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Acoustophoresis is an emerging method for tuning the microstructure in composites as a way to improve their functional properties. This method uses standing sound waves to push functional particles in a fluid to the pressure nodes of that field. That patterned arrangement is then transformed into a material with microstructure determined by the pattern of the acoustic field. Controlling the pattern of particles can enables a wide range of functional materials, including patterned energy storage electrodes, flexible electronics, and sensor arrays. Particle patterning via acoustics offers an attractive path to generate a wide variety of 2D periodic patterns that introduce tailorable hierarchical porosity, useful for controlling surface area, transport distances, and other properties. This work explores a variety of improvements to the technique and develops models to allow for informed adjustment and improvement of these processes and patterns. In this work multiple new scalable processing methods are developed. Acoustophoretic direct ink writing is extended from single line printing to simultaneous deposition of many patterned microstructural features. This technique is developed on test materials mimicking the properties of Lithium ion battery electrodes and then successfully demonstrated with actual battery materials to generate large samples of cathodes with controlled microstructure enabling faster charging. This technique is then extended into a new approach which is used to rapidly form 2,400 cm2 of patterned particles. This represents an orders of magnitude increase in the scale of acoustics experiments which has previously been limited to several cm2. To better enable improvements in these systems,the motion of particles in non-newtonian fluids like the battery slurries are modeled using several classic rheological models. Both of these printing approaches generated linear micro-structures. To enable a wider range of microstructural features patterning of particles in multi-wave fields is also explored. A simple energy minimization model is proposed for predicting the patterns that form from high loadings of particles in arbitrary acoustic fields. This model is validated both with more complex discrete particle modeling and with experiments. Development of this model enabled the demonstration of new multi-scale hierarchical microstructures. To further increase microstructural control, systems utilizing fibers are investigated. Acoustic fields can control not only the position of fibers, but also their orientation. Patterning fibers in 2D fields is shown to form grid-like microstructures which span 2D space at very low loadings. Models were developed to describe the motion of fibers in 2D fields and predict what microstructures would form as a function of the applied field and fiber characteristics such as length. Understanding of microstructure gained from this modeling is used to design flexible conductive composites. Finally this work takes a broad look at all of the other existing approaches for manufacturing composites using acoustophoresis, and then proposes new motifs for enabling finer control of more aspects of microstructure in diverse materials systems.

A versatile class of composite materials composed of functional filler particles in polymer matrices are increasingly used in high-performance applications that leverage their adaptable mechanical, electrical, thermal, and other functional properties. The choice of constituent materials largely determines these properties: for example, long fibers redistribute stress efficiently, highly conductive filler particles impart their conductivity to the material, and combinations of ionic and electrically conductive fillers with energy storage materials increase the capacity of battery electrodes. The performance of these composites, however, is highly dependent on the internal arrangement of particles. Consequently, controlling this internal structure enables property improvements and novel functionalities. In particular, combining microstructure control with the design freedom of 3D printing presents opportunities to maximize the performance of functional components by spatially modulating properties and their directionality (e.g. reinforcing high-stress regions, prescribing electrical interconnects, or directing heat away from hot spots), as well as introducing novel combinations of properties.To develop this structural control in printed materials, this work utilizes pressure fields to assemble filler particles into patterns within composites during 3D printing. Particle patterns are engineered to improve material properties by leveraging microscopic acoustic forces on particles, tailoring the particle arrangement for improvements in the functionality of the material. This acoustic patterning technique is integrated into 3D printing with attention to processing constraints (e.g. component and feature sizes, material properties, cost, throughput rate, etc.) required in existing and emerging technological applications. In particular, 3D printed composites with high electrical or thermal conductivity, which are simultaneously mechanically flexible or strain-tolerant, are targeted for advancing the emerging fields of flexible electronics and soft robotics, and for alleviating the bottleneck in cooling of electronic devices.Acoustically patterned composites exhibit increased electrical and thermal conductivity (by many orders of magnitude under some conditions) compared to conventional, unpatterned composites via concentrated particle contact density and optimized transport pathways. Simultaneously, patterning enhances mechanical flexibility by reducing the required loading of filler particles and encapsulating conductive particle networks in thick sheathes of strain-absorbing polymer. The magnitude and directionality of electrical and thermal transport is configurable over a wide range via manipulation of the orientation and connectivity of filler particles, introducing processing routes for printing components with embedded electrical interconnects or directional cooling networks.Computational modeling of acoustic forces probes the design space of possible particle structures, which are compared to detailed particle-level material characterization to understand and then optimize the patterning process for desired microstructures. These structural details inform the physics of electrical and thermal conduction between particles in the material as well as particle rearrangements during mechanical deformation. Finally, this work investigates methods for expanding control over composite microstructure, including patterning hierarchically structured particles and manipulating particles with multiple external fields.

