Abstract: A capacitive accelerometer includes a proof mass, first and second fixed capacitive electrodes, and a DC biasing element arranged to apply a DC voltage (VB) to the proof mass based on a threshold acceleration value. A first closed loop circuit is arranged to detect a signal resulting from displacement of the proof mass and control the pulse width modulation signal generator to apply the first and second drive signals V1, V2 with a variable mark:space ratio. A second closed loop circuit keeps the mark:space ratio constant and to change the magnitude, VB, of the DC voltage applied to the proof mass by the DC biasing element so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position, when the applied acceleration is greater than a threshold acceleration value.

Abstract: 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.

Abstract: 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.

Abstract: An angular velocity sensor comprises: an insulative support layer (10); a substrate layer (8) formed of a silica-based material and comprising a planar ring structure (2) mounted to vibrate in-plane; and a plurality of conductive electrodes (14), each comprising a first set of moveable conductive electrode tracks (14a) formed on a surface of the planar ring and a second set of fixed conductive electrode tracks (14b) formed on a surface of the insulative support layer axially spaced from the surface of the planar ring. The first and second sets of conductive electrode tracks are interdigitated with a lateral spacing between them in a radial direction. Each moveable conductive electrode track has a radial offset from a median line between adjacent fixed conductive electrode tracks such that each moveable conductive electrode track has a different lateral spacing from two different adjacent fixed conductive electrode tracks in opposite radial directions.

Abstract: A capacitive accelerometer includes a proof mass, first and second fixed capacitive electrodes, and a DC biasing element arranged to apply a DC voltage (VB) to the proof mass based on a threshold acceleration value. A first closed loop circuit is arranged to detect a signal resulting from displacement of the proof mass and control the pulse width modulation signal generator to apply the first and second drive signals V1, V2 with a variable mark:space ratio. A second closed loop circuit keeps the mark:space ratio constant and to change the magnitude, VB, of the DC voltage applied to the proof mass by the DC biasing element so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position, when the applied acceleration is greater than a threshold acceleration value.

Abstract: A navigation system comprising: an inertial navigation system arranged to output a first position estimate; a terrain based navigation unit arranged to output a second position estimate; a gravity based navigation unit arranged to output a third position estimate; a stored gravity map arranged to receive a position and to output gravity information for that position; and an iterative algorithm unit arranged to determine an INS error state in each iteration; wherein in each iteration the iterative algorithm unit is arranged to: receive the first position estimate, the second position estimate, and the third position estimate; determine a gravity corrected position estimate based on the first position estimate, the INS error state and the gravity information; and update the INS error state for the next iteration based on the INS error state, the gravity corrected position estimate, the second position estimate and the third position estimate.

Abstract: An accelerometer closed loop control system comprising: a capacitive accelerometer comprising a proof mass moveable relative to first and second fixed capacitor electrodes; a PWM generator to generate in-phase and anti-phase PWM drive signals with an adjustable mark/space ratio, wherein said drive signals are applied to the first and second electrodes such that they are charged alternately; an output signal detector to detect a pick-off signal from the accelerometer representing a displacement of the proof mass from a null position to provide an error signal, wherein the null position is the position of the proof mass relative to the fixed electrodes when no acceleration is applied; a PWM servo operating in closed loop to vary the mark/space ratio of said PWM drive signals in response to the error signal so that mechanical inertial forces are balanced by electrostatic forces.

Abstract: A sensing structure for an accelerometer includes a support and a proof mass mounted thereto by flexible legs. The proof mass has moveable electrode fingers perpendicular to the sensing direction and at least four fixed capacitor electrodes, with fixed capacitor electrode fingers perpendicular to the sensing direction. The fixed capacitor electrode fingers interdigitate with the movable electrode fingers and the proof mass is mounted to the support by an anchor on a centre line of the proof mass. The proof mass has an outer frame surrounding the fixed capacitor electrodes and the flexible legs extend laterally inwardly from the proof mass to the anchor. The fixed capacitor electrodes comprise two inner electrodes, one on each side of the proof mass centre line, and two outer electrodes, one on each side of the proof mass centre line.

Abstract: 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.

Abstract: An accelerometer includes a planar proof mass mounted to a fixed substrate so as to be linearly moveable in an out-of-plane sensing direction in response to an applied acceleration. The proof mass includes first and second sets of moveable capacitive electrode fingers extending from the proof mass perpendicular to the sensing direction in a first in-plane direction and laterally spaced in a second in-plane direction perpendicular to the sensing direction. The moveable capacitive electrode fingers interdigitate with corresponding sets of fixed capacitive electrode fingers mounted to the substrate. The first set of fixed fingers has a thickness less than a thickness of the first set of moveable fingers; and wherein the second set of fixed fingers has a thickness greater than a thickness of the second set of moveable fingers.

Abstract: 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.

