Acoustic inspection of structures

A method for inspecting a concrete structure comprising the steps of:

• dragging a chain across the structure;
• receiving with a microphone not physically coupled to the structure sounds generated by the structure while the chain is being dragged;
• digitizing a signal from the microphone;
• processing the digitized signal to remove frequencies outside a frequency range of interest;
• calculating the mean square of the processed signal;
• comparing the mean square of the processed signal to a threshold to determine whether a defect is present in the structure;
• and
• wherein defects in the structure are detected from acoustic waves resulting from vibration of the structure.

An apparatus for detecting the presence of a defect in a structure, the apparatus comprising:

• a mobile platform;
• an excitation device mounted to the platform such that the excitation device excites the structure when the platform is in close proximity to the structure by moving an object across the structure;
• a microphone mounted on the mobile platform such that the microphone is not physically coupled to the structure and is positioned to receive acoustical energy form the structure;
• and
• a processor connected to the microphone, the processor being configured to process a signal received from the microphone over a period of time to remove frequencies that do not correspond to defects to be detected and compare the processed signal to a threshold;
• wherein defects in the structure are detected from acoustic waves resulting from vibration of the structure.

An apparatus for inspecting a concrete structure, the apparatus comprising:

• a cart;
• a sensor attached to the cart and connected to a processor;
• a sound dampening box mounted to the cart, the sound dampening box having an open end, the sound dampening box being positioned such that the open end faces a surface of structure to be inspected when the cart is moved across the surface;
• a plurality of chains attached to the cart, the chains being positioned to drag on the surface when the cart is moved across the surface;
• a microphone mounted in the box and positioned such that the microphone is not in contact with the surface when the cart is moved across the surface;
• an amplifier connected to the microphone;
• an analog to digital converter connected to the amplifier;
• a processor connected to the analog to digital converter, the processor being configured to perform the steps of processing the signal from the converter to remove frequencies outside of a frequency range of interest, calculating a mean square of the processed signal, comparing the mean square of the signal to a threshold to determine whether a defect is present, and correlating signal to a location on the surface using the sensor;
• and
• a display connected to the processor for displaying a location of a defect;
• wherein defects in the structure are detected from acoustic waves resulting from vibration of the structure.