infrasound waves, also known as infrasound waves, are sound waves whose frequency is lower than that of human audible sound waves. The frequency range of infrasound is approximately 1-4 Hz ~ 2 Hz. ?
Infrasound sound sources are quite extensive. Now people have known infrasound sources: volcanic eruption, meteor falling into the atmosphere, aurora, earthquake, tsunami, typhoon, thunderstorm, tornado, ionospheric disturbance, and so on. Infrasound waves can also be generated by artificial methods, such as nuclear explosion, rocket launch, chemical explosion and so on. ?
Because the frequency of infrasound is very low, it shows various strange properties. Among them, the most striking feature is that it spreads far and is not easy to be absorbed. ?
we know that the attenuation of sound in the atmosphere is mainly caused by molecular absorption, heat conduction and viscous effect, and the corresponding absorption coefficient is directly proportional to the quadratic square of sound wave frequency. Because the frequency of infrasound is very low, the absorption coefficient of the atmosphere is very small during its propagation. For example, the absorption coefficient of air for infrasound with a frequency of ．1Hz is about that for infrasound with a frequency of 1Hz. One hundredth of the sound absorption coefficient. Because infrasound is not easily absorbed, it travels a long distance. When Krakato volcano in Indonesia erupted on August 27th, 1883, the infrasound waves generated by it made three rounds around the earth and spread over hundreds of thousands of kilometers. At that time, people used a simple micro barometer to record it. Infrasound not only "runs" far, but also its speed is faster than the speed of storm propagation, so it has become a prelude to the ocean storm warning, and people can use infrasound to predict the coming of storms. ?
the application of infrasound began in 195s, and people gradually paid more and more attention to it. The application prospect of infrasound is roughly as follows:
(1) By studying the characteristics and mechanism of infrasound generated by natural phenomena, we can deeply study and understand the characteristics and laws of these natural phenomena. For example, the law of aurora activity can be studied by using infrasound waves generated by aurora. ?
(2) Using the received infrasound generated by the measured sound source, the position and size of the sound source can be detected and other characteristics can be studied. For example, by receiving infrasound waves generated by nuclear explosion, rocket launch or typhoon, the relevant parameters of these infrasound sources can be detected. ?
(3) Predicting natural disastrous events. Many disastrous natural phenomena, such as volcanic eruption, tornado, thunderstorm, typhoon, etc., may radiate infrasound before they occur, so it is possible for people to use these precursor phenomena to predict and predict the occurrence of these disastrous natural events. ?
(4) When infrasound propagates in the atmosphere, it is easily influenced by atmospheric medium, which is closely related to factors such as wind and temperature distribution in the atmosphere. Therefore, the properties and laws of some large-scale meteorology can be detected by measuring the propagation characteristics of naturally or artificially generated infrasound in the atmosphere. The advantage of this method is that it can continuously detect and monitor a large range of atmosphere. ?
(5) By measuring the results of the interaction between infrasound waves and other fluctuations in the atmosphere, these activity characteristics can be detected. For example, the propagation of radio waves is disturbed by infrasound in the ionosphere, and the law of ionospheric disturbance can be further revealed by measuring the characteristics of infrasound. ?
(6) People and other creatures can not only react to infrasound, but also some organs of them can emit weak infrasound. Therefore, the characteristics of these infrasound waves can be used to understand the activities of the corresponding organs of human body or other organisms. Overview of infrasound waves
1. Mystery of unmanned ships
So far, people have found dozens of unmanned ships in the vast sea, which are lonely, strange and mysterious, like telling stories, but they can't tell them. On February 28, 1855, the British sloop Maraton met an American boatman, Remus Cheshire, in the North Atlantic. The ship's sails drooped and it was empty, but the ship was intact, the goods remained the same, the food and fresh water were abundant, and there were no signs of struggle and violence. Only no one was seen, and the navigation diary and compass could not be found.
in p>188, an unmanned ship named Sybil was also found off the sea near the town of Eastons Beach in Newport, Rhode Island, USA. The breakfast in the captain's cabin was still there, but the crew was nowhere to be found. Even more mysterious is what happened to the American fast sail gunboat Ellen Austin at the end of 1881. On December 12th, this year, an unmanned sailboat was found in the North Atlantic when the fast sail gunboat was cruising. Except for no one in the ship, everything is normal, and fruits, bottled wine, fresh water and food are intact. Captain Griffin ordered several sailors to stay on the sailboat, which was towed by his warship. Three days before the coast, there was a strong wind at sea, the cable used for tugboat broke, and the night was boundless. The two ships lost contact and the call was silent. The next day, when the Ellen Austin found the sailboat, all the sailors sent by the captain were gone! At this time, it is only 3 kilometers away from new york, and we will be home soon. Captain Griffin paid a lot of money to buy a few more people to go to that sailboat. The visibility was good and the breeze was blowing gently that day. Before dawn, the helmsman Ellen Austin found that the ship had deviated from its course. When he looked back at the towed sailboat, he couldn't help but be surprised: the sailboat was gone! In this way, the disappearance of this sailboat has become another mysterious mystery in the history of navigation.
