Measurement of acoustic properties for passive-material samples using multichannel inverse filter

Abstract

The measurement of acoustic properties for passive-material samples is strongly interfered by reverberations in a limited space. A multichannel inverse filter (MIF) can achieve spatio-temporal focusing by retransmitting the optimal signal estimated from multichannel impulse responses of the transmitter channel and the underwater acoustic channel. To decrease the influence of reverberations on measurements and improve the measurement precision, a MIF is employed to measure the echo reduction and insertion loss, respectively. The method is demonstrated by simulations and experiments, which were performed in a cylindrical tank to measure the two acoustic parameters for a steel plate sample.

Measurement of reflection coefficient for a double-layered scaled model using the inverse filter

“…The main idea of this paper is how to use the IFT to realize the special-temporal focusing and the separating of the direct signal and the multiple reflections of the double-layer-scaled-model layers, and finally evaluating the reflection coefficient for a double-layered scaled model with more implementable procedures than that proposed in Ref. (12).…”

“…Many methods were proposed in measuring the reflection coefficient, either for a small sample in sound tube or a large sample in free field environment. (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) Y. Z. Pan, X. P. Mo, et al presented a wideband transducer for sound tube system, which satisfied the performance measurement for acoustic materials above 1.4 kHz to 23 kHz.…”

“…The measurement methods for large samples in free field or a limited space environment overcome most of the drawbacks of that for a small sample in sound tube. (6)(7)(8)(9)(10)(11)(12) U. Ingård and R. H Boltpresented a free field method of measuring the absorption coefficient of acoustic materialsfor large samples and the experimental values were good agreement with calculations, but the effect of reverberation at low frequencies was inevitable. (6) M. Mintenet al applied the two-microphone technique to characterizing the absorption coefficient for large samples in an anechoic room and obtained reliable results with a harsh condition of anechoic performance of the room.…”

“…What's more, the width of the main lobe is widening as the frequency decreasing, and once the main-lobe width is wider than the sample's size, the influence of the diffraction cannot be neglected. The multichannel inverse filter method (MIF) degraded the side lobe, enhanced the resolution of the main lobe and realized the optimal focusingby utilizing the coherent information of the different transmitting-receiving channel, (12) but the more complicated procedures were necessary, and the focusing effect was influenced by the number of transmitted transducers and the receivers, i.e. a high requirement of the hardware was necessary.…”

“…This paper presents a method for measuring the reflection coefficient of the doublelayered scaled model using the inverse-filter transmission (IFT), which is distinguished with the method given by Ref. (12) by different objective functions. To construct the inverse filter, the response of the circuit and the underwater acoustical channel is estimated at first, and the retransmitted inverse signal can be estimated with the least square method for solving the cost function constructed by the inverse filtering theory.…”