Impact detection system with three or more optical fiber sensors

1. An impact detection system, comprising:

three or more optical fiber sensors disposed respectively in different positions of a subject to be inspected, the sensors not being in alignment with one another, in which the optical fiber sensors each includes a core portion having a grating portion formed therein, the grating portion having a plurality of gratings reflecting light so that a wavelength band of reflected light changes when a distance between adjacent gratings changes, and the three or more optical fiber sensors vibrates the wavelength band depending on an elastic wave propagating through the subject;

a light source to input light into the core portion, in which a spectrum bandwidth of the light includes at least a desired vibration width of the wavelength band;

two or more optical filters connected to an output end of the three or more optical fiber sensors, the optical filters having different pass bands to one another with respect to an output light of one of the optical fiber sensors; and

an arithmetic processing apparatus to perform arithmetic processing of output values of the three or more optical fiber sensors through the optical filters so as to specify a position on the subject where an impact is loaded, the output values being obtained when the impact is loaded on the subject,

wherein the arithmetic processing apparatus measures a difference of arrival times between two elastic waves having different propagation speeds, the two elastic waves caused by the impact as a vibration source, at each of the three or more optical fiber sensors, so as to specify the position where the impact is loaded on the subject on a basis of a measurement result.

2. The impact detection system according to claim 1 , wherein the arithmetic processing apparatus performs the arithmetic processing of the output values of the optical fiber sensors through the optical filters so as to specify a magnitude of the impact loaded on the subject, the output values being obtained when the impact is loaded on the subject.

3. The impact detection system according to claim 1 , wherein the three or more optical fiber sensors comprise four or more optical fiber sensors,

wherein the arithmetic processing apparatus measures an arriving time of the a single elastic wave caused by the impact as a vibration source, at each of the said optical fiber sensors, so as to specify the position where the impact is loaded on the subject on a basis of a measurement result.

4. The impact detection system according to claim 1 , wherein the optical filters comprise arrayed waveguide grating type optical filters.

5. The impact detection system according to claim 1 , wherein the three or more optical fiber sensors comprise more than one optical fiber.

6. The impact detection system according to claim 1 , wherein at least one of the three or more optical fiber sensors is embedded in the subject.

7. The impact detection system according to claim 1 , wherein at least one of the three or more optical fiber sensors is attached onto the subject.

8. The impact detection system according to claim 1 , wherein one of the two elastic waves having different propagation speeds comprises an S-wave, and one of the two elastic waves having different propagation speeds comprises a P-wave.

9. An impact detection system, comprising:

three or more optical fiber sensors disposed respectively in different positions of a subject to be inspected, the sensors not being in alignment with one another, in which the optical fiber sensors each includes a core portion having a grating portion formed therein, the grating portion having a plurality of gratings reflecting light so that a wavelength band of reflected light changes when a distance between adjacent gratings changes, and the three or more optical fiber sensors vibrates the wavelength band depending on an elastic wave propagating through the subject;

a light source to input light into the core portion, in which a spectrum bandwidth of the light includes at least a desired vibration width of the wavelength band;

two or more optical filters connected to an output end of the three or more optical fiber sensors, the optical filters having different pass bands to one another with respect to an output light of one of the optical fiber sensors; and

an arithmetic processing apparatus to perform arithmetic processing of output values of the three or more optical fiber sensors through the optical filters so as to specify a position on the subject where an impact is loaded, the output values being obtained when the impact is loaded on the subject,

wherein the arithmetic processing apparatus measures a difference of arrival times between two elastic waves having different propagation speeds. the two elastic waves caused by the impact as a vibration source, at each of the three or more optical fiber sensors, so as to specify the position where the impact is loaded on the subject on a basis of a measurement result, and

wherein the arithmetic processing apparatus calculates a distance between a position on the subject where an impact is loaded and each of a plurality of optical fiber sensors based on a difference between arrival times of the two elastic waves having different propagation speeds and a known propagation speed difference.

10. The impact detection system according to claim 9 , wherein the arithmetic processing apparatus calculates the position on the subject where an impact is loaded by calculating a point which corresponds to an intersection of a plurality of circles, wherein each of three or more optical fiber sensors comprise a center of a circle and a corresponding distance between a position on the subject where an impact is loaded and each of the three or more optical fiber sensors comprise a radius of a circle.

11. The impact detection system according to claim 10 , wherein the arithmetic processing apparatus calculates a magnitude of the impact based on a vibration energy detected at a closest of said three or more optical fiber sensors to the impact and a distance between the position on the subject where an impact is loaded and a closest of a plurality of optical fiber sensors.

12. An impact detection system, comprising:

three or more optical fiber sensors disposed respectively in different positions of a subject to be inspected. the sensors not beans in alignment with one another, in which the optical fiber sensors each includes a core portion having a grating portion formed therein, the grating portion having a plurality of gratings reflecting light so that a wavelength band of reflected light changes when a distance between adjacent gratings changes, and the three or more optical fiber sensors vibrates the wavelength band depending on an elastic wave propagating through the subject;

a light source to input light into the core portion, in which a spectrum bandwidth of the light includes at least a desired vibration width of the wavelength band;

two or more optical filters connected to an output end of the three or more optical fiber sensors, the optical filters having different pass bands to one another with respect to an output light of one of the optical fiber sensors; and

an arithmetic processing apparatus to perform arithmetic processing of output values of the three or more optical fiber sensors through the optical filters so as to specify a position on the subject where an impact is loaded, the output values being obtained when the impact is loaded on the subject,

wherein the three or more optical fiber sensors comprise four or more optical fiber sensors,

wherein the arithmetic processing apparatus measures an arriving time of the a single elastic wave caused by the impact as a vibration source, at each of the said optical fiber sensors, so as to specify the position where the impact is loaded on the subject on a basis of a measurement result,

wherein the arithmetic processing apparatus calculates a difference of a plurality of arrival times of a single elastic wave caused by the impact as a vibration source, the plurality of arrival times being calculated based on a time difference between the single elastic waves time of arrival at a first of a plurality of optical fiber sensors and the time of arrival at a plurality of other of a plurality of optical fiber sensors,

wherein the arithmetic processing apparatus calculates the location of the impact represented by a center of a common circumcircle, and

wherein the circumcircle is determined by creating a plurality of circles with centers located at a plurality of the other of a plurality of fiber sensors, and radii determined by a propagation distance based on the time of a arrival of the single elastic wave caused by the impact as a vibration source at the first of said optical fiber sensors and the time of arrival of the single elastic wave caused by the impact as a vibration source at each of the other of said optical fiber sensors and a known propagation speed.

13. The impact detection system according to claim 12 , wherein the arithmetic processing apparatus calculates a magnitude of the impact based on a vibration energy detected at a first of said three or more optical fiber sensors to the impact and a radius of the calculated circumcircle.