Damage detection system

1. A damage detection system comprising:

a vibration actuator to apply vibration to a subject to be inspected;

an optical fiber sensor including a core portion to have a grating portion formed therein, the grating portion having a plurality of gratings reflecting light, wherein a wavelength band of the reflected light changes when a distance between adjacent gratings changes, and the optical fiber sensor vibrates the wavelength band depending on an elastic wave transmitted from the subject;

a light source to input broadband light which includes at least a vibration range of the wavelength band, into the core portion;

two optical filters connected to an output end of the optical fiber sensor; and

an arithmetic processing apparatus to perform arithmetic processing on output values of the two optical filters, the values being obtained when the vibration actuator applies vibration,

wherein each of passbands of the two optical filters overlaps with the vibration range of the wavelength band, in which a center wavelength of one of the passbands is fixed to an upper area with respect to a vibration center of a center wavelength of the reflected light and a center wavelength of the other of the passbands is fixed to a lower area with respect to the vibration center of the center wavelength of the reflected light, and said center wavelengths are positioned apart from the vibration center not less than an amplitude of wavelength vibration of the reflected light.

2. The damage detection system according to claim 1 ,

wherein the optical filters are arrayed waveguide grating type optical filters.

3. The damage detection system according to claim 2 ,

wherein the grating portion of the optical fiber sensor has a length not more than one-thirds of a wavelength of the elastic wave transmitted from the subject.

4. The damage detection system according to claim 2 ,

wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in the subject.

5. The damage detection system according to claim 1 ,

wherein the grating portion of the optical fiber sensor has a length not more than one-thirds of a wavelength of the elastic wave transmitted from the subject.

6. The damage detection system according to claim 5 ,

wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in the subject.

7. The damage detection system according to claim 1 ,

wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in the subject.

8. A damage detection system comprising:

an optical fiber sensor including a core portion to have a grating portion formed therein, the grating portion having a plurality of gratings reflecting light, wherein a wavelength band of the reflected light changes when a distance between adjacent gratings changes;

a light source to input broadband light which includes the wavelength band, into the core portion;

two optical filters connected to an output end of the optical fiber sensor and the two optical filters having passbands which the reflected light passes through; and

an arithmetic processing apparatus to perform arithmetic processing on output values of the two optical filters,

wherein a central wavelength of one of the passbands is positioned not greater than a minimum central wavelength of the reflected light and a central wavelength of the other of the passbands is positioned not smaller than a maximum central wavelength of the reflected light.

9. The damage detection system according to claim 8 , further comprising:

a vibration actuator to apply vibration to a subject to be inspected.

10. The damage detection system according to claim 9 ,

wherein the grating portion of the optical fiber sensor has a length not more than one-thirds of a wavelength of an elastic wave transmitted from the subject.

11. The damage detection system according to claim 8 ,

wherein the optical filters are arrayed waveguide grating type optical filters.

12. The damage detection system according to claim 8 ,

wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in a subject to be inspected.