The increasing demand for enhanced performance in cutting-edge technology has fueled extensive research in engineering materials. Thanks to their unique mechanical properties, engineered materials have been used to manipulate the propagation of acoustic and elastic waves. The literature review primarily focuses on state-of-the-art Locally Resonant Mechanical Metamaterials (LRMMs), designed for vibration isolation by utilizing the principles of local resonances. It explores their working principles and performance in terms of bandgap tunability, aiming to get a better understanding of the available designs and identify their limitations, with the goal of enhancing the performance and applicability of this concept. Locally resonant mechanical metamaterials in this work are classified as passive or active materials based on their ability to alter the range of band gaps during operation. Passive LRMMs can effectively isolate constant vibrations in specific regions where the band gap remains fixed. However, they are unable to attenuate frequencies that lie outside the fixed bandgap range. Active LRMMs, on the other hand, can dynamically alter the band gaps during operation through external stimuli or integrated actuation. The applicability and tunability of band gaps in large lattices are the main limitations of the LRMMs reported in the literature. Moreover, the designs aimed at achieving low-frequency band gaps are often complex and challenging to realize. Additionally, the actuation principles used to maintain design functionality significantly contribute to these limitations, as nearly all reported active LRMM designs rely on either complex or impractical actuation mechanisms. This research work proposes a tunable vibration isolation system based on locally resonant mechanical metamaterials. The system consists of four unit cells capable of altering the bandgap across a wide range of frequencies by adjusting the stiffness of the resonators. It operates by applying global pres training to the lattice, which in turn compresses the resonators through the other masses in each unit cell, reducing their effective stiffness. The FEM resonator stiffness measurements revealed a reduction in the stiffness, which remains positive up to an applied strain of 0.72%. Specifically, the resonator stiffness decreased from 287.3 N/m at the initial state to 188.8 N/m at a strain of 0.36%, and further decreased to 74.1 N/m at 0.72%. At a higher applied strain of 1.09%, the stiffness became negative, reaching approximately -213.8 N/m and continuing to decrease with greater strain values. The transmissibility simulations demonstrated a wide tunability range for the formulated bandgap, confirming the effectiveness of the proposed design in altering the bandgap. The design was realized using Fused Deposition Modeling (FDM). Experimental results supported the modeling findings, with the bandgap shifting from an initial range of 77.14 Hz to 99.11 Hz to a wider range of 69.71 Hz to 97.47 Hz under a pre-applied strain of 0.54% on a lattice of four unit cells. These findings highlight the capability of the proposed lattice design to shift the bandgap to a lower frequency range.

Modern internet–based technologies require devices that can generate, acquire, and
compute data. Typically, these devices rely on conventional batteries, which limit device
size, lifespan, and introduce maintenance costs due to replacements.
A promising alternative is using piezoelectric energy harvesters, which convert mechanical
stress into voltage via the piezoelectric effect. These harvesters need to be activated
by external vibrations, but most current systems operate in a frequency range of 50 to
300 Hz. However, ambient vibrations often occur at lower frequencies (5 to 40 Hz) and
are not constant,making it challenging to harvest energy efficiently when the frequency
mismatch occurs.
The objective of this research is to develop a design that can harvest energy from a broad
range of low and non–constant frequencies and develop a testing methodology for its
dynamic characterization that represents a real–world scenario, by using square wave
and noise excitation.
The proposed design is based on the frequency up–conversion principle. The design
features a driving oscillator, a bi–stable oscillator that resonates at low frequencies and
collects energy during its snap–through motion. The generating oscillator, on the other
hand, resonates at higher frequencies and contains the piezoelectric material. The energy
harvesting is achieved by the transfer of energy from the driving to the generating
oscillator.
The dynamic characterization of the design resulted in several findings. The proposed
design can up–convert frequency by a factor of 208 and harvest energy at low input vibration
(0.1–20 Hz) and noise excitation (0–300 Hz).
Overall this research contributes to the field of energy harvesting by introducing a new
design that can harvest energy fromambient vibrations and a new testing procedure that
replicates a real–world scenario.

