The increasing use of visible and near infrared light in therapeutic and diagnostic techniques has created a need to model its propagation in tissue. One of the fundamental objectives of such a model is the noninvasive evaluation of the optical properties of tissue. The focus of this thesis was the development of the diffusion approximation in the semi-infinite, slab, cylindrical and spherical geometries. This development required the derivation of approximate boundary conditions which included the zero, extrapolated and partial current boundary conditions. Calculations of the fluence and its related quantities arising from the extrapolated boundary condition were found to be in excellent agreement with the results of the more rigorous partial current boundary condition. A preliminary evaluation of the validity of diffusion theory was performed by comparing its predictions to exact analytical calculations of the fluence in an infinite medium as well as Monte Carlo simulations of the reflectance and transmittance in 1-dimensional planar geometries. In all cases the agreement at late times was excellent. A practical test of the diffusion model was accomplished with the analysis of the reflectance data from a phantom of known optical properties in both the semi-infinite and slab geometries. The model performed well at low concentrations of added absorber, but a considerable discrepancy was found at the highest concentration. A systematic examination of the accuracy of the diffusion model as a function of the fundamental parameters is required to resolve this inconsistency. Approximate expressions describing the equivalent information in the frequency domain were also developed for a semi-infinite medium. These expressions were then used to analyze the phase and modulation obtained from phantoms of known optical properties. Once again reasonable results were obtained at low concentrations of added absorber while a significant discrepancy arose at the highest concentration. The resolution of these discrepancies requires further investigation. / Thesis / Master of Engineering (ME)

The propagation of intense picosecond laser pulses in air in the presence of strong nonlinear self-action effects and air ionization is investigated experimentally and numerically. The model used for numerical analysis is based on the nonlinear propagator for the optical field coupled to the rate equations for the production of various ionic species and plasma temperature. Our results show that the phenomenon of plasma-driven intensity clamping, which has been paramount in femtosecond laser filamentation, holds for picosecond pulses. Furthermore, the temporal pulse distortions in the picosecond regime are limited and the pulse fluence is also clamped. In focused propagation geometry, a unique feature of picosecond filamentation is the production of a broad, fully ionized air channel, continuous both longitudinally and transversely, which may be instrumental for many applications including laser-guided electrical breakdown of air, channeling microwave beams and air lasing.

The potential of Additive Manufacturing (AM) for microwave and mm-wave applications is increasingly being revealed thanks to recent advancements in research. AM empowers engineers with new capabilities to manufacture complex conformal geometries quicker and at lower costs. It allows, for instance, the embedding of RF front ends into functional structures. In this dissertation, two aspects of AM are explored: (a) The development and characterization of techniques that improve the performance of AM microwave circuits and antennas, and (b) study of complex geometries, such as meshed structures, as an alternative to reduce material usage, cost, and weight of the components. Micro-dispensing of silver paste (CB028) is extensively used in this work as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper-frequency range of these lines are limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around 100 μm. In this work a picosecond Nd:YAG laser is used to machine slots in a 20-25 μm-thick layer of silver paste (Dupont CB028) that is micro-dispensed on a Rogers RT5870 substrate, producing coplanar waveguide transmission lines with 16-20 μm-wide slots. It is shown that the laser solidifies 2 μm wide region along the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 MS/m to 30 MS/m, which represents a 100x improvement when compared to the values obtained with the exclusive use of micro-dispensing. Another main aspect of this dissertation is the study of meshed structures in coplanar waveguides. For most AM processes the