Sound waves are very familiar to everyone, which ranked the eldest is ultrasound. It is the highest frequency of sound, greater than 200,000 hertz (vibrations per second); ranked second is the sound wave, the sound frequency of 200,000 ~ 20 hertz, which is the sound of human beings can hear; ranked third is the infrasound, the lowest frequency of sound, less than 20 hertz.
Exploring the Earth
What we usually say about ultrasound is that the B-type ultrasound imaging diagnostic equipment used in hospitals for medical checkups reflects whether there are tumors, cysts, nodules, and fluid buildups in the internal organs of the human body through the dots of light on the screen. In fact, when the doctor examines you, you can also turn your head to look at the screen, there are light and dark areas. When the doctor finished checking, withdrawing in your body "probe" (acoustic transducer), and in the physical examination form written: "liver, gallbladder, spleen, kidney examination did not see abnormal echoes", you can clap your hands.
Sound wave detection schematic
Inaudible ultrasound can also be spread underground, and can detect underground objects and their structure, is very wonderful
To the Earth to do ultrasound and ultrasound to the human body, in fact, the principle is similar. Such as the use of probes (i.e., "transducer"), are first converted to electrical energy into sound energy (ultrasound), "sound beam" into the body after encountering two different media, in the medium of the interfaces produce reflections, known as echoes, the remaining energy The remaining energy "sound beam" continues to go deeper, when again encountered two different media interface, and reflections, and so on. And the human body of an organ of the various layers of tissue interface echoes, or a part of the earth, different rock or soil interface reflection, are through the probe recovery to the ultrasound diagnostic instrument or ultrasound detector, the instrument and the acoustic energy into electrical energy, after the computer processing and display to the fluorescent screen or within the recorder.
Dense rock for the ultrasonic reflection signal is stronger, the image shows a bright area, while there are cracks or cavities in the rock, for the ultrasonic reflection signal is weaker, the image shows a dark area.
Ultrasonic waves have high resolution due to their high vibration frequency and short wavelength, and have strong penetrating power, reflecting the microstructure of the probe object, so they are very suitable for human medical diagnosis. However, the rock to the high frequency ultrasound absorption, so the ultrasound energy attenuation is more serious, and therefore only used to detect the distance is not too large geological body or building components. Then, much larger than the human body, rock, geological formations such as detection, can be borne by sound waves and infrasound. Because the vibration frequency is reduced, the wavelength is lengthened, the vibration energy attenuation is smaller, the penetration distance in the medium can be increased.
Rock ultrasonic perspective
Underground fissures and cavities in the image and the recorder can be reflected, the underground is also a lot of changes
In general, the sonic in the oldest, the oldest two, the oldest three together, can be made for the mother earth for a number of times, "physical examination". Such as caves, faults, cracks, rock stability, land relaxation, engineering firmness and quality, landslides and collapses monitoring, earthquake and volcanic activity prediction and so on.
For example, in Guangzhou Baiyun New International Airport, using acoustic wave technology (land sonar method) to identify the depth of 20-30 meters between the 2-3 meters in diameter between the caverns and soil holes, for the construction of the airport to provide important information. The excitation and reception signals utilized have a wide range of frequencies, generally 5 to 20 Hz, including a portion of infrasound.
Exploring the earth
Again, when constructing bridges and mountainous road tunnels in Shanxi and Shaanxi provinces for site selection, ultrasonic and acoustic wave detection techniques were utilized to circle areas where rocks were stable and solid, with good results. The principle of this method and technique is simple, based on the fact that there is a clear correlation between wave velocity and the characteristics of the rock mass. A large wave velocity reflects a dense, hard and stable rock mass, while a small wave velocity reflects a broken, loose and unstable rock mass. See elastic wave velocity and rock body characteristics against the table.
Summary table of elastic wave velocity and rock body characteristics