Technical Support

I. Basic Definition

Phase reversal refers to the phenomenon where the signal phase undergoes a $180^\circ$ inversion (or shift) during the propagation of an ultrasonic wave, primarily due to differences in acoustic impedance at a material interface. When an ultrasonic wave encounters internal defects within a material—such as delaminations or voids—the phase of the backscattered signal reverses due to the unique reflection characteristics at these interfaces.

II. Trigger Conditions and Mechanism

Interface Reflection Disparity

When an ultrasonic wave travels across an interface between two media with significantly different acoustic impedances (e.g., a resin matrix and an air void), the reflected wave's phase may undergo a $\text{180}^\circ$ reversal. This reversed signal creates a distinct contrast against normal interface reflection signals.

Influence of Defect Type

Defects like delamination and cracks create discontinuous acoustic interfaces. The resulting phase reversal signal therefore serves as a critical and characteristic feature for the reliable identification of structural flaws.

III. Technical Applications

Defect Detection

Phase reversal signals can visually and reliably mark the boundaries of delamination defects. For instance, in the inspection of Carbon Fiber Reinforced Polymers (CFRP), the area corresponding to a reversed phase is often highlighted (e.g., marked in red) to precisely indicate the defect location.

Imaging Enhancement

By utilizing Fourier Transform techniques to extract phase information, the system can perform a $\text{180}^\circ$ phase correction in the negative frequency region. This process significantly enhances the overall image resolution and improves the discriminative capability for recognizing defects.

IV. Equipment Function Implementation

Ultrasonic scanning microscopes are equipped with integrated phase analysis algorithms. These algorithms can automatically detect the phase-reversed signals, generating color-coded images. Furthermore, the system can quantitatively calculate defect metrics, such as the percentage of the detected area occupied by delamination.

Conclusion: Phase reversal analysis is the core physical phenomenon enabling micro-defect detection in ultrasonic scanning microscopy. Its precise analytical capability significantly enhances the reliability and depth of structural assessment for internal material evaluation.