Nonlinear Acoustic Shear Wave Detection of Zero Gap Kissing Bonds in Encapsulated Packs
Nonlinear acoustic shear wave harmonic detection resolves zero gap kissing bonds in encapsulated battery packs by measuring contact acoustic nonlinearity.
Dynamic Wave Modulation
Meaning
Ultrasonic material characterization utilizes the interaction of multiple mechanical frequencies to reveal microscopic structural changes within a medium. Through the process of dynamic wave modulation, a low-frequency pump wave and a high-frequency probe wave are simultaneously injected into the target material. The large-amplitude pump wave continuously stresses and relaxes the internal micro-cracks, altering the propagation velocity and attenuation of the probe wave.
This cross-modulation generates sideband frequencies in the received spectrum, revealing localized material degradation with high sensitivity. Such approach detects early-stage fatigue before macroscopic cracks develop.
Modulating Mechanism
Mechanical stress variation at the boundary of a closed defect shifts the contact stiffness nonlinearly. During the compressive phase of the pump wave, the defect faces are pressed together, which increases the local acoustic transmission. Conversely, the tensile phase separates the faces and reduces the transmission.
This periodic change in transmission coefficient modulates the amplitude of the co-propagating probe wave, creating a complex modulated envelope.
Interrogation Strategy
Excitation setups require dual transducers positioned to maximize the overlap of both acoustic fields. Frequency selection is tuned to ensure the pump wave excites the system resonance while the probe wave operates at a much higher frequency to resolve fine structural details.
Analytical Result
Processing the modulation spectrum isolates the amplitude of the first-order sidebands. High sideband ratios correspond to a higher density of micro-defects within the joint.