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A New Tube Method for Measuring Complex Pressure Reflection Cofficients of Absorbers in Water

Motoyoshi Okushima
1961 Acoustical Science and Technology  
The author devised a new tUbe method for measuring the complex pressure reflection c 伍cient in water , constructed the apparatus , and measured several samples . This method is a sort of the stationary wave method . In this set up , the bottom surface of a vertical steel tube with thick wall ( length 400 mm , inner radius 17 . 5mm , wall thickness 6 mm )is driven at one of the longitudinal resonant frequen(y ( about 9 , 18,27 and 36 kc)of a Langevin type transducer of barium titan且 te , and the
more » ... titan且 te , and the stat1onary wave 丘eld is . formed in the water oolumn between the botto 皿 surface and the satlple inserted in the tube fro 【n the ‡ oP ・ By this method , the principle that the mechanical impedance toward the sample at the bQttom takes the mini 匚 num or the max 圭 mum values , when the sample is Inoved up and down and as the botto 皿 surface coincides w 互 th the node or the Ioop plane of pressure in the stationary wave 丘eld is used . Namely , the amplitude of the oomplex reflection coe Hcient 三 sderived from values of these two i 皿 pedances, which are obtained by measuring the reac − tion to the transducer surface from the field in the tube , while the phase of the complex refle 〔 rtion coethcient is derived by measuring the distance between the sample and the pressure node plane in which the mechanical impedance takes the minimum value . ・ Two methods , the motional admittance method and the vibrometer method , were devise . d for the p ロ rpose of measuring the mechanical impedan . The transducer for the vibrometer method has two bar三 um titanate elements for driving and for measuring the velocity amplitude , and it is so designed as to become a multiresonant transducer which Vibrates with the same intensity for the 皿 ost part and is capable of being ernployed for measur 三 ng with equal easiness at feur resonant frequencies( 9,17 ,27 and 36 kc ) , Wooden wedges is generally used for the 賎 ning of the unechoic water tank in this country , so the author measured the reflection coe 伍 cient of wooden ( pihe )wedges and plates
doi:10.20697/jasj.17.3_213 fatcat:hgt57eovujd5hoc3wd2dn2np7u