Which search unit frequency would contain the thickest crystal?

The search unit frequency that corresponds to thicker crystals is typically lower in frequency. In ultrasonic testing, lower frequencies are used in applications where deeper penetration into the material is required, allowing the sound waves to travel further before being absorbed or scattered. A 1 MHz frequency is effective for scanning through thicker materials because the longer wavelength associated with lower frequencies enables it to penetrate the material more efficiently.

Conversely, higher frequencies, such as 5 MHz, 15 MHz, and 25 MHz, are associated with thinner crystals and have shorter wavelengths. While they provide better resolution and are useful for detecting smaller flaws, they are not as effective for deep penetration through thicker sections of material. Therefore, the frequency of 1 MHz represents the choice that would contain the thickest crystal, as it’s designed for applications requiring the ability to inspect larger or thicker components.