This thesis aims to characterize the photopolymer resins designed for the 3D printing of Gradient Refractive Index (GRIN) lenses. This thesis focuses explicitly on preparing UV-curable inks doped with nanoparticles that are custom-synthesized for sophisticated optical applications. Four different ink formulations have been studied, including epoxy-based and PMMA-based, together with two commercial UV-curable resins, which are a combination of acrylates and epoxies. Spectroscopy testing of these inks is conducted to study their optical performance for properties like the transmittance and absorbance over the UV, visible light, and NIR regions. The results show that it is possible to obtain significantly different behavior in the optical properties of materials compared to the inks without nanoparticles, offering a promising pathway for developing GRIN lenses with superior characteristics. This research also reports on some modifications performed on an Elegoo Mars 4 DLP printer to control a projector and the DMD device for arbitrary exposure times, further contributing to the development of high-performance optical devices through additive manufacturing.

As of 2020, flexible packaging market is growing rapidly, leading to a demand for technological advancements in the industry. Flexographic relief plates, used to transfer ink onto substrates, are currently cut with a knife-based system. This method is slow, suffers from high tool wear, and cannot cut complex shapes. A laser-based system could offer a solution, but little is known about laser machining these specific types of polymers. This thesis focuses on the development of an integrated laser marking and cutting system for these specific polymers. The research commenced with an investigation into laser processing of polymers, including an optical absorption analysis of the utilised material. With this knowledge, predictions of laser-material interactions were made, to identify the feasibility of available laser sources that for marking and cutting the substrate. Experiments were conducted to evaluate contrast created by chosen lasers during engraving of the material and to determine sufficient cutting parameter. Based on the acquired knowledge, informed decisions were made regarding the design and development of the machine. A 60 W CO2 9.3 μm laser source was chosen to implement into the machine, together with belt drives powered by AV high torque NEMA 34 stepper motors. To steer the beam into the intended direction with 20 mm silicon silver coated mirrors and a 20 mm Zinc Selenide (ZnSe) lens was used. This research demonstrates a new method for cutting and marking flexographic plates, which could contribute to improved automation in the printing industry.

The thesis investigates the feasibility of using stencil printing to fabricate piezoelectric vibrational energy harvesters. The primary goal was to develop and improve techniques for applying a piezoelectric composite material directly onto a stainless steel substrate. The research encompassed theoretical background, fabrication processes, and experimental validations. Stencil printing, known for its scalability, allows efficient production of large systems and offers flexibility in optimizing the piezoelectric layers' shape, location, and thickness. The study demonstrated that thinner layers (up to 0.25 mm) generated significantly more power than thicker layers. However, challenges like porosity and cracks limit the power output, necessitating further refinement in the fabrication process

PVDF actuators can be employed as a propulsion mechanism to miniaturise and simplify soft robotic fish for underwater exploration. Practical realization of soft robots such as robotic fish requires understanding a multitude of aspects, including fabrication and behaviour of the actuators, locomotion of the robot and application-specific electronics. Respectively, the literature review addresses these aspects. The main paper of this thesis examines the working principles of these actuators and develops an understanding of how they function in underwater environments. Various fish actuator designs, including samples with reinforced front stiffness, were fabricated using an enhanced airbrush printing platform. Comsol is used to model the soft robotic fish and actuator. The study examines the effects of PVDF annealing temperatures on maximum voltage and displacement. It also evaluates the interaction between electrode sheet resistance and water-resistant coatings. Fish performance and possible failures are explored. PDMS was found to have the least impact on actuator performance doubling the electrode resistance when applied to the top electrode layer. Samples annealed at 130 $\degree$C show higher maximum allowable voltage than 110 $\degree$C annealed samples, but maximum displacements are similar. Fishtail displacements up to 2.8 mm at 1640 V are measured in air, but no propulsion is observed when the fish is free-floating in water. Tail displacements of about 5 mm were observed at low frequencies in samples made with Novele substrate, which is five times larger than displacements at eigenfrequency. In contrast, the opposite effect was observed in fish samples using Kapton substrate. The observed motion at the eigenfrequency, when the fish was free-floating in water, is hypothesized to be too small, with whole-body vibrations instead of the expected tail-beating motion. The findings from this study provide insight into actuator capabilities and current fish design shortcomings. A deeper understanding of swimming dynamics may lead to future designs of soft robotic fish that can effectively propel themselves in water using PVDF actuators.

