harvesting (VEH) has attracted by far the most research attention. Two of the key persisting issues of VEH are the limited power density compared to conventional power supplies and confined operational frequency bandwidth in light of the random, broadband and fast-varying nature of real vibration. The convention has relied on directly excited resonance to maximise the mechanical-to-electrical energy conversion efficiency. This thesis takes a fundamentally different approach by employing parametric resonance, which, unlike the former, its resonant amplitude growth does not saturate due to linear damping. Therefore, parametric resonance, when activated, has the potential to accumulate much more energy than direct resonance. The vibrational nonlinearities that are almost always associated with parametric resonance can offer a modest frequency widening. Despite its promising theoretical potentials, there is an intrinsic damping dependent initiation threshold amplitude, which must be attained prior to its onset. The relatively low amplitude of real vibration and the unavoidable presence of electrical damping to extract the energy render the onset of parametric resonance practically elusive. Design approaches have been devised to passively minimise this initiation threshold. Simulation and experimental results of various design iterations have demonstrated favourable results for parametric resonance as well as the various threshold-reduction mechanisms. For instance, one of the macro-scale electromagnetic prototypes (∼1800 cm3) when parametrically driven, has demonstrated around 50% increase in half power band and an order of magnitude higher peak power (171.5 mW at 0.57 ms−2) in contrast to the same prototype directly driven at fundamental resonance (27.75 mW at 0.65 ms−2). A MEMS (micro-electromechanical system) prototype with the additional threshold-reduction design needed 1 ms−2 excitation to activate parametric resonance while a comparable device without the threshold-reduction mechanism required in excess of 30 ms−2. One of the macro-scale piezoelectric prototypes operated into auto-parametric resonance has demon-strated notable further reduction to the initiation threshold. A vacuum packaged MEMS prototype demonstrated broadening of the frequency bandwidth along with higher power peak (324 nW and 160 Hz) for the parametric regime compared to when operated in room pressure (166 nW and 80 Hz), unlike the higher but narrower direct resonant peak (60.9 nW and 11 Hz in vacuum and 20.8 nW and 40 Hz in room pressure). The simultaneous incorporation of direct resonance and bi-stability have been investigated to realise multi-regime VEH. The potential to integrate parametric resonance in the electrical domains have also been numerically explored. The ultimate aim is not to replace direct resonance but rather for the various resonant phenomena to complement each other and together harness a larger region of the available power spectrum

A Three – tier bio-implantable sensor monitoring and communications platform

One major hindrance to the advent of novel bio-implantable sensor technologies is the need for a reliable power source and data communications platform capable of continuously, remotely, and wirelessly monitoring deeply implantable biomedical devices. This research proposes the feasibility and potential of combining well established, ‘human-friendly' inductive and ultrasonic technologies to produce a proof-of-concept, generic, multi-tier power transfer and data communication platform suitable for low-power, periodically-activated implantable analogue bio-sensors. In the inductive sub-system presented, 5 W of power is transferred across a 10 mm gap between a single pair of 39 mm (primary) and 33 mm (secondary) circular printed spiral coils (PSCs). These are printed using an 8000 dpi resolution photoplotter and fabricated on PCB by wet-etching, to the maximum permissible density. Our ultrasonic sub-system, consisting of a single pair of Pz21 (transmitter) and Pz26 (receiver) piezoelectric PZT ceramic discs driven by low-frequency, radial/planar excitation (-31 mode), without acoustic matching layers, is also reported here for the first time. The discs are characterised by propagation tank test and directly driven by the inductively coupled power to deliver 29 μW to a receiver (implant) employing a low voltage start-up IC positioned 70 mm deep within a homogeneous liquid phantom. No batteries are used. The deep implant is thus intermittently powered every 800 ms to charge a capacitor which enables its microcontroller, operating with a 500 kHz clock, to transmit a single nibble (4 bits) of digitized sensed data over a period of ~18 ms from deep within the phantom, to the outside world. A power transfer efficiency of 83% using our prototype CMOS logic-gate IC driver is reported for the inductively coupled part of the system. Overall prototype system power consumption is 2.3 W with a total power transfer efficiency of 1% achieved across the tiers