Patent Number: 
Section: claims

1. An active sensor positioned on an outside of a pipe so as to detect a thickness of the pipe, the active sensor comprising:an oscillator to input oscillatory waves into the pipe and scan a frequency of the oscillatory waves within a desired range; andan optical fiber sensor mounted on the pipe to detect reflected waves and resonant waves generated in the pipe. 2. The active sensor according to claim 1, whereinthe oscillator has a permanent magnet positioned so as to generate a magnetic flux in a normal, line direction of a pipe surface, and an electric coil disposed on the permanent magnet on a side of the optical fiber sensor. 3. The active sensor according to claim 1, whereinthe oscillator has a permanent magnet positioned so as to generate a magnetic flux in a normal line direction of a pipe surface, an electric coil disposed on the permanent magnet on a side of the optical fiber sensor, and a holding member that holds the electric coil and the optical fiber sensor in such a manner that the electric coil and the optical fiber sensor are not brought into direct contact with each other. 4. The active sensor according to claim 1, whereinthe oscillator has a pair of permanent magnets positioned so as to generate a magnetic flux in a direction perpendicular to a normal line direction of a pipe surface, and an electric coil disposed between the pair of permanent magnets. 5. The active sensor according to claim 1, whereinthe oscillator has a pair of permanent magnets positioned so as to generate a magnetic flux in a direction perpendicular to a normal line direction of a pipe surface, and an electric coil disposed between the pair of permanent magnets, and a holding member that holds the pair of permanent magnets, the electric coil, and the optical fiber sensor in such a manner that the pair of permanent magnets, the electric coil, and the optical fiber sensor are not brought into direct contact with each other. 6. The active sensor according to claim 1, whereinthe oscillator is formed from an electromagnetic oscillator or a piezoelectric oscillator. 7. The active sensor according to claim 1, whereinthe optical fiber sensor is formed from a fiber-optic Doppler (FOD) sensor that detects a kinetic strain of the pipe, which is generated by the oscillatory waves inputted from the oscillator into the pipe. 8. The active sensor according to claim 1, wherein:the optical fiber sensor has a circularly or elliptically winding sensing part; andthe oscillator is positioned at a center of the sensing part. 9. The active sensor according to claim 8, whereinthe sensing part of the optical fiber sensor is subjected to a heat-resistant process. 10. The active sensor according to claim 8, whereina conductive material is disposed on a surface of the sensing part of the optical fiber sensor. 11. The active sensor according to claim 1, whereinthe optical fiber sensor has an inner diameter not less than 5 mm, and an outer diameter not more than a value that is obtained by adding, to the inner diameter, one half of a wavelength of the oscillatory waves propagating in the pipe. 12. A multi-point active sensor comprising a plurality of active sensors according to claim 1,wherein the active sensors are linearly arranged or arranged in a matrix. 13. The multi-point active sensor according to claim 12, whereinthe respective active sensors are connected to each other by a connection member having a plasticity or flexibility. 14. A method of diagnosing deterioration of a pipe using the multi-point active sensor according to claim 12, the method comprising the steps of:inputting oscillatory waves into a pipe by the oscillator of at least one active sensor;detecting the reflected waves and the resonant waves generated in the pipe by the optical fiber sensor of at least one active sensor; andcalculating a thickness of the pipe by deriving a relationship between a frequency and a vibration strength, based on a frequency of the oscillatory waves inputted by the oscillator into the pipe and an amplitude of the reflected waves and the resonant waves at this frequency detected by the optical fiber sensor. 15. An apparatus for diagnosing deterioration of a pipe, comprising:the multi-point active sensor according to claim 12;a waveform analysis unit connected to the respective active sensors, the waveform analysis unit calculating a thickness of a pipe by deriving a relationship between a frequency and a vibration strength, based on a frequency of oscillatory waves inputted by the oscillator of this active sensor into the pipe and an amplitude of the reflected waves and the resonant waves at this frequency detected by the optical fiber sensor of this active sensor;a diagnostic database storing judgment threshold values relating to the deterioration of the pipe; anda diagnostic unit connected to the waveform analysis unit and the diagnostic database, the diagnostic unit comparing the thickness of the pipe calculated by the waveform analysis unit with the judgment threshold values stored in the diagnostic database, so as to diagnose the deterioration and the malfunction of the pipe. 16. The apparatus for diagnosing deterioration of a pipe according to claim 15, whereinthe waveform analysis unit calculates the thickness of the pipe by deriving a relationship between a frequency and a vibration strength, based on a frequency of the oscillatory waves inputted into the pipe by the oscillator and an effective value of an amplitude of the reflected waves and the resonant waves or a frequency spectral intensity obtained by Fourier converting the reflected waves and the resonant waves at the frequency detected by the optical fiber sensor. 17. A method for diagnosing deterioration of a pipe using the multi-point active sensor according to claim 12, the method comprising the steps of:passively detecting oscillatory waves generated in a pipe by the optical fiber sensor of at least one active sensor; andanalyzing the oscillatory waves generated in the pipe and detected by the optical fiber sensor, so as to detect deterioration and malfunction of the pipe. 18. The method for diagnosing deterioration of a pipe according to claim 17, whereinthe oscillatory waves detected by the optical fiber sensors of the respective active sensors are analyzed referring to information relating to deterioration of the pipe, which information having been stored in a diagnostic database beforehand, so as to detect deterioration and malfunction of the pipe. 19. An active sensor positioned on an outside or an inside of a pipe so as to detect a thickness of the pipe, the active sensor comprising:an oscillator to input oscillatory waves into the pipe and scan a frequency of the oscillatory waves over a desired range; andan optical fiber sensor mounted on the pipe to detect reflected waves and resonant waves generated in the pipe.