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| [* black] Shown in this photo is the ST LYPR540AH Tri-axis MEMS gyroscope. | |
| - | [* black] Arrays of central capacitive plates oscillate two semi-annular surfaces about a central axis perpendicular to the top plane of the gyro, while arrays of sensing capacitive plates line the outer edge of the semiannular plates. |
| + | [* black] To achieve the linear displacement needed to sense movement, a plate called a proof mass is oscillated by capacitive actuators. |
| + | [* black] When the package is rotated about the X or Y axes (in the plane of the die surface), coriolis forces cause the plate to move perpendicular to the die surface. When the package is rotated about the Z axis (perpendicular to the plane of the die surface), the resulting displacement of the mass is in the plane of the die surface. |
| + | [* black] Capacitive plates between the proof mass and the oscillator base produce a small change in capacitance as the proof mass moves in response to rotation about the X, Y, or Z axes. |
| [* black] Capacitors store electrical charge between two sets of plates, and that charge induces a mechanical force between the plates. This effect is used by the driving capacitive plates to produce oscillation. | |
| - | [* black] To achieve the linear displacement needed for the gyroscope to produce a signal, two equal masses are oscillated about the vertical axis. Since their velocities are opposite at any given point in time, external rotation (a user moving the iPhone 4) of the device will induce [link|http://en.wikipedia.org/wiki/Coriolis_effect|coriolis] forces opposite to each other, causing equal and opposite linear displacement of the plates. |