A Position Calibration Method (PCM) is proposed for a single cell measurement with Electrochemical Impedance Spectroscopy (EIS). It improves the measurement accuracy by reducing the error induced by position difference. First, the relationship between the impedance and the position is explored with numerical simulation. The impedance is calculated in different positions of the single cell with the finite model. Second, a mathematical model is established based on the relationship between the impedance and the position. Then, the experiments are conducted to verify the valid of the PCM. In the experiments, Na2O∙CaO∙6SiO particles and Zebrafish eggs are used. The result shows that the impedance near the electrode is less than the center of the sensor, while the impedance of the sensor center is less than the sensor boundary, which is the same as the numerical simulation. Finally, a coincidence degree is employed to evaluate the position calibration method. After position calibration, the coincidence degree of numeric simulation could reach to 99.999%, and the experimental coincidence degree reaches to 99.87%. In this paper, the reasons of impedance varying with positions are also explored. The electric field intensity turns out to be the main internal factor that causes the impedance varying with positions. Furthermore, the PCM is expected to realize the detection of a cell structure.

In this paper the design of coaxial probe feed one layer microstrip patch antenna (MSA) . for 1.433 GHz WLAN application is presented, The impedance equivalent and the radiation physiognomies of this proposed assembly are planned and analyzed. by CPU Simulation Knowledge (CST) Microwave Studio. which is a commercially obtainable electromagnetic simulant founded , on the technique of fixed change time sphere method to attain. the wanted specification, The projected antenna founded on coaxial probe feed structure has the supreme possible bandwidth gotten. around 9.3 MHz -10 dB replication coefficient which agrees to WLAN 1.433 GHz frequency band, the supreme possible gain is 4.48 dB. Stable radiation physiognomies exist found crossways the frequency band .

In this paper, a meta-surface inspired flexible antenna prototype is proposed for bio-medical applications. A 1.5 mm Rogers high frequency laminate with permittivity of 3.3 and loss tangent of 0.002 is used as substrate owing to its flexible nature. The proposed antenna is suitable for on-body applications and as such the performance of the prototype was verified on a multilayer phantom model using HFSS tool. Unique properties of meta-surface make miniaturization of the antenna possible with optimum antenna dimensions of 0.24 λ 0 × 0.15 λ 0 × 0.013 λ 0 . The designed antenna is investigated for on-body applications and thereof it is observed that the radiator radiates in the range of 2.14 GHz − 3.4 GHz resulting in resonance at 2.67 GHz.

The Constitution and the geometry aspects of any sensor is influenced by several factors involved in the assembling of sensor. It is basically influenced by parameter to be measured, method of measuring the measurand, nature of the parameter i.e. weather the parameter is chemical, biological, physical, optical, electrical, magnetic, mechanical or acoustic etc., environment around it, etc. In most of the cases, several sensors are developed, meant to measure a single parameter with maximum achievable sensitivity. In the present paper a fiber optic multipurpose sensor is described, which can be used to measure various physical quantities of liquids with well defined combination at room temperature (30 °C), employing a specific set of materials and methods in the design operation of the sensor. Exploiting all the advantages offered by the fiber optic technology, the sensor was calibrated to measure ultrasonic velocity, refractive index, density, dielectric constant, viscosity, molar volume, acoustic impedance, molar refraction, viscous relaxation time, adiabatic compressibility, free intermolecular length, Gibb’s free energy, absorption coefficient, internal pressure, free volume, mole fraction, concentration, effective mass at room temperature and examined to exhibit superiority in all respects compared to the conventional sensors.

