In a micromachined silicon pressure sensor comprising a resonantly vibratable beam supported on a diaphragm, the beam is indirectly excited into resonant vibration by directing an optical excitation signal at the beam resonant frequency onto a part of the sensor other than the beam, preferably the diaphragm. Preferably, the optical excitation signal is of a wavelength to which the sensor is fairly transparent, and is directed through the beam and diaphragm to be absorbed by a suitable coating on the underside of the diaphragm. The optical excitation signal produces local heating, and the resulting expansions and contractions at the beam resonant frequency propagate through the sensor structure to excite the beam into resonant vibration. Another optical signal is used to detect the frequency of vibration of the beam, and a positive feedback loop maintains the frequency of the excitation signal equal to the detected beam vibration frequency. In a modification, the indirect excitation is achieved by forming resistors or piezoelectric devices in a part of the sensor other than the beam, so that the expansions and contractions mentioned above can be excited electrically rather than optically.
A microsensor for application in measurements of pressure including a temperature compensated vibratory bar comprises means for measuring the resonance frequency of the vibratory bar, means for measuring the temperature by interferometric determination of the optical thickness of the bar and means for determining a physical quantity to be measured based on resonance frequency and temperature.
In pressure sensor systems based upon a micromachined silicon pressure sensor comprising a resonantly vibratable beam supported on a diaphragm, the beam is excited into resonant vibration by directing an optical excitation signal at the beam resonant frequency, via an optical fibre 26, onto a part of the sensor other than the beam, preferably the diaphragm. To detect the vibrations, the underside of the beam 16 and the adjacent upper surface of the diaphragm 18 are together arranged to define a Fabry-Perot cavity, and a continuous optical detection signal is directed at this cavity, also via the optical fibre 26. The optical detection signal is thus modulated at the vibration frequency of the beam 16 by the cavity, and the modulated signal is reflected back into the optical fibre 26.
A self-exciting optical strain sensor (20) includes dual parallel bridges (22,24) having parallel facing surfaces (32,34). Light energy (38) entering a Fabry-Perot cavity (36) formed by this surfaces (32,34) induces a periodic buildup and release of energy in the cavity (36) which is directly related to the natural resonant frequency of the bridges (22,24). Analysis of the intensity of light emitted (50) from the cavity (36) determines the bridge natural frequency.
A differential pressure transducer is provided in which first and second diaphragms are formed within a block of material, such as monocrystalline silicon. Each diaphragm carries a support for a bridge. The supports are offset from the center of the diaphragms such that deflection of the diaphragms imparts a degree of lateral motion to the respective support. The bridge is held within an evacuated cavity and the resonant frequency of the bridge is a function of the difference in pressure action of the diaphragms.
A sensor formed from a semiconductor material. The device comprises a support frame, a sensing element; and means for vibrating the sensing element at a frequency corresponding generally to a first resonant frequency vibration mode. Error detection means detects the resonant frequency vibration mode, the output of the error detection means being indicative of existence or otherwise an expected response of the resonant frequency vibration mode to the excitation. Means for detecting the deformation of the sensing element provides an output indicative of the parameter to be sensed, the deformation detecting means and error detection means being formed from the same elements.
