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Often in medical applications a single measurement does not give sufficient information to the clinicians. IC technology allows the combination of several sensors in a small volume for instantaneous multi-measurements at a single location. This paper presents two multi-parameter sensors for catheter applications, with initial experimental results, along with the packaging issue - an important aspect for biomedical sensors.

This thesis describes the research for, and the assessment of a new type of energy source and actuation, applicable to a Micro Aerial Vehicle (MAV). From the preliminary study resulted a promising energy source: hydrogen peroxide (H2O2) which is combined with the basic principle of the internal combustion engine for conversion to mechanical energy. The combination of this energy carrier and the conversion into mechanical energy is achieved by applying catalytic decomposition. The focus of this thesis is to assess whether a catalytic driven process using H2O2, is suitable for functioning as: means of energy conversion at micro scale. To verify the potential of the proposed combination of principles, experiments are performed. A number of different catalysts are prepared and tested in an experimental setup which monitors process behavior, speed and temperature. The process behavior is recorded by a high speed camera, pressures are measured simultaneously by means of pressure sensors and the temperature is measured using a small thermocouple. Test results show that the use of manganese oxide deposited using acetate as precursor, leads to the fastest processes and highest pressures. Reaction times as low as 70ms have been recorded, resulting in pressure peaks exceeding 13kPa which is higher than predictions. The static pressures do correspond with theory and consist of only the pressure caused by the generation of oxygen. The water vapor generated during the reaction quickly condensates as the gas mixture cools down, leaving behind only oxygen gas at room temperature. This indicates an advantage of using a cyclic process, using the short term high pressure. The temperatures occurring during the decomposition process of H2O2, are around the 100oC due to the production of water vapor. This temperature is not exceeded since too little energy is present in the used 30% weight to weight (w/w) concentration of H2O2, as predicted. From high speed camera recordings the process behavior is monitored and shows that a catalyst deposited on a blank ceramic tile without the use of a porous zirconia layer, comes loose from the tile during reaction. This allows for an increased reaction surface which corresponds to shorter reaction times. Based on the theory and the tests performed, flight duration for 1ml of H2O2, will be around 17-57 minutes for respectively 30-98% w/w concentrated H2O2. Regarding the use of the proposed means of energy conversion from liquid chemical energy into mechanical motion, a number of sub system components are proposed, for smart system design. At the chemical side, further developments lie in the characterization, miniaturization and optimization of the catalytic process for use at micro scale. At the mechanical side, developments lie in the actuation system design which operates on the gas formation driven by catalysis of H2O2. Smart system design has to be applied in order to obtain a sufficiently high energy density regarding weight while still allowing for sufficient system endurance and fabrication.

This paper presents an overview of a new type of thermal micro-actuators using thermally expandable polymers with embedded skeletons. Embedding a stiff skeleton enhances the actuation capability of the thermally expandable polymer. Consequently, the skeleton-reinforced polymers feature a large maximum actuation stress (often above 100 MPa) and a moderate maximum strain (often above 1%) besides a faster thermal response. In addition, the present composite design has room for performance improvement by tuning the volume fraction of the polymeric expander or selecting a proper expander material. Furthermore, the micro-actuators can be taylored for different motion characteristics, using various skeleton shapes. Finally, we discussed the possible applications using the present actuators.

A powerful and effective design of a polymeric thermal microactuator is presented. The design has SU-8 epoxy layers filled and bonded in a meandering silicon (Si) microstructure. The silicon microstructure reinforces the SU-8 layers by lateral restraint. It also improves the transverse thermal expansion coefficient and heat transfer for the bonded SU-8 layers. A theoretical model shows that the proposed SU-8/Si composite can deliver an actuation stress of 1.30 MPa/K, which is approximately 2.7 times higher than the unconstrained SU-8 layer, while delivering an approximately equal thermal strain.

In this letter, the dominant role of surface stress and surface elasticity on the overall elastic behavior of ultrathin cantilever plates is studied. A general framework based on two-dimensional plane-stress analysis is presented. Because of either surface reconstruction or molecular adsorption, there exists a surface stress and a surface elasticity imbalance between top and bottom surface of the cantilever. The surface elasticity imbalance creates an extra bending-extensional coupling which has not been taken into account previously. This leads to a modified extensional stiffness, bending stiffness and bending-extensional coupling stiffness. Due to the surface stress imbalance, an extended Stoney’s formula for self-bending of ultrathin cantilevers is derived.

