Sound does not travel in a vacuum. We must know, we will know

A new phenomenon in condensed matter is described - the “jumping” of phonons from one solid body to another through a void. Due to it, a sound wave can overcome thin vacuum gaps, and heat can be transferred through a vacuum billions of times more efficiently than with ordinary thermal radiation.

A sound wave is a synchronous vibration of atoms of a substance relative to an equilibrium position. For sound to propagate, obviously, a material medium is needed that supports these vibrations. Sound cannot travel in a vacuum simply because it is not there. However, as it turned out quite recently, sound vibrations can jump from one body to another through a vacuum gap of submicron thickness. This effect, called "vacuum tunneling of phonons", was described in two articles published in the latest issues of the journal Physical Review Letters. Let us immediately note that since vibrations of the crystal lattice carry not only sound, but also heat, the new effect also leads to abnormally strong heat transfer through vacuum.

The new effect works through the interaction between sound waves in the crystal and an electric field. Vibrations of the crystal lattice, reaching the end of one crystal, create alternating electric fields near its surface. These fields are “felt” at the other edge of the vacuum gap and rock the lattice vibrations in the second crystal (see Fig. 1). In general, it looks as if a separate phonon - a “quantum” of vibration of the crystal lattice - jumps from one crystal to another and propagates further in it, although, of course, there is no phonon in the space between the crystals.

The authors of the discovery used the word “tunneling” to describe the effect, since it is very similar to the tunneling of quantum particles when they jump through energetically forbidden regions. However, it is worth emphasizing that the new phenomenon can be fully described in the language of classical physics and does not require the involvement of quantum mechanics at all. It is somewhat related to the phenomenon of electromagnetic induction, which is widely used in transformers, induction stoves and contactless charging devices for gadgets. In both cases, a certain process in one body generates electromagnetic fields, which are non-radiatively (that is, without loss of power due to radiation) transmitted through the gap to the second body and cause a response in it. The only difference is that with ordinary inductance, the electric current “works” (that is, the movement of electrons), while with vacuum tunneling of phonons the atoms themselves move.

The specific mechanism leading to such an effective coupling between crystal vibration and electric fields may vary. In a theoretical article by Finnish researchers, it is proposed to use piezoelectrics for this purpose - substances that become electrified when deformed and deform in an electric field. This in itself is not enough: for effective jumping of phonons through the vacuum gap, it is necessary to organize a resonance between the “incoming” phonons, alternating electric fields and “runaway” phonons in another crystal. Calculations show that, given realistic parameters of substances, such a resonance actually exists, so that at certain angles of incidence, phonons can tunnel with a probability of up to 100%.

Lately, the design of tube audio equipment has become increasingly popular. In this article I will try to tell you what you need to know when starting work.

1 . Anatomy

The operating principle of electron tubes is based on the movement of charged particles (electrons) in an electrostatic field. Let's consider the device of a radio tube. The figure shows a diagram of the design of the simplest indirect incandescent lamp (diode).

Actually, the lamp is a glass container in which a high vacuum is created (10-5 - 10-7 torr). For classic lamps, the shapes of the electrodes are similar and are concentric “cylinders”. The point of it all is that when the cathode is heated, electrons are excited and leave it. The direct filament cathode is simply a tungsten filament, as in an ordinary lighting lamp. Such cathodes are used in cases where there is no need to create a special regime at the cathode. Most lamps use an indirect filament cathode. In this case, the filament is placed in a metal tube. At some distance from the cathode there is an anode - an electrode, which is the “final stop” of the electron flow. To control the speed of electron movement from the cathode to the anode, additional electrodes are used. Grids are divided into 3 types. Control, screen and protective (anti-dynatron). The mesh is a wire spiral wound on metal posts (traverses), sandwiched between two mica flanges. The same flanges hold the anode and cathode traverses. There are also lamps containing several electrode systems. Such lamps are called combination lamps. Depending on the power of the lamp, its electrodes and body can be made of various materials, because As the current passing through it increases, the power dissipated increases.

2. Morals

It is quite clear that each type of lamp has its own original parameters and characteristics. First of all, let's find out the operating modes of the lamps. To create a normal electron flow, special electrostatic potentials are created in the interelectrode spaces of the lamp. These potentials are determined by the voltages acting on its electrodes. Let's look at the main operating modes:
1. Maximum permissible anode voltage (Ua max). The voltage between the anode and the cathode, if exceeded, a breakdown occurs. With a cold cathode this voltage is higher. The same applies to grid voltages.

