Method and apparatus for acoustic detection and location of defects in structures or ice on structures
First Claim
1. An apparatus for detecting the presence and characteristics of a defect in or ice on a structure comprising:
- means for creating and delivering a low frequency signal to the structure;
means for creating and delivering a high frequency probe signal to the structure; and
receiver means for receiving a modulated signal from the structure caused by the low frequency signal modulating the high frequency signal in response to a defect in or ice on the structure, the modulated signal indicating the presence of a defect in or ice on the structure.
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Abstract
The invention relates to a method and apparatus for nondestructive testing and evaluation of materials and mechanical structures to determine their integrity reducing contact-type flaws such as cracks, fractures, delamination, unbondings, etc. and also presence of ice on a structure. The invention employs an ultrasonic probing signal and a low frequency vibration applied to a structure tested. In a structure without flaws or ice, these signals propagate independently without any interaction. If the structure contains a defect or ice thereon, the vibration varies the contact area of the defect or ice/structure interface, modulating the phase and amplitude of the higher frequency ultrasonic probing signal passing through the structure. In the frequency domain the result of this modulation manifests itself as sideband spectral components with respect to frequency of the probe wave. This can be considered as a new signal generated by a defect, so that the defect can be detected more easily when such a signal is observed. There are three modes of detection including, vibro-modulation, impact-modulation and self-modulation. The location of defects can be determined in two modes. In a first mode defect is located by moving the low frequency signal about the structure and triggering the high frequency signal immediately after the low frequency signal. Defects can be located in a second mode with a sequence of short burst high frequency signal and a signal-processing algorithm which selects the sequences reflected from various areas of the tested structure. A defect can be quantitatively analyzed by sweeping the high frequency signal over a defined frequency range and measuring, averaging and normalizing the amplitudes of the side bands.
77 Citations
39 Claims
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1. An apparatus for detecting the presence and characteristics of a defect in or ice on a structure comprising:
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means for creating and delivering a low frequency signal to the structure;
means for creating and delivering a high frequency probe signal to the structure; and
receiver means for receiving a modulated signal from the structure caused by the low frequency signal modulating the high frequency signal in response to a defect in or ice on the structure, the modulated signal indicating the presence of a defect in or ice on the structure. - View Dependent Claims (2, 22, 23, 24)
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3. A method of detecting the presence and characteristics of a defect in or ice on a structure comprising the steps of:
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applying a low frequency signal to the tested structure;
applying a high frequency probe signal to the tested structure;
modulating the high frequency signal by the low frequency signal in response to the presence of a defect in the structure; and
receiving a modulated signal through a receiver means applied to the tested structure. - View Dependent Claims (4, 25, 26, 27, 28, 29, 30, 31, 32)
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5. A method for detecting the presence and characteristics of a defect in or ice on a structure comprising the steps of:
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propagating an ultrasonic probe signal in the structure;
propagating a low frequency vibration signal in the structure;
detecting said ultrasonic probe signal and analyzing said detected ultrasonic probe signal for interaction between said ultrasonic probe signal and said low frequency vibration signal caused by a defect in or ice on the structure, said interaction being indicative of a defect in or ice on the structure. - View Dependent Claims (6, 7, 8, 9)
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10. A method of determining the location and characteristics of defects in or ice on a structure comprising the steps of:
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propagating sequences of an ultrasonic probe signal in a structure;
said ultrasonic probe signal having a first frequency;
said sequences being propagated at a second repetition frequency;
propagating a low frequency vibration signal in said structure the low frequency vibration signal modulating the ultrasonic probe signal in response to a defect in or ice on the structure;
detecting said propagated sequences of the probe signal, and selecting and processing only propagated sequences which are indicative of an area of said structure having a defect or ice. - View Dependent Claims (11, 12)
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13. An apparatus for non-destructive testing of a structure comprising:
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means for transmitting an ultrasonic signal into said structure;
means connected to said structure for receiving said ultrasonic signal;
means connected to said structure for generating a low frequency signal in said structure; and
control means connected to said transmitting means and to said low frequency generating means for transmitting said ultrasonic signal into said structure at a repetition frequency which is greater than twice the frequency of said low frequency signal;
wherein, the low frequency signal modulates the ultrasonic signal in response to a defect in the structure. - View Dependent Claims (14)
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15. An apparatus for determining the location and characteristics of defects in ice on a structure comprising:
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means for generating a low frequency signal in a structure;
means for generating a high frequency signal in the structure;
means for receiving a modulated signal from the structure caused by said low frequency signal modulating said high frequency signal in response to a defect in or ice on the structure; and
means for analyzing side bands in said received signal for analyzing a defect or ice. - View Dependent Claims (16, 17, 18, 20)
means for moving location of said low frequency generating means on said structure relative to the location of said means for generating said high frequency signal; and
control means for triggering said high frequency signal after said low frequency signal is triggered, whereby the amplitude of said side bands is increased as the location of said low frequency signal generating means is moved towards a defect.
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19. An apparatus for quantitatively analyzing defects in a structure comprising:
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means for generating a high frequency signal in a structure;
means connected to said high frequency signal generating means for varying the frequency of said high frequency signal over a predetermined frequency range;
means for generating a low frequency signal in said structure;
means for receiving frequency modulated signals from said structure caused by the low frequency signal modulating the high frequency signal in response to a defect in the structure, said received modulated signals being indicative of a defect in said structure; and
means connected to said receiving means for measuring, averaging and normalizing the amplitudes of side bands in said received modulated signals to generate an indication of the size of a defect in the structure.
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21. An apparatus for locating defects in structures comprising:
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means for generating a low frequency signal in a structure;
means for generating sequences of a short burst high frequency signal in the structure;
means for receiving a signal from the structure, said signal being a modulated combination of said low frequency signal and said high frequency signal;
means for analyzing selected sequences of said received signal from areas of the structure;
whereby a presence of modulation in a selected sequence indicates the presence of a defect in an area of the structure. - View Dependent Claims (39)
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33. A method of analyzing defects in a structure comprising:
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generating a high frequency signal in a structure;
sweeping the frequency of the high frequency signal over a frequency range;
generating a low frequency signal in the structure;
receiving modulated signals caused by the low frequency signal modulating the high frequency signal in response to a defect in the structure; and
analyzing side bands of the modulated signals to analyze the defect. - View Dependent Claims (34, 35, 36, 37)
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38. A method for locating defects in a structure comprising:
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generating a low frequency signal in a structure;
generating sequences of a short burst high frequency signal in the structure;
receiving a modulated signal from the structure caused by the low frequency signal modulating the high frequency signal in response to a defect in the structure;
analyzing modulation of sequences of the received signal from areas of the structure to locate a defect in the structure.
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Specification