For the case of unmanned ships, scientists have provided people with an answer: the sound of the ocean. To be exact, most of these incidents may be caused by ocean infrasound waves.
Generally, the ocean infrasound appears under storms and strong winds, and its frequency is lower than 2 Hz. The energy of infrasound is determined by the degree of wave-current fracture at the wave crest. If it is a big storm, the power of infrasound can reach tens of kilowatts. Infrasound waves belong to weak attenuation energy), so they can travel far. When a seagoing ship encounters this kind of high-energy infrasound, the infrasound will cause radiation to living things. Infrasound waves of certain frequencies can cause fatigue. Pain, even blindness. At the same time, too strong infrasound often scares people and leads to missing people.
in view of the above situation. At present, some countries have established institutions to predict infrasound waves. When it receives life-threatening infrasound waves, it immediately issues a forecast to the relevant parties to reduce the harm brought by the "sound of the sea" to seafarers.
second, infrasound waves that can cross mountains and mountains
infrasound is sound with a frequency lower than that of audible sound, and its frequency range is roughly 1× 1-5hz ~ 2hz. Infracoustics is a science that studies the generation, propagation and reception of infrasound waves in media, their effects and applications.
because the frequency of infrasound is very low, the absorption coefficient of infrasound in the atmosphere is very small, so its penetrating power is very strong, and it can spread to the extreme distance with little energy attenuation. Infrasound waves below 1Hz can cross mountains and oceans, and travel as far as several meters in Qian Qian. In the summer of 1983, the Krakato volcano between Sumatra and Java in Indonesia exploded, which shocked the whole world. The infrasound waves generated once circled the earth three times, lasting 18 hours. At : 38 on January 29, 1986, the American space shuttle Challenger exploded, and the infrasound wave produced lasted for 12 hours and 53 minutes. The usual sound insulation and sound absorption methods have little effect on the ultra-strong penetration of infrasound waves. The sound wave at 7 Hz can be blocked by a piece of paper, while the infrasound wave at 7 Hz can't be stopped by a thick wall. Infrasound waves can penetrate more than ten meters thick reinforced concrete.
the propagation of intense infrasound through solid media will directly destroy buildings, causing them to be damaged or collapsed.
in p>198, during the construction of a building in a square in Nanjing, China, the wall of a cinema near the construction site was shattered by the strong vibration wave generated by the pile driver, which forced the cinema to be demolished and rebuilt.
In the summer of p>1983, Krakato volcano erupted between Sumatra Island and Java Island in Indonesia. The intense infrasound generated during the volcanic eruption circled the earth three times, and it took 18 hours to slowly disappear. Micro-barometers all over the world have recorded its vibration aftermath.
On January 29th, 1986, the American space shuttle Challenger exploded during liftoff. The infrasound generated by the explosion lasted for 12 hours and 53 minutes, and its explosion power was so strong that even the monitor of the monitoring station of the Institute of Acoustics, Chinese Academy of Sciences in Xiangshan, Beijing, was "heard" more than 1, kilometers away.
The atmospheric temperature density and wind speed are unevenly distributed with height, which causes the phenomena of "shadow zone", focusing and waveguide when infrasound propagates in the atmosphere. When the height increases, the temperature gradually decreases, and a minimum value appears around 2 kilometers; After that, with the increase of height, the temperature rises again, and it drops again at about 5 kilometers, forming a second minimum at about 8 kilometers. Then it rises again. The phenomenon of atmospheric infrasound conduction is closely related to this temperature distribution. Sound waves mainly propagate along the channel (called sound channel) formed by the minimum temperature. Usually, the atmosphere near the minimum height of 2 kilometers is called the atmospheric lower channel, and the atmosphere near the height of 8 kilometers is called the atmospheric upper channel. When infrasound propagates in the atmosphere, it can be influenced by the action of two channels at the same time. At a distance of 1 ~ 2 kilometers from the sound source, the infrasound signal is very weak, and such an area is usually called the shadow zone. Under a certain atmospheric temperature distribution condition, infrasound waves transmitted through sound channels gather in a certain area, which is called the focus area.
wind will also have a great influence on the propagation of infrasound in the atmosphere. The propagation of infrasound is very different between downwind and headwind: when downwind, sound rays are concentrated in the lower atmosphere; When the wind is against the wind, a larger shadow area is produced. The propagation speed of infrasound with different frequencies is different in the atmospheric channel, resulting in dispersion phenomenon, which makes the waveform of infrasound measured at different places different.