2. Maximum permissible anode current (Ia max). Maximum permissible current value in the anode circuit. Essentially, the current passing through the lamp, minus the small fraction “stretched” by the grid potentials.

3. Filament voltage (Un). Typical voltage applied to the filament (heater), at which the cathode reaches the temperature required for thermionic emission, while at the same time the lamp maintains the declared durability parameters.

4. Filament current (In). Current consumed by the filament.

There are also a number of characteristics determined by the design of the lamps that affect the parameters of the assembly assembled on this lamp:

1. Characteristic slope (S). The ratio of the anode current increment to the voltage increment on the control grid. Those. we can determine how much the anode current will change when the control voltage changes by 1V.

2. Internal resistance of the lamp (Ri). The ratio of the anode voltage increment to the corresponding anode current increment. In some ways, this can be compared with the current transfer coefficient of a transistor because as the control (positive) voltage increases, the anode current increases. Outwardly, this looks like a decrease in resistance. Naturally, the lamp does not have any active resistance as such. It is determined by interelectrode capacitances and is reactive in nature.

3. Static gain (µ). The ratio of the anode voltage increment to the control increment causing the same increment in the anode current. Those. essentially shows how many times more effective an increase in control voltage by 1V is than a similar increase in the anode voltage.

3. Names

Some parameters and design features of lamps can be recognized by their markings:

1st element – ​​a number showing the rounded filament voltage

2nd element – ​​letter indicating the type of lamp:
A – frequency-converting lamps with two control grids.
B – diode pentodes
B – lamps with secondary emission
G – diode-triodes
D – diodes, including damper ones
E – electronic light indicators
F – high-frequency pentodes with a short characteristic. Including dual controlled pentodes
And - triode-hexodes, triode-heptodes, triode-octodes.
K - pentodes with an extended characteristic.
L – lamps with a focused beam.
N – double triodes.
P – output pentodes, beam tetrodes
P – double tetrodes (including beam ones) and double pentodes.
C – triodes
F – triode-pentodes
X – double diodes, including kenotrons
C – kenotrons belonging to the category of receiving and amplifying lamps. (specialized rectifying devices have special markings)
E – tetrodes

The 3rd element is a number indicating the serial number of the device type (i.e. the serial number of the development of the lamp in this series. For example, the 1st developed lamp from the series of 6-volt finger-type double triodes - 6N1P).

The 4th element is a letter characterizing the design of the lamp:

A - in a glass case with a diameter of up to 8 mm.
B – subminiature, in a glass case with a diameter of up to 10.2 mm
G - subminiature, in a metal-glass case with a diameter of more than 10.2 mm
D – in a metal-glass case with disk solders (found mainly in microwave technology)
K – in a ceramic case
N - subminiature, in a metal-ceramic case (nuvistors)
P - miniature in a glass case (finger)
P - subminiature, in a glass case with a diameter of up to 5 mm.
C – in a glass case with a diameter of more than 22.5 mm.
Octal lamps with a diameter of more than 22.5 mm in a metal case do not have the 4th marking element.

4. Working conditions

There is a preconception that lamps are more demanding to install than semiconductor devices. Actually, the operating conditions of EVP are not much different from those imposed by semiconductor devices. Moreover, lamps are less demanding on thermal conditions than semiconductors. Thus, the output stages of tube amplifiers with a power of up to 20W do not require forced cooling, unlike semiconductor ones. Most lamps are installed in a special kind of connectors - lamp sockets. Some lamps have terminals at the top of the bulb. Most often these are the terminals of the anode or screen grid, to which a relatively high voltage is applied. This is done to avoid breakdown between it and the terminals of other electrodes. If the lamps become very hot during operation, it is advisable to space them as far apart as possible. Recently, a special trend has emerged in the construction of lamp technology. Lamps and transformers are placed on the top panel of the device, and the remaining parts are mounted in the basement of the chassis. Such devices are cooled much better, and I consider this approach quite reasonable if there are no anode terminals in the upper part of the lamps that threaten the user with high voltage damage. Lamps do not have to be positioned strictly vertically. Any angle of inclination relative to the horizon is allowed if there is no danger that the grids will heat up and sag, thereby creating an interelectrode short circuit.

