Microcantilever sensors are commonly used as chemical and biological sensors. Interactions between the functionalisation layer on the cantilever and the analytes in the sample cause the cantilevers to bend. When the analyte concentration is low, these interactions are localized. Then, the same concentration can cause different deflections, depending upon the locations of interactions. The deflections will thus depend on the location of interaction, as well as the concentration of the analyte. This paper presents a model to calculate the deflection, when uni-axial surface stresses are distributed and localized. Results of this model are compared with finite element method simulation results. Biaxial stresses are then considered, and the one dimensional model is shown to be a valid approximation when the stresses are not applied at the ends. Using the model, characteristic response curves of a cantilever, when the surface stresses are localized, are obtained. The probability of determining a concentration based on an observed deflection is shown to be as low as 20%.
The increasing requirements for antenna apertures with multiple functions in terms of frequency diversity, beam steering and beam shaping have lead to the concept of re-configurable antennas. RF MEMS switch technology is promising to enable the development of such structures. Through electromagnetic analysis, this research demonstrates the feasibility of using RF MEMS switches to facilitate the phase shifting required for phased array beam steering. A particular problem associated with the practical implementation of RF MEMS switches, the substrate choice, was investigated. Ceramic substrates have appropriate loss tangent coefficients and dielectric constant, however, the thermal mismatch between silicon nitride and other materials used to construct the mechanical parts of the switch introduces thermal mismatch stress and process problems during fabrication. Micro RF relay switches on a ceramic substrate have been fabricated and their pull-in voltage characteristics were measured and compared to the theoretical results for the RF relays.
Glaucoma is one of the leading causes of blindness affecting millions of people worldwide. Regular monitoring of intra ocular pressure (IOP) in the eyes is an important component in the treatment of this affliction. Current manual measurements do not give room for continuous indication of the progression of the disease. Microelectromechanical System (MEMS) technology lends itself to the development of devices capable of in-situ monitoring of the phenomenon that occur at the micro and nano scales, inside the human body. The paper reports on the complex flow and pressure relationships in the eye and the current methods of monitoring Glaucoma. The comparison highlights the requirements of an implantable miniature device that can indicate the changes leading to an increase of IOP inside the eye. An analysis of the pressures in the anterior chamber of the eye was undertaken to estimate the out put voltages that could be obtained from a micro structure implanted in the eye.
Microcantilevers are commonly used as part of sensor elements in Microelectromechanical Systems (MEMS). Deflection or the shift of resonance frequency of microcantilever beams are regularly used to measure chemical, physical or biological quantities. An important characteristic of any sensor is its sensitivity to a given input. This paper explores the possibility of improving the sensitivity of a microcantilever by modifying the mechanical properties using partial perforations on the surface of the microcantilever. This paper presents two analytical models that quantify the deflection and the fundamental resonant frequency in terms of the perforation dimensions for a microcantilever beam. Beams with a single partial perforation are considered first, and the models are then expanded to include multi-perforated cantilevers. Results obtained from the analytical models are compared to Finite Element Analysis (FEA) simulations of perforated microcantilever beams. The analytical models of a microcantilever with a single perforation show high accuracies compared to the FEA, while the accuracy of results for a cantilever beam with many perforations decrease as the number and size of perforations are increased. The results of the models are used to design a cantilever beam with the desired mechanical properties.
A new bulk micromachined Fabry-Perot modulator fabricated using (110) silicon is presented. The modulator has been developed to reduce the alignment and packaging restrictions imposed on surface micromachined Fabry-Perot modulators. The Fabry-Perot modulator consists of two vertical micromachined cantilever mirrors. The modulator is capable of a modulation depth of 7.8dB for modulation frequencies of up to 100kHz making it suitable for multiplexing low bandwidth sensors. Analytical results of the performance of the modulator compared to current microelectromechanical systems (MEMS) modulators are given and experimental results of the fabrication process indicate the practical realisation of the modulator. The design aspects of the modulator are analysed including the trade-off between bandwidth, beam length and drive voltage.
The coupled interaction between the mechanical deflection of a cantilever beam and an applied electrostatic field is a non-linear problem. A simple and efficient model is desirable in the initial design phase of MEMS structures. A new analytical model is developed which is versatile and applicable to complex cantilever structures. The model is verified and compared to current analytical approaches and Coventorware. The model is used to examine the novel electromechanical properties of double cantilever beams. Double cantilever beams exhibit a minimum pull-in voltage when the overlap distance between the beams is one half the length of the beams. This result has application to tunable micro-cantilever switches, and the geometrical relationship of the cantilever beam to dynamic range of the switching voltage is discussed.
The development of an optical modulator that can be integrated directly with different types of MEMS sensors and multiplexed onto a single optical fibre network will provide an improved functionality over current optical interfacing techniques. Narrow bandwidth modulators are required for linear sensor arrays to allow rapid connection of sensors, such as MEMS inertial sensors, with relative ease and low insertion loss to an optical network. A new MOEMS Fabry-Perot modulator fabricated using bulk micromachining is proposed. The modulator has been developed to reduce the alignment and packaging restrictions, the complexity and weight of a large sensor system. The modulator allows multiple sensors to be connected to the same optical fibre. Analytical and experimental results of the optical characteristics of the modulator are compared to current MEMS modulators and the fabrication constraints of the modulator are described.