Abstract: A broadband weak-motion inertial sensor includes a frame, a movable inertial mass, a forcing transducer for keeping the inertial mass stationary relative to the frame during operation, and a flexure for suspending the movable mass in the frame. Two or more closely spaced, substantially parallel capacitor plates, at least one attached to the frame, and one attached to the movable inertial mass, form a capacitive displacement transducer. The capacitor plates have a plurality of apertures with dimensions and arrangement chosen to simultaneously minimize damping induced thermal noise and give a high spatial efficiency. In an implementation, three capacitor plates are provided. The capacitor plates each have a same hexagonal pattern of circular holes; the holes are aligned on all included capacitor plates. Radius and spacing of the holes are dictated by a relationship that determines the minimum damping per unit capacitively effective area for a desired spatial efficiency, gap height and capacitor plate thickness.

Abstract: A broadband weak-motion seismometer includes: a frame, a mass, a suspension means for movably connecting the mass to the frame, a sensing transducer for measuring displacement of the mass with respect to the frame and for generating a sensing transducer output signal, which is a function of the measured displacement, a forcing transducer for applying a feedback force in a predetermined direction to the mass, and a control circuit. The control circuit receives the sensing transducer output signal and generates a forcing transducer input signal that includes a self-noise component. The forcing transducer input signal is processed by the forcing transducer to apply the feedback force to maintain the mass at rest with respect to the frame. The feedback force is sufficient to counterbalance a constant acceleration of the frame of at least 0.2 m/s2 in the predetermined direction of the feedback force.

Abstract: A seismic sensor includes a frame, a pendulum pivotably mounted to the frame, a mechanism for sensing angular position of the pendulum, and a monolithic flat spring oriented between the frame and the pendulum for balancing the pendulum at an equilibrium position. The monolithic flat spring includes: (i) an operating region for providing a restoring force to the pendulum proportional to an angular displacement of the pendulum; and (ii) a suspension region for transmitting a force to a portion of the operating region and applying a negligible bending moment to the portion of the operating region.

Abstract: A broadband weak-motion seismometer includes: a frame, a mass, a suspension means for movably connecting the mass to the frame, a sensing transducer for measuring displacement of the mass with respect to the frame and for generating a sensing transducer output signal, which is a function of the measured displacement, a forcing transducer for applying a feedback force in a predetermined direction to the mass, and a control circuit. The control circuit receives the sensing transducer output signal and generates a forcing transducer input signal that includes a self-noise component. The forcing transducer input signal is processed by the forcing transducer to apply the feedback force to maintain the mass at rest with respect to the frame. The feedback force is sufficient to counterbalance a constant acceleration of the frame of at least 0.2 m/s2 in the predetermined direction of the feedback force.

Abstract: A broadband weak-motion inertial sensor includes a frame, a movable inertial mass, a forcing transducer for keeping the inertial mass stationary relative to the frame during operation, and a flexure for suspending the movable mass in the frame. Two or more closely spaced, substantially parallel capacitor plates, at least one attached to the frame, and one attached to the movable inertial mass, form a capacitive displacement transducer. The capacitor plates have a plurality of apertures with dimensions and arrangement chosen to simultaneously minimize damping induced thermal noise and give a high spatial efficiency. In an implementation, three capacitor plates are provided. The capacitor plates each have a same hexagonal pattern of circular holes; the holes are aligned on all included capacitor plates. Radius and spacing of the holes are dictated by a relationship that determines the minimum damping per unit capacitively effective area for a desired spatial efficiency, gap height and capacitor plate thickness.

Abstract: A long-period weak-motion inertial sensor includes a frame having a frame mounting surface, a movable mass having a movable mass mounting surface, a transducer for sensing displacements of the movable mass with respect to the frame, and a monolithic flexure element for suspending the movable mass in the frame. The monolithic flexure element includes: a stiff frame integral clamp attachable to the frame mounting surface of the frame, a stiff movable mass integral clamp attachable to the movable mass mounting surface of the movable mass, and a stiffest flexible region for operatively connecting the frame integral clamp to the movable mass integral clamp. The frame and movable mass mounting surfaces do not overlap the stiffest flexible region, thereby minimizing the generation of creep and hysteresis noise. The variation in stiffness of the monolithic flexure element is controlled by varying thickness along the length of the flexure element.

Abstract: A long-period weak-motion inertial sensor includes a frame having a frame mounting surface, a movable mass having a movable mass mounting surface, a transducer for sensing displacements of the movable mass with respect to the frame, and a monolithic flexure element for suspending the movable mass in the frame. The monolithic flexure element includes: a stiff frame integral clamp attachable to the frame mounting surface of the frame, a stiff movable mass integral clamp attachable to the movable mass mounting surface of the movable mass, and a stiffest flexible region for operatively connecting the frame integral clamp to the movable mass integral clamp. The frame and movable mass mounting surfaces do not overlap the stiffest flexible region, thereby minimizing the generation of creep and hysteresis noise. The variation in stiffness of the monolithic flexure element is controlled by varying thickness along the length of the flexure element.

Abstract: A mass positioning apparatus for use with seismic sensors is described. The seismic sensor includes axis mechanics including a pivotable boom with a defined null point. The mass positioning apparatus comprising: adjustment means for positioning the boom at the null point; actuator means for moving the adjustment means; and means for determining a position of the adjustment means relative to an operational range of travel.

Abstract: A seismic sensor includes a frame, a pendulum pivotably mounted to the frame, a mechanism for sensing angular position of the pendulum, and a monolithic flat spring oriented between the frame and the pendulum for balancing the pendulum at an equilibrium position. The monolithic flat spring includes: (i) an operating region for providing a restoring force to the pendulum proportional to an angular displacement of the pendulum; and (ii) a suspension region for transmitting a force to a portion of the operating region and applying a negligible bending moment to the portion of the operating region.

Abstract: A mass position adjustment apparatus for use in a seismic sensor having axis mechanics including a pivotable boom with a defined null point is described. The apparatus comprising: (a) adjustment means for positioning the boom at the null point; (b) actuator means for moving the adjustment assembly; and (c) interface means having hard mineral members for interfacing the actuator means with the adjustment means for reducing occurrences of micro-mechanical movement when the mass position adjustment apparatus is not being operated.