In the section on the question Does sound not travel in a vacuum? given by the author Flush the best answer is Light and sound in a vacuum
Why does light travel through a vacuum but sound does not?
SEED expert Claude Beaudoin responds:
Light is an electromagnetic wave—a combination of electric and magnetic fields—that does not require the presence of gas to propagate.
Sound is the result of a pressure wave. Pressure requires the presence of some substance (for example, air). Sound also travels in other substances: in water, the earth's crust, and passes through walls, which you might notice when your neighbors make noise.
Michael Williams says:
Light is basically electromagnetic energy carried by fundamental particles - photons. This situation is characterized as “wave-particle duality” of wave behavior. This means that it behaves both as a wave and as a particle. When light propagates in a vacuum, the photon behaves like a particle and therefore propagates freely in this medium.
On the other hand, sound is vibration. The sound we hear is the result of vibration of the eardrum. The sound emitted by a radio is the result of vibration of the speaker membrane. The membrane moves back and forth, causing the air around it to vibrate. Air vibrations travel, reaching the eardrum and causing it to vibrate. The vibration of the eardrum is converted by the brain into a sound you recognize.
Thus, sound requires the presence of matter to vibrate. In an ideal vacuum there is nothing to vibrate, so the vibrating membrane of a radio receiver cannot transmit sound.
SEED expert Natalie Famiglietti adds:
The propagation of sound is movement; The propagation of light is radiation or emission.
Sound cannot travel in a vacuum due to the lack of an elastic medium. British scientist Robert Boyle discovered this experimentally in 1660. He put a watch in a jar and pumped out the air from it. After listening, he could not distinguish the ticking.

Rice. 1. Phonon tunneling through a vacuum gap. An incoming sound wave from the left creates alternating electric fields on the surface, which generate synchronous vibrations of atoms in the second body, on the right. Image from the discussed article Phys.Rev.Lett.105, 125501

A new phenomenon in condensed matter is described - the “jumping” of phonons from one solid body to another through a void. Due to it, a sound wave can overcome thin vacuum gaps, and heat can be transferred through a vacuum billions of times more efficiently than with ordinary thermal radiation.

A sound wave is a synchronous vibration of atoms of a substance relative to an equilibrium position. For sound to propagate, obviously, a material medium is needed that supports these vibrations. Sound cannot travel in a vacuum simply because it is not there. However, as it turned out quite recently, sound vibrations can jump from one body to another through a vacuum gap of submicron thickness. This effect, called "vacuum tunneling of phonons", was described in two articles published in the latest issues of the journal Physical Review Letters. Let us immediately note that since vibrations of the crystal lattice carry not only sound, but also heat, the new effect also leads to abnormally strong heat transfer through vacuum.

The new effect works through the interaction between sound waves in the crystal and an electric field. Vibrations of the crystal lattice, reaching the end of one crystal, create alternating electric fields near its surface. These fields are “felt” at the other edge of the vacuum gap and rock the lattice vibrations in the second crystal (see Fig. 1). In general, it looks as if a separate phonon - a “quantum” of vibration of the crystal lattice - jumps from one crystal to another and propagates further in it, although, of course, there is no phonon in the space between the crystals.

The authors of the discovery used the word “tunneling” to describe the effect, since it is very similar to the tunneling of quantum particles when they jump through energetically forbidden regions. However, it is worth emphasizing that the new phenomenon can be fully described in the language of classical physics and does not require the involvement of quantum mechanics at all. It is somewhat related to the phenomenon of electromagnetic induction, which is widely used in transformers, induction stoves and contactless charging devices for gadgets. In both cases, a certain process in one body generates electromagnetic fields, which are non-radiatively (that is, without loss of power due to radiation) transmitted through the gap to the second body and cause a response in it. The only difference is that with ordinary inductance, the electric current “works” (that is, the movement of electrons), while with vacuum tunneling of phonons the atoms themselves move.

The specific mechanism leading to such an effective coupling between crystal vibration and electric fields may vary. In a theoretical article by Finnish researchers, it is proposed to use piezoelectrics for this purpose - substances that become electrified when deformed and deform in an electric field. This in itself is not enough: for effective jumping of phonons through the vacuum gap, it is necessary to organize a resonance between the “incoming” phonons, alternating electric fields and “runaway” phonons in another crystal. Calculations show that, given realistic parameters of substances, such a resonance actually exists, so that at certain angles of incidence, phonons can tunnel with a probability of up to 100%.

Rice. 2. An abnormally strong heat exchange between the very last atom at the tip of a scanning tunneling microscope and the substrate. The atom induces a charge on the substrate, which tracks the thermal vibration of the atom and generates phonons on the substrate, while removing energy from the atom. Image from the discussed article Phys.Rev.Lett.105, 166101

In another paper, physicists stumbled upon the effect under discussion while studying a seemingly completely technical question: what temperature is the very tip of a warm tip of a scanning tunneling microscope when brought (without touching) to a cold substrate (see Fig. 2)? Using subtle experimental techniques, they were able to measure the temperature of literally the very last atom at the tip of the needle and discovered an astonishing fact: this atom is at the temperature of the substrate, not the needle! This means that the non-contact heat exchange of the very last atom of the tip with the substrate was much stronger (through vacuum!) than with the rest of the tip.