To calibrate non-contact sensors with fast response and high scale factor, it is critical to develop step pulse generators capable of generating standard high voltage step pulses and accurately measuring the generated waveform. In this paper, two types of step pulse generators are designed with output voltages of 2 kV and 100 kV. The 2 kV step pulse generator can generate a step pulse with a rise time of ~300 ps and an adjustable pulse width. A step pulse with a rise time less than 5 ns and a pulse width over 1 s can be generated with the 100 kV step pulse generator. The uncertainty of 2 kV step pulse generator is then analyzed by simulations and experiments. Finally, a performance comparison with step pulse generators in previous studies is carried out. Bandwidth, linearity and repeatability of the sensors can be verified with the designed two step pulse generators.

Wear debris sensing is an important approach for machine condition monitoring. To date, different types of debris sensors have been developed, among which the magnetostatic inductive debris sensor is preferable for monitoring ferromagnetic debris, but the existing induced voltage model cannot be used to quantify wear debris in lube oil. Accordingly, a modeling method was proposed for the debris sensor based on a high-gradient magnetostatic field. First, a Gaussian curve is used to fit the magnetic field along the axis of the sensor. Then, time-harmonic electromagnetic field analysis and Fourier series decomposition are combined to establish an induced voltage model. Furthermore, the influence of the relative permeability, size, and velocity of wear debris and induction coil parameters on the output voltage is analyzed. The results show a linear relationship between the theoretical calculations and experimental results. Therefore, the proposed model can be used to realize quantitative analysis of wear debris, laying a foundation for optimizing the sensor structure, and extracting features from output voltage signals.

The safety issue of robot becomes a key challenge in modern manufacturing industry, especially in the scenario of frequent human-robot collaboration. This paper presents a flexible ultrasonic proximity sensing skin which can be integrated on the surface of robot arm to ensure the safe human-robot collaboration. The sensing skin is composed of three pieces of aluminum nitride based piezoelectric micromachined ultrasonic transducers (PMUTs) arrays at the resonance frequency of 115 kHz and chip size of 4 mm × 4 mm × 0.5 mm. The three pieces of PMUTs arrays are evenly integrated on the flexible printed circuit board (FPCB) with a device size of 8.8 mm × 60 mm × 1.7 mm. The proximity sensing skin can detect obstacles within 300 mm and 60 degrees in front, and shows a large sensing coverage in comparison with capacitive/infrared devices. Besides, it is capable of sensing transparent materials like glass. Finally, since the small size and good scalability of micro-electro-mechanical system (MEMS), the PMUTs are easy to install onto robots and to integrate with other ultrasonic transducers in the future. This PMUTs based sensing skin will greatly enhance the sensing capability of robots and human safety during collaborative work.

Micro-Electro-Mechanical Systems (MEMS) micro-mirrors have shown great potential in consumer applications, such as Light Detection and Ranging (LiDAR) devices and portable laser projectors. The LiDAR based on electromagnetic MEMS micro-mirror is usually exposed to vibration loads for autonomous vehicles, which results in the necessity for the destructive reliability assessment of micromirrors under vibration environment, but such studies are rarely reported. This paper explores the destructive reliability of electromagnetic MEMS micromirror under vibration environment according to the JESD22-B103B standard. The reliability evaluation is conducted by experimental tests, finite element stress analysis and theoretical dynamic response analysis. Micromirrors are tested under sweep excitation, and they are failed with the vibration level of around 33 g. The failure and stress analysis demonstrate that the crack fracture is located at the root of the slow axis. The nonlinear relationship between the peak displacement of the balance frame and acceleration levels is investigated through theoretical analysis. The nonlinearity of stiffness hardening is induced by the axial tensile strain of the beam, which contributes to the displacement-reduction of the gimbal. This work provides some valuable suggestions for the optimization design of MEMS micromirrors to improve the acceleration tolerance level in vibration environment.

