声管中的宽带脉冲法的水声材料吸声系数测量

现有的水声管吸声系数测量的脉冲法,由于水声管高度的限制,存在低频限制。提出了基于\     

阻抗管法测量水下吸声系数的系统误差分析*

利用阻抗管法测量吸声系数是水下吸声材料研制过程中的重要环节,实验测量结果相比理论计算结果更具说服力。然而在待测样品的制备和安装过程中容易引入的系统误差往往被忽略,从而影响实测结果可信度。为了降低系统误差,本文提出缝隙宽、垂直度和光洁度三种可能引入系统误差的因素,搭建传递函数法水下吸声系数测量的有限元模拟实验环境并验证仿真计算算法的正确性,研究相关参量对橡胶吸声系数的影响规律,并给出一定误差下对相关参量的限制要求。所得结论对降低测量误差、提升实测结果可信度具有一定参考价值。     

水下材料吸隔声性能测试近场长脉冲传递函数法

为消除有限空间壁面反射对大样水下材料声学性能测试的影响,利用传递函数法和脉冲法测试原理,建立声波垂直入射情况下水下材料吸隔声性能测试近场长脉冲传递函数法,10mm均匀钢板模型声学性能试验表明,压力环境下钢板反射及隔声性能测试值与理论值基本一致,反射系数测试偏差小于0.1,隔声量测试偏差小于1dB,可以采用近场长脉冲传递函数法测量声波垂直入射情况下材料声学性能,可有效克服边界反射对测试的影响。     

在瞬态自动测量仪上用脉冲法测量材料的热物理系数

简述了热物理性质瞬态自动测量仪的结构和原理，应用该仪器采用脉冲法测量了材料的热扩散系数和热导率。     

The method eliminating nearfield effect for measurement sound absorption coefficient

The numerical simulation is used in this work to study the nearfieldradiation pressure of a piston projector,the smooth effect on the pressure fieldby using a“big”receiver and the influence of the nearfield and in the transitionregion on measurement of sound absorption coefficient.The result indicatesthat the big error would appear when using usual absorption coefficientmeasurement method.According to the reason causing the error,the methodeliminating nearfield effect (MENE) is proposed and some digital results aregiven for a/λ=3,9 and b=0,0.5a,a(a and b are the transducer and re-ceiver radii respectively).The calculation results show that the method not onlywidens measurement range in nearfield,but also gives accurate results.     

水声材料性能的自由场宽带压缩脉冲叠加法测量

水声材料的许多声学特性一般可以通过对复反射系数和透射系数计算得到。本文提出一种新的自由场测量方法,即应用宽带脉冲压缩技术在消声水池中测量有限尺寸的大面积材料样品的性能参数,从而使这种标准测量的低频限被明显降低。除传统的回声降低和插入损失参数等外,两个新的参数——消声系数和去耦系数也在评价之列。文中对两块平板样品进行了实验测量,其尺寸约为1m×1m,测量频率范围为 2~20kHz。     

Measurement of sound absorption by underwater acoustic material using pulse-separation method

An alternative pulse-separation method is presented for measuring the sound absorption at normal incidence of an underwater acoustic material in a water-filled impedance tube. A damped sine pulse was generated in the water-filled impedance tube with a regular waveform and a short duration time of approximately 1 ms. During the generation of the pulse, the inverse filter principle was used to compensate for the transducer response. In addition, the effects of the characteristics of the tube termination can be eliminated during the generation of the pulse to obtain a single plane pulse wave in the impedance tube, which is a necessary condition for this technique. Measurements of the sound absorption coefficient of the rubber material and the reflection coefficient from a water/air interface were used to verify the pulse-separation method.     

水声测量用声脉冲瞬态抑制方法的研究

脉冲声技术是一种很常用的水声测量技术，但由于脉冲声存在着瞬态过程，严重影响了它在低频下的使用，本文中研究的水声测量用声脉冲瞬态抑制方法，通过瞬态抑制等效消除换能器的瞬态过程，从而为在有限尺寸水域内扩展水声测量低频限创造了条件。     

水声无源材料插入损失虚拟聚焦测量方法

提出了一种适合在有限尺寸水池中测量水声材料插入损失的方法,称为\     

采用伪随机信号激励的驻波管三点测量法

本文对伪随机信号激励的驻波管三点测量法(TPM)进行了讨论和误差分析,并与驻波比法(SWR)及双传声器传递函数法(TTF)进行了比较。结果表明,伪随机信号三点法具有较高的精度,与驻波比法所得结果吻合甚好,并很好地解决了双传声器传递函数法存在的缺陷,可用于实际测量。     

A method for calculating the absorption coefficient of a multi-layer absorbent using the electro-acoustic analogy

A theoretical method for calculating the absorption coefficient of the multi-layer absorbers composed of perforated plates, airspaces and porous materials is proposed. Initially, for multi-layer absorbers composed either of perforated plates and airspaces or perforated plates and porous materials, the acoustic impedance is calculated using an electro-acoustic analogy. Then, for multi-layer absorbers composed of perforated plates, airspaces and porous materials, the acoustic impedance is calculated using an iterative method. Finally, theoretical calculations for the absorption coefficient of three types of multi-layer absorbers composed of different materials and including perforated plates are carried out. The results are validated by experimental results.     

