| A threshold accelerometer array has been successfully designed, fabricated, and tested that is 40 times more sensitive than has been previously reported in the literature. The intended application is for use as a wake-up sensor for an environmental monitoring system with a 10-year battery life. The requirements for such a device are low power consumption, high sensitivity, and a wide dynamic range. There are many other potential applications, including biomedical monitoring and earthquake detection.; The threshold accelerometer array consists of 19 elements to detect accelerations ranging from 10 g to 150 g in 10 g increments. The 20 g and 100 g sense elements are triply redundant for better fault tolerance. The threshold accelerometer is a passive device that minimizes power consumption.; Two types of built-in test may be performed: a pull-in voltage test, and a transit time test. The pull-in voltage test is the standard test reported in the literature. The transit time test is a new test that performs a more thorough test.; Additional features of significance include the use of tall structures manufactured with a modified sacrificial LIGA technique, the use of a gold coated contact, and the use of design features that improve reliability and yield. The sacrificial LIGA technique is a two mask process that incorporates all the structural materials on one mask, permitting perfect alignment between components.; The theory behind the threshold accelerometer's operation is presented. The theory includes a discussion of the built-in test feature, the static and dynamic response, and the mechanical noise. The theory is in close agreement with results obtained from the finite-element analysis program ANSYS.; The sacrificial LIGA fabrication sequence is detailed, and measurement results of the fabricated devices show that the devices work as expected. The built-in test feature was verified to work for both the pull-in voltage method and the new transit time method. Additional measurements were taken using applied accelerations. In both cases, the measured performance is within 20% of theory, which is commensurate with the uncertainty in material properties and structural dimensions. These measurements confirm a working threshold accelerometer array. |
