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The objective of this dissertation is to investigate several dynamical approaches aiming to improve the sensitivity and performance of microelectromechanical systems (MEMS) resonant sensors. Resonant sensors rely on tracking shifts in the dynamic features of microstructures during sensing, such as their resonance frequency. We aim here to demonstrate analytically and experimentally several new concepts aiming to sharpen their response, enhance the signal to noise ratio, and demonstrate smart functionalities combined into a single resonator. The dissertation starts with enhancing the excitations of the higher order modes of vibrations of clamped-clamped microbeam resonators. The concept is based on using partial electrodes with shapes that induce strong excitation of the mode of interest. Using a half electrode, the second mode is excited with a high amplitude of vibration. Also, using a two-third electrode configuration is shown to amplify the third mode resonance amplitude compared with the full electrode under the same electrical loading conditions. Then, we demonstrate the effectiveness of higher order mode excitation and metal organic frameworks (MOFs) functionalization for improving the sensitivity and selectivity of resonant gas sensors. Also, using a single mode only, we show the possibility of realizing a smart switch triggered upon exceeding a threshold mass when operating the resonator near the dynamic pull-in instability. The second part of the dissertation deals with the dynamics of the microbeam under a two-source harmonic excitation. We experimentally demonstrate resonances of an additive and subtractive type. It is shown that by properly tuning the frequency and amplitude of the excitation force, the frequency bandwidth of the resonator is controlled. Finally, we employ the multimode excitation of a single resonator to demonstrate smart functionalities. By monitoring the frequency shifts of two modes, we experimentally demonstrate the effectiveness of this technique to measure the environmental temperature and gas concentration. Also, we present a hybrid sensor and switch device, which is capable of accurately measuring gas concentration and perform switching when the concentration exceeds a specific (safe) threshold. In contrast to the single mode operation, we show that monitoring the third mode enhances sensitivity, improves accuracy, and lowers the sensor sensitivity to noise.

Using biogas to partially replace diesel fuel in agriculture tractors seems a good solution to reduce greenhouse gases and other pollutants. For this reason, a research project to convert a tractor to dual-fuel operation was initiated; this paper's specific aim was to develop a control algorithm feeding biogas to the engine's intake manifold. The effect of biogas addition on engine performance, focusing on brake specific heat consumption and fuel replacement rates, was first studied. Then several load estimation methods were assessed and the Manifold Absolute Pressure (MAP) sensor was chosen as a main load detector. Finally, a prototype algorithm was built upon an engine control unit and was tested. The algorithm was able to change biogas flow with engine speed and load, without knock and misfire.

The research on biogas tractor was started as a possible solution to reduce tractor's fuel consumption and increase farmer's benefit out of a biogas plant. The tractor was equipped with a fontal gas unit containing 4 cylinders of purified biogas (more than 95% methane) with a volume of 26.5 L each at 19.6 MPa. A pressure regulating system was used to insure constant pressure potential across the biogas injectors. Based on previous study regarding biogas effects on the diesel engine, two possible algorithms were developed and tested. In the field tests, the first one was successful at replacing the high amounts of fuel (about 80%) while the other was able to run the engine at its best efficiency point.

In this study, we present analytical and experimental investigation of electrically actuated micro cantilever based resonators. These devices are fabricated using polyimide and coated with chrome and gold layers from both sides. The cantilevers are highly curled up due to stress gradient, which is a common imperfection in surface micro machining. Using a laser Doppler vibrometer, we applied a noise signal to experimentally find the first four resonance frequencies. Then, using a data acquisition card, we swept the excitation frequency around the first four natural modes of vibrations. Theoretically, we derived a reduced order model using the Galerkin method to simulate the dynamics of the system. Extensive numerical analysis and computations were performed. The numerical analysis was able to provide good matching with experimental values of the resonance frequencies. Also, we proved the ability to excite higher order modes using partial electrodes with shapes that resemble the shape of the mode of interest. Such micro-resonators are shown to be promising for applications in mass and gas sensing.