Abstract: A method for controlling closed loop operation of a capacitive accelerometer comprises applying first in-phase and anti-phase PWM drive signals, respectively, to a first pair of fixed capacitive electrodes and applying second in-phase and anti-phase PWM drive signals, respectively, to a second pair of fixed capacitive electrodes. A displacement of a proof mass relative to fixed capacitive electrodes is sensed by measuring a pickoff signal from the proof mass and adjusting the mark-space ratio of the first and/or second PWM drive signals to provide a restoring force on the proof mass that balances an applied acceleration and maintains the proof mass at a null position. The first and second PWM drive signals applied to the first and second pairs of fixed capacitive electrodes are offset in time from one another by an offset period.

Abstract: A capacitive accelerometer including: at least one additional fixed capacitor electrode with a plurality of additional fixed capacitive electrode fingers extending along the sensing direction. The proof mass comprises a plurality of moveable capacitive electrode fingers extending from the proof mass along the sensing direction and arranged to interdigitate with the plurality of additional fixed capacitive electrode fingers of the at least one additional fixed capacitor electrode. A means is provided for applying a voltage to the at least one additional fixed capacitor electrode to apply an electrostatic force to the plurality of moveable capacitive electrode fingers that acts to pull the proof mass towards the at least one further fixed capacitor electrode and thereby reduces the lateral spacings between the movable capacitive electrode fingers of the proof mass and the first and second sets of fixed capacitive electrode fingers that provide electrostatic forces for sensing purposes.

Abstract: A sensing structure for an accelerometer includes a support and a proof mass mounted thereto by flexible legs. The proof mass has moveable electrode fingers perpendicular to the sensing direction and at least four fixed capacitor electrodes, with fixed capacitor electrode fingers perpendicular to the sensing direction. The fixed capacitor electrode fingers interdigitate with the movable electrode fingers and the proof mass is mounted to the support by an anchor on a centre line of the proof mass. The proof mass has an outer frame surrounding the fixed capacitor electrodes and the flexible legs extend laterally inwardly from the proof mass to the anchor. The fixed capacitor electrodes comprise two inner electrodes, one on each side of the proof mass centre line, and two outer electrodes, one on each side of the proof mass centre line.

Abstract: An accelerometer comprises a support, a first mass element and a second mass element, the mass elements being rigidly interconnected to form a unitary movable proof mass, the support being located at least in part between the first and second mass elements, a plurality of mounting legs securing the mass elements to the support member, at least two groups of movable capacitor fingers provided on the first mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support, and at least two groups of movable capacitor fingers provided on the second mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support.

Abstract: A MEMS sensor package includes a MEMS sensor fixed to a vibration damping mount. The mount includes a silicon substrate defining an outer frame; a moveable support to which the MEMS sensor is fixed; and a vibration damping structure connected between the outer frame and the moveable support to damp movement of the support. The MEMS sensor and vibration damping mount are enclosed by a casing that is backfilled with gas.

Abstract: An angular velocity sensor comprises: an insulative support layer (10); a substrate layer (8) formed of a silica-based material and comprising a planar ring structure (2) mounted to vibrate in-plane; and a plurality of conductive electrodes (14), each comprising a first set of moveable conductive electrode tracks (14a) formed on a surface of the planar ring and a second set of fixed conductive electrode tracks (14b) formed on a surface of the insulative support layer axially spaced from the surface of the planar ring. The first and second sets of conductive electrode tracks are interdigitated with a lateral spacing between them in a radial direction. Each moveable conductive electrode track has a radial offset from a median line between adjacent fixed conductive electrode tracks such that each moveable conductive electrode track has a different lateral spacing from two different adjacent fixed conductive electrode tracks in opposite radial directions.

Abstract: 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.

Abstract: An accelerometer closed loop control system comprising: a capacitive accelerometer comprising a proof mass moveable relative to first and second fixed capacitor electrodes; a PWM generator to generate in-phase and anti-phase PWM drive signals with an adjustable mark/space ratio, wherein said drive signals are applied to the first and second electrodes such that they are charged alternately; an output signal detector to detect a pick-off signal from the accelerometer representing a displacement of the proof mass from a null position to provide an error signal, wherein the null position is the position of the proof mass relative to the fixed electrodes when no acceleration is applied; a PWM servo operating in closed loop to vary the mark/space ratio of said PWM drive signals in response to the error signal so that mechanical inertial forces are balanced by electrostatic forces.

Abstract: A navigation system comprising: an inertial navigation system arranged to output a first position estimate; a terrain based navigation unit arranged to output a second position estimate; a gravity based navigation unit arranged to output a third position estimate; a stored gravity map arranged to receive a position and to output gravity information for that position; and an iterative algorithm unit arranged to determine an INS error state in each iteration; wherein in each iteration the iterative algorithm unit is arranged to: receive the first position estimate, the second position estimate, and the third position estimate; determine a gravity corrected position estimate based on the first position estimate, the INS error state and the gravity information; and update the INS error state for the next iteration based on the INS error state, the gravity corrected position estimate, the second position estimate and the third position estimate.