EXPERIMENTAL STUDY ON IMPEDANCE MEASUREMENT OF PERFORATED PLATE IN LOW-FREQUENCY RANGE

Perforated plates have gained wide application in industrial noise reduction, suppression of thermoacoustic instabilities, and elimination of acoustic fatigue. Many models have been developed to predict the acoustic impedance of the perforated plate, which are primarily effective at medium and high frequencies. To meet the needs of low-frequency thermoacoustic oscillation suppression, more accurate impedance models are needed for the perforated plates under low-frequency conditions. In this paper, experimental research work has been conducted to investigate the impedance characteristics of perforated plates in the low-frequency range. Firstly, based on the transfer function method, a dual microphone impedance tube was designed. The measurement point spacing was optimized, and the anechoic ends were redesigned based on the COMSOL simulation. The optimized anechoic ends are able to achieve 99% absorption above 150Hz in the low-frequency range. Then, the acoustic impedance was extracted for perforated plates with different thicknesses, apertures and open area ratios. This experimental design is capable of extracting the acoustic impedance under 200Hz in the low-frequency range. In this work, the four-microphone method is applied to avoid the difficulty of constructing the low-frequency anechoic ends. The results show that the acoustic impedance of the perforated plate extracted experimentally under low-frequency conditions is in good agreement with the theoretical value. In a word, this study presents experimental investigations on the impact of different parameters on the acoustic impedance of perforated plates under low-frequency conditions for the first time.