Background
The measurement of the thickness of wave-absorbing coatings is a crucial technical aspect in the modern aerospace field. Wave-absorbing coatings can not only effectively absorb electromagnetic waves, but also improve the stealth performance of aircraft. However, due to the material properties and thin thickness of wave-absorbing coatings, it is often difficult for traditional measurement methods to meet the accuracy requirements. Today we will combine the actual situation of the wave-absorbing coating samples, introduce how to use ultrasonic thickness gauge, through high-precision measurement methods to solve the wave-absorbing coating thickness measurement problems.
Absorbent coating is a special material capable of absorbing electromagnetic waves, usually coated on the surface of metallic or non-metallic substrates. Due to their unique electromagnetic properties, absorptive coatings are widely used in stealth technology, electromagnetic shielding and other fields. However, the thickness of absorbing coatings is usually thin (0.3-1.2 mm) and the material itself has complex acoustic properties, which poses a great challenge for thickness measurement.
As a non-destructive testing method, ultrasonic thickness measurement technology can accurately measure coating thickness without damaging the material. By choosing the right probe and instrument parameters, ultrasonic thickness gauges can effectively cope with the difficulties in measuring acoustic coatings and ensure the accuracy and reliability of the measurement results.
About Tested Samples
The sample we received this time was an absorptive coating covering a non-metallic substrate with a thickness of about 0.58 mm. The customer wanted us to use an ultrasonic thickness gauge to measure the thickness of the absorbing coating.
The wave-absorbing materials we come into contact with are usually metallic substrates. For example, we have received a request from an airline company to measure the thickness of an absorptive coating on the surface of an aircraft.
Acoustic coatings on aircraft surfaces are usually applied to a metallic substrate (e.g. steel, aluminium, titanium), which is about 2 mm thick.
However, the acoustic properties of non-metallic substrates are very different from those of metallic substrates:
Lower speed of sound - The speed of sound in non-metallic materials is usually lower than in metallic materials, which affects the propagation time of ultrasound waves and the reception of echo signals.
Small acoustic impedance difference - The small acoustic impedance difference between the non-metallic substrate and the absorbing coating may result in a weak echo signal at the interface, making it difficult to clearly identify.
High signal attenuation - Non-metallic materials typically have a high attenuation of ultrasound, especially if the absorbing coating has inherently high attenuation properties, which can further reduce signal penetration.
Industrial Measurement Solution
For thickness measurement of absorbing coatings on metal substrates, we provided a measurement solution using a YUSHI PM5 Gen2 ultrasonic thickness gauge with a 5MHZ 13mm delay line probe, which was a good solution to the customer's needs.
We can still solve the challenges of measuring absorbing coatings on non-metallic substrates with the PM5 Gen2.
Choosing the right probe
For absorbed coatings on non-metallic substrates, we chose the D5A6 delay line probe. With its high resolution and sensitivity, this probe effectively solves the problem of signal attenuation in absorbing coatings, capturing the echo signal of thin coatings.
Correctly Adjusting Instrument Parameters
The PM5 Gen2 has a variety of parameter adjustments (e.g., fading, E-banking, phase, gate, etc.) to lock in the correct waveform and ensure the accuracy of the measurement results.
Gain Adjustment: Increase the gain appropriately to enhance the reception of weak signals, but be careful to avoid noise interference.
Blanking and electronic blanking: By adjusting the blanking parameters, unwanted noise can be hidden to ensure that the instrument can correctly identify the interface between the coating and the substrate echo.
Gate Setting: Reasonable setting of the gate position to lock the interface echo between the coating and the substrate to ensure the accuracy of the measurement results.
Measurement Results
The sample was measured using PM5 Gen2 Ultrasonic Thickness Gauge with D5A6 delay line probe, and gel couplant was used to enhance the propagation of ultrasonic waves. Adjust Gain, Blank, E-Blank, Gate, Range and other parameters to determine the interface echo between the coating and the substrate, and the sound velocity was calibrated with the known coating thickness, and then the thickness of other parts was verified.
Summarize
The use of ultrasonic thickness gauges in the measurement of absorbing coating thicknesses not only allows for the accurate measurement of coating thicknesses without damaging the material, but also provides strong technical support for the development and application of absorbing coatings. By using high performance ultrasonic thickness gauges, such as the PM5 Gen2, and high resolution probes, such as the D5A6 and D5A13 delay line probes, we can effectively address the challenges of measuring wave-absorbing coatings on both non-metallic and metallic substrates, ensuring the accuracy and reliability of the results.
If you are experiencing similar problems when measuring wave-absorbing coatings, or would like to know more about the application of ultrasonic thickness measurement technology, please contact us and we will provide you with professional solutions and technical support.