In the era of advancing technology, the demand for specialized engineering materials has risen significantly. Active Mechanical Metamaterials (AMMs) offer a novel approach to engineering materials with tunable mechanical properties. This research focuses on developing tunable damping active mechanical metamaterials (AMMs) by incorporating magnetorheological fluid (MRF) damper into a compliant mechanism unit cell. This unit cell transforms linear displacement into rotation at the centre, precisely where the damper is located. First, The AMM unit cell has been designed with a compliant structure that converts the unit input into an embedded MRF damper. After that, the dynamic behaviour of the unit cell was studied by combining analytical and FEM modelling to characterize the stiffness and damping of the unit cell. A prototype has been built, and the damping and stiffness have also been experimentally characterized.
The results highlight key findings, including numerical data, offering insights into the efficiency of the unit cell's compliant transformation mechanism and the tunable damping achieved through MRF dampers, where the damping ratio can be adjusted from 0.02 to approximately 0.03 when 1.4 A of current is applied. This study represents a significant advancement in active mechanical metamaterials, showcasing a novel unit cell design where the magnetorheological fluid has been used for the first time to achieve tunable damping in active mechanical metamaterials.
The success of this study is evident in the convergence of theoretical predictions with experimental outcomes, emphasizing the robustness of the proposed design and modelling methodologies. The implications of this research extend to diverse applications in structural engineering and vibration control, with a particular focus on high-tech systems. These findings provide valuable guidance for researchers and engineers working in high-tech industries, offering practical insights that can significantly impact the development and implementation of innovative solutions in these fields.

Shape morphing is a prevalent feature in all living organisms. Incorporating shape-morphing capabilities into engineered scaffolds in the field of tissue engineering by virtue of 4D printing would allow for structures to closely mimic in-vivo conditions, and dynamically interact with changing cellular microenvironments. Engineered scaffolds subjected to external mechanical loads have recently drawn interest to study the impact of altering Poisson's ratio and pore size of cellular scaffolds on the properties of cells growing on it. However, this approach limits its applications to in-vitro environments. The ability to remotely actuate scaffolds would allow for precise, non-invasive, and controlled activation of these engineered structures. Towards this, the current research work aimed at the design and fabrication of a dynamic metamaterial-based unit cell microstructure capable of exhibiting a varying Poisson’s ratio in response to thermal stimulus. The microstructure was fabricated using a biocompatible Poly(N-isopropylacrylamide) (pNIPAM) based photoresist and a two-photon polymerization (2PP)-based direct laser writing technique. Systematic characterizations were first performed on a simplified model to evaluate the correlation between the printing parameters which include laser power, scanning speed, and hatching angles to the shape-morphing characteristics of the printed microstructures. The learnings were implemented to fabricate the proposed varying Poisson's ratio model. The fabricated microstructure exhibited a rapid and reversible change in Poisson’s ratio when subjected to a thermal stimulus by virtue of the inherent properties of hydrogels and heterogeneity introduced within the structures by varying the laser parameters during the printing process. In a broader context, this research serves as the first step towards the realization of a dynamic stimulus-responsive 3D scaffold for cell culture applications.

