Design and Analysis of Ultrasonic Horns Operating in Multiple Vibration Modes

A number of recent studies have shown that combining different modal responses can provide opportunities to improve the vibration behaviour of the output faces of tuned ultrasonic horns to provide a more effective use of the ultrasonic energy. Investigation the benefits of combining different modal responses with a view to optimizing the energy transfer from a range of power ultrasonic devices that rely on tuned horns is essential. This research will therefore aim to investigate the use of combining and exciting different vibration modes in order to design more effective resonant horns for use in high power ultrasonics applications such as metal forming, welding, cleaning and surgical devices. The research is extended to study the possibility of design an ultrasonic transducer which can operate in multiple vibration modes by modify its geometric features. The longitudinal- torsional mode is selected first because of its wide applications in ultrasonic field. The effect of geometrical modifications of transducer's matching part is being analyzed analytically, numerically and experimentally. The suggested modifications are including cut of slots and reduce the cross sectional area so that the excited longitudinal vibrational mode can be regenerated into a longitudinal-torsional mode. The considerations of simplicity of manufacturing and exciting and the efficient of energy conversion are the main advantages of the proposed transducer. Keywords–ultrasonic transducer, design horn; resonant frequency; model and harmonic analysis DOI: 10.7176/JIEA/9-3-02 Publication date:May 31st 201

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

Ultrasonic disinfection using large area compact radial mode resonators

Ultrasonic water treatment is based on the ability of an ultrasonic device to induce cavitation in the liquid, generating physical and chemical effects that can be used for biological inactivation. Effective treatment requires the ultrasonic device to generate intense cavitation field in a large treatment volume. Most conventional ultrasonic radiators fulfil only the first of these two requirements, rendering such devices highly unsuitable for use in high-volume, high-flow liquid processes. The present research investigates the design and performance of a new type of radial resonator in terms of their electromechanical characteristics, nonlinear behaviour, and their ability to treat synthetic ballast water with lower power consumption and short treatment times. The radial resonators were designed using finite element (FE) modelling, and the best designs related to their predicted modal behaviour and vibration uniformity were selected for fabrication and experimental evaluation. Experimental modal analysis (EMA) of the radial resonators showed excellent correlation with the FE models, deviating by only 0.3% at the tuned mode. Impedance analysis showed that the mechanical quality factor of the radial resonators are 28–165% higher than the commercial high-gain probe, but their coupling coefficients are 40–45% lower. Harmonic response characterisation (HRC) revealed shifts in the resonance frequencies at elevated excitation voltages. Duffing-like behaviour were observed in all resonators. RP-1 exhibited the Duffing-like behaviour to a far greater extent compared to the RPS-16 and RPST-16 multiple orifice resonators, indicating the influence of geometric parameters on the overall stiffness of the structure. Finally, experiments with Artemia nauplii and Daphnia sp. showed excellent biological inactivation capability of the radial resonators. Comparison with previous studies showed that 90% reduction in Artemia nauplii can be achieved with up to 33% less energy and using just one radial resonator compared to the dozens of conventional resonators used in precedent investigations. The present research have successfully demonstrated the use of FE modeling, EMA, and HRC to develop, validate, and characterise a new type of radial resonator. Experimental analysis showed that the radial resonators exhibited promising electrical, mechanical, and acoustical characteristics that has the potential to be cost-efficient, scalable, and a viable alternative water treatment method

Applied Measurement Systems

Measurement is a multidisciplinary experimental science. Measurement systems synergistically blend science, engineering and statistical methods to provide fundamental data for research, design and development, control of processes and operations, and facilitate safe and economic performance of systems. In recent years, measuring techniques have expanded rapidly and gained maturity, through extensive research activities and hardware advancements. With individual chapters authored by eminent professionals in their respective topics, Applied Measurement Systems attempts to provide a comprehensive presentation and in-depth guidance on some of the key applied and advanced topics in measurements for scientists, engineers and educators

Master of Science

thesisThe design, working principle, fabrication, and characterization of ultrasensitive ferromagnetic and magnetoelectric magnetometer are discussed in this thesis. Different manufacturing techniques and materials were used for the fabrication of the two versions of the magnetometer. The ferromagnetic microelectromechanical systems (MEMS) magnetometer was fabricated using low-pressure chemical vapor deposition (LPCVD) of silicon nitride, yielding low compressive stress, followed by patterning. The built-in stress was found to be -14 Mpa using Tencor P-10 profilometer. A neodymium magnet (NdFeB) was used as a foot-mass to increase the sensitivity of the device. A coil (Ø=3 cm), placed at a distance from the sensor (2.5-15 cm), was used to produce the magnetic field. The response of the ferromagnetic MEMS magnetometer to the AC magnetic field was measured using Laser-Doppler vibrometer. The ferromagnetic sensor's average temperature sensitivity around room temperature was 11.9 pV/pT/-C, which was negligible. The resolution of the ferromagnetic sensor was found to be 27 pT (1 pT = 10-12 T). To further improve the sensitivity and eliminate the use of the optical detection method, we fabricated a Lead Zirconate titanate (PZT) based magnetoelectric sensor. The sensor structure consisted of a 9 mm long, and 0.17 mm thick PZT beam of varying widths. A neodymium permanent magnet was used as a foot-mass in this case as well. The magnetic field from the coil generated a driving force on the permanent magnet. The driving force displaced the free end of the PZT beam and generated a proportional voltage in the PZT layer. The magnetoelectric coupling, i.e., the coupling between mechanical and magnetic field, yielded a sensor resolution of ~40 fT (1 fT = 10-15 T); an improvement by three orders of magnitude. We used high permeability Mu sheets (0.003"") attached to copper plates (0.125"") to shield stray magnetic fields around the sensor. For both the ferromagnetic MEMS and the magnetoelectric magnetometer, the initial output was improved by using external bias and parametric amplification. By applying an external DC magnetic field bias to the sensor, the effective spring compliance of the sensor was modified. Electronic feedback reduced the active noise limiting the sensor's sensitivity. We used magnetic coupling to enhance the sensors' sensitivity and to reduce the electronic noise. Two identical sensors, with identical foot-mass (permanent magnet), was used to show coupling. The magnet on one of the sensors was mounted in NS polarity, whereas, on the other it was in SN polarity. When excited by the same external AC magnetic field (using coil), one of the sensors was pulled towards the coil and the other was pushed away from it. Adding the individual sensor output, using a preamplifier, an overall increase in sensors' output was observed. The techniques mentioned above helped to improve the output from the sensor. The sensitivity of the sensor can be improved further by using a 3-axis magnetic field cancellation system, by eliminating the AC and DC stray magnetic field, by using coupled-mode resonators and by increasing the surface field intensity of the foot-mass. The magnetometers, thus, developed can be used for mapping the magnetic print of the brain