At this time, people will think of some phenomena on animals, which humans have long known, but they have not paid attention to. For example, on a bat's midsummer night, when everything was silent, a noctuid fled in panic in the air, flapping its wings desperately and hovering, and suddenly turned upside down. What happened?
It turns out that the bat, the natural enemy of Noctuidae, followed! It flapped its gray-black wings, pressed hard and opened its greedy mouth. ...
The above thrilling and intriguing biological wars are phenomena that biophysicists often observe.
Bats rarely come out during the day, but come out for food at night when visibility is extremely poor. How does it capture food flexibly and accurately at night? Especially when humans find that bats have poor eyesight and are blind in a sense, it is even more difficult to imagine how bats find prey and accurately measure the direction and distance of prey. So, someone experimented with bats. They removed the bat's sense of smell and weak vision, tied some ropes in a room, hung many bells on the ropes, and then let bats who lost their sight and smell fly in the room. Surprisingly, without the bell ringing, bats can fly freely in the house without encountering any obstacles.
Surprisingly, the bat's throat can emit strong ultrasonic waves. When ultrasonic waves bounce off objects, bats' big ears and inner ears are the best "antennas" and "receivers". After receiving the "echo", we can not only identify the orientation and distance of the object, but also identify the size of the object, and even distinguish between food, enemies or insurmountable obstacles.
As we all know, submarines have a set of "sonar" system when sailing underwater. It uses "sonar" to detect the direction and position of enemy warships, thus launching attacks. The echolocation system of bat amplitude is very similar to the sonar of submarine. "SONAR" is a transliteration of the English abbreviation SONAR, which means "acoustic navigation and ranging". But the bat's "sonar" is alive and much more sensitive than the artificial "sonar", which is still a research topic in bionics.
In particular, the bat's natural sonar can capture and distinguish 250 "echoes" (targets) within 1 second, and the ability of modern new high-tech radar to capture and distinguish targets (aircraft) is just that.
It should also be noted that the bat's natural "sonar" has strong anti-interference ability. Even if people try to create interference noise that is one or two hundred times stronger than the ultrasonic waves emitted by bats, it is impossible to interfere with bats' effective tracking and pursuit of targets. This is beyond the reach of modern artificial sonar. Moreover, the bat's natural sonar weighs only a few grams at most, and its compactness makes the designers of sonar weighing hundreds of kilograms or heavier radar dumbfounded.
Because bats have natural sonar, they can prey on more than a dozen mosquitoes in a second in the dark night. Because of this, some people call bats "living sonar". Some people call it "live radar".
Biologists have studied this strange phenomenon and found that bats intermittently make sounds that people can't hear when flying. The frequency of this sound is 25000-70000Hz, while the frequency of the sound that people can hear is1.6,000-0.2,000 Hz. The bat's amplitude barks about 30 times per second on average, and it barks about 60 times per second when approaching the target, and the sound waves emitted are reflected back when they hit the surrounding objects. Bat's hearing is very sensitive, and it can accurately receive reflected sound waves and judge the distance, direction and nature of reflected sound waves. In this way, bats can not only pounce on prey accurately, but also avoid various obstacles. The ability of bats to search, detect and locate distant targets has given people profound enlightenment. Obviously, as long as we find a fast-reflecting substance and make equipment that can transmit and receive this substance, we can realize over-the-horizon viewing and over-the-horizon listening. It is found that both light wave and sound wave have this property, just because the detection distance to be reached is long and the sound wave speed is too slow, which not only has a large error, but also has a slow response. The flight speed of the plane can exceed twice the speed of sound, which means that the sound wave has not reflected back and the plane has arrived. Although the speed of light waves is very fast, exceeding the speed of sound by 800,000 times, light waves are greatly affected by meteorological conditions, and will stop when encountering clouds, and neither can meet the needs.
Later, people found that radio wave is the most ideal substance, which has the speed of light wave, can penetrate clouds and fog, and can be reflected by the target. The speed of radio waves in the air is the same as the speed of light, and it is not affected by the climate. It has the ability to break through clouds and fog, and can work in bad weather or at night. As long as a device that can transmit and receive radio waves is developed, over-the-horizon viewing and over-the-horizon listening can be realized.
The English name of this equipment, which completes the search and detection task by transmitting and receiving radio waves, is RADAR, the original full name is "radio direction finding and ranging", which is translated into Chinese as radar.
1864, British physicist Maxwell put forward the theory that both light and radio waves are electromagnetic waves, and came to the conclusion that the propagation speed of radio waves is the same as that of light.
1888, German physicist Hertz obtained radio waves by using spark oscillating discharge of electrodes, which proved Maxwell's theory, but Hertz thought that radio waves could not be used in communication and other aspects.
1895, Russian popov invented an instrument that can receive radio waves, and discovered the reflection of radio waves by ships, which showed that radio waves could be used to find targets that people could not see.
1904, German inventor Christian? Hueers Mayer experimented with the original radar in the laboratory, and obtained a patent for radar design, but the detection distance of this original radar can't reach the distance of the acoustic locator.
In this way, although the radar failed to achieve practical application results before the end of the First World War, the demand for radar and the progress of science and technology have made mankind only one step away from making a real radar.
The attitude of the Japanese is the most unforgettable thing about the early development of radar in various countries. Japan's technical foundation for developing radar is relatively weak, and it can even be said that it has no understanding of radar. But Japan also had the opportunity to make radar technology, but because of Japanese ignorance, it didn't seize this opportunity.
1930, although there was a major breakthrough in radar manufacturing technology, it was still in the transition period from experiment to practical use. At this time, an American electronic scientist named Spicci wanted to sell the radar prototype he invented and successfully tested-"electromagnetic wave detector" to the Japanese navy for $300,000. Although this equipment is huge and its performance is not perfect, it contains the basic technology of making radar. If the Japanese get this instrument, they can quickly develop practical military radar.
At that time, the Japanese didn't know much about radar, especially its military significance. What makes it difficult for the Japanese army to accept is that the radar uses polar coordinates instead of X and Y biaxial coordinates to determine the azimuth. It is hard for them to believe that this heavy guy can find a long-distance target with electromagnetic waves emitted from one point and measure the direction and distance of the target at the same time. But they finally bid $654.38 million to buy this instrument, and it is not clear whether it is really useful. But Spitz refused to accept the price. When I bargained with spitz that day, the American military became interested in spitz's invention, and foresaw the military value of this instrument and the losses it would cause if it was bought by the Japanese. The U.S. military not only bought bulky equipment at Shpits's asking price, but also prohibited Shpits from contacting the Japanese, which made the Japanese make radar at least 10 years late. Until the Pacific War broke out, Americans had equipped a large number of radars on warships to find and track Japanese warships, and the Japanese navy did not know what radar was.