Vibration isolators reduce the transmission of unwanted disturbances to a sensitive payload, thereby protecting mounted instruments and enhancing their operational accuracy.
This thesis focuses on improving and validating experimentally a topology optimization framework that aims to design passive vibration isolators using both structurally stiff and viscoelastic materials. The framework models the in-plane system dynamics in three degrees of freedom while accounting for frequency-dependent material properties and stress constraints. The objective is to optimize damping either for individual rigid-body modes or for all modes simultaneously.

The designs are then converted into 3D models, manufactured using multi-material additive manufacturing, and validated through finite-element simulations and experimental shaker testing. The framework shows strong agreement with 2D finite-element models, accurately predicting primary rigid-body modes and damping characteristics. Experimental results confirm the intended dynamic behavior of the optimized designs, although discrepancies in resonance frequencies and damping remain.

Overall, this research demonstrates the potential of multi-material topology optimization for the creation of customized passive vibration isolators, while identifying key modeling and manufacturing refinements required for practical application. ... Read more

Environmental noise, particularly within the disruptive frequency range of 500 Hz to 6.4 kHz, poses a significant impact on global health, as well as economic challenges. While Triply Periodic Minimal Surfaces (TPMS) have been researched for their mechanical and energy-absorption properties, the continuous, periodic internal architectures also present an effective candidate for acoustic metamaterials. This thesis investigates the acoustic attenuation capabilities of sheet-based Primitive (P) and Neovius (N) TPMS structures, evaluating their ability to reduce sound transmission by generating acoustic band gaps via Bragg scattering.

The research combines implicit geometrical modelling and numerical Finite Element Analysis (FEA) to simulate Sound Transmission Loss (STL), followed by experimental validation of the structures using FDM 3D-printed PLA prototypes in an impedance tube setup. To determine how these band gaps can be tuned to specific frequency ranges, the study evaluates uniform arrays alongside several geometrical design strategies, including longitudinal unit cell elongation, continuous multi-topology hybridisation, and functional relative density grading.

The findings show that topology fundamentally dictates acoustic attenuation. The Neovius structure exhibited superior STL compared to the Primitive topology, driven by extreme periodic cross-sectional variations that induce strong acoustic impedance mismatches. Experimental measurements strongly validated the numerical models regarding band gaps and primary attenuation peaks, despite some high-frequency discrepancies, likely arising from the finite stiffness of the prototypes. The study also proved that elongating unit cells effectively shifts attenuation peaks to lower frequencies, multi-topology hybridisation successfully blends distinct acoustic characteristics, and relative density grading results in tailored attenuation profiles that bridge the amplitude and bandwidth of its uniform base densities.

Ultimately, this research establishes TPMS structures as highly tunable, effective acoustic metamaterials, providing a methodology for engineering multifunctional, load-bearing noise barriers tailored to specific frequencies.
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Repurposing waste materials is essential to reduce our dependency on raw materials. Binder jet 3D printing shows potential for cost-effective freeform production from wood waste due to its high material compatibility. This thesis uses a granulated wood powder and optimizes process parameters through a structured Design of Experiments followed by Bayesian Optimization to maximize the bending strength of as-printed structures. The resulting parameter set yields a modulus of rupture of 1.85 MPa. A dedicated test artifact is 3D-scanned to characterize design insights and dimensional accuracy. While the in-plane accuracy is within 1.2%, the part height along the build direction can exceed its nominal height by 8.6% due to the compressibility of the powder, depending on the positioning in the print box. Drying-induced fractures are inherent to the process and are the main limitation for scaling up to large print sizes.



