Device and method for acoustic diagnosis and measurement by pulse electromagnetic force

• US 20040025593A1
• Filed: 05/14/2003
• Published: 02/12/2004
• Est. Priority Date: 11/17/2000
• Status: Active Grant

• Current Assignee: Amic Co., Ltd.
• Original Assignee: Amic Co., Ltd.
• Inventors: Takanabe, Masanori, Hashimoto, Mitsuo
• Granted Patent: US 6,962,082 B2
• Time in Patent Office: Days
• US Class Current: 73/643
• CPC Class Codes: G01N 17/006 of metals
• CPC Class Codes: G01N 2291/015 Attenuation, scattering
• CPC Class Codes: G01N 2291/02458 Solids in solids, e.g. granules
• CPC Class Codes: G01N 2291/0255 (Bio)chemical reactions, e.g. on biosensors
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 29/2412 using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01N 33/383 Concrete, cement

Abstract

The invention provides an acoustic diagnosis/measurement apparatus/method using a pulse of electromagnetic force, capable of non-destructively and precisely diagnosing or measuring corrosion, adhesion, the. cover depth, and/or the diameter of a reinforcing iron rod in a structure made of reinforced concrete. A coil 12 is attached to a surface of a structure 11 including a conductor 11a and a non-conductive material 11b covering the conductor 11a. A current pulse is applied to the coil 12 thereby generating a magnetic field pulse. The magnetic field pulse causes an eddy current to be induced in the conductor 11a. The conductor 11a is oscillated by interaction between the eddy current and the magnetic field pulse. As a result, an acoustic signal is generated by the conductor 11a and the acoustic signal is converted into an eclectic signal by an acoustic transducer 14 disposed to the surface of the structure 11. The resultant electric signal is measured by a measurement unit 15 to diagnose/measure the location of the conductor 11a or the state of the structure 11.

Claims

1. An acoustic diagnosis/measurement apparatus using a pulse of electromagnetic force, comprising a coil attached to a surface of a structure including a conductor and a non-conductive material covering the conductor;

a power supply unit for supplying a current pulse to the coil;

an acoustic transducer attached to the surface of the structure or to a part of the conductor, the part being exposed from the non-conductive material; and

a measurement unit for measuring an output waveform of the acoustic transducer, whereby corrosion of the conductor, adhesion strength of the conductor, the cover depth of the conductor, and/or the diameter of the conductor are diagnosed or measured.

4. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force, according to one of claims 1 to 3, wherein the acoustic diagnosis/measurement apparatus using a pulse of electromagnetic force includes a plurality of subcoils, the plurality of subcoils being disposed coaxially such that adjacent subcoils are in close contact with each other;

and the power supply unit includes charge storage capacitors connected in series to the respective coils and a power source connected, via a common switch and in parallel, to each series connection of one coil and one capacitor whereby a current pulse is applied to coils by turning on the switch thereby generating a magnetic field pulse.

5. An acoustic diagnosis/measurement apparatus using a pulse of electromagnetic force, according to one of claims 1 to 3, wherein a magnet for generating a static magnetic field is added to the coil.

6. An acoustic diagnosis/measurement apparatus using a pulse of electromagnetic force, according to one of claims 1 to 3, wherein the acoustic transducer is an element for converting an acoustic signal into an electric signal, selected from a group consisting of an acoustic emission sensor, an acceleration sensor, and a microphone.

7. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 1, wherein the measurement unit for measuring the output waveform measures the output waveform in the time domain, displays the measured output waveform, extracts a feature associated with corrosion and/or adhesion from the waveform in the time domain, and displays the extracted feature, or the measurement unit for measuring the output waveform calculates a waveform in the frequency domain, that is, a frequency spectrum, by performing a Fourier transform on the original output waveform, displays the calculated waveform in the frequency domain, extracts a feature associated with corrosion and/or adhesion from the waveform in the frequency domain, and displays information associated with the corrosion and/or adhesion.

8. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 7, wherein the feature extracted from the waveform in the time domain is a pattern, a shape factor, or a crest factor of the waveform in the time domain;

and the displaying of information associated with the corrosion and/or adhesion includes comparing the form factor or the crest factor with a predetermined threshold value and displaying whether or not there is a problem in terms of the corrosion and/or the adhesion.

9. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 7, wherein the feature extracted from the waveform in the time domain is a similarity factor extracted from the shape of the envelope curve of the waveform in the time domain;

and the displaying of information associated with the corrosion and/or adhesion includes comparing the similarity factor with a predetermined threshold value and displaying whether or not there is a problem in terms of the corrosion and/or the adhesion.

10. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 7, wherein the feature extracted from the waveform in the time domain is a normalized waveform obtained by dividing each value of the waveform in the time domain by the effective value of the waveform in the time domain or a waveform obtained by exponentiating the normalized waveform.

11. An acoustic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 10, wherein a similarity factor is extracted from the envelope curve of the normalized waveform and compared with a predetermined threshold value, and information indicating whether or not there is a problem in terms of the corrosion and/or the adhesion is displayed.

12. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 7, wherein the feature extracted from the waveform in the frequency domain is a waveform pattern in the frequency domain;

and the displaying of information associated with the corrosion and/or adhesion includes comparing the waveform pattern with a predetermined pattern, and displaying whether or not there is a problem in terms of the corrosion and/or the adhesion.

13. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 7, wherein the feature extracted from the waveform in the frequency domain is a normalized waveform obtained by dividing each value of the waveform in the frequency domain by the effective value of the waveform in the frequency domain or a waveform obtained by exponentiating the normalized waveform;

and the displaying of information associated with the corrosion and/or adhesion includes extracting the similarity factor from the envelope curve of the normalized waveform, comparing the similarity factor with a predetermined threshold value, and displaying whether or not there is a problem in terms of the corrosion and/or the adhesion.

2. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force, comprising a coil attached to a surface of a structure including a conductor and a non-conductive material covering the conductor;

a power supply unit for supplying a current pulse to the coil;

a plurality of acoustic transducers attached at different locations on the surface of the structure; and

a measurement unit for measuring acoustic propagation delays from outputs of the acoustic transducers, whereby the location of the conductor is measured.

3. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force, comprising:

a coil attached to a surface of a structure including a conductor and a non-conductive material covering the conductor;

a power supply unit for supplying a current pulse to the coil; and

a displacement detector for optically measuring displacement of the surface of the structure thereby measuring a vibration of the surface of the structure, whereby the location of the conductor, corrosion of the conductor, and/or adhesion strength of the conductor are diagnosed or measured.

14. An acoutic diagnosis/measurement apparatus using a pulse of electromagnetic force according to claim 3, wherein the displacement detector is a laser interferometer for illuminating a surface of the structure with a coherent laser beam and detecting a phase difference as an interference pattern of a reflected laser beam, the phase difference varying depending on a vibration of a surface of the structure.

15. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

attaching a coil to a surface of a structure including a conductor and a non-conductive material covering the conductor;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in the conductor by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

converting an acoustic signal of the acoustic wave into an electric signal by using an acoustic transducer attached to the surface of the structure or attached to a part of the conductor, the part of the conductor being exposed from the non-conductive material; and

measuring the waveform of the electric signal to perform diagnosis and/or measurement in terms of corrosion and/or adhesion of the conductor.

16. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

attaching a coil to a surface of a structure including a conductor and a non-conductive material covering the conductor;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in the conductor by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

converting an acoustic signal of the acoustic wave into electric signals by using a plurality of acoustic transducers attached at different locations on the surface of the structure; and

measuring propagation delay times of the acoustic wave corresponding to the respective electric signals; and

measuring the location of the conductor on the basis of the propagation delay times.

17. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

attaching a coil to a surface of a structure including a conductor and a non-conductive material covering the conductor;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in the conductor by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

detecting an optical displacement corresponding to a surface vibration of the structure generated by the acoustic wave thereby diagnosing the location of the conductor and the state of the structure.

18. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

attaching a coil to a surface of a structure including a conductor and a non-conductive material covering the conductor;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in the conductor by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

converting an acoustic signal of the acoustic wave into an electric signal by using an acoustic transducer attached to the surface of the structure; and

measuring the waveform of the electric signal to measure the diameter of the conductor or measure the cover depth of the conductor.

19. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

disposing a coil at a location exactly above a connecting part of a plurality of conductors bound with each other via a binding member;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in a conductor facing the coil by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

converting an acoustic signal of the acoustic wave into an electric signal by using an acoustic transducer attached to the conductor facing the coil and by using an acoustic transducer attached to another conductor bound with the former conductor; and

comparing the waveform of the electric signal output by the acoustic transducer attached to the conductor facing the coil with the waveform of the electric signal output by the acoustic transducer attached to the other conductor, thereby performing diagnosis and/or measurement as to whether the binding member is in a securely fastened state.

20. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, according to claim 19, wherein the binding member is a set of a bolt and a nut.

21. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

disposing a coil on a surface of a non-conductive material covering a conductor;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in the conductor by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

converting an acoustic signal of the acoustic wave into an electric signal by using an acoustic transducer attached to a part of the conductor, the part of the conductor being exposed from the non-conductive material;

changing the location of the coil disposed on the surface of the non-conductive material; and

measuring a change in the electric signal caused by the change in the location of the coil there by measuring the location of the conductor.

22. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force according to claim 21, wherein the conductor is a water pipe or a gas pipe buried in the ground;

and the non-conductive material is the ground.

23. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force, comprising the steps of:

disposing a coil on a surface of a structure including a conductor and a non-conductive material covering the conductor;

applying a current pulse to the coil thereby generating a magnetic field pulse;

inducing an eddy current in the conductor by the magnetic field pulse;

oscillating the conductor by interaction between the eddy current and the magnetic field pulse thereby generating an acoustic wave;

converting an acoustic signal of the acoustic wave into an electric signal by using an acoustic transducer attached to a part of the conductor, the part of the conductor being exposed from the non-conductive material; and

diagnosing whether the conductor has a fracture, on the basis of the strength of the electric signal and, if necessary, diagnosing the location of the fracture of the conductor by changing the location of the coil disposed on the surface of the structure and measuring a change in the electric signal caused by the change in the location of the coil.

24. A method of acoustic diagnosis/measurement using a pulse of electromagnetic force according to claim 23, wherein the structure is prestressed concrete.