materials utilized for the conductive layer are the most expensive ones; hence, there is value in minimizing the conductor surface area used in a circuit. In this work, the approach of meshed ground coplanar waveguide (MGCPW) is analyzed by simulating, fabricating and measuring a broad set of meshed ground geometry sizes. Furthermore, a physical-mathematical model is presented, which predicts the characteristic impedance and the capacitance per unit length of MGCPW with less than 5.4% error compared to simulated data. A set of filters is designed and fabricated in order to demonstrate the approach. The main parameter affected by meshing the ground plane is the attenuation constant of the waveguide. It is shown that 50% mesh density in the ground plane of a MGCPW line can be used with less than 25% increase in the loss. In contrast, the loss of finite ground coplanar waveguide (FGCPW) can increase by as much as 108% when the ground size is reduced by the same factor (50%). Both 3D printing (micro-dispensing) and traditional printed circuit board manufacturing are used in this work, and most of the propagation characterization is performed at 4 GHz. A meshing technique is also applied to rectangular waveguides, and its effects are studied. It is presented as an option for high power, low loss, but also reduced weight applications. A set of meshed Ku-band waveguides was fabricated using binder jetting 3D printing technology showing that the weight can be reduced by 22% with an increase in loss of only 5%, from 0.019 dB/cm for the solid part to 0.020 dB/cm average across the band with the meshed design. Further weight reduction is possible if higher loss is allowed. To demonstrate the concept, a comparison is made between non-meshed and meshed waveguide 4 pole Chebyshev filters. Finally, the BJ technology is characterized for Ku-Band rectangular waveguide and reflector antenna applications. This technology is characterized using electron beam microscopy (SEM) and energy dispersive spectroscopy (EDS). The RF performance of the 3D printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator Q of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

Carbon fibre reinforced polymer (CFRP) composites have found a wide range of applications in the aerospace, marine, sports and automotive industries owing to their lightweight and acceptable mechanical properties compared to the commonly used metallic materials. The currently dominating method of machining CFRP is by mechanical means that has found many problems including extensive tool wear, fibre pull-out and delamination. Lasers as non-contact tools have been widely applied for cutting and drilling materials. However, machining of CFRP composites using lasers can be challenging due to inhomogeneity in the material properties and structures, which can lead to thermal damage such as charring, heat affected zones (HAZs), resin recession and delamination. In previous studies, Nd:YAG, diode pumped solid state (DPSS), CO2 (continuous wave), disk and fibre lasers were used in machining CFRP composites and the control of damage such as the size of heat affected zones (HAZ) and achieving comparable material removal rate with the mechanical processes remain a challenge. Most reported work showed a typical heat affected zone of 0.2-1.2 mm. The availability of short pulsed transversely excited atmospheric (TEA) CO2 lasers and ultra-short laser pulse sources such as picosecond lasers make it possible to improve the laser machining quality of CFRP materials. In this research, the machining of CFRP composites using a microsecond pulsed TEA CO2 laser, a state of the art high power picosecond laser and a 1 kW single mode fibre laser system was investigated. The yielded heat affected zone was less than < 25 µm for the TEA CO2 and the picosecond laser machining, although the material removal rate was low. Additionally, it has been shown that the pulsed fibre laser improved the machining quality compared to that with the continuous mode. A potential application of the fibre laser for composite repair and remanufacturing was investigated. The interactions between picosecond laser beam and CFRP composite were studied in more detail including understanding the self-limiting effect in single and multiple parallel tracks drilling/machining through both experimental and theoretical studies. Furthermore, a sequential laser and mechanical drilling of CFRP was investigated to improve the machining rate. The work performed in this PhD was driven by aerospace industry needs, with the collaboration of Rolls-Royce plc and BAE Systems as industrial partners.