The characteristic porosity of as-printed structures makes the material a promising candidate for sustainable sound absorption. The porosity is evaluated through micro-CT scanning, and non-acoustical (Johnson-Champoux-Allard-Lafarge) parameters are inversely characterized on impedance tube measurements. Building on these results, a poro-acoustic metastructure is proposed in accordance with the identified design insights and evaluated numerically using the identified non-acoustical parameters. The structure outperforms printed bulk material below 1200 Hz and the impervious reference structure above 1400 Hz. The results demonstrate the potential of wood-based binder jetting and the possible application in sustainable acoustic attenuation. ... Read more

Loudspeaker cabinet design has historically been constrained by conventional manufacturing methods, which favour rectangular panel construction due to its simplicity and repeatability. Large Format Additive Manufacturing (LFAM) removes this constraint by enabling complex curvatures and geometries at manageable production costs. This introduces new possibilities for geometry-driven acoustic performance improvement, but also new challenges. In particular, the anisotropic material properties of 3D-printed polymers and a general lack of research on vibroacoustic behaviour in this context. This thesis develops a computational framework for simulating and optimising the vibroacoustic performance of sealed, low-frequency loudspeaker cabinets. The core problem is the coupled interaction between structural vibrations of the cabinet panels and the acoustic field they radiate, which is a multiphysics problem that requires numerical methods to solve. A hybrid FEM/BEM simulation model is implemented in COMSOL Multiphysics, combining finite element structural analysis with boundary element acoustic radiation modelling. The framework is validated against anechoic measurements of a physical prototype provided by partner Addit Audio. The validated simulation model is integrated into a gradient-based shape optimisation framework. Cabinet panel geometries are parameterised and iteratively deformed to suppress panel resonances and improve sound dispersion, using adjoint sensitivity analysis to efficiently compute gradients. Manufacturability constraints imposed by the LFAM process are incorporated throughout. The optimisation is applied to a rectangular reference cabinet, and the results are analysed in terms of physical mechanism, robustness, and transferability. The findings are broadly applicable to the vibroacoustic optimisation of thin-walled structures beyond the loudspeaker domain, wherever panel resonances and radiated sound are of concern.
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This thesis investigates crumpled thin-sheet bellows as a more compliant alternative to traditional corrugated bellows in vibrationally isolated mechatronic systems (ASML lithography machines). While conventional bellows rely on carefully engineered corrugations, the crumpled foil bellows studied here achieve compliance through an irregular, crumpled morphology, making their dynamic stiffness and vibrational transmissibility difficult to predict. The first part of the thesis is a stand-alone literature review into the diverse approaches employed to model wrinkled and crumpled thin sheets, with their structural dynamics of particular interest. The second part presents original research in which realistic crumpled bellow geometries are generated using explicit non-linear simulations via the dynamic relaxation method, and subsequently dynamically analysed using Hintz–Herting modal reduction. In this way, the static and frequency-dependent emergent stiffness can be extracted and examined as functions of compaction ratio and foil thickness. Experimental measurements of dynamic stiffness are used to validate the numerical trends and to identify the limitations of linearised models for these systems. ... Read more

Vibration isolation is essential for spacecraft payloads, where both launch loads and on-orbit micro-vibrations can degrade performance. Passive isolators are favoured for their simplicity and reliability but face trade-offs between low-frequency performance, stiffness, and compactness. This thesis introduces a topology optimisation framework for designing passive viscoelastic vibration isolators that distributes aluminium and nearly incompressible rubber within the design domain, moving beyond conventional constrained-layer damping layouts used in literature.

The framework combines a modal design approach with a bi-material finite element formulation using selective reduced integration to handle incompressibility. Modal objectives are defined through rigid-body dominated eigenfrequencies of the combined isolator–payload system, with damping enforced via Q-factor constraints.

