On acoustic very near field measurements

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

“…It generally employs an easily available and economical microphone array to measure the pressure in the near field, and then reconstruct the surface normal velocity with the measured pressure as the input [8]. Similar to NAH, a direct inverse method based on the discretized Rayleigh integral was proposed recently [9]. In that method, the Rayleigh integral was discretized to establish the transfer relationship between surface velocity and sound pressure, and the microphones were placed close to the vibrating structure to provide a transfer matrix with a low condition number; then, the surface velocity could be calculated by directly inverting the transfer matrix.…”

Sound pressure around dipole source above porous surface

“…Therefore, another approach by using Rayleigh integral for calculation of sound in a Very Near Field of the plate is needed. 17 …”

Hair tension influence on the vibroacoustic properties of the double bass bow

“…However, by placing the microphone in the Very Near Field (VNF), 5 just 3 mm above the vibrating structure, measurement reproducibility increases dramatically. 6 Visualization of vibration modes by scanning the microphone in the Very Near Field of the vibrating structure was used in the presented experiments. In such an arrangement, sound pressure above the vibrating structure and under the microphone is directly proportional to the vibration velocity.…”

“…6,7 The boundary of the Very Near Field is affected by the size of the antinode a (vibrating part of the surface between two nodes), and by the shape of the vibrating surface. In literature, the boundary of the Very Near Field is estimated to 0.11a.…”

“…In literature, the boundary of the Very Near Field is estimated to 0.11a. 6,7 In such an arrangement sound pressure above the vibrating structure and under the microphone is directly proportional to the vibration velocity.…”