Surface-enhanced Raman spectroscopy (SERS) is a powerful non-destructive molecule identification technique. The technique is made viable by the enhancement of the Raman effect which is caused by metallic nanoparticle (MNP) structures. A fabrication method that can manufacture highly consistent SERS substrates is important. Aerosol Direct Write (ADW) is a promising method to achieve consistent SERS substrates. Previous research did not achieve reproducible substrates due to inconsistencies in particle deposition. To improve the quality of SERS substrates fabricated using ADW, key factors within the ADW setup contributing to the substrate quality are identified and analysed. A particle deposition model is created to analyse the impact of those key factors on the substrate quality and to analyse if different operating velocities of the moving stage can minimise the impact of those key factors. The deposition model results are validated by fabricating substrates using a range of operating velocities. It is found that the nozzle diameter has a linear correlation with the spot size. The particle generation is inconsistent and a dominant factor for the SERS substrate quality. The effect of the fluctuating particle generation rate can be minimised by multiple path coverages and higher operation velocities. It is found that the XYZ-stage in the used setup operates optimally between 1000 and 2000 micrometer per second. The deposition model correctly showed that the particle generation rate is the dominant factor for the substrate quality and correctly predicted the ideal operating velocity of the XYZ-stage used in the setup. The model can be used in the future to find an ideal operating velocity and to look at the effects of stage movement characteristics and particle generation fluctuations in ADW setups. SERS measurements show that the SERS substrate fabricated at the ideal operating velocity performed more consistently than substrates fabricated at other velocities.

This research investigates the implementation of electroactive polymer (EAP) actuators for the propulsion of a robotic fish. An efficient manufacturing procedure is developed which uses a combination of stencil printing and inkjet printing to manufacture P(VDF-TrFE-CTFE) actuators. The influence of layer thicknesses is studied theoretically and experimentally, in order to optimize the actuation output. The effect of the fabrication process on the EAP breakdown strength is studied as well. Unimorph cantilever actuators were successfully produced on both Novele and PEN substrates. Layer thickness of the EAP
layer was controlled by changing the stencil thickness, producing layers ranging from 5 - 24 µm. A maximum quasistatic tip deflection of 760 µm was achieved for an 18 mm cantilever actuator at 560 V. Operating at the resonance frequency of 52 Hz, a 5.59 mm displacement was attained. Subsequently, a robotic fish with a length of 60 mm was designed with an integrated EAP actuator in the tail. In addition to the actuator manufacturing procedure, the fish was coated with silicone and attached to a floating device in order to perform experiments in water. The fish tail showed clear deflection underwater, especially when operating at the resonance frequency. However due to limitations related to the underwater operations and a large resisting force of the floating device and connected wires, propulsion power was insufficient to propel the robotic fish.

In up to 39% of reduced distal radius fractures, re-displacement of the fracture occurs in the cast. In most cases, the cast becomes too loose as soft tissue swelling decreases over time and the cast no longer provides sufficient support to keep the fracture reduced. This issue could be addressed by introducing a smart memory cast, a cast that would employ soft polymer foam to relieve stress concentration while providing the required support stiffness to maintain the reduction throughout the whole cast treatment period. Soft polymer foams are characterised by a plateau phase in which the pressure does not increase as the material is compressed. The concept is tested by placing a soft polyurethane foam between an artificial arm that mimics soft tissue swelling and a synthetic cast. The pressure in the smart memory cast is measured by thin film pressure sensors. The average pressure in the smart memory cast was 15.4 mmHg and was reduced by 47.8% compared to the average pressure measured, 29.5 mmHg, in a traditional cast. The pressure in the smart memory cast remained under 25.0 mmHg which was set as a threshold value that could lead to a compartment syndrome. In contrast with the traditional cast where the pressure kept increasing above the threshold value as the artificial arm kept swelling, in the smart memory cast the pressure plateaued. The results from this study show that by introducing a filler material with non-linear elastic properties in a synthetic cast, the pressure concentration is reduced compared to a traditional cast and the pressure plateaus as soft tissue swelling increases.

Materials and material structures with highly specialised and unique mechanical properties are sought after in order to gain the most performance from a system. Materials generally have fixed mechanical properties and are unable to adapt in the case of new or unforeseen situations. Active mechanical metamaterials are able to alter the fundamental mechanical properties in real-time.

The literature review looks at the state of the art active mechanical metamaterials from the perspective of their control strategies and actuation principles. This is done to get a better view of what materials are out there, what applications are suitable for specific active mechanical metamaterials and what gaps can be explored in the future.

The literature review found that the active mechanical metamaterials can be classified by type of control into closed loop and open loop control, as well as the location of actuation into locally actuated and globally actuated materials. Furthermore, the active mechanical metamaterials are highly specialised for their respective applications.