The main purpose of this thesis is to find a future direction for the engine project for the FWM of the Atalanta project. Based on previous work done by Arjan Meskers [60], it was indicated that hydrogen peroxide is a good candidate as energy source for small scale engines because of its ease of implementation and relatively high energy content. Using hydrogen peroxide as a starting point, further research has to be done to explore different possibilities for the FWM engine. The first step is done in Chapter 1: an exploration of other projects on a similar scale. By learning from these projects that are described in literature, it is observed that certain directions are certainly not suitable for the FWM engine. For example, the bladed turbine has not the potential to become the FWM engine since the performance is too low and the requirements to make the system work are too substantial. Also, there is a clear indication that engines with a traditional cylinder piston assembly are dominated by leakage effects and therefore are also not successful on small scale. With this information a subset of the possibilities for the FWM engine is assembled in the form of concepts. These concepts are selected on their potential on small scale, their potential to be realized in a relatively short time span and their diversity. A candidate that does have potential is the small scale heat engine, represented by Concept 3. The performance is too low of similar projects found in literature, but they are not optimized for the FWM situation. Also, an indication in literature is found that the power density of these types of engines has good scaling behavior. Another potential candidate for the FWM is formed by applying a solution for the leakage problems of the small scale piston cylinder assembly. In Concept 1 flexible material is used between a piston and cylinder such that no fluid can leak through the gap. The blade-less turbine, also called a Tesla turbine, is used in Concept 2. It is described in literature to have a good theoretical potential on small scale, although not much experimental projects are found. The next step is to indicate what determines the performance characteristics for these small scale engines and how it relates to the requirements for the FWM engine. This is done in Chapter 2. The very basics for the thermodynamic cycle theory is the Carnot cycle, which closely resembles the operation principle of Concept 3. This is used as a starting point for approximating the performance of the concepts. The extension of the Carnot cycle is the Curzon Ahlborn model, which shows that the performance is completely determined by a certain potential and the utilization of that potential. The potential determines the magnitude of the incoming energy flow. The utilization determines how much of that incoming energy is converted into useful mechanical work. The nondimensionalization of the Curzon Ahlborn model shows that the utilization of the engine does not depend on any absolute scale, but merely on the ratio’s between certain engine parameters. These findings are tested on a more complicated model of the same system. By introducing the energy balance of the working fluid into the model, a time response of its temperature is obtained. This model shows that similar characteristics can be expected regarding the potential and utilization. This information is used to formulate a search method for finding the optimal configuration of the engine model to ensure maximum utilization for a given potential. By making an estimate of the engine potential based on measurements found in literature, this search method is used to give an indication of the performance characteristics as function of the scale of the engine. The study of Curzon Ahlborn type models is mainly focused on engines that have a compression and expansion step in the cycle and engines that use heat conduction as main energy transfer mode. Also all the models in the beginning of Chapter 2 are based on the assumption that work is extracted by a pressure force. Concept 2, the Tesla turbine, uses a different method of work extraction and has no compression step. Therefore, a separate model is presented at the end of Chapter 2 to characterize this concept. It is observed how the power output can be improved and how the efficiency is influenced accordantly. Measurements are found in literature from Tesla turbines at the exact scale that is opted for the FWM engine. These measurements are done with very small pressure differences, because the tests are done with a different application in mind. By combining the measurement results and the information from the simple model it is concluded that Concept 2 has no potential as FWM engine. One of the selection criteria for the engine concepts was that they all have different operating principles. Consequently, they all have different types of energy inflows. The energy flows of the remaining two concepts are explored more thoroughly in Chapter 3. Heat flow is studied first, since it is indicated by literature as the most significant loss mechanism for small scale engines. The characteristics of the complex real life situation are modeled in a multi physics simulation and linearized around the scale of interest for the FWM. The catalytic reaction is the primary energy inflow for all concepts, but based on measurements done by A.J.H. Meskers [60] it was observed that for Concept 1 the catalytic reaction characteristics might be critical. This is because the reaction time of small drops was found to be in the same order as the opted cycle time for the FWM in its current size. To study the characteristics of the catalytic reaction in more detail, a model is constructed based on the energy balance and fitted to the experimental data. The last energy flow identified is the exhaust fluid flow in concept 1. Due to time restrictions a full detailed analysis of this subject needs to be done in future work, but a basic analysis using the theory of gas dynamics is given. By approximating the shape of the exhaust as a round nozzle and assuming that friction has not much influence, the mass flow is given as function of a pressure difference. The findings of Chapter 3 are used in Chapter 4 to construct two models for the two remaining concepts. A numerical method for finding the steady state of these models is discussed and tested by comparison with analytical results. The performance of the models is obtained using these steady states. For Concept 3 it is observed that the performance is too low for the FWM in its current size, but has potential if the geometric scale of the system is reduced. This is due to favorable power density scaling of Concept 3. Of course this is only true if the operation principle of the real engine closely resembles the model. In the model a fixed temperature difference between the two heat sinks is assumed. This might be problematic in a real situation because it will be more difficult to accomplish a temperature difference when the geometric scale is reduced. For Concept 1, the engine model is a combination of the energy balance of the species inside the cylinder and the exhaust flow model described in Chapter 3. To reduce the sensitivity of the conclusions to the uncertainties of these models, two sets of parameters are used. One is considered optimistic and the other pessimistic. It was found that the performance for both sets is in the right region for the FWM engine requirements. This suggests that among the considered concepts, Concept 1 is the best way forward for the engine project of the FWM.