<p> Lithium niobate has interesting characteristics such as the electro-optic effect, the acousto-optic effect, piezoelectricity and large nonlinear optical coefficients. Potential applications in MEMS field could be explored if microstructures are fabricated in lithium niobate substrates,. This thesis presents the fabrication and characterization of a lithium niobate MEMS device. As lithium niobate crystal is difficult to process using standard semiconductor techniques including both wet etching and dry etching, new methods are required to process lithium niobate. In our project, picosecond laser pulses were chosen to produce bridges on lithium niobate. Fabrication of grooves with high aspect ratio were attempted and grooves with clean morphology were obtained when laser pulses with low cutting speed, medium pulse energy, and large number of passes were employed. This shows picosecond laser machining is a viable method to process lithium niobate.</p> <p> Waveguides in Z cut lithium niobate crystal were fabricated using Ti-indiffusion techniques. After the fabrication of waveguides in lithium niobate, a SiO2 film with a thickness of 0.3μm was deposited as a buffer layer. Ti-Pt-Au electrodes for actuation function were then deposited through lift-off technique. Finally a bridge structure (80um in width and 600um in length) with a waveguide embedded in it was fabricated with picosecond laser. The insertion loss before and after laser machining was 6.99dB and 5.01dB respectively.</p> <p> Optical and electrical tests were performed in an effort to determine the resonance frequency of bridge. In the optical test, many bulk piezoelectric resonance peaks were presented in the frequency spectrum. After damping the vibration of substrate, these spikes disappeared and only a background noise with small spikes were obtained. As those small spikes are not reproducible, the optical test is not a viable method to determine resonance frequency of the bridge structure in our device. The electrical test was then carried out in a vacuum environment in order to find the resonance frequency. The spectrum presents a spike with large amplitude. However, the phase and amplitude of the spike remained the same when the vacuum condition was removed, which indicates the spike is not related to the resonance of the bridge. In summary, the resonance frequency of bridge structure could not be determined by these two approaches.</p> <p> Future work could involve directly investigating the material properties surrounding the machining region to see whether the piezoelectricity of the material has been damaged from laser ablation process. New laser machining process of lithium niobate may also need to be studied to avoid this damage to the substrate structure. Even though our device could not be driven to vibrate at its resonance frequency, it is worth making microstructures in lithium niobate substrates. The combination of optical, mechanical and electrical elements will make lithium niobate a great potential material for optical MEMS applications.</p> / Thesis / Master of Applied Science (MASc)

Four main aspects are studied and explored throughout this dissertation: (1) On-Package Multipolar antenna system design for integration with commercial wireless sensor nodes for machine-to-machine communication applications; (2) Development of a novel MMIC packaging process and subsequent antenna integration for chip-to-chip communication applications, (3) Design and characterization of additively manufactured lumped passive elements for integration with MMIC and hybrid circuits, (4) Design and characterization of antennas for on- and off-metal radio frequency identification (RFID) applications. This work presents the design of different 3-D printed tripolar antenna systems operating at 2.4 GHz. The antennas are designed for integration with commercial wireless nodes with the purpose of mitigating multipath and depolarization channel effects that might be present in many machine-to-machine (M2M) deployments. The antennas are fabricated utilizing an additive manufacturing (AM) approach that combines fused deposition modeling (FDM) of ABS plastic for dielectric parts and micro-dispensing of silver paste Du-Pont CB028 for conductive layers as the majority of the devices presented in this work. Over the air testing demonstrates a 1% channel improvement of up to 14 dB, achieved in a highly-reflective, Rayleigh-like fading environment by implementing selection diversity between three mutually orthogonal monopoles. This improvement leads to better bit error rate (BER) performance (as is also shown). Additionally, RSSI measurements show significant improvement