Controlling the active mechanical metamaterials effectively, especially with a large amount in unit cells is the main challenge for most of the active mechanical metamaterials. For this propose, globally actuated and open loop control principles provide the best opportunities for simple, large scale controllable active mechanical metamaterials, though the actuation domains used for the globally actuated active mechanical metamaterials is less precise than the domains used in the closed loop active mechanical metamaterials.

The main report proposes an approach to place and manipulate the band gaps in local resonance mechanical metamaterials via open loop actuation. The state of the art local resonance mechanical metamaterials are lacking in tunability of the band gaps, even though the ability to change the location of these band gaps is very desirable to alter the dynamics of the system.

The design concept is based on the working principle of a local resonance mechanical metamaterial and incorporates a method for tuning the resonator stiffnesses. The tunable stiffness is achieved through the straining of opposing flexures, which are actuated by externally applying a strain to the unit cell through the use of chevron motion amplifiers.

The fabricated prototype showed comparable stiffnesses to the stiffnesses obtained using the FEM analysis, and showed an increase of the resonator stiffness from 1530 N/m to 3290 N/m. Furthermore, the prototype showed a change in band gap from between 73 Hz and 86 Hz to between 78 Hz and 92 Hz in response to the application of lattice pre-strain of 0.50mm. This mechanical metamaterial is therefore successful in the tuning of antiresonances in local resonance mechanical metamaterials through externally applying a strain to the metamaterial. In the future, mechanical metamaterials with this tunable band gap behaviour can be useful for applications where a lightweight, open loop, tunable vibration isolation approach is required.

Vibrations have been studied in various engineering fields due to their detrimental and even destructive effects on structures. Suppressing low-frequency vibrations has been a research challenge for decades and is mostly achieved by implementing active vibration control techniques. In the last two decades, the emergence of locally resonant metamaterials has sparked the interest of several researchers to create passive vibration attenuation structures as an alternative to active vibration-suppressing techniques. This research focuses on developing a local resonator-based unit cell that is able to attenuate vibrations at a wide range of low frequencies. A literature research is performed on the state-of-the-art in the field of locally resonant metamaterials and their wave-suppressing properties. Several wave directions and types are considered,
while low-frequency vibration attenuating structures are actively discussed. A comparative study is done on current local resonator-based structures from which a novel compliant metamaterial is proposed that can suppress a wide range of low-frequency vibrations. The proposed novel compliant negative stiffness local resonator (NSLR) unit cell has the ability to attenuate low-frequency vibrations at a wide range of frequencies while exhibiting a large load-bearing capacity. This concept is based on compliant mechanisms and relies on the snap-through motion of buckled beams for its negative stiffness, whereas folded beams are used in the design as load-bearing positive stiffness components. The stiffness and load-bearing capacity of the unit cell is determined by analytical and FEM-based numerical models, while dispersion relations and transmissibility functions are used to identify the dynamic vibration attenuation behavior. A prototype is produced by FDM additive manufacturing and tested in an experimental setup to verify the load-bearing capacity. An analytical and numerical load-bearing capacity between 100 N and 102 N, and 111 N to 115 are established, respectively, with an effective vibration
attenuation displacement range of 2.5 mm. The FEM simulated band gap of a single unit cell ranges from 6.0 Hz to 64.8 Hz, while the analytical model shows a band gap from 9.6 Hz to 59.5 Hz. The manufactured NSLR prototype features parasitic resonator rotations, requiring additional stiffness constraints to test its vibration attenuation properties in practice. These analyses show the promising capabilities of the NSLR unit cell as a building block in metamaterials to protect
structures from low-frequency vibrations at a wide range.