Conventional thermal radiation, the first thought that comes to mind in such situations, turned out to be completely insufficient. According to the researchers, heat transfer from the tip to the substrate was billions (!) times more efficient than what thermal radiation could provide. This fact, coupled with the results of detailed measurements, indicates that here, too, tunneling of phonons through the vacuum takes place.

The authors of the article explain the dynamics of this effect as follows. Any charge brought to a metal surface induces a charge on it (in problems in electrostatics it is often modeled with a fictitious charge-image). If the original charge trembles, for example, due to thermal vibrations, then the induced charge will also tremble with approximately the same frequency and amplitude (due to the fact that electrons are much lighter than atoms, they have time to “adjust” to each movement of the atom). As a result, it turns out that a certain electron bunch appears right on the surface of the substrate, which trembles like a “hot” atom. This bunch rocks the vibrations of atoms on the substrate, energy is wasted on them, it is taken away from the electron bunch, and therefore from the initially hot atom - after all, it is “rigidly” connected to the bunch by electrical forces! It is through this mechanism that the very last atom on the tip manages to become very cold, even if the rest of the needle is warm.

Apparently, for applied problems the new effect will be interesting precisely from the point of view of heat transfer, which in certain situations can be much more efficient than previously thought. This observation will be very important in the design of micromechanical devices and in the study of thermal conductivity of polycrystalline piezoelectric samples. Additionally, in microdevices that combine piezoelectric and metal components, electrons can come into play. All the prospects this opens up for the rapid transfer of energy between electrons and phonons from one substance to another through a vacuum have yet to be explored.

A new phenomenon in condensed matter is described - the “jumping” of phonons from one solid body to another through a void. Due to it, a sound wave can overcome thin vacuum gaps, and heat can be transferred through a vacuum billions of times more efficiently than with ordinary thermal radiation.

A sound wave is a synchronous vibration of atoms of a substance relative to an equilibrium position. For sound to propagate, obviously, a material medium is needed that supports these vibrations. Sound cannot travel in a vacuum simply because it is not there. However, as it turned out quite recently, sound vibrations can jump from one body to another through a vacuum gap of submicron thickness. This effect, called "vacuum tunneling of phonons", was described in two articles published in the latest issues of the journal Physical Review Letters. Let us immediately note that since vibrations of the crystal lattice carry not only sound, but also heat, the new effect also leads to abnormally strong heat transfer through vacuum.

The new effect works through the interaction between sound waves in the crystal and an electric field. Vibrations of the crystal lattice, reaching the end of one crystal, create alternating electric fields near its surface. These fields are “felt” at the other edge of the vacuum gap and rock the lattice vibrations in the second crystal (see Fig. 1). In general, it looks as if a separate phonon - a “quantum” of vibration of the crystal lattice - jumps from one crystal to another and propagates further in it, although, of course, there is no phonon in the space between the crystals.

The authors of the discovery used the word “tunneling” to describe the effect, since it is very similar to the tunneling of quantum particles when they jump through energetically forbidden regions. However, it is worth emphasizing that the new phenomenon can be fully described in the language of classical physics and does not require the involvement of quantum mechanics at all. It is somewhat related to the phenomenon of electromagnetic induction, which is widely used in transformers, induction stoves and contactless charging devices for gadgets. In both cases, a certain process in one body generates electromagnetic fields, which are non-radiatively (that is, without loss of power due to radiation) transmitted through the gap to the second body and cause a response in it. The only difference is that with ordinary inductance, the electric current “works” (that is, the movement of electrons), while with vacuum tunneling of phonons the atoms themselves move.

The specific mechanism leading to such an effective coupling between crystal vibration and electric fields may vary. In a theoretical article by Finnish researchers, it is proposed to use piezoelectrics for this purpose - substances that become electrified when deformed and deform in an electric field. This in itself is not enough: for effective jumping of phonons through the vacuum gap, it is necessary to organize a resonance between the “incoming” phonons, alternating electric fields and “runaway” phonons in another crystal. Calculations show that, given realistic parameters of substances, such a resonance actually exists, so that at certain angles of incidence, phonons can tunnel with a probability of up to 100%.