Surface Micromachined Sensors for Vehicle Navigation Systems

Today, most vehicle navigation systems use a GPS receiver as the primary source of information to calculate position. While the systems have become increasingly accurate in generating coordinates under ideal conditions of operation, it is a widely acknowledged fact, and studies have shown, that such systems can become highly unreliable in urban environments. Recently, much work has been accomplished and many solutions have been proposed to improve accuracy and minimize problems associated with poor signal reception. Nevertheless, dead reckoning relying on inertial navigation has become the de facto back up method to generate position in the absence of GPS signals. Together with gyroscopes which are an intrinsic part of such inertial navigation systems, accelerometers are now being considered for the function of measuring velocity, one of the requirements of dead reckoning. Recent progress in the development of Integrated MicroElectro Mechanical Systems (iMEMS) using surface micromachining technology are now enabling new form factors and price points for this function. In this paper, we introduce the concept of dead reckoning and its requirements, describe the process of surface micromachining and propose a cost effective solution for velocity measurement in an inertial navigation system with the use of the ADXL202, a low-cost, low-g dual axis accelerometer from Analog Devices.