System and method of determining porosity in composite materials using ultrasound

A system for ultrasonically measuring the porosity in a sample composite material by accessing only one side of the sample composite material, comprising:

• an ultrasonic laser detection system to generate and measure a sample ultrasonic signal from the sample composite material;
• a processor which:
• normalizes said sample ultrasonic signal relative to a surface echo of the sample composite material;
• isolates a sample back-wall echo signal from said sample ultrasonic signal;
• determines a sample frequency spectrum of said sample back-wall ultrasonic signal;
• normalizes a reference ultrasonic signal relative to a surface echo of a reference composite material;
• isolates a reference back-wall echo signal from the sample ultrasonic signal;
• determines a reference frequency spectrum of said reference back-wall ultrasonic signal;
• derives the ultrasonic attenuation of the sample ultrasonic signal as the ratio of the sample frequency spectrum to the reference frequency spectrum over a predetermined frequency range;
• and
• compares said derived ultrasonic attenuation to predetermined attenuation standards to for evaluating the porosity of the sampled composite material.

A method for detecting ultrasonic surface displacements on a target including method for ultrasonically measuring the porosity in a sample composite material by accessing only one side of the sample composite material, comprising the steps of:

• generating ultrasonic surface displacements at the target;
• using a first pulsed laser beam to detect the ultrasonic surface displacements at the target;
• collecting phase modulated light from the first pulsed laser beam scattered by the target;
• optically amplifying the phase modulated light after the phase modulated light has been collected;
• preventing reflected phase modulated light feedback into an optical amplifier with at least one optical isolation assembly placed in the path of propagation of the phase modulated light which has been collected;
• processing the phase modulated light to obtain data representative of the ultrasonic surface displacements at the target;
• and
• ultrasonically measuring the porosity in a sample composite material by accessing only one side of the sample composite material, wherein the step of ultrasonically measuring further comprising the steps of:
• measuring a sample ultrasonic signal from the sample composite material;
• normalizing the sample ultrasonic signal relative to the surface echo of the sample composite material;
• isolating a sample back-wall echo signal from the sample ultrasonic signal;
• determining a sample frequency spectrum of the sample back-wall ultrasonic signal;
• measuring a reference ultrasonic signal from a reference composite material;
• normalizing the reference ultrasonic signal relative to the surface echo of the reference composite material;
• isolating a reference back-wall echo signal from the sample ultrasonic signal;
• determining a reference frequency spectrum of the reference back-wall ultrasonic signal;
• deriving the ultrasonic attenuation of the sample ultrasonic signal as the ratio of the sample frequency spectrum to the reference frequency spectrum over a predetermined frequency range;
• and
• comparing the derived ultrasonic attenuation to predetermined attenuation standards to for evaluating the porosity of the sampled composite material.