The room‐temperature ferromagnetic resonance (FMR) spectra of γ‐Fe₂O₃, CrO₂, and barium ferrite particulate magnetic recording tapes have been measured at microwave frequencies of 9.35 and 35 GHz for various orientations of the static and high‐frequency magnetic fields with respect to the tape. For CrO₂ tapes, the influence of the width of the angular distribution of the particle orientations on the FMR spectra has been studied from the nearly isotropic case up to the highly oriented case. Hysteretic behavior for a CrO₂ tape as well as the effect of tape calendering for a γ‐Fe₂O₃ tape has been observed by FMR. Experimental results are found to be in reasonable agreement with results of theoretical calculations based on a model of an ellipsoidal single‐domain particle with both shape and magnetocrystalline anisotropy. Magnetostatic interaction inside the magnetic film has been introduced by expressing the total magnetostatic energy as a combination of a part dependent on particle shape and a part dependent on the shape of the tape. As a result of a comparison of experimental data with calculated data from the model, the magnetocrystalline easy axis of the CrO₂ particles is found to be parallel with the particle axis.

A survey on theory, characteristic quantities and the experimental technique of induction thermography is given. Induction thermography is used for surface defect detection in forged parts of ferromagnetic steel at typical frequencies of 100–300 kHz. The sensitivity for crack detection is comparable to magnetic particle inspection. A hidden defect in ferritic steel with a coverage of 140 μm was detected by lowering the induction frequency down to 1500 Hz. Defects of fibres were detected in carbon fibre reinforced polymer (CFRP). Inductive excitation is complementary to flash excitation. By increasing the induction frequency up to 52 MHz, surface heating of CFRP can be realised. Cracks in silicon solar cells were detected. The crack tip is revealed with very high contrast. A new field is crack detection in railway components like rails and wheels. In rails, a larger defect could be detected from a test car moving at a speed of up to 15 km/h. A fully automated wheel testing system was built up as a demonstrator, that can detect defects with comparable sensitivity to magnetic particle testing. Standardisation of thermography has gained progress in the last years and will lead to standards on active thermography, flash excited and induction thermography in the next future.

Porosity, microcracks, or secondary phase inclusions alter the sound velocities of materials, Ultrasonic scattering at grain and phase boundaries in polycrystalline, multi-phase, or porous media causes attenuation of sound waves and dispersive sound velocities. These effects and also the amplitudes of the scattered waves can be exploited for materials characterization if their dependence on the structure properties is known quantitatively. In this paper the usefulness of sound velocity, attenuation, and backscattering measurements to detect and value damage in steel e.g caused by hydrogen attack is discussed. Numerical evaluations of theoretical results and experimental investigations are presented. It turns out that in most cases velocity measurements do not yield sufficient quantitative information about damage because the variations in sound velocity caused by slight differences of the undamaged material are often larger than those caused by damage. Sound attenuation and back scattering amplitude measurements are more appropriate to estimate damage in steel.

Magnetic materials were investigated by induction thermography at induction frequencies of 80–300 kHz. The influence of an external magnetic field on the thermal crack contrast was studied. With proper orientation of the external field, the contrast increased by a factor more than three. Numerical simulations of the static and high-frequency magnetic fields and the temperature distribution were performed. Using a stationary induction field and a modulated external field in the frequency range of 0.28–36.5 Hz, lock-in thermography was realised, which shows cracks with good contrast. The technique was applied to crack detection in ferritic steel profiles.