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Research in acoustics and acoustic projects, generally involving the physical test of the acoustic frequency, wavelength, sound pressure, sound intensity, speed, media parameters such as sound resistance, but also waveform, spectrum analysis and other features. Learning this lesson the propagation velocity of acoustic measurement, the consolidation and extension of the theory of vibrations and waves / practical knowledge, the initial understanding of the area of acoustic analysis, problem-solving ideas and methods.
Sound waves are mechanical vibrations in the elastic medium in the medium provoked and spread along the elastic longitudinal wave machine.
Can be interpreted from the above definition of "mechanical wave" and "sound" is almost synonymous. Asked the good fortune of nature, mechanical waves can stimulate certain biological and hearing, the hearing in the construction process, highly civilized human beings have an irreplaceable role; However, not all of the mechanical wave can stimulate hearing, depends on its frequency the level and intensity of the size. The definition of the sound waves in bold above, which should, in principle, the frequency range is from 0 to ∞ Hz; only 20Hz ~ 20kHz sound is heard of the senses can be. To this end, it is again lower than the 20Hz frequency of the sound waves known as infrasound, frequencies higher than 20kHz as the ultrasonic sound waves. The two on the "sound" in the title seems to imply that he is a strange sound, which is contrary to the definition above in bold type. Science can be seen with the conventional definition of the vocabulary is sometimes difficult to coordinate. Very similar to sound waves and electromagnetic waves, electromagnetic waves are also some visible light, visible light is called the frequency lower than infrared light, visible light is higher than the frequency of ultraviolet light called. Topic and then back to acoustic intensity: arbitrary intensity of the sound waves not be able to stimulate hearing, only higher than the hearing threshold (sound pressure level of about 0 dB), less than the pain threshold (sound pressure level of about 140 dB) of sound by humans to listen to to. Logarithm of frequency for the abscissa (for longitude) to sound intensity level for the longitudinal coordinates (for latitude) to establish a two-dimensional plane, which is a marine acoustic; on that ocean, the human hearing range of a island for a half-moon, we call it listening to the island.
If the experimental measurement of the teaching division audible sound waves interfere with each other instruments in each group, the scene will become noisy. Fortunately, in the same medium, different frequency sound waves have the same velocity, which is similar to electromagnetic waves. Therefore, ultrasound measurements can choose to not listen to sound waves, so that the relative quiet of the environment. Because ultrasound is less than the wavelength of audible sound waves, the benefits brought about by three points: the necessary gun range, wavelength (or half-wavelength) is the basic unit of distance, the shorter the wavelength, which is equivalent to more closely gauge scale, the sub-ranging braided higher fineness. with electromagnetic waves similar to the three, the shorter the wavelength, the better characteristics of directional spread, the more close to a plane wave, edge effects, the smaller the system error. Further leads to: Directional propagation characteristics of the better units in the spread of the energy attenuation of the smaller distance, allowing longer distance sampling, to ensure sufficient measurement sensitivity and signal to noise ratio at the same time to improve the measurement accuracy. Engineering practice in the field of ultrasound in its direction, and energy to focus and Ranging widely used in sonar, positioning, imaging, ultrasonic cleaning, ultrasonic machining, ultrasonic scalpel, measure the liquid flow rate, measurement of material elastic modulus, transient, such as gas temperature measurement technology. Sporadic in this experiment involves a number of acoustic and electronic circuits preliminary knowledge, but seeks to avoid the terms set out in show. Analysis of physical model, introducing scientific and technological knowledge, as far as possible in layman's language, substance, sound, those words, words of love, and guide operators across time and space experiments and experimental designers resonate the soul. Learn to discover and appreciate the wonderful nature, in the hands when the brain can move in the understanding of the basis of the initiative on the completion of the operation, according to side to avoid falling into the hands of the helplessroutines. I hope students are able to experiment in this lesson as a starting point for the study of acoustic range and entry.