Plasma actuators are devices that with two electrodesand a dielectric material can ionize the air around itand thus control the airflow. They have considerable potentialfor a multitude of reasons, one of which being that they haveno moving parts, making them easy to produce and hard tobreak. Using this technology on the front of vehicles like truckscould be revolutionary in increasing fuel efficiency and thusreducing emissions. A model of a plasma actuator in COMSOLMultiphysics was used to simulate the effect it has on the airaround it. The focus of the project has been to optimize thedesign of an actuator for increased velocity in the air around it.This has been done with regards to properties of the appliedvoltage, the distance between the electrodes and material ofthe dielectric. Parametric analyses of all the above propertieswas performed. Close-to-optimal values of some of the abovementioned parameters were successfully calculated. However,other parameters, such as the horizontal distance between theelectrodes, were beyond the model’s capability to determine usingthe described method. / Plasmaställdon är anordningar som medtvå elektroder och ett dielektriskt material kan jonisera luftenrunt sig och på detta sätt styra luftflödet. De har betydandepotential av en mängd anledningar, varav en är att de inte har några rörliga delar, vilket gör dem lätta att producera och ochsvåra att förstöra. Användande av denna teknologi på fronterav fordon som lastbilar skulle kunna vara revolutionerande förökad bränsleeffektivitet och därmed minska utsläpp. En modellav ett plasmaställdon i COMSOL Multiphysics användes för attsimulera effekterna den har på luften runt sig. Projektets fokushar varit på att optimera ett ställdons design för ökad hastigheti luften runt den. Detta har gjorts med avseende på egenskaperhos den tillförda spänningen, avståndet mellan elektroderna ochdielektrikumets material. Parametriska analyser för alla dessaegenskaper har genomförts. Nästintill optimala värden för någraav de ovan nämnda parametrarna beräknades med framgång.Andra parametrar, som det horisontella avståndet mellan elektroderna,var bortom modellens förmåga att bestämma vidanvändande av den beskrivna metoden. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

