ON THE INVESTIGATION OF THE SOUND ABSORPTION OF LINEAR TRANSITION WEDGES

In this article the reflection coefficient of linear transition wedges is discussed,and an analyticalexpression and a simple real expression of the reflection coefficient under W.K.B.approximationare derived.The approximate expression of the reflection coefficient proves to be simple and con-venient for the design of absorbers. The sound absorbent structure of rib is also computed and analyzed,with emphasis on the rela-tionship between the size of the structure and the parameters of the material. In design of two types of wedges mentioned above,for the required frequency range,the materialperameters can be chosen properly and the dependence of the Wedge length on the lower limit fre-quency can be determined easily based on the derived expression.The theoretical computationsagree well with the experimental results.     

MEASUREMENT OF MECHANICAL INPUT IMPEDANCE OF PLANE ARRAY ELEMENT USING IMPULSE SOUND TUBE

In this paper,a method of measuring the mechanical input impedance of the array element(longitudinal vibrating transducer)with square radiation head by using impulse sound tube is proposed.Theresonant frequencies determined from the measured mechanical input impedance are quite in agreementwith those obtained from the electrical admittance cycle diagram of the element.This indirectly shows thatthe proposed method is feasible.     

宽频带水声吸声材料

我们研究了消声水池用的宽带吸声器.为了增加丁基胶的损耗和可压缩性,用石粉作填料,得到了具有高损耗的吸声材料.用含气泡的(石至)石粉,可将橡胶的体积压缩形变转变为材料的剪切形变,致使材料的有效损耗因子随着气泡的体积率的增加而增加. 为了节省材料,选择了平板尖劈平行通道型吸声结构,它的总长是20cm和15cm(过渡部分分别为15cm和10cm).通道宽度是3cm,在频率范围5—80kc/s,声压反射系数小于10%.     

线性过渡尖劈吸声性能的研究

吸声结构从形式上可分为共振式和非共振式两种,目前各国建立的消声水池多用非共振式尖劈吸声结构.对于尖劈吸声结构,当波长比劈之横向线度大时,作为波动理论的一级近似,常将其转变为渐变吸收层的问题进行讨论,在文献[2]中导出了反射系数在W.K.B.近似下的一般表式,并具体研究了圆锥型尖劈.本文的工作是对水池大量应用的线性过渡尖劈,在W.K.B.近似条件下,对垂直入射时的反射系数进行了计算,得到比较简单的解析结果.并给出对各类吸声材料均适用的反射系数的实数表式.     

利用声脉冲管测量平面阵阵元的输入力阻抗

本文提出了以声脉冲管测量辐射头为方形的一种阵元(纵向振动换能器)的输入力阻抗的方法。从电导纳圆图的测量所得到的并联共振频率与从输入力阻抗曲线上确定的共振频率两者非常一致,从而间接证明了这种方法是可行的。