Building a distributed fluidic actuation system is a challenge due to every actuator needs its own control valve. Due to this, an n by an array of actuators needs n 2 number of valves. A logic network of valves provides a solution by reducing the number of valves needed to operate such distributed fluidic actuation system. These compliant fluidic networks could have a broad application in different fields such as biomedical, microfluidics, or in soft robotics. An example in the biomedical field is for creating an actuated surface that is controlled by a fluidic logic that goes around a hollow organ. This sleeve could provide support to the organ by externally providing actuation. The main goal of the paper is to design a compliant valve that easily could be integrated into a large fluidic logic network, to demonstrate the network a demultiplexer is built. Compliant is defined as soft material (small E modules) with hyperplastic properties. To get a better understanding of what is already done in the field of distributed actuation systems a literature study is conducted. The thesis will provide information on the design steps of creating a valve and how to integrate them in a fluidic network that is a demultiplexer. The operating principle of this valve is that there are 2 channels on top of each other on a 90-degree angle, one channel will be inflated and will choke the other channel. Different valve designs based on this principle have been built and tested using different shapes and combinations of materials. Using FEM software the closing pressure is calculated. After that prototypes have been built and experiments are conducted. During experiments, the pressure drop has been measured in the channel that will be closed. The next step is to understand how these valves operate in a large network. A Simulink model of a demultiplexer has been built, it was shown that 2.4 seconds to inflate an array of 8 small bellow actuators with a stroke of 5 mm. After simulating a demultiplexer is created. Experimental results show that the best-performing valve completely closes a line with a pressure of 12 kPa with an operating pressure of 26 kPa. As a demonstrator of a large-scale network a demultiplexer is built, unfortunately, it did not perform due to manufacturing problems. To answer the main question of this paper a fully functioning logic network has not yet been achieved however, it could be said that this paper has laid a good foundation for further improvement of the creation of a scalable solution for an actuating surface. It also has to be noted that the valve designs that are discussed in this paper operate on an mm scale instead of an cm-scale which is commonly found in the literature.

Shape changing active metamaterial could form the structural backbone of an object as well as deliver the actuation. The integration of these two functions saves design space and allows for creative topologies. The literature study of this thesis investigated smart material actuator solutions that could be used to enable such active metamaterials, covering PVDF, dielectric elastomers, IPMC, conducting polymer, carbon nanotubes and piezoelectric ceramics. It is found that dielectric elastomers achieve high strains, low stress and need high driving voltages. Conducting polymers are able to deliver both high stress and high strain, but consume relatively much power. If power consumption is a priority, Electronic EAPs are preferred. PVDF does not excel on stress or strain, but is an overall good performer. The outlook of realizing active metamaterials via integration of actuation paves the way for non-rigid body deformations and broadens the view on potential applications. At the moment such a system cannot be realized due to the lack of appropriate designs and manufacturing methods. The objectives of this report are (1) the employment of smart materials to make metamaterials active, (2) proposing a method of how to realize this using production materials and (3) employing these methods to build a small metamaterial demonstrator that functions both as the actuator and the structure. In this work this was done by designing and constructing a tube shaped metamaterial demonstrator of a high precision positioning system. The 3D geometry of the metamaterial was built by layering planar pre-fabricated structures which use smart material for actuation. The design of the unit cells can be implemented in metamaterial of any shape and allows for miniaturization, which extends its applicability. The metamaterial was capable of vertical displacements. The constructed metamaterial tube was able to bend itself. Measured maximum amplitudes of a single layer, and the three layered stack were respectively 4.60 μm and 6.91 μm. Roll movement of the top layer of the stack was achieved with a lowest point of -0.13 μm and a highest point of 8.49 μm. The system showed that smart materials are a suitable choice to make metamaterial active, and that active metamaterial could be produced using production material. The planar approach for design and fabrication, provides a relatively simple and fast method for building metamaterial in general.

Proteins play a key role in many biological processes and are thus useful indicators of health and disease states. Since the size of proteins is few hundred nanometers, it is necessary to explore new techniques to manipulate and 'read' them. This thesis aims to identify and build a platform that enables sub-micron bead manipulation, which will be used to actively deliver the biomolecules attached to the beads to the single-molecule sensor. During this process, accurate positioning, speed control, and multiplexing of the beads need to be solved to give high-resolution and high-throughput sequencing capabilities. We identify surface acoustics wave (SAW) devices as powerful tools to achieve both beads transport and massively parallel manipulation. Our hypothesis is that we can increase the efficiency and precision of bead capture and manipulation by using SAW devices combined with a microcavity layer. In this master thesis, we fabricate the SAW device with an average 2 $\mu m$ thick film, and there are cavity arrays on the film. In addition, we investigate the performance of trapping sub-micron objects during the actuation. Further more, we discuss few challenges found through the experiments and provide possible solutions for them. At last, this thesis is concluded by discussing the work been done and providing suggestions for future experiments.