När ett ställdon får som krav att kunna överföra höga krafter i relativt höga hastigheter med en dessutom väldigt hög precision är elektromekaniska ställdon oftast att föredra. En traditionell pinjong-kuggstång-uppställning uppfyller vissa av de kraven, men om kraften ska ökas behövs det fler än ett pinjongpar. Begränsningar på tillverkningsprecisionen för dessa kugghjul gör att deras ansättning på kuggstången blir omöjlig för uppsättningar med fyra eller åtta pinjongpar eftersom ett sådant ställdon blir statiskt överbestämt och på grund av tillverkningstoleranser kan det bli svårt att erhålla jämn lastfördelning mellan pinjongerna. Därför utvecklade företaget Cascade Drives innovativa kugghjul (cdGear) med s.k. Flex Units som har en självinställningsfunktion i själva kugghjulen vilken tillgodogör för tillverkningstoleranser och spelet som ska undvikas. Flex Units består av bl.a. av gummielement som förutom att tillåta enstaka pinjongers rotation för inställning även har en mycket bra dämpningsförmåga, särskilt vad det gäller plötsliga stötlaster. Stötbelastningar förekommer ofta vid drift av arbetsmaskiner där Cascade Drives-ställdonet har hittat sin största användning. Plötsliga och höga stötbelastningar, som t.ex. när en grävmaskin kör in i ett gupp eller en snöröjare kör på en kantsten kan påverka maskinkomponenternas livslängd betydligt. Ett eventuellt maskinhaveri riskerar skador på både fordonet, föraren och omgivningen. Rapporten redogör för hur en teoretisk modell byggdes upp för att matematiskt beskriva dessa stötbelastningar och metoder som användes i datorprogrammet MATLAB för att beskriva det dynamiska förloppet i ställdonet under stötbelastningens inverkan. Ytterligare redogörs avgränsningar som görs på modellen och tills slut ges förslag på möjliga förbättringar för vidare arbete med modellen. Projektets syfte är inte att utvärdera hela Cascade Drives-ställdonet utan endast skapa en modell som kan tillämpas på alla möjliga scenarion av stötmoment. Rapporten innehåller några exempel på stötbelastningar och redogör för hur de påverkar olika kugghjul som ingår i ställdonet och hur det påverkar maskinen i sin helhet. För de scenarion som MATLAB-koden testades för noteras en mycket god dämpningsförmåga även vid förhållandevis höga laster (flera ton av last). Detta tack vore de patenterade flexenheterna och gummikutsarna, som kan dimensioneras och väljas för material beroende på tillämpningsområde och det tillåtna monteringsutrymmet i ställdonet. Denna modell baseras på dimensioner och materialdata tillförda av uppdragsgivaren för det aktuella ställdonet. Mer noggranna värden och en bättre kännedom om tillämpningsområdet skulle ge möjligheter för omdimensionering av flexenheterna och en mer optimal dämpnings- och momentöverföringsfunktion i ställdonet. / When requirements for an actuator include big momentum, fast transfer of the forces with a very high positioning precision, electro-mechanical actuators are often the constructor's first choice. A traditional rack-pinion setup answers to some of the requirements, but if the goal is to increase the forces which the rack undergoes, more than one pair of pinions is necessary. Production limitations, inevitable tolerances and gaps as a result make it almost impossible to have setups of four or eight pinion-pairs on one single rack because a such actuator would be statically overdetermined and out of manufacturing costs it can be difficult to procure equal load distribution between the pinions. Overcoming this challenge helped the company called Cascade Drives based in Stockholm, Sweden, to patent a new type of gear they call cdGear. CdGear give pinion the ability to position itself to the rack automatically, due to the rubber parts inside the gear that also work as shock load-absorbers for the whole actuator. Shock loads are very frequent in the type of work where these actuators found their biggest application. Heavy-duty machines are often exposed to sudden and high loads on their moving parts, i.e. when an excavator drives over a bump or a snow-plowing machine drives into a curbstone. The sudden impact on the working parts will cause a greater stress on the equipment, shorten its lifespan and a machine part's failure can even cause serious damage on workers, machine, and the environment. This thesis describes a theoretical model created for the purpose of calculating the effects of shock loads on the actuator based on the mathematical description of gear behaviour during the impact. It also includes the methods used to create a model in MATLAB that simulates the dynamical forces, model's limitations, and suggestions on how to improve its accuracy. This project does not aim to improve the overall performance of the Cascade Drives-actuator, but rather deliver a sufficient virtual model that works for the most shock load scenarios, that in the end will give the commissioner useful data and clues on how to improve their product. The thesis does include a few different shock load scenarios that prove the code's functionality and give answers to how some shock loads affect gears inside the actuator and performance of the machine itself. For the virtual tests done Cascade Drives-actuator performs very good in damping the shock loads, even when the loads reach a corresponding force of a few tons. CdGear and elasticity inside its rubber parts are the main reason why the actuator performs so well, and the rubber parts inside the gear can be changed in respect to the application and the mounting space allowed. The model described in the report includes dimensions and material's data provided by the commissioner for the actuator in question. More exact and relevant results can be acquired if the input values are more precise, and the area of usage is described in more detail. More optimal rubber parts inside the CdGear would result in a better performing actuator that besides being able to transfer huge torque also could absorb the inevitable shock loads in a very satisfactory manner.

This research reviews and extends the impedance-based structural health monitoring technique in order to detect and identify structural damage on various complex structures. The basic principle behind this technique is to apply high frequency structural excitations (typically higher than 30 kHz) through the surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. Several case studies, including a pipeline structure, a composite reinforced aluminum plate, a precision part (gear), a quarter-scale bridge section, and a steel pipe header, demonstrate how this technique can be used to detect damage in real-time. A method to process impedance measurements to prevent significant temperature and boundary condition changes registering as damage has been developed and implemented. Furthermore, the feasibility of using the technique for high temperature structures and for condition monitoring of critical facilities subjected to a severe natural disaster has been investigated. While the impedance-based structural health monitoring technique indicates qualitatively that damage has occurred, more information on the nature of damage is necessary for remote structures. In this research, two different damage identification schemes have been combined with the impedance method in order to quantitatively assess the state of structures. One is based on a wave propagation modeling, and the other is the use of artificial neural networks. A newly developed wave propagation model has been developed and combined with the impedance method in order to estimate the severity of damage. Numerical and experimental investigations on 1-dimensional structures were presented to illustrate the effectiveness of the combined approach. Furthermore, to avoid the complexity introduced by conventional computational methods in high frequency ranges, multiple sets of artificial neural networks were integrated with the impedance-based health monitoring technique. By incorporating neural network features, the technique is able to detect damage in its early stage and to determine the severity of damage without prior knowledge of the model of structures. The dissertation concludes with experimental examples, investigations on a quarter-scale steel bridge section and a space truss structure, in order to verify the performance of the proposed methodology. / Ph. D.

