Abstract: A method and apparatus for the determination of thickness of plastic materials, as well as of bonding and coating materials, by high frequency electric and magnetic alternating fields. The method enables a simple test of components, as well as of coatings and bondings, even if the plastic parts to be tested or the coatings or bondings to be tested are not yet completely cured and the surfaces to be tested are located, so as to be concealed or are accessible only with difficulty. The method and apparatus consists in that electrically conductive or ferromagnetic particles are added to the materials to be measured and subsequently the electrical conductivity or magnetic permeability is measured at the completed or coated test specimen by high-frequency electrical and magnetic alternating fields, whose progression in space and time is adapted to the measuring task.

Abstract: In a method of and an apparatus for detecting flaws inside articles, the flaw area for detection being subjected to ultrasonic pulses on which, after reaction with the flaw, a reference beam is superimposed, whereupon the resulting interference field is holographically detected, reconstructed and evaluated. This method can be applied to thin and sound-scattering materials with improved resolution and a description of the flaw configuration and detection of the deformation behavior of flaws. In the method, a load is applied to the flaw area under investigation and this area is subjected to ultrasonic pulses at least at two different times each corresponding to an extreme value of the loading, the ultrasonic pulses being short with respect to the load period and, after reaction with the flaw, reference pulses are superimposed on the ultrasonic pulses, whereupon the holograms of these ultrasonic applications are superimposed to give an interferogram which can be evaluated.

Abstract: In the disclosed method and structure a pulse of a sound filed to be mapped is illuminated at at least two extremes values at different moments with a laser beam of short duration compared to the period of the illuminated sound pulse and interference produced between the resulting reflected beam and a reference beam. A holographic image is formed. The relative phase of the laser pulse and the reference is changed between the individual illuminations by a preselectable amount which deviates from .pi. and which suppresses the optical and/or acoustical noise. Specifically, a time delay initiates the first illumination process when an extreme value is reached at the beginning of the sound pulse to be mapped. A counter is started by this time delay and counts the half and quarter waves of the sound pulse. The counter initiates an additional illumination process after a preselectable odd number has been reached. A phase shifter changes the relative phase between the object beam and the reference beam.

Abstract: A method and device for generating acoustic pulses, preferably ultrasonic, and the use of such pulses, more particularly for non-destructive material testing. The acoustic pulses are produced by a modulation or multiplication technique.