This thesis aims to solve the problems and fabricate fully inkjet-printed dielectric elastomer actuators with silver electrodes and a PDMS middle layer. First, a conductive silver electrode is printed on a coated PET substrate, followed by a printing of the dielectric elastomer middle layer to cover the bottom electrode. Then, the top silver layer is printed on the PDMS to achieve the top electrode. The problems intended to be solved in this work include printing the dielectric elastomer middle layer, treating
the PDMS layer, the significant surface cracking, and the non-conductivity of the top electrode. During the fabrication process, different concentrations of PDMS solution are tested printing. Observations on these printed samples are made to validate the most suitable printing solution and printing process/settings. Different surface treatment cycles for the PDMS layer are also adopted to determine the most suitable one, what effect is brought to the PDMS layer surface, and how they influence the top electrode. For the fabrication of the top electrodes, experiments are accomplished and repeated, coming with failures, which will be presented and discussed later. Lastly, displacement and frequency response measurements are essential to check the performance of the DEAs, being critical sections of the thesis.

Airbrushing is an affordable contactless printing technology capable of spraying fine lines to large areas with minimal adjustments. In the literature, deposition of conductive inks on substrates has primarily been researched using inkjet printing or direct ink writing. Despite its advantageous features, airbrushing is seldom used, and when so, it is commonly in combination with stencils or dissolvable structures.
The aim of the research was to combine airbrushing with fused filament fabrication to enable integrated fabrication of functional materials. For this study, a carbon paste was chosen as the active material to be sprayed on 3D printed polylactic acid (PLA) substrates. Beginning with the characterization of an airbrush-compatible acrylic paint, a carbon ink solution was formulated to match the paint viscosity characteristics. This solution was airbrushed on dedicated microporous substrates for characterization, using different positions of the airbrush needle and varying spray distance. In parallel, simulation of the multi-phase airbrushing process was approached using separate air and liquid COMSOL models. Based on the characterization results, the second phase was to study the deposition of carbon ink on 3D printed PLA. Following deposition challenges with the ink, improvement of the PLA surface characteristics using acetone was investigated. While contact angle measurements indicate no wetting improvement, experimental sprays demonstrated an improved deposition. This research has shown the possibility to airbrush conductive lines down to millimeter resolution on dedicated substrates and the possibility of combining airbrushing with acetone-treated 3D printed PLA substrates to realize initial multi-material prints. Although the resistance of the sprayed lines on the prints is between the high kΩ and low MΩ range, it shows potential for further research.

Going beyond naturally occurring materials, Metamaterials exploit a design at the microscale resulting in macroscopic behaviour, to achieve different or even new properties that can have a wide range of applications. By incorporating sensors, actuators and control, Robotic Metamaterials can achieve even more extremely different behaviour such as odd elasticity. By using local control and non-reciprocal couplings between actuators, an asymmetric elastic response can be achieved. Due to the non-conservative nature of this coupling, the system has a tendency to cycle and give rise to complex behaviours such as locomotion. Through simple and localized control, complex material behaviour is achieved, where the body is performing the computation and no complex control or computations systems are required.

In this work, a new unit cell for a metamaterial that achieves this odd elasticity is designed, manufactured, and finally tested. The unit cell consists of 3 hexagonal mechanisms with compliant joints and a linear actuator inside and is locally controlled. By using a novel Actuator design and engineering principles such as compliant mechanisms, a unit cell design is achieved that has 10 times smaller scale per area and 15 times higher strength-to-weight ratio compared to existing work. Finally, this unit cell was characterized and combined into a larger lattice showcasing the possibilities for future research into the behaviour of odd elastic metamaterials.