思考才皱眉
发表于 2025-3-28 15:35:00
Introduction, human perception, because of the high frequencies involved. This term is by no means limited to sound waves travelling in gases and liquids but includes, in particular, the more complicated elastic waves in solids. Since the upper frequency limit of human hearing differs not only from one individua
DAFT
发表于 2025-3-28 19:12:08
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方便
发表于 2025-3-29 02:35:35
Sound Radiation and Sound Diffraction,tion. An additional subject also covered in this chapter is the diffraction of sound by obstacles of finite size, a phenomenon which can be thought of as some kind of secondary radiation and hence closely related to sound radiation.
Hallowed
发表于 2025-3-29 06:09:12
,Generation of Ultrasound—Part I,er to obtain a real sound source from such a piston, ways must be found to excite it into vibration. As is well known, in the audio range, i.e. with the loudspeaker, this is accomplished in most instances by an electrodynamical transducer which generates the vibrations and transfers them to a paper
讲个故事逗他
发表于 2025-3-29 07:27:37
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吗啡
发表于 2025-3-29 14:04:57
Generation and Detection of Sound with Frequencies Above 1 GHz (Hypersound),y called ‘microwave acoustics’, another frequently used name is ‘hypersound’. At first glance this linguistic separation from the range of ‘normal’ ultrasound seems even more arbitrary than the fixing of the lower frequency limit of ultrasonics at 20 kHz. Some justification for it, however, may be s
带来
发表于 2025-3-29 18:23:31
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伪书
发表于 2025-3-29 20:32:12
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描绘
发表于 2025-3-30 01:51:37
Application of Ultrasound in Medical Diagnostics,ts by echoes has also been exploited in medical diagnostics with great success. The methods employed in this context are often summarized by the term ‘sonography’. Today, they are an extremely important supplement to diagnostics with X-rays and to other diagnostic techniques.
conspicuous
发表于 2025-3-30 04:45:58
Special Methods of Ultrasonic Imaging,rp ‘images’ of objects embedded in an irradiated medium; what they detect are just spatial disturbances of sound diffracted or scattered by these objects. Although under favourable conditions the contours of an object can be recognized from these secondary sound fields, this kind of representation i