Real-time nearfield acoustic holography for reconstructing the instantaneous surface normal velocity

A pressure-velocity impulse response is deduced in this work to establish the relationship between the pressure and the particle velocity in the time-wavenumber domain. By virtue of it, real-time nearfield acoustic holography (RT-NAH) is extended to reconstruct the instantaneous surface normal velocity of a vibrating structure from the time-dependent pressure measured in the near field, which provides a non-contact and real-time method to measure and visualize the transient vibration of the structure. An experiment of an impacted steel plate is investigated, in which the surface normal velocity of the plate is measured by laser Doppler vibrometry and reconstructed by RT-NAH. The comparison of surface normal velocities obtained by using these two methods shows a satisfactory agreement not just for the time-evolving surface normal velocity signals but also for the vibration mode shapes. Accordingly, it demonstrates that RT-NAH is a viable approach for reconstructing the instantaneous surface normal velocity.