Core body temperature (CBT) is a basic physiological parameter that reflects the level of human metabolism and is therefore clinically important for the diagnosis of various diseases. The traditional method of CBT evaluation based on heat flux is susceptible to errors caused by horizontal heat flux and the sensor is usually large in size. In this study, a novel miniaturized sandwich-like CBT monitoring sensor (SCBTS) based on negative temperature coefficient (NTC) temperature sensor and heat flux sensor was constructed. The sandwich-like structure minimized the effect of horizontal heat flux and reduced ambient temperature disturbance. In addition, a novel numerical method was explored to predict CBT during unsteady heat flux. Effectiveness of SCBTS was verified by finite element method (FEM) simulation, mock-up experiments and human experiments. The proposed sensor was effective within the range of human body temperature fluctuations (35°C-42°C) with an average error of 0.02°C on the hot plate. In human trials, resting experiments (eight participants for 13 trials) showed 0.02°C average difference with a 95% CI of [-0.16, 0.12]°C. Furthermore, the sensor showed distinct temperature changes in different periods using exercise experiments (6 participants). The proposed SCBTS continuously monitors temperature without causing inconvenience to the subject, therefore, it is highly suitable for application.

The hollow-cup Permanent Magnet (PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element (FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.

This paper presents a novel configuration of the eddy current speed sensor to measure the rotating speed of iron rods and shafts up to 3000 rpm. The proposed eddy current speed sensor has an axial airgap structure with one excitation coil and two antiserially connected pick up coils. The speed sensor is mounted in the end shaft part region. Different solid iron materials for rotating shaft are considered in the measurements and calculations to evaluate solid iron material effect on the eddy current speed sensor performance. 2D and 3D finite element method is utilized for the performance analysis of the speed sensor. Also, a 2D analytical method is developed for parametric analysis. A copper rod is also used to compare the speed sensor with the rotating iron shaft and copper shaft. Finally, two thin copper discs with different diameters are mounted on the solid iron shaft and their influences on the eddy current speed sensor were evaluated and measured to increase sensitivity and decrease sensor dependency on the permeability of the solid iron shaft. The achieved nonlinearity errors are about 0.2%.

Mixing and evaporation processes play an important role in fluid injection and disintegration. Laser-induced thermal acoustics (LITA) also known as laser-induced grating spectroscopy (LIGS) is a promising four-wave mixing technique capable to acquire speed of sound and transport properties of fluids. Since the signal intensity scales with pressure, LITA is effective in high-pressure environments. By analysing the frequency of LITA signals using a direct Fourier analysis, speed of sound data can be directly determined using only geometrical parameters of the optical arrangement no equation of state or additional modelling is needed at this point. Furthermore, transport properties, like acoustic damping rate and thermal diffusivity, are acquired using an analytical expression for LITA signals with finite beam sizes. By combining both evaluations in one LITA signal, we can estimate mixing parameters, such as the mixture temperature and composition, using suitable models for speed of sound and the acquired transport properties. Finally, direct measurements of the acoustic damping rate can provide important insights on the physics of supercritical fluid behaviour., Deutsche Forschungsgemeinschaft, Projekt DEAL

Recently, thinning an antenna has resulted in attractive antenna radiation characteristics enhancement. This performance enhancement using a thin antenna array is achieved because the inter-coupling effects of the array elements are reduced. Though the thinning both reduces the weight of the antenna and enhances the radiation characteristics, iterative algorithms can further enhance the performance and hence, in this research, an optimizer algorithm and inter-coupling reducing mechanisms are applied. The excitation weights of the individual array elements are thinned by turning some of the elements off while some of the elements are turned on. The purpose of the thinning is to enhance the antenna performances like reduced SLL, high directivity, reduced power consumption and flexible radiation pattern. The SLL attenuation mechanism is applied to reduce the SLL in addition to the SLL reduction using the thinning and beamforming. Hence, in this paper, the three techniques (thinning, beamforming and SLL attenuation) are proposed to be integrated to enhance the antenna radiation characteristics. In general, the proposed combined method has resulted in much better SLL reduction, directivity improvement, and power wastage reduction.

