Wireless diagnosis apparatus for structure using nonlinear ultrasonic wave modulation technique and safety diagnosis method using the same

A method for measuring a fatigue crack of a structure using a nonlinear ultrasonic wave modulation technique, the method comprising:

• applying one of ultrasonic waves of different ultrasonic frequencies to the inside of a concentric dual piezoelectric transducer attached to the structure and applying the other one ultrasonic wave to the outside of the concentric dual piezoelectric transducer to make the structure vibrate;
• converting the responses of the structure generated by the vibration into first digital signals;
• converting the responses of the structure generated by applying only the one ultrasonic wave to the concentric dual piezoelectric transducer into second digital signals;
• converting the responses of the structure generated by applying only the other one ultrasonic wave to the concentric dual piezoelectric transducer into third digital signals;
• and
• deciding whether the structure is cracked through synchronous demodulation of signals acquired by removing the second digital signals and the third digital signals from the first digitals signals.

A system for measuring a fatigue crack of a structure using a nonlinear ultrasonic wave modulation technique, the system comprising:

• a low-frequency generation unit generating an ultrasonic wave of a low frequency according to a first control signal;
• a high-frequency generation unit generating an ultrasonic wave of a high frequency according to a second control signal;
• a first piezoelectric transducer attached to the structure to apply the ultrasonic wave of the low frequency to the structure;
• a second piezoelectric transducer attached to the structure to apply the ultrasonic wave of the high frequency to the structure;
• a third piezoelectric transducer converting the structural responses into electric signals;
• a digitizer converting an output of the third piezoelectric transducer into digital signals;
• a control unit controlling activation timings of the first control signal and the second control signal;
• and
• a digital signal processing unit subtracting linear responses and harmonic responses from an output of the digitizer and synchronously demodulating the corresponding responses to output the synchronously demodulated responses as fatigue crack information of the structure.

A wireless diagnosis apparatus for a structure using a nonlinear ultrasonic wave modulation technique, the apparatus comprising:

• a frequency generation unit outputting a pumping signal and a probing signal of different ultrasonic frequencies;
• a piezoelectric transducer unit making vibration by applying the pumping signal and the probing signal to the structure and outputting responses of the structure as electric signals;
• a digitizer converting an output of the piezoelectric transducer unit into digital signals;
• a digital signal processing unit constructing a first sideband spectrogram through linear response subtraction and synchronous demodulation of an output of the digitizer;
• and
• a wireless transmission unit wirelessly transmitting the first sideband spectrogram to an inspection system of a remote place.