Each optimised layout consists of a main load-carrying structure that provides stiffness and smaller damping substructures that create localised regions of energy dissipation. They adapt their shape and location to the inertial properties of the setup and targeted vibration mode, strategically placing viscoelastic material where it contributes most to damping without compromising stiffness. In doing so, the framework enables novel damping mechanisms and tunable multi-directional performance, offering an insight for future passive isolation design in vibration-sensitive applications. ... Read more

In industries such as oil and gas, power generation, and chemical processing, the structural integrity of piping systems is crucial for operational safety and reliability. Various factors such as corrosion, erosion, and manufacturing defects can result in a loss of wall thickness, potentially leading to catastrophic failures. Detecting and assessing the integrity of piping systems without causing disruption to operations or compromising their structural integrity is a challenge in asset management and maintenance.
Guided Wave Tomography (GWT) is a promising non-destructive testing (NDT) technique for assessing the integrity of a pipeline by mapping its wall thickness. Using tomographic algorithms that use forward wavefield extrapolators, based on the gradient of the misfit a defect reconstruction can be made. Although the forward model is computationally inexpensive, the currently implemented gradient calculation is costly due to the large number of simulations required for each inversion parameter. This study explores the feasibility of using the adjoint state method for gradient computation in GWT, requiring only a single forward simulation independent of the number of model parameters.
A nonlinear conjugate gradient optimization method is implemented to iteratively update the wall thickness based on the misfit between simulated and observed data. The inversion process makes use of the dispersion curves to establish the relationship between phase velocity, frequency, and wall thickness. The study specifically focuses on the $S_0$ mode, analysing its suitability for complex defect reconstruction. Numerical experiments demonstrate that the adjoint method effectively localizes defects in both noise-free and noise environments, provided that there is a sufficient contrast in the sensitivity kernel between the defect and its surroundings. The technique achieves a resolution of approximately $1$ to $1.5\lambda$, with frequency continuation and multimodal inversions improving reconstruction accuracy. However, challenges arise in handling noise and wall thickness interchanges, which can be mitigated using adaptive regularization strategies.
The results suggest that the adjoint method is a viable alternative to traditional finite-difference sensitivity calculations. Future research should focus on experimental validation with real-world or as noise-free alternative 3D elastodynamic data evaluating the method on complex defect geometries and varying pipe configurations. Finally, the algorithm can be enhanced by integrating Hessian-based optimization techniques, thereby implementing a second-order adjoint method.
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Piezoelectric energy harvesters convert vibrational energy into electrical energy, thereby reducing the dependence of wireless devices on batteries. However, most existing harvesters have a limited bandwidth, generating usable power only within a narrow range of excitation frequencies. Buckled beam harvesters address this issue by intentionally introducing nonlinear behaviour, but systematic design strategies for such devices are still missing due to the absence of versatile models and limited understanding of their dynamics.
In this thesis, these challenges are addressed by developing a model that combines finite element analysis with lumped-parameter equations and validating it experimentally. The resulting framework captures higher-order vibration modes and nonlinear dynamic phenomena such as secondary resonances and softening behaviour. It is demonstrated that these effects can be exploited to optimize the design and broaden the bandwidth of buckled beam piezoelectric energy harvesters. Based on the improved physical understanding, several practical design improvements are proposed. ... Read more

Surface acoustic wave (SAW) is widely used in biological research and sensor applications, acomprehensive understanding of SAW propagation and visualization on suspended 2D membranes is crucial for the manipulation of nanoparticles in biological research and sensitivity improvement of SAW sensors based on 2D material. The initial step of this project involved exciting a standing SAW field on the SAW device and attempting to use Digital Holography Microscopy (DHM) for imaging the standing SAW field on the substrate. This attempt was very challenging and unfortunately was not successful. We used an Atomic Force Microscope (AFM) as an alternative solution for SAW field imaging. Initially, AFM was used to image the SAW field on the SAW device substrate, and the impacts of input frequency and power on the amplitude of the SAW field were investigated. Subsequently, microcavities were fabricated on the SAW device to record images of the SAW field within the microcavities and their surrounding areas, aiming to investigate the impact of microcavities on the SAW field. Finally, the prepared graphene membrane was transferred to the microcavities, the SAW propagation was recorded on the suspended membrane and the influence of the suspended membrane on SAW propagation was analyzed. ... Read more