The insulation impedance monitoring methods such as capacitance/dissipation factor (C/DF) monitoring methods have been proposed for the online stator insulation condition monitoring. By measuring the insulation leakage currents and the phase-to-ground voltages, the groundwall and phase-to-phase insulation impedances can be calculated in frequency domain. In the existing methods, the calculation is based on the assumption that the differential mode phase-to-ground voltage decreases linearly along the stator winding and no phase angle deviation is considered. However, the phase angles of the induced electromagnetic forces in stator winding in different slots depend on the slot positions. The assumption in the existing methods neglects this phase deviation and causes errors in the monitoring results. In order to eliminate this effect, the effect of the phase angle deviation on monitoring results is analyzed in this paper. Its dependency on the turn number, the winding configuration and the frequency of the selected monitoring signals is studied. A compensation method is proposed and the compensation coefficients are calculated for different winding cases for the demonstration purpose. The online experimental results prove that the accuracy of the online monitoring results is improved after the compensation.

A novel ultrasonic burnishing (UB) system with a flat tool using a piezoelectric longitudinal transducer (PLT) is proposed. High-precision no-feeding mark planar burnishing can be achieved by the compact system with a size of only 280 mm 224 mm 558 mm without the need for machine tools. Above all, the structure of the burnishing system is presented and the operation principle is analyzed in detail. A resonant frequency design method of the PLT with a tool head is discussed. Based on thisthe PLT achieves the expected resonant frequency precisely. Subsequently, the test system for the PLT is built and the resonant frequency and vibration amplitude are tested, which are in good agreement with the simulation results. Ultimately, the UB experiments are carried out and the results indicate that the surface roughness of the workpiece is reduced from Ra 1.6 m to Ra 0.182 m, which is reduced by 88.31%. Furthermore, the surface topography shows that the surface without the feeding mark is generated, which is beneficial to improve the burnishing accuracy and expand the application in ultra-precision processing.

In recent years, the development of electronic devices are trending to be smaller and lighter, the techniques for suppressing electromagnetic (EM) radiation need to comply with these trends. EM shields are widely used to suppress EM radiation from transmission lines. EM shield for interconnection cable such as flexible-printed-circuits (FPC) requires flexibility of shielding-material. Consequently, EM shield becomes much more thin metallic shield and may be implemented near the transmission lines in the future. However, frequency response of the transmission coefficients of the shielded-FPC has dispersion due to insufficient shielding performance for near magnetic field. Elucidating the relationship between dispersion of frequency response and time response of transmission characteristics of shielded-FPC turns to be an important indicator of shielding techniques. In this paper, experimental extraction has been proposed for detailed investigating the frequency dispersion of shielded-FPC by using the RLGC equivalent-circuit model. The experimental extraction method used S-parameters measured by using vector network analyzer. The unnecessary components such as connectors are compensated correctly by using proposed method. The frequency response of primary and secondary parameters extracted using the proposed method reproduces all the dispersion characteristics of shielded-FPC successfully. More importantly, quantitative evaluation using the RLGC equivalent-circuit model considering dispersion characteristics can be performed experimentally.

Modeling the electromagnetic response of carbon nanotube (CNT) reinforced composites is inherently a three dimensional (3D) multi-scale problem that is challenging to solve in real-time for nondestructive evaluation applications. This article presents a fast and accurate full-wave electromagnetic solver based on a multi-layer dyadic Green’s function approach. In this approach, we account for the effects of the dielectric slab, where the CNTs are embedded, without explicitly discretizing its interfaces. Due to their large aspect ratios, the CNTs are modeled as arbitrary thin wires (ATWs), and the method of moment (MoM) formulation with distributed line impedance is used to solve for their coupled currents. The accuracy of the inhouse solver is validated against commercial method of moment (MoM) and finite element method (FEM) solvers over a broad range of frequencies (from 1 GHz to 10 THz) and for a wide range of dielectric slab properties. Examples of 100nm long vertical and horizontal CNTs embedded in a 1 μm thick lossy dielectric substrate are presented. The in-house solver provides more than 50 ✕ speed up while solving the vertical CNT, and more than 570 ✕ speed up while solving the horizontal CNT than a commercial MoM solver over the GHz to THz frequency range.

