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 method for forming a MEMS structure for an inertial sensor from fused silica includes: depositing a conductive layer on one or more selected regions of a first surface of a fused silica substrate, and illuminating areas of the fused silica substrate with laser radiation in a pattern defining features of the MEMS structure for an inertial sensor. A masking layer is deposited at least on the one or more selected regions of the first surface of the fused silica substrate where the conductive layer has been deposited, such that the illuminated areas of the fused silica substrate remain exposed. A first etch of the exposed areas of the fused silica substrate is performed so as to selectively etch the pattern defining features of the MEMS structure for an inertial sensor.

Abstract: A vibrating structure angular rate sensor includes a mount, a planar vibrating structure and a plurality of compliant supports extending between the mount and the planar vibrating structure to support the vibrating structure thereby allowing the planar vibrating structure to oscillate in its plane relative to the mount in response to an electrical excitation. A first set of transducers is arranged on the planar vibrating structure to apply, in use, an electrical excitation to the planar vibrating structure and to sense, in use, motion resulting from oscillation of the planar vibrating structure in its plane. A plurality of capacitive regions is fixed at a distance from the planar vibrating structure in its plane. The capacitive regions form a second set of transducers configured to apply, in use, an electrostatic force to the planar vibrating structure which induces a change in the frequency of oscillation of the planar vibrating structure.

Abstract: A method for closed loop operation of a capacitive accelerometer includes applying a first drive signal V1 to a first fixed capacitive electrode and a second drive signal V2 to a second fixed capacitive electrode the first and second drive signals each having a periodic waveform varying in amplitude between zero and a maximum value Vref and sensing a displacement of the proof mass and applying pulse width modulation to the first and second drive signals with a constant frequency fmod and a variable mark/space ratio. The method also includes applying a voltage offset Vref/2 to the proof mass and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at Vref or zero the other drive voltage is at Vref/2.

Abstract: A vibrating structure angular rate sensor comprises a MEMS structure includes a mount, a plurality of supporting structures fixed to the mount, and a vibrating planar ring structure flexibly supported by the plurality of supporting structures to move elastically relative to the mount. At least one primary drive transducer is arranged to cause the ring structure to oscillate in a primary mode at the resonant frequency of the primary mode. At least one primary pick-off transducer arranged to detect oscillation of the ring structure in the primary mode. At least three secondary pick-off transducers are arranged to detect oscillation of the ring structure in a secondary mode induced by Coriolis force when an angular rate is applied around an axis substantially perpendicular to the ring structure. At least one secondary drive transducer is arranged to null the induced oscillation in the secondary mode.

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 method for closed loop operation of a capacitive accelerometer includes applying a first drive signal V1 to a first fixed capacitive electrode and a second drive signal V2 to a second fixed capacitive electrode the first and second drive signals each having a periodic waveform varying in amplitude between zero and a maximum value Vref and sensing a displacement of the proof mass and applying pulse width modulation to the first and second drive signals with a constant frequency fmod and a variable mark/space ratio. The method also includes applying a voltage offset Vref/2 to the proof mass and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at Vref or zero the other drive voltage is at Vref/2.

Abstract: A vibrating structure angular rate sensor comprises a MEMS structure includes a mount, a plurality of supporting structures fixed to the mount, and a vibrating planar ring structure flexibly supported by the plurality of supporting structures to move elastically relative to the mount. At least one primary drive transducer is arranged to cause the ring structure to oscillate in a primary mode at the resonant frequency of the primary mode. At least one primary pick-off transducer arranged to detect oscillation of the ring structure in the primary mode. At least three secondary pick-off transducers are arranged to detect oscillation of the ring structure in a secondary mode induced by Coriolis force when an angular rate is applied around an axis substantially perpendicular to the ring structure. At least one secondary drive transducer is arranged to null the induced oscillation in the secondary mode.

Abstract: A sensor comprises a substrate 16 and a sensor element 20 anchored to the substrate 16, the substrate 16 and sensor element 20 being of dissimilar materials and having different coefficients of thermal expansion, the sensor element 20 and substrate 16 each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer 26, the spacer 26 being located so as to space at least part of the sensor element 20 from at least part of the substrate 16, wherein the spacer 26 is of considerably smaller area than the area of the smaller of face of the substrate 16 and that of the sensor element 20.