Submicron cantilever structures have been demonstrated to be extremely versatile sensors and have potential applications in physics, chemistry and biology. The basic principle in submicron cantilever sensors is the measurement of the resonance frequency shift due to the added mass of the molecules bound to the cantilever surface. This paper presents a theoretical model to predict the resonance frequency shift due to molecular adsorption on submicron cantilevers. The influence of the mechanical properties of the adsorbed molecules bound to the upper and lower surface on the resonance frequency has been studied. For various materials, the ratio between the thicknesses of the adsorbed layer and the cantilever where either stiffness or added mass is dominant will be determined. The critical ratio (which contribution of effect cancel each others) between the thickness of the adsorbed layer and the cantilever and ratio between stiffness and density of adsorbed layer and cantilever have been determined. The calculations show the added mass and stiffness how contribute to the resonant behavior. This model gives insight into the decoupling of both opposite effects and is expected to be useful for the optimal design of resonators with high sensitivity to molecular adsorption based on either stiffness or mass effects.

In this paper, we illustrate and study the opportunities of resonant ring type structures as wing actuation mechanisms for a flapping wing Micro Air Vehicle (MAV). Various design alternatives are presented and studied based on computational and physical models. Insects provide an excellent source of inspiration for the development of the wing actuation mechanisms for flapping wing MAVs. The insect thorax is a structure which in essence provides a mechanism to couple the wing muscles to the wings while offering weight reduction through application of resonance, using tailored elasticity. The resonant properties of the thorax are a very effective way to reducing the power expenditure of wing movement. The wing movement itself is fairly complex and is guided by a set of control muscles and thoracic structures which are present in proximity of the wing root. The development of flapping wing MAVs requires a move away from classical structures and actuators. The use of gears and rotational electric motors is hard to justify at the small scale. Resonant structures provide a large design freedom whilst also providing various options for actuation. The move away from deterministic mechanisms offers possibilities for mass reduction.

This letter presents the application of electrostatic pull-in instability to study the size-dependent effective Young’s Modulus Ẽ ( ~170–70 GPa) of [110] silicon nanocantilevers (thickness ~1019–40 nm). The presented approach shows substantial advantages over the previous methods used for characterization of nanoelectromechanical systems behaviors. The Ẽ is retrieved from the pull-in voltage of the structure via the electromechanical coupled equation, with a typical error of ≤ 12%, much less than previous work in the field. Measurement results show a strong size-dependence of Ẽ. The approach is simple and reproducible for various dimensions and can be extended to the characterization of nanobeams and nanowires.

Micro/nano resonant cantilevers with a laser deflection readout have been very popular in sensing applications over the past years. Despite the popularity, however, most of the research has been devoted to increasing the sensitivity, and very little attention has been focused on effects-induced errors. Among these effects, the surface effects and the so-called readout back-action are the two most influential causes of errors. In this paper, we investigate (1) the influence of the surface effects such as water adsorption, gas adsorption, and generally surface contaminations, and (2) the effect of the laser deflection detection, including power and positions of the laser, on the resonance frequency of silicon cantilevers. Our results show that both the surface contaminations and the laser back-action effects can significantly change the resonant response of the cantilevers. We conclude that the effects have to be taken into account, particularly in the case of ultra high sensitivity cantilevers.

A method for determining a spring constant k for a deformable probe element (102) of a scanning probe microscope SPM (100). The probe (102) has an outer surface area consisting of a tip area (112) on a first probe side (108) and a tip-less area (113). The probe (102) also has a probe electrode (114) and a scanning probe tip (104) in the tip area (112). The method comprises: providing an actuation electrode (116) that is spatially separated from the probe (102); adjusting a potential difference V applied between the probe electrode (114) and the actuation electrode (116); deflecting the probe (102) into a contacted state of the actuation electrode (116) with only a contact portion of the tip-less probe area (113); measuring an EPI-potential difference Vpi between probe electrode (114) and actuation electrode (116), and deriving the spring constant k, based on the EPI-potential difference Vpi. Furthermore, an SPM (100) and calibration device with this method functionality are provided.

The size-dependent elastic behavior of silicon nanocantilevers and nanowires, specifically the effective Young’s modulus, has been determined by experimental measurements and theoretical investigations. The size dependence becomes more significant as the devices scale down from micro- to nano-dimensions, which has mainly been attributed to surface effects. However, discrepancies between experimental measurements and computational investigations show that there could be other influences besides surface effects. In this paper, we try to determine to what extent the surface effects, such as surface stress, surface elasticity, surface contamination and native oxide layers, influence the effective Young’s modulus of silicon nanocantilevers. For this purpose, silicon cantilevers were fabricated in the top device layer of silicon on insulator (SOI) wafers, which were thinned down to 14 nm. The effective Young’s modulus was extracted with the electrostatic pull-in instability method, recently developed by the authors (H Sadeghian et al 2009 Appl. Phys. Lett. 94 221903). In this work, the drop in the effective Young’s modulus was measured to be significant at around 150 nm thick cantilevers. The comparison between theoretical models and experimental measurements demonstrates that, although the surface effects influence the effective Young’s modulus of silicon to some extent, they alone are insufficient to explain why the effective Young’s modulus decreases prematurely. It was observed that the fabrication-induced defects abruptly increased when the device layer was thinned to below 100 nm. These defects became visible as pinholes during HF-etching. It is speculated that they could be the origin of the reduced effective Young’s modulus experimentally observed in ultra-thin silicon cantilevers.