We consider geometric and material nonlinearities when studying numerically, by the finite element method, transient three-dimensional electroelastic deformations of a graphite-epoxy square plate sandwiched between two piezoceramic (PZT) layers. Points on the four edges of the bottom surface of the plate are restrained from moving vertically. The two opposite edges of the plate are loaded by equal in-plane compressive loads that increase linearly with time and the other two edges are kept traction free. The plate material is modeled as orthotropic and neoHookean. For the transversely isotropic PZT the second Piola-Kirchhoff stress tensor and the electric displacement are expressed as second degree polynomials in the Green-St. Venant strain tensor and the electric field. Both direct and converse piezoelectric effects are accounted for in the PZT. The plate is taken to have buckled when its centroidal deflection equals three times the plate thickness. The dynamic buckling load for the plate is found to strongly depend upon the rate of rise of the applied tractions. With the maximum electric field limited to 1kV/mm, the buckling load is enhanced by 18.3% when the PZT elements are activated. For a peak electric field of 30kV/mm, the buckling load increased by 58.5%. When more than 60% of the surface area of the top and the bottom surfaces of the plate are covered by the PZT layers, then square PZT elements placed symmetrically about the plate centroid provide a larger enhancement in the buckling load than rectangular shaped or cross-shaped PZT elements. An increase in the plate thickness relative to that of the PZT actuators decreases the effectiveness of the PZT in enhancing the buckling load for the plate. The finite element code was modified to also analyze, in time domain, transient deformations of a viscoelastic material for which the second Piola-Kirchhoff stress tensor is expressed as a linear functional of the strain history of the Green-St. Venant strain tensor. It was used to analyze three-dimensional deformations of a thick laminated plate with layers made of aluminum, a viscoelastic material and a PZT. The following two arrangements of layers are considered. In one case a central PZT layer is surrounded on both sides by viscoelastic layers and aluminum layers are on the outside surfaces. The PZT is poled in the longitudinal direction and an electric field is applied in the thickness direction. Thus shearing deformations of the PZT layer are dominant. In the second arrangement, the aluminum layer is in the middle and the PZT layers are on the outside. The poling direction and the electric field are in the thickness direction; thus its extensional deformations are predominant. Three indices are used to gauge the damping of motion of plate particles, and the effectiveness of PZT actuators in enhancing this damping. It is found that the optimum thickness of the viscoelastic layers for maximum total energy dissipation is the same for each set-up. Also, the total thickness of the PZT layers which results in the maximum value of one of these indices of energy dissipation is the same for the two set-ups. Both arrangements give the largest value of this index for a plate of aspect ratio 10. Buckling behavior of a sandwich plate containing a soft core is also studied. The effects of the ratio of the elastic moduli of the outer layers to those of the core, and of the core thickness on the buckling load are analyzed. The top and the bottom layers are connected by very stiff blocks on two opposite edges where in-plane compressive time-dependent tractions are applied. / Ph. D.

This thesis presents work done to improve the switching speed and contrast performance of electrochromic devices. Layer-by-Layer (LbL) assembly was used to deposit thin electrochromic films of materials ranging from organic, inorganic, conducting polymers, etc. The focus was on developing new materials with high contrast and long lifecycles. A detailed switching-speed study of solid-state EC devices of already-developed (PEDOT (Poly(3,4-ethylenedioxythiophene)), polyviologen, inorganic) materials and some new materials (Prodot-Sultone) was performed. Work was done to achieve the optimum thickness and number of bilayers in LbL films resulting in high-contrast and fast switching. Device sizes were varied for comparison of the performance of the lab-made prototype device with the commercially available "small pixel" size displays. Symmetrical EC devices were fabricated and tested whenever conducting polymers are used as an EC material. This symmetrical configuration utilizes conducting polymers as an electroactive layer on each of two ITO-coated substrates; potential is applied to the two layers of similar conducting polymers and the device changes color from one redox state to another. This method, along with LbL film assembly, are the main factors in the improvement of switching speed results over already-published work in the literature. PEDOT results show that EC devices fabricated by LbL assembly with a switching speed of less than 30 ms make EC flat-panel displays possible by adjusting film thickness, device size, and type of material. The high contrast value (84%) for RuP suggests that its LbL films can be used for low-power consumption displays where contrast, not fastest switching, is the prime importance. In addition to the electrochromic work, this thesis also includes a section on the application of LbL assembly in fabricating electromechanical bending actuators. For bending actuators based on ionic polymer metal composites (IPMCs), a new class of conductive composite network (CNC) electrode was investigated, based on LbL self-assembled multilayers of conductive gold (Au) nanoparticles. The CNC of an electromechanical actuator fabricated with 100 bilayers of polyallylamine hydrochloride (PAH)/Au NPs exhibits high strain value of 6.8% with an actuation speed of 0.18 seconds for a 26 µm thick IPMC with 0.4 µm thick LbL CNCs under 4 volts. / Ph. D.

