Resonant acoustic nonlinearity for defect-selective imaging and NDT

The bottleneck problem of nonlinear NDT is a low efficiency of conversion from fundamental frequency to nonlinear
frequency components. In this paper, it is proposed to use a combination of mechanical resonance and nonlinearity of defects to
enhance the input-output conversion. The concept of the defect as a nonlinear oscillator brings about new dynamic and frequency
scenarios characteristic of parametric oscillations. The modes observed in experiment include sub- and superharmonic resonances
with anomalously efficient generation of the higher harmonics and subharmonics. A modified version of the superharmonic
resonance (combination frequency resonance) is used to enhance the efficiency of frequency mixing mode of nonlinear NDT. All
the resonant nonlinear modes are strongly localized in the defect area that provides a background for high-contrast highlysensitive
defect- and frequency-selective imaging.