METHOD OF BISPECTRAL PULSE-FREQUENCY INSPECTION Russian patent published in 1998 - IPC

FIELD: flaw detection. SUBSTANCE: broadband and narrow band heat waves are excited in sample. Radiation of heat waves is absorbed by IR detector of sandwich type sensitive in two spectral ranges of 2.0-5.0 μm and 8.0-14.0 μm. Element sensitive in range of 2.0-5.0 μm absorbs radiation with low frequency and frequency ω_m on which photosignal has maximum value with phase difference 2πm between it and modulated radiation of source of heat waves is measured. Element of spectral range of 8.0-14.0 μm measures signal I₂ and rate dI₂/dτ of its change caused by heat pulse. Thermophysical parameters and depths of laying of flaws are determined by ω_m and relation (dI₂/dτ)/I₂. EFFECT: enhanced authenticity of method. 2 dwg