Method of determining the porosity of a workpiece

1. A method of determining the porosity of a workpiece, which comprises:

injecting an ultrasonic signal into the workpiece;

receiving an ultrasonic echo signal generated in a depth within the workpiece; and

determining a variation of an amplitude of the ultrasonic echo signal with respect to said depth, and using the variation of the amplitude as a measure of the porosity at the respective depth.

2. The method according to claim 1 , which comprises injecting the ultrasonic signal into a workpiece made of a fiber composite material.

3. The method according to claim 1 , which comprises:

dividing the workpiece in an area region to be investigated into a plurality of layers of mutually different depths;

placing an ultrasonic test head onto the area region in a test position, injecting the ultrasonic signal into the workpiece with the test head, receiving the ultrasonic echo signal from the workpiece, and measuring the amplitude belonging to each layer; and

using a variation of the amplitude with respect to the depth of the layer as a measure of the porosity in the respective layer.

4. The method according to claim 3 , wherein the area region is defined with a number of test positions and the method further comprises averaging the amplitude of the ultrasonic echo signal belonging to the individual layers respectively measured in the individual test positions.

5. The method according to claim 3 , which comprises analyzing the received ultrasonic echo signal and determining the amplitudes of the ultrasonic echo signals belonging to a layer by identifying amplitudes within a time window belonging to said layer being of an amount greater than the amplitudes of the echo signal a half-wave before and a half-wave after the amplitudes.

6. The method according to claim 1 , which comprises using an average slope of the ultrasonic echo signal, in dependence on a depth d, as the measure of the porosity.