Atlantic Inertial Systems, Inc.

Kiran Harish

Alan R Malvern

Alan Richard Malvern

A sensor package comprising: a sensor, wherein the sensor comprises a sensing structure formed in a material layer and one or more further material layers arranged to seal the sensing structure to form a hermetically sealed sensor unit; a support structure; one or more springs flexibly fixing the hermetically sealed sensor unit to the support structure; wherein the one or more springs are formed in the same material layer as the sensing structure of the sensor unit; and one or more external package wall(s) encapsulating the sensor unit, the support structure, and the one or more springs, wherein the support structure is fixed to at least one of the package wall(s). The springs decouple mechanical stresses between the sensor unit and the external package wall(s) so as to reduce the long term drift of scale factor and bias.

Sensor packages

A capacitive accelerometer comprises: a substantially planar proof mass mounted to a fixed substrate by flexible support legs so as to be linearly moveable in an in-plane sensing direction. The proof mass comprises first and second sets of moveable capacitive electrode fingers. First and second sets of fixed capacitive electrode fingers interdigitates with the first and second sets of moveable electrode fingers respectively. A set of moveable damping fingers extend from the proof mass substantially perpendicular to the sensing direction, laterally spaced in the sensing direction. A set of fixed damping fingers mounted to the fixed substrate interdigitates with the set of moveable damping fingers and comprises an electrical connection to the proof mass so that the interdigitated damping fingers are electrically common. The damping fingers are mounted in a gaseous medium that provides a damping effect.

Accelerometers

A sensing structure for an accelerometer includes a support and a proof mass mounted to the support by flexible legs for in-plane movement in response to an applied acceleration along a sensing direction. The proof mass includes a plurality of moveable electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction. The structure also includes at least one pair of fixed capacitor electrodes comprising first and second sets of fixed electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction; the first set of fixed electrode fingers arranged to interdigitate with the moveable electrode fingers with a first offset in one direction from a median line therebetween, and the second set of fixed electrode fingers arranged to interdigitate with the moveable electrode fingers with a second offset in the opposite direction from a median line therebetween.

A closed loop method of controlling a capacitive accelerometer uses two servo loops. A Vcrit servo loop uses an output signal (S) modulated by a sine wave signal (S). The Vcrit control signal adjusts the magnitude of the PWM drive signals applied to the fixed capacitor electrodes of the accelerometer, thereby optimising open loop gain.

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Plymouth, United Kingdom

Kiran Harish