Which frequency is generally considered low frequency for ultrasonic testing?

In ultrasonic testing (UT), frequency plays a crucial role in determining the capabilities and limitations of the ultrasonic waves used for inspection. Generally, frequencies below 5 MHz are classified as low frequency. Frequencies in this range are used for inspecting thicker materials and can better penetrate through them, providing satisfactory data for different types of materials and structures.

A frequency of 1 MHz is particularly beneficial for applications involving larger and denser materials. Lower frequencies have longer wavelengths, which allows them to travel deeper into the material without being significantly attenuated. They are effective for detecting larger flaws or discontinuities and are often used in applications like weld inspections or testing of large components where depth of penetration is more critical than resolution.

Higher frequencies, such as 5 MHz, 10 MHz, and 25 MHz, are typically considered mid-range to high frequencies. These frequencies provide better resolution, capable of detecting smaller flaws, but their penetration ability is reduced compared to lower frequencies. Consequently, they are more suited for thinner materials and surfaces where greater detail is required. Therefore, the choice of using a 1 MHz frequency aligns with the needs of many applications that require deeper penetration and the ability to handle thicker materials effectively.