Shulou(Shulou.com)11/24 Report--

For RF people, electromagnetic waves are the high-tech we are most familiar with. To borrow the encyclopedia definition: electromagnetic waves are oscillating particle waves derived and emitted in space by electric and magnetic fields in the same direction and perpendicular to each other. They are electromagnetic fields propagating in the form of waves and have wave-particle duality. The electric field and magnetic field which are oscillating in the same phase and perpendicular to each other move in the form of waves in space, and their propagation direction is perpendicular to the plane composed of electric field and magnetic field. The speed of electromagnetic wave is fixed in vacuum, and the speed is the speed of light.

However, the process of discovering electromagnetic waves is extremely difficult. Today, let's explore the story behind electromagnetic waves.

Parallel electricity and magnetism then we know that electromagnetic wave is a kind of objective material form, a kind of real matter which is not changed by man's subjective will, and is a kind of wave. Why is it so hard to find? Mainly because it is invisible and imperceptible. People are always interested in what they can feel and discover it earlier, such as light waves, such as sound waves. However, the electromagnetic wave is silent, colorless and tasteless. But it exists objectively.

People discovered magnetism a long time ago, and there was a compass in the era of the Yellow Emperor. Electricity was discovered a long time ago, and the ancient Greeks discovered it by rubbing amber with fur, as well as lightning in nature. But for a long time, electricity and magnetism exist as two kinds of material forms, and the development of almost parallel lines never seems to intersect.

So why can electricity and magnetism be discovered respectively? The answer is still because of people's senses, people can see the rotation of small magnetic needles, but also can see the flames of lightning.

In the West, the first research on magnetism is the British doctor Gilbert, whose work has transformed the whole magnetism from experience to science. It seems that the world is really driven by unscrupulous people. On magnetism, published in 1600, tests complex magnetic theories through detailed experiments. For an introduction to Gilbert, please take a look at Gilbert and Magnetics, which is launched today.

As another line of parallel lines-electricity. Although people discovered lightning very early, they also found electrical phenomena in daily life: for example, combs can attract scraps of paper after combing their hair. But the real milestone was Franklin's kite experiment. (please do not imitate, there is a reason why there are few foreigners.)

Franklin's story, please move to another tweet today, "awesome Franklin".

Franklin came to the conclusion through experiments:

Electric charge is divided into positive charge and negative charge.

In the process of friction electrification, an equal amount of heterogeneous charge is formed, and the charge lost by one side is equal to the charge obtained by the other.

Conservation of electric charge, that is, electric charge can neither be created nor destroyed, but can only be transferred from one charged object to another, and the total amount remains the same.

The spark of electricity and magnetism 1800 years later, due to various coincidences, electricity and magnetism slowly crossed and advanced hand in hand from two parallel development trajectories. Once the electromagnetic wave was discovered, the great power of its explosion was previously unimaginable. Man first added the information he needed to the electromagnetic wave-the Telegraph was invented. Later, human beings mastered the technology of controlling electronics, so they invented semiconductors and chips, from which television, telephone, computer and even radio technology, an information age that no one can control, is like a tsunami. In the 5G era, the intelligent era, the application of electromagnetic waves will be more extensive and in-depth.

The first major event of the intersection of electricity and magnetism was a small discovery released by Oster, a professor at the University of Copenhagen in Denmark, in July 1820: a small magnetic needle deflected in a ring around the current line.

Any great invention is done inadvertently, like Newton's apple or Fleming's penicillin. However, in fact, many people may have encountered this phenomenon, but Lady Luck only cares for one prepared person. Because of the incredible results, Oster himself was particularly cautious and repeated more than 60 experiments from April to July 1820, including shelving a piece of paper between an electric current and a small magnetic needle. the attempt to block this mysterious force between them was unsuccessful. Finally, on July 21, 1820, Oster published his famous paper on the experiment of "collision" between a magnetic needle and an electric current.

The significance of the Oster experiment is that it is discovered that electricity can produce magnetism, thus putting an end to the split between electricity and magnetism. Electricity and magnetism met for the first time in Oster's experiment. It is worth noting that there is another reason why this work appeared after 1800: it was only during this period that people mastered the technology of high-power power supply and were able to generate enough current to be much larger than the earth's magnetic field. from this we can also see the stimulation and influence of productivity on the development of science.

At that time, China was still on the eve of the first Opium War, at the end of the prosperous period of Kangqian. So we can only sigh for the start of modern science. May we work hard and never fall behind again.

We should not underestimate this small "deflection", which is closely related to Faraday's profound thinking on the field of electromagnetics. as a result of this improvement, "field", one of the most important physics concepts of the 20th century, has been highlighted. Oster passed it by. Sometimes it is true that regret and luck coexist. In Faraday's mind, the electric current produces a magnetic field, which pervades the space around the current. Then, Faraday further put forward the concept of advanced field force line.

Faraday made no effort, and he thought again and again: since electricity can produce magnetism, why can't magnetism produce electricity? His ideas are profound and simple, and his experiments are wonderful and straightforward: he hopes to generate electricity in a circuit made of magnets. From 1821 to 1831, during the most creative decade of Faraday's life (30 to 40), he experienced numerous failures. Suddenly, with a sudden insertion of their magnet into the air coil, the pointer of the ammeter was deflected, thus inventing that magnetic time changes can produce electricity.

So, R & D brothers, do not be afraid of failure, do not be afraid of bug, any small breakthrough may change your understanding of existing technology.

Later generations summarized the work of Oster and Faraday into the following two equations:

At this point, electricity and magnetism finally achieved the first handshake-electricity can produce magnetism, and magnetism can produce electricity.

