Fiber-optic vibration sensor based on frequency modulation of light-excited oscillators

• US 6,246,638 B1
• Filed: 03/30/1999
• Issued: 06/12/2001
• Est. Priority Date: 03/30/1999
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Zook, J. David, Burns, David W., Herb, William R.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US09/281,388
• Time in Patent Office: 805 Days
• Field of Search: 367/140, 367/149, 385/12, 250/227.16, 736/55
• US Class Current: 367/140
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A sensor device for detecting vibration, including a light source for providing a laser light, a first optical fiber connected to the source for transmitting the laser light, an oscillator positioned to receive the transmitted laser light and adapted to reflect the light as a frequency modulated light; a second optical fiber positioned to capture the frequency modulated light to transmit the frequency modulated light; and a frequency modulated discriminator for receiving the frequency modulated light from the second optical fiber and producing a signal responsive of vibration of the oscillator. In a preferred embodiment, the frequency modulated discriminator further includes a frequency meter for determining the average number of cycles per unit time to provide a second signal responsive of the temperature of the oscillator. The optical fibers may be a pair of different fibers positioned for transmitting the laser light and the frequency modulated light respectively, or the same fiber positioned for transmitting both the laser light and the frequency modulated light. In this latter embodiment, the device further includes a beam splitter to direct the frequency modulated light to the discriminator. The preferred oscillator includes a microchip having a microbeam mounted on a thin silicon cantilever such that deflection of the beam perpendicular to the plane of the microchip changes the tension in the microbeam to change its resonant frequency. Also preferred is a microbeam including a thin metal deposit to create a bimorph structure.

Claims

1. A sensor device for detecting vibration, comprising:

a power source for powering an ocsillator,

an oscillator having an output signal frequency depending on acceleration;

a frequency modulated discriminator for receiving said output signal and producing a signal responsive of vibration of said oscillator in response to bending of said discriminator by said vibration to change its resonant frequency; and

a frequency meter for determining the average number of cycles per unit time to provide a signal responsive of the temperature of said oscillator.

2. The device of claim 1, wherein said frequency modulated discriminator further includes a frequency meter for determining the average number of cycles per unit time to provide a second signal responsive of the temperature of said oscillator.

6. The device of claim 1, wherein said microbeam includes a thin metal deposit to create a bimorph structure.

3. A method for detecting vibration in an object, comprising the steps of:

powering an ocsillator with a power source;

deriving output signal frequency depending on acceleration from said oscillator;

receiving said output signal and producing a signal responsive of vibration of said oscillator using a frequency modulated discriminator in response to bending of said discriminator by said vibration to change its resonant frequency; and

determining the average number of cycles per unit time to provide a signal responsive of the temperature of said oscillator.

4. A sensor device for detecting vibration, comprising:

power source means for powering ocsillator means,

oscillator means having an output signal frequency depending on acceleration;

frequency modulated discriminator means for receiving said output signal and producing a signal responsive of vibration of said oscillator in response to bending of said discriminator by said vibration to change its resonant frequency; and

frequency meter means for determining the average number of cycles per unit time to provide a signal responsive of the temperature of said oscillator means.

5. A sensor device for detecting vibration, comprising:

a power source for powering an ocsillator,

an oscillator having an output signal frequency depending on acceleration;

a frequency modulated discriminator for receiving said output signal and producing a signal responsive of vibration of said oscillator, said oscillator including a microchip having a microbeam mounted on a thin silicon cantilever such that deflection of the beam perpendicular to the plane of said microchip changes the tension in said microbeam to change its resonant frequency.

7. A method for detecting vibration in an object, comprising the steps of:

powering an ocsillator with a power source;

deriving output signal frequency depending on acceleration from said oscillator;

receiving said output signal and producing a signal responsive of vibration of said oscillator using a frequency modulated discriminator, said oscillator including a microchip having a microbeam mounted on a thin silicon cantilever such that deflection of the beam perpendicular to the plane of said microchip changes the tension in said microbeam to change its resonant frequency.

8. The method of claim 7, wherein said microbeam includes a thin metal deposit to create a bimorph structure.