Therefore, the British began to seriously study and solve this problem. What makes modern people feel ridiculous is that the original idea of the British is to find a way out from the blind people whose hearing is slightly better than ordinary people. At that time, in order to know the time and direction of German air strikes in advance, Britain took great pains to find some blind people with particularly sensitive hearing in London, and let them be on duty on high-rise buildings, responsible for monitoring whether there were planes coming and issuing air raid prevention forecasts in time. Now it seems that we can't help but admire the British imagination and the scientific attitude of appointing people on their merits. But to the regret of the British, the hearing of the blind is slightly higher than that of the normal people, but it is far from meeting the requirements of air raid prevention. After all, they are human beings, and their hearing is slightly better than that of normal people, but it is only a few kilometers beyond the hearing distance of normal people. Such a short distance can only provide early warning time of tens of seconds to 1 minute, which cannot meet the requirements of air raid prevention. To this end, the British specially developed a hearing aid device for the blind, which is to let the blind use huge trumpet-shaped metal objects to improve their hearing. Although this method has achieved obvious results, the direction is poor and the distance cannot be measured, especially the sound propagation speed in the air is too slow. In the time it takes for the sound to reach the listener from the maximum distance that the listener can hear, the enemy plane flies forward for several kilometers. That is to say, monitoring is carried out in this way. Air defense should not only know the direction of enemy planes, but also know the distance of enemy planes. The sooner the better. At this point, the British have to admit that even a simple hearing aid can't meet this requirement. Therefore, the British tried to use optical rangefinder to measure the distance of incoming enemy planes. However, due to the great influence of meteorological conditions, the optical rangefinder can only work in the daytime with good visibility, and its ranging is limited, which still has little effect on air defense.
How to realize over-the-horizon viewing and super-listening? Before 19 16, there was only one way, and that was to use the acoustic locator. This instrument is very bulky, its performance is very unstable, and it rarely works normally. Even if it works normally, its maximum measuring distance is only 13km. Although the distance of 13km far exceeds the sight distance and hearing distance of people, it only takes 4 minutes to fly for an enemy plane with a speed of hundreds of kilometers per hour. Under the conditions at that time, with a warning time of 4 minutes, it was difficult for the fighter plane to take off and intercept effectively. Obviously, air defense needs to be equipped with more advanced positioning equipment.
Enlightenment from bats
At this time, people will think of some phenomena in animals, which have been known for a long time, but have not attracted attention, such as bats. Bats rarely come out during the day, but come out for food at night when visibility is poor. This phenomenon has attracted people's attention. How do bats catch 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 for people to imagine how bats find prey and accurately measure the direction and distance of prey. So, someone conducted an experiment on bats, artificially removed their 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 sense of smell and smell fly in the room. Surprisingly, without the bell ringing, bats can fly freely in the house without encountering any obstacles.
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 25,000 to 70,000 Hz, while the frequency of the sound that people can hear is 16 to 200,000 Hz. Bats bark about 30 times per second on average, and bark about 60 times per second when approaching the target, and the sound waves emitted are reflected by objects around them. 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 great enlightenment to mankind. As long as we find a fast-reflecting substance and make equipment that can emit and receive this substance, we can realize the dream of over-the-horizon viewing and over-the-horizon listening. It is found that both light wave and sound wave have this property, only because the detection distance that human beings want to reach is far, and the speed of sound wave is too slow, which is not only a big error, but also a slow response. Now it seems that the flight speed of the plane can exceed twice the speed of sound, indicating that the sound wave has not reflected back and the plane has arrived; Although the speed of light waves is very fast, more than 800,000 times faster than the speed of sound, when they meet clouds, they will stop. These two waves obviously cannot meet the needs of human beings.
What waves have the speed of light waves, can penetrate clouds, and can be reflected by targets? People find that radio waves are the most ideal substance. 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, human beings can realize their fabulous dreams.
The English name of this equipment, which completes the search and detection task by transmitting and receiving radio waves, is RADAR, which means "radio reconnaissance and ranging", which is translated into Chinese as radar. Since 1880, the scientific and technological progress of human beings has basically mastered the technology of making 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, the German inventor Christian Hueers Mayer conducted experiments on the original radar in the laboratory and obtained a patent for radar design, but the detection distance of this original radar could not reach the distance of the acoustic locator. In this way, although radar failed to achieve practical application results before the end of the First World War, human demand for radar and the progress of science and technology have made human beings only one step away from making a real radar.
Ignorance made the Japanese repeat Napoleon's mistakes.
After World War I, mankind did not win permanent peace, and it was only a matter of time before the war broke out again. Human aviation and navigation need radar, and the aircraft that showed great power in World War I and the air force victory theory founded by Italian militarists made people feel the importance of radar. Major countries in the world have begun to develop radar in full swing.
1922 In September, Taylor and Yang of the United States found that high-frequency radio communication would be blocked and interrupted when a ship passed between the radio transmitter and receiver, so they suggested using the phenomenon of radio signal interruption to measure ships sailing in the dark or fog. 193 1 1 In June, the US Naval Engineering Bureau ordered the Naval Research Institute to start the research work of "detecting enemy ships and enemy planes by radio". 1 in March, 934, Yang and Peggy of the United States developed the earliest radar, and successfully tested a single-wooden-frame skin plane at1mile away. 1938 65438 In February, the US Navy warship "new york" began to be equipped with radar, and in the following year's voyage, buoys at 4 nautical miles, birds at 5.5 nautical miles, 14 inch shells flying at 7 nautical miles, 8 to 15 nautical miles and 100 were detected. 1940 10 with the support of the national defense commission, the Institute of Radiology of MIT made further research on radar technology and began to develop microwave radar.
1935 In February, Watson Watt of Britain suggested the manufacture and use of radar, and the first experimental radar in Britain was successfully developed in June the following year. During the test, it successfully detected the plane flying 27 kilometers away. A month later, Watt improved the radar, making its detection distance reach 65 kilometers, and by the end of September, the detection distance could reach 88 kilometers. 1937 In April, the British government decided to establish a radar detection network on the eastern and southern coasts of England and the Thames Bay.
The development of radar in Germany started very early and has a solid foundation. As early as 1904, Hueers Mayer obtained the patent of radar design. In 1930s, German scientists made great progress in radar research, and developed practical air defense early warning radar, and then developed air defense early warning radar. Nazi Germany, which was frantically expanding its army and preparing for war, was on the verge of war. Radar, a tool to realize human's dream of "clairvoyance" and "clairvoyance", will definitely show its talents in the war. Therefore, Germany should develop radar rapidly. But who would have thought that the practical air defense early warning radar was not only ignored, but was put into the "cold palace" and almost died.