Bushing plays a significant role in insulation and mechanical support for power transformers. Its working state is closely related to the reliable operation of power transformers. To overcome the electromagnetic interference and security risks during sensor installation, a Sagnac interference optical technique for partial discharge (PD) detection is proposed in this paper. By establishing a simulation model of the sensing structure, it is verified that output signal amplitude varies periodically with the length of sensing and delay fibers. Moreover, the output value decreases with increasing probe radius. The results show that a delay fiber of 1.5 km, a sensing fiber of 3 m, and a bending radius of 5 mm are optimal parameter combinations to detect PD in a 72.5 kV defective bushing. In addition, consistent detection waveforms induced by both internal and external defects are obtained by the optical sensor and high frequency current transformer (HFCT) simultaneously, then the effectiveness of the optical sensor on detecting PD signals for bushing is verified. It is of great help to carry out online monitoring of bushing insulation defects through optical non-destructive installation.

Ultrasonic surface rolling process (USRP) is one of the effective mechanical surface enhancement techniques. During the USRP, unstable static force will easily do harm to the surface quality. In order to achieve a higher surface quality on the part with a curved surface, an active and passive compliant USRP system has been developed. The compliant USRP tool can produce the natural obedience deformation along the part surface. Force control based on the fuzzy Proportional-integral-derivative (PID) method is then designed to maintain the static force during the USRP. Experiments have been performed on a real aero-engine blade with curved surface. It is proved that the deigned active and passive compliant USRP system can significantly reduce the force variation from 42.2 N to 4.2 N, and achieve a uniform surface quality after processing.

A novel and small sized implantable antenna has been proposed for scientific industrial & medical (ISM) band applications. The proposed antenna is — shaped antenna and it is a circular patch antenna which has been designed based on the previous research articles and the lower size is achieved by implementing different miniaturization techniques. The radiating structure has a circular shaped patch and it has fillet edges with square shape. The back reflections have been avoided by extending the ground plane over the complete plane. The proposed antenna has been structured by using ROGER 3010 substrate which has the thickness of 1.6 mm and dielectric permittivity of 10.2 in order to achieve the geometries of an antenna with rigidity, the proposed structure has been designed. This antenna structure is operated at 2.45 GHz with the most recommended omni-directional pattern that has been used for transmitting with other in body devices.

Flexible piezoelectric sensors have attracted much attention due to good dynamic response, high sensitivity, and self-powered sensing advantages. However, piezoelectric outputs are usually affected by temperature variation, thus limit their applications on industrial intelligent equipment. Here, a new flexible piezoelectric sensor with in-situ temperature sensing and piezoelectricity calibration function is developed. The sensor can calibrate the piezoelectric output based on temperature to achieve high-accuracy sensing capability. It consists of a flexible polyimide substrate, S-shaped platinum interdigital electrodes and aligned piezoelectric fibers. The temperature sensor has a high sensitivity of 19.2 /C with good linearity, and keeps good accuracy under bending deformation. And when the working temperature range is 25-60C, the sensor has a good piezoelectricity calibration effect, so that it maintains a stable sensitivity of 244mV/without being affected by temperature. Furthermore, this paper systematically studied the influence of temperature on piezoelectric output, and established a calibration method to improve the accuracy of piezoelectric output under temperature changes. Finally, the flexible integrated sensor was conformably attached on the bearing surface to in-situ sensing temperature and vibration. The structural design and piezoelectricity calibration method can promote the application of flexible piezoelectric sensors in the industrial field.

