Normal contact ultrasonic testing is performed using which frequency range?

• A. 1 Hz to 10 Hz
• B. 1 MHz to 10 MHz
• C. 100 MHz to 1 GHz
• D. 10 kHz to 100 kHz

Answer: (B)

In ultrasonic testing, the frequency you use controls both resolution and how deeply the sound can travel through a material. For normal contact testing on metals, you want enough frequency to clearly resolve small flaws, but not so high that the sound is quickly attenuated and can’t inspect through the thickness of the part. The low-to-mid megahertz range achieves this balance, making 1 to 10 MHz the typical and most practical band for standard contact inspections. Frequencies far below this would give poor resolution and risk missing small defects, while very high frequencies would be heavily attenuated in metal and limit depth of penetration, which is not suitable for most routine inspections. In practice, transducers around 2–5 MHz are common, with up to 10 MHz used for thicker sections or higher resolution needs.