The density of the atmosphere decreases with the increase of altitude. If the wavelength of infrasound is large, such as tens of kilometers, at this time, the density of the atmosphere has changed significantly within a wavelength range. When the atmospheric medium is compressed by sound waves, its center of gravity is higher than that of the surrounding medium. At this time, besides the elastic restoring force, it is also affected by gravity. On the contrary, when it expands under the action of sound waves, there is also additional gravity to restore it to equilibrium. Therefore, long-period infrasound waves are attached with gravity besides elastic force. In this case, infrasound waves are usually called acoustic gravity waves. When acoustic gravity waves propagate in the atmosphere, they can be regarded as the superposition of some normal waves in theory. It can be basically divided into acoustic branch and gravity branch. They all have dispersion phenomenon in the atmosphere. Because the main energy of gravity branch propagates near the ground. The temperature near the ground is relatively high, so the propagation speed is relatively high.
third, the silent killer-infrasound weapon
infrasound is destructive. Infrasound waves generated by high-altitude atmospheric turbulence can break the mast on the 1,-ton ship and tear the plane apart; Infrasound waves excited by earthquakes or nuclear explosions can destroy tall buildings; The infrasound waves brought by the tsunami can destroy houses on the shore. The frequency of infrasound is close to the natural frequency of human organs (the natural frequency of human organs is 3~17Hz, the natural frequency of head is 8 ~12Hz, and the natural frequency of abdominal viscera is 4~6Hz). When infrasound acts on human body, human organs are prone to * * * vibration, causing dysfunction or damage of human body, rising blood pressure and general malaise. The balance function of the brain will also be destroyed, so people will have a sense of rotation and nausea. Many people who live in high-rise buildings will feel dizzy and sick when there is a storm, which is the cause of infrasound waves. If the power of infrasound is very strong, the human body will vomit, have difficulty breathing, have muscle spasms, lose consciousness, and even die because of the rupture of visceral blood vessels. Because the frequency of infrasound is very close to the natural frequency of the main organs of human beings and organisms, under its action, the main organs of human beings and organisms will involuntarily produce * * * vibrations, which will make people panic and lose their minds; Powerful infrasound can cause damage and injury to human internal organs to varying degrees until death. The so-called infrasound weapon is a new concept weapon that uses this principle to influence and kill human body. Because people can't hear, see or touch infrasound, some people call infrasound weapons "silent killers" and "dumb weapons".
In p>1988, in a rural area in Montana, USA, armed religious fanatics lay dormant in a building, threatening FBI agents by claiming to die with the building. When the agents were at a loss, someone pushed a device like a big horn to "talk" with them. A few minutes later, as if possessed by evil spirits, the fanatics staggered and dizzy one after another, some were insane, fidgety, some had diarrhea, vomiting, etc. When the agents handcuffed them easily, the fanatics did not know that they had been assassinated by the "silent killer"-infrasound weapons.
infrasound weapons have unique advantages compared with traditional conventional weapons. First of all, its use is truly concealed, and it is easy to achieve the suddenness of the attack on the living forces, without polluting the environment or destroying natural substances; Secondly, infrasound travels a long distance because of its low frequency and little attenuation. For example, the sound waves produced by the explosion of a shell can't be heard several kilometers away, but the infrasound waves produced by it can travel 8 kilometers away. When a hydrogen bomb explodes, infrasound waves can travel up to hundreds of thousands of kilometers and circle the earth several times. Military can also use the long-distance propagation of infrasound waves to detect and identify the launch of rockets; In addition, infrasound weapons have strong penetration ability. Ordinary buildings or sound insulation walls are difficult to block the propagation of infrasound, and even it can penetrate reinforced concrete with a thickness of more than ten centimeters. Therefore, even if people hide in shelters, or sit in tanks, armored vehicles and planes, or in submarines in the deep sea, it is difficult to escape the attack of infrasound weapons. In addition, as long as there are holes or gaps in the protective facilities, infrasound waves will also penetrate everywhere.
infrasound weapons can be classified into two categories. The first category is "neurotic": it mainly stimulates the brain of the staff to paralyze the nerves of the staff, which will have a certain psychological and conscious impact. Mild people feel unwell, unable to concentrate, emotionally fearful, causing headaches, nausea, dizziness, etc. In severe cases, people will be insane, crazy, shocked and syncope, and lose their thinking ability. Using this effect can make combatants unable to perform occupation tasks. The second type is "organ type": under the action of this kind of infrasonic weapons, the main internal organs of human beings vibrate, ranging from muscle spasm, whole body trembling and dyspnea to blood vessel rupture and visceral injury until death. (Science and Technology Daily, December 9, 1997)
Infrasound waves can kill the enemy without causing environmental pollution or destroying the other side's weapons and equipment, and can be used as trophies.
It is said that the first infrasound generator was invented by the French in 1972, and the infrasound generated by it can harm people 5km away. The inventor also concluded that infrasound with a frequency of 7Hz can cause a fatal blow to human body. It is reported that the US military has tried some samples of sound or sound weapons during its intervention in Somalia. These weapons can make people's internal organs vibrate and make people