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Advanced sensor systems


The CAS group has acquired a considerable expertise in the field of advanced sensor systems. Here, research is typically carried out in close cooperation with industrial partners. For instance, in the past, work has been done around very accurate speed measurement systems, aiming for applications in the steel cable industry.

 

In the last years, a substantial amount of knowledge has been acquired related to micro-mechanical (MEMS) inertial sensors with high accuracy. These sensors can be used to measure accelerations (accelerometers) and rotation speeds (gyroscopes). The interest from industry in this type of sensors is very high. An appealing application is the development of a low-cost inertial navigation systems which can take over during GPS blackouts. Next to this, there are plenty other automotive applications in which inertial sensors have a prominent role: ESP (Electronic Stability Program), EAS (Electronics Active Steering), ACC (Adaptive Cruise Control), etc.

 

The development of advanced sensors like MEMS gyroscopes requires a multidisciplinary approach, where the mechanical and electrical designs are tuned towards each other. Even so, unavoidable technological imperfections of the mechanical structure cause a number of difficult problems. In order to tackle these problems, an appropriate system-level approach has been worked out by our group. In this, Sigma-Delta conversion techniques applied to mixed mechanical-electrical systems play a prominent role. The whole setup has been validated in a state-of-the-art prototype (photo right). Note that the micromechanical sensor is not directly visible. This is because the MEMS gyroscope structure is encapsulated to allow operation under reduced pressure conditions.

 

The second generation of these Sigma-Delta based gyroscopes (photo left) contains some optimizations at the level of the readout circuits. By operating these readout circuits in continuous time, it is possible to reduce the noise floor (basically by avoiding aliasing), which translates into a higher performance. This kind of circuit optimizations fits in a broader field of activities related to analog chip design.

The CAS group also designs micromechanical structures. An important verification tool during this design process is finite element analysis (FEA). The image to the right is a part of the result of a typical result of a modal analysis of an accelerometer. A mode represents a natural oscillation pattern of the structure and is associated with a fixed frequency. Every mechaniscal structure has an infinite number of modes; however, one is interested in only a few low-frequency modes.