when the prototype antenna system is integrated with commercial wireless sensor hardware. Implications of tripolar antenna integration on M2M systems include reduction in energy use, longer communication link distances, and/or greater link reliability. In order to incorporate the proposed multipolar selection diversity technique into short range wireless chip-to-chip communications, a novel and versatile 3D printed on-chip integration approach using laser machining is subsequently demonstrated for microwave and mm-wave systems in a process herein referred to as Laser Enhanced or Laser Assisted Direct Print Additive Manufacturing (LE-DPAM). The integration process extends interconnects laterally from a MMIC to a chip carrier. Picosecond laser machining is applied and characterized to enhance the 3D printing quality. Specifically, the width of micro-dispensed printed traces is accurately controlled within micrometer range (e.g. laser cuts ~12 μm wide), additionally, 150 μm probe pads are cut in order to facilitate RF measurement. The S-parameters of a distributed amplifier integrated into the package are simulated and measured from 2 to 30 GHz. It is seen how the overall performance is significantly better than a traditional wirebonded QFN package and previously reported AM MMIC interconnections. The attenuation of the microstrip line including interconnects is only 0.2 dB/mm at 20 GHz and return loss with the package is less than 10 dB throughout the operating frequency band A 17 GHz package integrated linearly polarized patch antenna, fabricated with a multi-layer and multi-material LE-DPAM process is then introduced for vertical interconnection with a MMIC die. Performance is successfully measured and characterized achieving a return loss greater than 19 dB at the desired design frequency. Good agreement between simulated and measured radiation patterns is also obtained with a peak gain of 4.2 dBi. Another section of this work utilizes LE-DPAM to fabricate lumped capacitors and inductors for coplanar waveguide (CPW) circuits, especially useful for filtering and matching network implementation. Laser machining is used to achieve ~12 µm slots on printed conductors, producing aspect ratios greater than 2:1, as well as to fabricate vertical interconnects or vias that allow for the fabrication of the multilayer inductors. Inductances in the range of 0.4-3 nH are achieved, with a maximum quality factor of 21, self-resonance frequencies up to 88 GHz, and an inductance per unit of area of 5.3 nH/mm2. Interdigital capacitors in the range of 0.05-0.5 pF are fabricated, having a maximum quality factor of 750 and self-resonances up to 120 GHz. All the components are made on the center line of a CPW that is 836 µm wide. The results show that LE-DPAM enables the fabrication of compact passive circuits that can be easily interconnected with MMIC dies, which at the same time, can be manufactured as part of a larger component. This enables the fabrication of structural electronics that are functional into the mm-wave frequency range. A final aspect of this work goes through antenna designs for specific RFID (radio frequency identification) applications. RFID tag design is generally focused specifically on either off-metal or on-metal configurations. In this work passive 2D and 3D RFID tags are presented which perform similarly in both configurations. The presented tags operate in the ISM RFID UHF bands that cover 864-868 MHz and 902-928 MHz. A matching loop consisting of two parallel stubs to ground is used for impedance matching to a passive integrated circuit, which has -18 dBm sensitivity. A planar 2D tag with a footprint of 13126.5 mm2 is first introduced, showing a simulated gain of approximately 3 dBi and a measured read range of 10 m (for 31 dBm transmit power from the reader) in both on-metal and off-metal conditions. The tag is miniaturized into a 3D geometry with a footprint of 2524.25 mm2 (520% reduction) and achieves the same broadside simulated on-metal gain. The antennas are fabricated using a DPAM process, and a meshed ground configuration is explored in order to accomplish a 50% conductive paste reduction without disrupting the performance. The proposed tags are compared with commercially available tags as well as previously published tags in terms of read range and size. The tags in this work present an improvement in terms of read range, gain, and area with respect to previous designs covering the ISM RFID UHF bands. Moreover, the performance of these tags is maintained in on- and off-metal conditions, achieving comparable performance and a reduction in volume of 11482% with respect to the best tag reported.