A criterion for the use of linear regression analysis in the determination of low values of absorption coefficient using the impedance tube method

This article describes a quick and convenient method for estimating the percentage error associated with any measurement of absorption coefficient using the impedance tube method. A parameter Z is calculated, using constants appropriate to the tube and the decibel difference between a pressure maximum and minimum. The value of this parameter can be used as a criterion as to whether a more accurate determination, using linear regression, should be employed. The technique is valuable as an aid when low values of absorption coefficient, particularly at low frequencies, are to be measured.     

A method of obtaining the oblique incident sound absorption coefficient through an on-the-spot measurement

A new method (tentatively called the ‘cancellation method’) of determining the sound absorption coefficient is presented. This method makes it possible to obtain the absorption coefficient of a wall material by means of an on-the-spot field measurement which has, until now, been considered very difficult. This paper shows that the reflection from a sample can be obtained by combining the outputs from two non-directional microphones through a phase inverter, and how, by comparing it with the direct sound, measured separately, the sound absorption coefficient can be estimated. Absorption coefficients of several kinds of samples obtained by this method are compared with those calculated theoretically for the locally reactive material.     

充水阻抗管中测量材料声学性能的校准方法研究

提出了一种在充水阻抗管中,应用传递函数测量材料声学性能的三参数校准方法。在双传感器传递函数法的基础上,考虑充水阻抗管中水听器间不一致性和管内结构对声场局部扰动等因素的校准,导出了三个综合的无量纲校准参数。通过改变充水阻抗管中测量面的三个已知反射系数,测量出对应的三个传递函数,可以求出这三个校准参数。在充水阻抗管中分别对水/空气界面和一种水声材料进行了测量试验,应用该方法对测量结果的进行了校准,并对校准前后的结果进行了分析比较。     

A restraining multipath effect method for the measurement of insertion loss of underwater acoustic materials

A method suppressing multipath effect when measuring the underwater acoustic materials in a reverberant field is proposed, which is called "virtual end-fire array method".To weaken the coherence of the same-frequency reflection interference of each path, signal of different phases at different positions was transmitted by a single transducer in the simulation design, and a sharp directionality in the direction of the array length was formed. All signals at the above positions were superimposed t...     

水声材料插入损失测量中的声波多途效应抑制方法

提出了一种在非自由声场中测量水声材料插入损失时抑制多途效应的方法,称为\     

简易自相关仪对飞秒激光脉冲宽度的测量

用自制的简易自相关仪测量了飞秒的光脉冲宽度,测量结果与理论结果基本一致,并在此基础上分析了一些实验中的光学器件对飞秒激光脉冲宽度的影响.     

多阶声模态分解的改进阻抗管法测量材料的高频吸声系数

为了测量高频材料吸声系数,采用声模态分解的方法,基于阻抗管构建测试设备,在阻抗管内测量超过平面波截止频率的的高频吸声系数。测量过程中,通过在阻抗管的周向和轴向分别布置传声器阵列,分离管道内前3阶周向声模态以及各阶声模态的轴向传播入射波和反射波,从而得到最高频率达10000 Hz的材料吸声系数,并通过对比常规阻抗管测试方法的测量结果,说明采用声模态分解法对高频材料吸声系数的准确性。     

Two-photon absorption coefficient in relation to the typical pulse models of laser

The two-photon absorption (TPA) coefficient (β) relating to pulse models of laser is theoretically studied based on the nonlinear absorption equation. An expression of nonlinear energy transmission is obtained, in which a factor (g) is introduced to describe the β deviation resulting from the pulse profile of laser. The relative deviation can be then expressed as (1/g − 1)% for comparing β obtained based on other pulse models of laser with β₀ based on the rectangular one. The values of g factor and the deviation of some typical ultra-short pulse models used nowadays are also calculated and presented. Our results suggest that the β deviations from the temporal pulse shapes should not be neglected in usual nonlinear transmission measurement. The g factor may become a useful parameter in taking account of this deviation.     

GaAs半导体中三光子吸收系数的光学测量

本文首次报道了采用非线性光透射技术(NLT)测量λ=2.06μm激光激发下GaAs本征半导体中三光子吸收的实验研究.观察到了三光子吸收及所伴随的自由载流子的激发态吸收,并测得了三光子吸收系数.实验测量结果与理论计算结果比较,符合较好.