Ultrasound is used for the measuring of hardness or elastic material properties under loads by the ultrasonic contact-impedance (UCI) method, in which a rod-shaped resonator , one end holding an intentation body, is pressed against a test specimen with a given test force, so that the indentation body penetrates the specimen, and the resulting change of df in the frequency f of the resonator is measured. With a wide variety of UCI probes, a large number of test problems can be solved, especially at hard-to-get-to locations. The probe usually contains a Vickers diamond (136° pyramid) and due to conversion scales, the reading can be performed in HV, HB, HRC, HRB and HS.
~ hardening depth: This is another application for the use of ultrasonics in the field of hardness testing. The hardening depth of induction hardening components can be measured with the Ultrasonic backscattering method. Higher backscattered signals can be measured at the beginning of the base material, thus the applied time of flight measurement gives a result for hardening depth