The need for miniaturized, and high performance microwave devices has focused significant attention onto new fabrication technologies that can simultaneously achieve high performance and low manufacturing complexity. Additive manufacturing (AM) has proven its capability in fabricating high performance, compact and light weight microwave circuits and antennas, as well as the ability to achieve designs that are complicated to fabricate using other manufacturing approaches. Direct print additive manufacturing (DPAM) is an emerging AM process that combines the fused deposition modeling (FDM) of thermoplastics with micro-dispensing of conductive and insulating pastes. DPAM has the potential to jointly combine high performance and low manufacturing complexity, along with the possibility of real-time tuning. This dissertation aims to leverage the powerful capabilities of DPAM to come-up with new designs and solutions that meet the requirements of rapidly evolving wireless systems and applications. Furthermore, the work in this dissertation provides new techniques and approaches to alleviate the drawbacks and limitations of DPAM fabrication technology. Firstly, the development of 3D packaged antenna, and antenna array are presented along with an analysis of the inherent roughness of 3D printed structures to provide a deeper understanding of the antenna RF performance. The single element presents a new volumetric approach to realizing a 3D half-wave dipole in a packaged format, where it provides the ability to keep a signal distribution network in close proximity to the ground plane, facilitating the implementation of ground connections (e.g. for an active device), mitigating potential surface wave losses, as well as achieving a modest (10.6%) length reduction. In addition, a new approach of implementing conformal antennas using DPAM is presented by printing thin and flexible substrate that can be adhered to 3D structures to facilitate the fabrication and reduce the surface roughness. The array design leverages direct digital manufacturing (DDM) technology to realize a shaped substrate structure that is used to control the array beamwidth. The non-planar substrate allows the element spacing to be changed without affecting the length of the feed network or the distance to the underlying ground plane. The second part describes the first high-Q capacitively-loaded cavity resonator and filter that is compatible with direct print additive manufacturing. The presented design is a compromise between quality factor, cost and manufacturing complexity and to the best of our knowledge is the highest Q-factor resonator demonstrated to date using DPAM compatible materials and processes. The final version of the single resonator achieves a measured unloaded quality factor of 200-325 over the frequency range from 2.0 to 6.5 GHz. The two pole filter is designed using a coupled-resonator approach to operate at 2.44 GHz with 1.9% fractional bandwidth. The presented design approach simplifies evanescent-mode filter fabrication, eliminating the need for micromachining and vias, and achieving a total weight of 1.97 g. The design is fabricated to provide a proof-of-principle for the high-Q resonator and filter that compromises between performance, cost, size, and complexity. A stacked version of the two-pole filter is presented to provide a novel design for multi-layer embedded applications. The fabrication is performed using an nScrypt Tabletop 3Dn printer. Acrylonitrile Butadiene Styrene (ABS) (relative permittivity of 2.7 and loss tangent of 0.008) is deposited using fused deposition modeling to form the antenna, array, resonator, and filter structures, and Dupont CB028 silver paste is used to form the conductive traces conductive regions (the paste is dried at 90 °C for 60 minutes, achieving a bulk DC conductivity of 1.5×106 S/m.). A 1064 nm pulsed picosecond Nd:YAG laser is used to laser machine the resonator and filter input and output feedlines.

La structuration des liquides près d'interfaces est liée aux forces d'interactions liquides/interface à des distances de quelques dimensions moléculaires. Cet effet universel joue un rôle primordial dans divers domaines tels que le transport de chaleur, le transport de particules à travers les membranes biologiques, la nanofluidique, la microbiologie et la nanorhéologie.Le but principal de cette thèse est de réaliser l'échographie par laser de liquides nanostructurés près d'une interface, afin de mieux comprendre les propriétés physiques de liquides confinés à des échelles moléculaires. La méthode utilisée est la technique d'acoustique picoseconde, qui est une technique tout optique impliquant des lasers impulsionnels pour la génération et la détection d'ultrasons picosecondes. Nous avons adapté la technique pour étudier les propriétés acoustiques longitudinales à haute fréquence des liquides ultra-minces. Les résultats de la diffusion de Brillouin dans le domaine temporel sont utilisés pour déterminer le profil de distribution de la température dans le volume de liquide étudié qui peut être extrapolé aux dimensions nanométriques. Les résultats sur le changement de la fréquence de Brillouin aussi bien que sur l’atténuation acoustique en fonction de la puissance du laser donnent un aperçu de la relation entre les propriétés thermiques et mécaniques des liquides. L'analyse de Fourier des résultats pour différentes épaisseurs de liquide donnent l'information sur la vitesse du son et de l’atténuation aux fréquences GHz. Ce nouveau schéma expérimental est une première étape vers la compréhension des liquides confinés mesuré par l'échographie d'ultrasons aux fréquences GHz. / The phenomenon of liquid structuring near interfaces is related to the liquid/interface interaction forces at distances of some molecular dimensions. Despite the fact that this universal structuring effect plays a key role in various fields such as heat transport, particle transport through biological membranes, nanofluidics, microbiology and nanorheology, the experimental investigation of liquid structuring remainschallenging.The aim of this PhD thesis is the experimental study of the structuring/ordering of liquids at nanoscale distances from their interfaces with solids. In this context, we have adapted the experimental technique of picosecond laser ultrasonics to investigate high-frequency longitudinal acoustic properties of ultrathin liquids confined between solid surfaces of different types. At first, we will present results of time-domain Brillouin scattering (TDBS) used to determine the temperature distribution profile in the investigated liquid volume which can be extrapolated to nanometer dimensions. Results for the evolution of the extracted Brillouin scattering frequencies and attenuation rates recorded at different laser powers give insight to the intrinsic relationship between thermal and mechanical properties of liquids. Second, we will describe our results for the measurements of mechanical properties of ultrathin liquids with a nanometric resolution. Fourier analysis of the recorded TDBS signals for different liquid thicknesses yield the value of the longitudinal speed of sound and attenuation at GHz frequencies. This novel TDBS experimental scheme is a first step towards the understanding of confined liquids measured by GHz ultrasonic probing.

