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Simple Fraunhofer approximation was unsuitable for analysing acoustic field of transducer arrays in tissue because linear array B- scanners image in near and middle field. But for a single element, far-field conditions easily satisfy most imaging area and a simpler distribution of acoustic field can be deduced by means of Fraunhofer approximation. The sonic field of the array is the superposition of fields of elements. Much less EPU times are required for calculating the superposing acoustic field... Simple Fraunhofer approximation was unsuitable for analysing acoustic field of transducer arrays in tissue because linear array B- scanners image in near and middle field. But for a single element, far-field conditions easily satisfy most imaging area and a simpler distribution of acoustic field can be deduced by means of Fraunhofer approximation. The sonic field of the array is the superposition of fields of elements. Much less EPU times are required for calculating the superposing acoustic field than calculating the classical Fresnel integral. The results indicate that the unfocused sonic fields of arrays are similar to that of rectangular plate radiator. Just the right dedays can effectively converge the beam of a transducer array to realize electronic focus. The minimum focus range is decided by the width of elements. The receiving of back scattering signals is the contrary procedu reof the ultrasonic transmitting and can be discribed by the same function as the transmitting, and also can be focused by proper delays to improve the ultrasonic image. 线阵B超的成象区域都是在近中场,用简单的Fraunhofer近似研究组织中的声场分布是不恰当的。然而,整个阵列的激励声场是各单个阵元的激励声场的迭加,而且单个阵元的声场在大部分成象区域内都满足远场条件,可以用Fraunhofer近似处理得到较简单的声场分布函数。用单阵元分布函数迭加所得的换能器声场分布的数值计算,比计算经典的Fresnel积分的运算量要小得多。计算结果表明:换能器阵列在成象区域内的非聚焦声场与矩形平板换能器声场的近中场分布规律相近,适当引入延时可以使阵列换能器的声束有效会聚而实現电子聚焦。当换能器口径一定时,电子聚焦的最小焦距受阵元宽度限制。超声仪器对组织后向散射信号的接收是发射的逆过程,可以用相同的函数描述。同样,也可以通过适当的延时实現电子聚焦,从而进一步提高成象的分辨力。 The sonic field transmission matrixes of perforated absorbent pipe is given after the transmission performance of perforated pipe is studied. Based on the defination of insortion loss, the mathematic model of muffler is set up in this paper, the tendency of accoustic performance of perforated absorbent pipe with different parameters is analysed through verify consistency of theory and experiment. 本文通过声波在穿孔声管中传播特性的研究,导出了声波在穿孔声管中传播的声场传递矩阵。文中运用插入损失的定义,建立了消声器消声性能的数学模型,并在实验验证基础上,分析了各种参数对穿孔声管消声器消声性能影响的变化规律。 Some experimental results and analyses from the measurements of the sound field in a single transonic axial compressorr inlet duct with single plastic glass lining are presented.The plastic glass linings are designed and made by ourselves (two kinds of perforate rating,σ 1=2 85% and σ 2=5 85%).The experimental results are firstly obtained in China from the real sonic fields in a single transonic axial compressor at high sound... Some experimental results and analyses from the measurements of the sound field in a single transonic axial compressorr inlet duct with single plastic glass lining are presented.The plastic glass linings are designed and made by ourselves (two kinds of perforate rating,σ 1=2 85% and σ 2=5 85%).The experimental results are firstly obtained in China from the real sonic fields in a single transonic axial compressor at high sound pressure conditions (>150dB).The experimental results and conclusions provide some reference for the further investigation on design of the acoustic treatment assemblies in aeroengine nacells and turbomachinery duct. 介绍用有机玻璃制作的两套结构尺寸不同的微穿孔消声声衬试件,在单级跨音压气机台上进行的3次降噪实验。目前国内尚无人获得微穿孔消声声衬在跨音、大流量、高声压级模拟声源环境条件下的噪声测试数据。通过实验,为进一步合理地设计声衬提供了参考数据,并看到了这种降噪方法在流体机械管道消声方面的应用前景。
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