There is no doubt that the third major event in the establishment of Maxwell's equations is the emergence of the genius Maxwell. The genius Maxwell entered high school at the age of 10, entered the university at 16, transferred to Cambridge at 19, and was elected a professor shortly after graduation at 23. A coincidence of fate is that Maxwell was born in exactly the same year as Faraday's experiment-1831.

His solid physical foundation and extraordinary love for his career prompted Maxwell to have a grand ambition to make Faraday's field concepts and ideas precise and mathematical.

In 1860, the 29-year-old Maxwell, with the preliminary results of "on the Line of Power of Faraday", met the nearly ancient Faraday, who spoke highly of Maxwell. Faraday said: I don't think my theory must be true, but you are the one who really understands her. And further encourage Maxwell: this is an excellent article, but you should not stay in mathematics to explain my point of view, but should break through it.

When we enjoy the achievements of our predecessors, we have to thank them for their greatness and selfless dedication.

On the other hand, Faraday, who is not deep in the culture of mathematics, Faraday, who has been engaged in scientific experiments all his life, also raised his concern: for fear that mathematics would cover up the physical essence of electromagnetism. Facts have proved that Maxwell not only lived up to Faraday's expectations, but also really pushed electromagnetism to the theoretical peak.

The above-mentioned Maxwell really understands Faraday, and its inner meaning is extremely profound:

Faraday put electricity and magnetism into all space, and introduced the concepts of field and line of force, which provided a broad stage for mathematical expression--

Curl:

Divergence:

And gradient:

The introduction of functions with equal spatial changes becomes inevitable. The field is invisible and untouchable, but it plays a key role in imperceptible influence.

Faraday proposed for the first time that in the field of electromagnetism, electricity and magnetism constitute a pair of contradictions, and there is a contradiction transformation, that is, electricity can produce magnetism, magnetism can also produce electricity. Obviously, he took electromagnetic physics to new heights.

Faraday negated the central force for the first time and replaced it with the mutual transformation of electromagnetic forces. As we all know, gravity is a typical central force in mechanics, but electromagnetic transformation is a ring-shaped phase.

If Maxwell simply summed up the mathematical formula of Ferrari, Oster and Ampere's findings, it was far from enough to prove its greatness. If that's all right, I can go through the ages.

Maxwell's greatest discovery was his discovery of displacement current.

Or he invented the displacement current. That is, the Maxwell equations, in equation 4.

As a talented young scholar, Maxwell not only really understood and absorbed the quintessence of Faraday's thought, but also made a great breakthrough. Maxwell said: from the straight line of Euclid to the line of force of Faraday, these are the characteristics of some of the ideas that enable science to move forward. Maxwell first discovered that the transformation between ampere and Faraday was completely asymmetric.

In short, ampere finds that the source (current J) produces a magnetic field, while Faraday is the field of change in the field. It is probably because of Maxwell's careful and profound comparison that he discovered the discontinuity of the current in the capacitor circuit-there is a current in the external circuit, but there is no current in the capacitor.

As a result, Maxwell put forward a new idea of displacement current, that is, the curl of the magnetic field not only corresponds to the conduction current density, but also has the displacement current density.

Only in this way can the continuity theorem of current be guaranteed:

Where the displacement current

And then:

The two most important equations of the corresponding Maxwell equations are obtained:

They really constitute a two-way change in time and space, and the aforementioned Faraday concerns are completely superfluous. The electromagnetic law derived by Maxwell, the Maxwell equations, not only accurately and uniformly expresses the experimental laws proposed by Oster, Ampere, Faraday and Gauss, but also has a comprehensive and systematic sublimation and improvement.

For a detailed introduction of the Maxwell equations, please move the carpenter to read the Maxwell equations to learn.

The significance of Maxwell's equations lies in:

The Maxwell equations formed by the displacement current clearly show that the electric field can be transformed into a magnetic field, and the magnetic field can also be transformed into an electric field, and the unity of time change and space change can be realized.

It is the mutual transformation between electric field and magnetic field and the mutual transformation between time and space that produces a solid foundation for electromagnetic waves. Electric field and magnetic field are interlinked in space and time, which can propagate away from the medium and realize the unity of electromagnetic waves and light.

Maxwell officially predicted electromagnetic waves and pointed out that the speed of electromagnetic waves, even at the speed of light, naturally produces a unified theory of light and electromagnetic waves.

In particular, Maxwell gave full play to his mathematical expertise and deduced the wave equation under passive conditions.

The confirmation of electromagnetic waves that Maxwell only predicted the existence of electromagnetic waves, but confirmed that the real existence of electromagnetic waves fell on a young German physicist-Hertz. At this point, the three giants of electromagnetism are finally in place, and the critical moment to influence history is coming.

From 1886 to 1888, Hertz did a series of experiments to produce electromagnetic waves, and proved that electromagnetic waves are completely similar to light, with important characteristics such as reflection, refraction, diffraction and polarization.

From the point of view of modern people standing on the shoulders of giants, it is not surprising that the Hertz experiment is just a simple LC oscillation circuit and exhaustive electric spark communication. However, it caused a sensation in academic circles at that time: because it was this experiment that proved Maxwell's great prediction with facts. At this point, people not only predicted the electromagnetic wave, but also finally discovered the electromagnetic wave.

Mankind has entered the wireless era.

With the construction of 5G, mankind will enter the intelligent era of the Internet of everything. I am grateful for the dedication of my predecessors.

So, has the journey of electromagnetic wave discovery come to an end? No, the asymmetry of Maxwell's equation still exists, like a heart disease troubling countless scientists-- magnetic charges and magnetic currents-- does it really exist? If it does exist, how will it change our lives?

Note: the article was originally published on the official account of [5G RF Circle], the predecessor of [Radio Frequency School] in 2020, but it was reedited and published today.

This article is from the official account of Wechat: radio Frequency School (ID:RF_Center), author: RF Carpenter

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