Le travail que j’ai effectué durant ce doctorat est dédié à l’utilisation de l’ultrason des lasers sous haute pression physique. La recherche est construite en utilisant les récentes techniques de mesure de laser ultrasonique dans une enclume de diamant, conduisant à l’exploration de la propagation du son et de sa détermination suivant la vitesse de l’onde acoustique sous ultra-hautes pressions. La diffusion Brillouin a été appliquée ici pour déterminer l’épaisseur de la glace polycristalline compressée dans l’enclume à diamant sous pressions de mégabars. La technique permet d’examiner les caractéristiques des dimensions des inhomogénéités élastiques et la texture de la glace polycristalline, de ce fait ce processus est commun pour les surfaces de l’enclume à diamant avec des sous micromètres de résolution spatiale via les mesures des variations résolues dans le temps sur la vitesse de propagation du pouls acoustique voyageant dans l’échantillon compressé. Ceci a été appliqué pour mesurer la vitesse acoustique dans du H2O à l’état de glace jusqu’à 84 Gpa. La technique d’imagerie développée contient, pour chaque cristallite (ou groupe de cristallites) dans un ensemble homogène chimique transparent, des informations utiles sur son orientation ainsi que sur sa valeur élastique modulée par rapport à la direction de la propagation du son. Cela répand les bases pour une application réussite sur la déformation de solides sous haut-développement de modèles micromécaniques sous la pression à mégabars. Pour une plus longue durée, ce genre d’expériences répandus sur les minéraux de la terre et avec des températures basses ou hautes, assurerait un progrès important dans la compréhension de la construction de la cape terrestre, son évolution ainsi que celle d’autres planètes. / This PhD research work is devoted to the use of laser ultrasound in high-pressure physics. The research is done using the recently established technique of laser ultrasonic measurements in a diamond anvil cell which allows investigation of the sound propagation and determination of the acoustic wave velocities at ultrahigh pressures. Time domain Brillouin scattering was applied here to depth-profiling of polycrystalline aggregate of ice compressed in a diamond anvil cell to megabar pressures. The technique allowed examination of characteristic dimensions of elastic inhomogeneities and texturing of polycrystalline ice in the direction, normal to the diamond anvil surfaces with sub-micrometer spatial resolution via time-resolved measurements of variations in the propagation velocity of the acoustic pulse travelling in the compressed sample. It was applied to measure the acoustic velocities in H2O ice up to 84 Gpa. The developed imaging technique provides, for each crystallite (or a group of crystallites) in chemically homogeneous transparent aggregate, usable information on its orientation as well as on the value of the elastic modulus along the direction of the sound propagation. This extends the basis for a successful application of highly developed micromechanical models of solids deformation at mbar pressure. On long term, such experiments extended to earth’s minerals and high or low temperatures would insure a significant progress in understanding of convection of the earth’s mantle and thus evolution of this and other planets.