Abstract: A method of tuning a vibratory ring structure includes determining an angular spacing for a pair of fine tuning holes of substantially the same size, located on or near the neutral axis of the vibratory ring structure, the angular offset being selected to reduce to an acceptable level the frequency split between the target normal mode and a further normal mode which is angularly offset relative to the target normal mode, and forming the pair of fine tuning holes in the vibratory ring structure at the determined angular spacing. A ring structure, for example, a gyroscope, tuned or balanced in this manner, is also disclosed.

Abstract: A vibratory ring structure is described which comprises a ring body and at least one ring electrode secured thereto, the or each ring electrode extending over a first angular extent and: being attached to the ring body over second angular extent, wherein the first angular extent is greater than the second angular extent.

Abstract: A sensor comprises a substrate 16 and a sensor element 20 anchored to the substrate 16, the substrate 16 and sensor element 20 being of dissimilar materials and having different coefficients of thermal expansion, the sensor element 20 and substrate 16 each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer 26, the spacer 26 being located so as to space at least part of the sensor element 20 from at least part of the substrate 16, wherein the spacer 26 is of considerably smaller area than the area of the smaller of face of the substrate 16 and that of the sensor element 20.

Abstract: A sensor comprises a substrate (16) and a sensor element (20) anchored to the substrate (16), the substrate (16) and sensor element (20) being of dissimilar materials and having different coefficients of thermal expansion, the sensor element (20) and substrate (16) each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer (26), the spacer (26) being located so as to space at least part of the sensor element (20) from at least part of the substrate (16), wherein the spacer (26) is of considerably smaller area than the area of the smaller of face of the substrate (16) and that of the sensor element (20).

Abstract: A silicon MEMS gyroscope is described having a ring or hoop-shaped resonator. The resonator is formed by a Deep Reactive Ion Fitch technique and is formed with slots extending around the circumference of the resonator on either side of the neutral axis of the resonator. The slots improve the Quality Factor Q of the gyroscope without affecting the resonant frequency of the resonator.

Abstract: An angular velocity sensor is described with improved ageing and hysteresis properties. The sensor may be of a ring type driven by a driver circuit, the sensor further comprising primary and secondary portions having corresponding signal pickoffs. The gain of the primary pickoff signal and the capacitance of the primary portions of the sensor are controlled relative to the gain of the secondary pickoff and the capacitance of the secondary portions of the sensor. Control electronics is provided that enables matching of the relative signals from the respective channels. In this way, temperature hysteresis and ageing effects of materials used in forming the sensor are overcome.

Abstract: A method of tuning a vibratory ring structure is described which comprises determining an angular spacing for a pair of fine tuning holes (16) of substantially the same size, located on or near the neutral axis of the vibratory ring structure (10), the angular offset being selected to reduce to an acceptable level the frequency split between the target normal mode and a further normal mode which Is angularly offset relative to the target normal mode, and forming the pair of fine tuning holes (16) in the vibratory ring structure (10) at the determined angular spacing, A ring structure, for example a gyroscope, tuned or balanced in this manner is also disclosed.

Abstract: A vibratory ring structure is described which comprises a ring body and at least one ring electrode secured thereto, the or each ring electrode extending over a first angular extent and: being attached to the ring body over second angular extent, wherein the first angular extent is greater than the second angular extent.

Abstract: A sensor comprises a substrate (16) and a sensor element (20) anchored to the substrate (16), the substrate (16) and sensor element (20) being of dissimilar materials and having different coefficients of thermal expansion, the sensor element (20) and substrate (16) each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer (26), the spacer (26) being located so as to space at least part of the sensor element (20) from at least part of the substrate (16), wherein the spacer (26) is of considerably smaller area than the area of the smaller of face of the substrate (16) and that of the sensor element (20).

Abstract: An angular velocity sensor is described with improved ageing and hysteresis properties. The sensor may be of a ring type driven by a driver circuit, the sensor further comprising primary and secondary portions having corresponding signal pickoffs. The gain of the primary pickoff signal and the capacitance of the primary portions of the sensor are controlled relative to the gain of the secondary pickoff and the capacitance of the secondary portions of the sensor. Control electronics is provided that enables matching of the relative signals from the respective channels. In this way, temperature hysteresis and ageing effects of materials used in forming the sensor are overcome.

Abstract: A silicon MEMS gyroscope is described having a ring or hoop-shaped resonator. The resonator is formed by a Deep Reactive Ion Fitch technique and is formed with slots extending around the circumference of the resonator on either side of the neutral axis of the resonator. The slots improve the Quality Factor Q of the gyroscope without affecting the resonant frequency of the resonator.