Magnetic sensors are widely used in the field of mineral, navigational, automotive, medical, industrial, military, and consumer electronics. Many magnetic sensors have been developed that are generated by specific laws or phenomena: such as search-coil, fluxgate, Hall Effect, anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), magnetoelectric (ME), magnetodiode, magnetotransictor, fiber-optic, optical pump, superconducting quantum interference device (SQUID), etc. Each of these magnetic field sensors has their merits and application areas. For low power consumption (<10uW), quasi-static frequency (<10Hz) and high sensitivity (<nT) application, magnetoelectric laminate sensors offer the best potential capability and thus are the topic of my dissertation. Here, in this thesis, I have focused on designs and optimizations of magnetoelectric sensor units (i.e., sensors and circuit). To achieve my goals, I have developed some useful rules for ME sensor and detection circuit design. For ME sensor optimization, designs should consider both frequencies far away from resonance and at resonance. For the former one, both internal and external noise contribution must be considered, as one of them will limit practical applications. With regards to the internal noise sources, I have developed two design optimization methods, designated as ”'scale effect” and “ME array”. I showed that they have the ability to increase the magnetic field detection sensitivity, which was verified by experiments. With regard to external noise consideration, I have investigated how the fundamental extrinsic noise sources (temperature fluctuation, vibration, etc) affect ME laminate sensors. A concept of separating signal and noise modes into difference is put forward. Optimization with this concept in mind required us to redesign the internal structure of ME laminate sensors. At the resonant frequency, the ME voltage coefficient α_ME is the most important parameter. To enhance resonant gain in α_ME, I have developed a three phase laminate concept, which is based on increasing the effective mechanical factor Q while reducing the resonant frequency. A ME voltage coefficient of α_ME ~40V/cm.Oe has been achieved at resonance, which is about 2x higher than that of a conventional bending mode. Investigations of detection circuit optimization were also performed. Component selection strategies and a new charge topology were considered. Proper component values were required to optimize the charge detection scheme. It was also found, under some specific conditions to satisfy the circuit stability, that if the lowest required measurement frequency of the charge source was f1, then that it was not necessary to make the high corner frequency <i>f</i>_p of the charge amplifier lower than <i>f</i>₁: as doing so would decrease the system's signal-to-noise ratio (SNR). A high pass, high order filter placed behind the charge amplifier was found to increase the charge sensitivity, as it narrows the intrinsic noise bandwidth and decreases the output noise contribution, while only slightly affecting the signal's output amplitude. Prototype ME unit were also constructed, and their noise level simulated by Pspice. Experimental results showed that prototypes ME unit can reach their detection limit. In addition, a new magneto-electric coupling mechanism was also found, which had a giant ME effect. / Ph. D.

This research discusses the mechanical characteristics of laminated piezoelectric actuators that are manufactured at an elevated temperature, to cure the adhesive bonding the layers together, or to cure the layers made of polymeric composite material, and then cooled to a service temperature. Mainly discussed are actuators that are composed of layers of passive materials and a layer of piezoelectric material. THUNDER (THin layer UNimorph ferroelectric DrivER and sensor) and LIPCA (LIghtweight Piezo-composite Curved Actuator) actuators, which consist of layers of metal, adhesive and piezoelectric material, and carbon-epoxy, glass-epoxy and piezoelectric material, respectively, are studied and investigated in detail to understand the thermal effects due to the elevated manufacturing temperature. Owing to the large out-of-plane deformations of the THUNDER actuators as a result of cooling to the service temperature, inclusion of geometric nonlinearities in the kinematic relations is taken into consideration for prediction of the thermally-induced deformations and residual stresses. The deformations and residual stresses are predicted by using a 23-term Rayleigh-Ritz approach and more rigorous, time-consuming, finite-element analyses performed with ABAQUS. The thermally-induced deformations of THUNDER actuators can result in multiple room-temperature manufactured shapes, whereas those of LIPCA actuators (LIPCA-C1 and LIPCA-C2) exhibit single room-temperature manufactured shape. Actuation responses of these actuators caused by a quasi-static electric field applied to the piezoelectric layer are also studied with the Rayleigh-Ritz approach. It is shown that geometrical nonlinearities play an important role in the actuation responses, and these nonlinearities can be controlled by the choice of actuator geometry and the materials in the passive layers. In addition, blocking forces representing load-carrying capability of THUNDER and LIPCA actuators are determined. Support conditions and again geometrical nonlinearities are vital factor in load-resisting performances. Amongst the actuators considered, the actuated deflection and blocking forces are compared. Finally, based on the outcome of this study, new criteria for designing a new type of laminated piezoelectric actuators with improvement of performance characteristics are proposed. / Ph. D.