The pump performance and occurrence of cavitation directly depends on different operating conditions. To cover a wide range of operation conditions for detecting cavitation in this work, investigations on the effect of various suction valve openings on cavitation in the pump were carried out. In order to analyse various levels of cavitation in different operation conditions, the effect of the decrease in the inlet suction pressure of the centrifugal pump by controlling the inlet suction valve opening was investigated using this experimental setup. Hence, the acoustic and pressure signals under different inlet valve openings and different flow rates, namely, 103, 200, 302 l/min were collected for this purpose. A detailed analysis of the results obtained from the acoustic signal was carried out to predict cavitation in the pump under different operating conditions. Also, the acoustic signal was investigated in time domain through the use of the same statistical features. The FFT technique was used to analyse the acoustic signal in the frequency domain. In addition, in this work an attempt was made to find a relationship between the cavitation and noise characteristics using the acoustic technique for identifying cavitation within a pump.

Cavitation is an essential problem that occurs in all kinds of pumps. This cavitation contributes highly towards the deterioration in the performance of the pump. In industrial applications, it is very vital to detect and decrease the effect of the cavitation in pumps. Using different techniques to analysis and diagnose cavitation leads to increase in the reliability of cavitation detection. The use of various techniques such as vibration and acoustic analyses can provide a more robust detection of cavitation within the pump. In this work therefore, focus is put on detecting and diagnosing the cavitation phenomenon within a centrifugal pump using vibration and acoustic techniques. The results obtained from vibration and acoustic signals in time and frequency domains were analysed in order to achieve better understanding regarding detection of cavitation within a pump. The effect of different operating conditions related to the cavitation was investigated in this work using different statistical features in time domain analysis (TDA). Moreover, Fast Fourier Transform (FFT) technique for frequency domain analysis (FDA) was also applied. Furthermore, the comparison and evaluation system among different techniques to find an adequate technique incorporating for accuracy and to increase the reliability of detection and diagnosing different levels of cavitation within a centrifugal pump were also investigated.

This work deals with the sensitivity to the plate roughness of Lamb waves. An experimental study is performed involving an air-coupling transducer system. Signal processing allows us to extract the Lamb waves characteristics: phase velocity and attenuation. Plate surface topographies are obtained by means of an optical surface profiler. The acoustic characteristics and the surface topographies are finally linked.

This dissertation reports the results of the investigation of nanoscale pillar structures with engineered phononic and photonic properties. It has been proven that phonon states in semiconductors can be tuned by external boundaries, either as a result of phonon confinement effects in individual nanostructures or as a result of artificially induced external periodicity, e.g., phononic crystals. The possibility of engineering acoustic phonon spectrum is of ultimate importance from scientific and application perspectives since they are the main heat carriers in nonmagnetic semiconductor and insulator materials. The change in acoustic phonon dispersion would affect the heat transport properties, alter the electron-phonon interactions, and affect the optical properties of the material system. It has been recently suggested that periodic structures with properly tuned dimensions can act simultaneously as phononic and photonic crystals, strongly affecting the light-matter interactions. In this dissertation research, I prepared nanoscale pillar structure samples and investigated their properties. The “pillar with hat” structures were fabricated using electron beam lithography on silicon substrates followed by inductively-coupled plasma cryogenic dry etching. The hats of the pillars were created with a unique design to have exactly the same orientation plane as the substrate. The structures were inspected with scanning electron microscopy. I used Brillouin-Mandelstam spectroscopy to measure the dispersion of acoustic phonons with energies in the range from 2 GHz up to 20 GHz through the entire second and higher order Brillouin zones. I analyzed the spectral signatures resulting from the surface ripple mechanism which dominates the light scattering in these specific samples. I found clear signatures of the phonon spectrum modification in the appearance of localized phonon sub-bands at energies between 2˗20 GHz. The variable angle ellipsometry measurements indicated modification of light scattering due to nanostructuring. The experimental data confirmed the dual functionality of the structure with engineered phononic-photonic properties. The results obtained in this dissertation research have important implications for the next generation of photonic and optoelectronic device technologies.