首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7篇
  完全免费   3篇
  物理学   10篇
  2008年   1篇
  2006年   7篇
  1998年   1篇
  1995年   1篇
排序方式: 共有10条查询结果,搜索用时 193 毫秒
1
1.
覆面层对玻璃棉吸声性能的影响   总被引:2,自引:0,他引:2       下载免费PDF全文
本文通过试验探讨了四种覆面怪对玻璃板吸声性能的影响,结果表明:在不同频率范围,铝箔及穿孔铝穆面层对的吸声性能影响较大,而玻纤毡和橡胶面层的影响较小。  相似文献
2.
A nonlinear imaging technique that demodulated the second harmonic component of the response of the Ultrasound Contrast Agent (UCA) was proposed. The UCA perfusion imaging method has been investigated from three aspects, mathematics principle, simulation and ultrasound experiment, respectively. Frequency-Modulated (FM) signal excitation has been introduced to increase Signal-to-Noise Ratio (SNR) in medical ultrasound imaging firstly. A theoretical simulation and an ultrasound experiment were performed to investigate if a cosine enveloped frequency-modulated signal excitation could be applied in UCA imaging to increase SNR and Contrast-to-Tissue Ratio (CTR). To obtain a good imaging, suitable parameters and a right envelope on the transmitted signal were needed, and a gap was also needed between the transmitted signal bandwidth and the decoded match filter bandwidth. A harmonic image was obtained with using of coded excitation and the decoded filter. The results suggested that using this harmonic imaging method, image could be got with good SNR and CTR. At the same time, the acoustical results were agreed with the theoretical results well.  相似文献
3.
Characteristics of broadband matching for piezoelectric ceramic transducer are fully analyzed. It is stated that in the case of without an all pass function, good matching characteristics of maximum bandwidth and gain-bandwidth product are implied in the Butterworth matching theorem. If the parameterσ< .252, it is not helpful to add an all pass function to the circuit following the rule of minimizing center frequency and maximizing gain-bandwidth product.  相似文献
4.
在2007年即将结束,2008年就要到来的时候,近两百名声学工程师和专家为了"给十三亿人民以更好的听觉关怀"而聚首北京。12月6-9日,2007建筑未来·声学工程师交流会在清华大学建筑物理实验室的组织倡议下胜利召开了。这次盛会标志着声学这个边缘学科的科研力量与生产力量正在全面的整合,以产业的形式高速发展  相似文献
5.
A multi-subarray subspace fitting method which take mutual coupling among array elements into account to estimate the directions of arrival was presented. The mutual coupling matrix of uniform linear arrays is modeled with a banded symmetric Toeplitz matrix. According to the DOF (Degree of Freedom) of mutual coupling matrix, part of the array elements at the two sides are neglected. The theoretical characteristics of ESPRIT algorithm, one of the subspace fitting algorithms, are studied. For large N and uniform linear array, the MCLS ESPRIT estimation error is asymptotically jointly Gaussian distributed with zero means, and its covariance expression is obtained. It is known from the simulation that there exists a subarray with lowest estimation error for certain number of the array elements and the signal sources, and its performance of estimating the directions of arrival is close to the ideal situation when mutual coupling does not exist while its variance has some increase. The method has been applied to bathymetric sidescan sonar with high resolution, and good results have been obtained. At the cost of increasing the number of the array elements, the method can reduce the affection of the mutual coupling among array elements.  相似文献
6.
A closed-form algorithm for two-dimensional wideband Direction-of-Arrival (DOA) estimation with an acoustic vector-sensor array was presented. The proposed algorithm can deal with coherent sources without loss of array aperture, and does not require a search procedure for the DOA parameters. The estimated azimuth and elevation angles can be automatically paired. Simulation results are presented to demonstrate the effectiveness of the proposed method.  相似文献
7.
Based on a theoretical motion equation of encapsulated microbubbles within an ultrasound field, the subharmonic characterizations of microbubbles are optimally designed and analyzed by a computer aided design system. The effects of size, shell elasticity and acoustic pressure on subharmonic response of microbubbles are calculated theoretically to obtain the optimal parameters for nondestructive subharmonic imaging. In addition, microbubbles with different shell elasticity are prepared, and their subharmonic responses are measured in vitro. The results of theoretical calculation and acoustic measurement show that good subharmonic enhancement can be obtained by using the encapsulated microbubbles with the mean size of 3 μm, which were prepared from the surfactant solution with the proper ratio of shell material. It is also shown that the best operating acoustic pressure is 200 to 400 kPa for nondestructive subharmonic imaging based on such kind of microbubbles.  相似文献
8.
On the fact that an isotropic metal solid produces anisotropic property in the state of static stress, based on the theory of the nonlinear acoustoelasticity, the equivalent second order elastic constants are calculated for metal plate with static stress. For the case of thin metal plate with stress, the two kinds of dispersion equation for Lamb waves propagating parallel and vertical to the direction of static stress are derived. Using the equations, the relationships between Lamb wave velocity and static stress in a metal plate are discussed.  相似文献
9.
A hybrid magnetostrictive-piezoelectric barrel-stave projector is designed and developed. The new type transducer is driven by the union of rare-earth giant magnetostrictive material Terfenol-D and PZT piezoelectric ceramic. Combining the advantages of low frequency performance within a compact size, it proves that the hybrid projector has a much broader band and higher sound power than that with single magnetostrictive or piezoelectric driver by the simulated and measured results. The prototype of the hybrid projector has a size of 88 mm in outside diameter and 316 mm in length, with an underwater resonant frequency of 1.30 kHz, Q factor of 1.43 for -3 dB bandwidth, and transmitting voltage response level of 135.1 dB at the resonant frequency.  相似文献
10.
吕玉恒 《应用声学》1995,14(3):47-47
应香港声学学会和英国声学学会香港分会邀请,上海声学学会代表团一行六人于1994年12月15日至ZI日访问了香港.上海声学学会正副理事长冯绍松和赵松龄教授任正副团长,团员有章奎生、王提贤、吕玉恒、朱茂林等高工.香港声学学会主席盛冠伟博士、英国声学学会香港分会主席陈炳祥先生精心安排并陪同访问.在港期间,代表团拜访了香港政府环境保护署,听取了环保署噪音政策组介绍.参观访问了从事噪声控制工程设计、施工、安装的雅士(IAC)消声器材(香港贿限公司、康冠伟顾问有限公司、仙垦工程有限公司、纳普(NAP)声学工程(远东)有…  相似文献
1
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号