In intelligent structures, structural deformation is generally controlled by either embedding or surface bonding the induced strain actuator to the structure. With bonded or embedded actuators used for inducing flexure, the developed in-plane force contributes indirectly through a locally-generated moment. Control authority in this configuration is thus limited by actuator offset distance. The focus of this research was to investigate a new concept in which the actuator, as opposed to being bonded, is attached to the structure at discrete points. This configuration is fundamentally different from the bonded/embedded configuration in that the actuator and the structure between the two discrete points can deform independently; and the in-plane force of the actuator, which contributes only indirectly in the case of bonded actuator, can directly influence out-of-plane displacements of the structure. Additionally, the actuator offset distance can be optimized with respect to actuator force/strain saturation for increased authority. Two implementations of this concept as applied to beam structures were investigated. In the first, the actuator (e.g., shape memory alloy actuator wire) does not possess any flexural stiffness; and therefore, remains straight between the two attachment points. In the second implementation, the actuator (PZT's and electrostrictive) possesses flexural stiffness, and bends with the structure. The formulation and experimental results for both implementations are presented. Enhanced authority is demonstrated by comparing the static response of the discretely attached actuator beam systems with their bonded counterpart systems. / Ph. D.

Piezoelectric patch-type actuators are being considered for use in acoustic control and vibration control of complex mechanical structures such as aircraft fuselages and automobile interiors. For complex structures, it is often difficult to predict the best location of actuator-structure interaction. Currently, piezoelectric patch-type actuators are bonded permanently to the host structure using a technique that requires surface preparation. This technique is not well suited for actuator performance testing and model verification since attaching the actuator is time-consuming, removing the actuator is difficult, and the actuator is destroyed when it is removed. We present three alternate techniques for bonding flat piezoelectric patch-type actuators to structures. These techniques allow the actuator to be attached quickly, removed easily, and reused. The alternate techniques and a permanent bonding technique are used to attach actuators to a clamped-free beam. For each attachment technique, we obtain the frequency response functions, actuator authority levels, and damping ratios. We also obtain the degradation of the actuator authority and damping ratio as the actuator is reused. For each attachment technique, we compare the measured performance to the performance predicted from a pin-force model of that actuator attachment. The attachment techniques that allowed us to make removable, reusable piezoelectric actuators were shown to provide structural actuation very similar to actuation provided by permanently attached piezoelectric actuators. A small but statistically significant change in authority occurred as a result of removing the actuator. The confidence intervals of actuator authority increased in frequency regions of antiresonance and closely spaced modes. The pin-force model did not provide an accurate analysis method for predicting actuator authority. / Master of Science

The effect of the shape of piezoceramic actuators on the vibration response of a simply supported beam is investigated. An equation is derived to convert between the shape of the piezoceramic actuator and the resulting moment distribution caused on the structure. A beam simulation program is then created to model the vibrations caused by various shaped moment distributions exciting a simply supported beam. The length of the moment distribution is iterated from the length of the beam to zero length, within the program, to show the trends in modal amplitudes. The amplitude of each mode is then plotted for each length of the moment distribution. An equation is then derived to explain the resulting minimums and maximums of the modal amplitudes. The equation is shown to be a useful tool in designing shapes to meet specific control criteria. An example is given showing how the shape of the actuator can be designed to give superior performance for specific control criteria than a traditional rectangular shape. Two possible actuator shapes are shown for the situation. One shape is optimized for the given control criteria by causing the maximum response for the critical mode. The results from the beam simulation for both shapes are shown. The shape of the actuator may now be used as a variable in the cost function for control optimization. / Master of Science