Coupling Agent in Scanning Acoustic Microscope
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author：admin
source：Hiwave
time：2025-03-14
catogory：Frequently Asked Questions
The coupling agent serves as a ‘bridge’ connecting the workpiece to the probe in Scanning Acoustic Microscope (SAM) inspections. The performance of the cou……
The coupling agent serves as a ‘bridge’ connecting the workpiece to the probe in Scanning Acoustic Microscope (SAM) inspections. The performance of the coupling agent directly determines the sensitivity and reliability of the detection. By selecting different coupling agents, it is possible to effectively detect micro-cracks, pores, voids, delamination, and other defects.
Functions of the Coupling Agent
Eliminate Interface Reflection
Ultrasonic waves can suffer over 90% energy reflection loss when contacting the workpiece due to air gaps. The coupling agent fills these gaps, reducing the acoustic impedance difference from air to liquid, thereby enhancing the energy transmitted into the workpiece.
Protect the Probe
Conducting inspections in a liquid or semi-liquid environment provides a buffer between the workpiece and the probe, mitigating mechanical shocks. This prevents signal distortion caused by poor contact and protects the probe from wear and tear.
Suppress Noise Interference
High-viscosity coupling agents (such as glycerin) can dampen minor vibrations on the workpiece surface, thereby reducing false signals.
How to Choose a Coupling Agent
High-Temperature Environments
In high-temperature environments, it is recommended to use silicone oil and heat-resistant wax as coupling agents because water tends to evaporate at high temperatures, and gels may carbonize. These types of coupling agents are typically used for brake disc inspections.
Precision Inspections
During precision inspections, high-frequency probes require low-viscosity media to ensure signal integrity. Therefore, deionized water is often used as a coupling agent. For example, semiconductor wafers are frequently inspected using deionized water.
Irregular Surfaces
For irregular surfaces, high-viscosity gels are chosen as coupling agents to fill microscopic grooves and reduce signal loss due to poor contact. This ensures better coverage and more reliable detection results.
