Inertial Element
Inertial sensing mechanisms rely on an internal suspended body to convert external acceleration into mechanical displacement. Micro-electromechanical accelerometers use a proof mass fabricated from single-crystal silicon to detect motion along defined physical axes. Applied acceleration forces the suspended structure to shift position relative to the sensor frame according to Newton’s second law of motion.
Analysis of this component ceases to apply when structural mechanical stress exceeds the elastic limit of the supporting suspension springs.
Mechanical Suspension
Micromachined silicon flexures support the central suspended structure while establishing structural stiffness along non-sensing directions. Spring design dictates structural resonant frequency and shock survival limits for the sensor assembly. Calibration procedures measure cross-axis sensitivity by rotating the sensor module through calibrated gravitational angles.
High impact loads can deform support flexures permanently, causing irreversible zero-g offset shifts in calibrated instruments.
Capacitive Sensing
Displacement of the internal mass varies the distance between fixed fingers and movable comb electrodes attached to its perimeter. Differential capacitance circuits convert sub-nanometer movements into output voltage signals proportional to input acceleration. High-resolution readout electronics detect minute capacitance variations while suppressing parasitic board-level capacitance.
Electrostatic attractive forces between comb fingers can alter spring stiffness if excitation voltages exceed design limits.
Damping Boundary
Hermetic packaging controls gas pressure around the suspended mass to achieve critical mechanical damping performance. Squeeze-film damping prevents unwanted resonant amplification when external vibration matches structural natural frequency. Temperature changes alter gas viscosity within the cavity, introducing temperature-dependent frequency response variations during operation.
