What is a field in physics - in simple and understandable language with explanations

Scalar field

For example, we can measure the temperature in winter at different points in the room.

At the same time, the closer to the central heating radiator and the higher to the ceiling, the higher the temperature will be. And at points near the floor and away from the heated battery, the temperature will be several degrees lower.

Let's consider three-dimensional space (Fig. 1) and some point located in this space. Let's denote the point with a capital letter, for example P.

Rice. 1. Each point in three-dimensional space is associated with three numbers on the axes

This point is associated with three numbers x, y, z, lying on the axes Ox, Oy, Oz. Such numbers are called point coordinates. Mathematicians usually write down the coordinates of a point next to its name: \(\large P\left( x ; y ; z \right)\).

We can additionally assign a fourth number to this point - temperature t in degrees Celsius (Fig. 2).

Rice. 2. Example of temperature distribution in a room during the heating season

Let's compile a table that will contain the coordinates of points in space and the temperature at these points. This way we will organize information about the temperature distribution in the room.

Using such a table, we can construct graphs on which we will depict exactly how the temperature will depend on any spatial coordinate.

This table and graphs contain information about the temperature field.

Since the temperature distributed throughout the room is a scalar quantity, the temperature field is called scalar. And the table specifies a scalar function that describes the temperature distribution in the room.

This function connects the coordinates of a point and the value of a physical quantity - temperature at this point.

This is a common function, like those with which you had to solve examples in school mathematics. Only this function depends not on one variable x, but on three variable quantities - the coordinates x, y, z of points located in three-dimensional space.

\[\large \varphi = f \left( x ; y ; z \right)\]

And the fourth value, temperature, will be the value of this function. Like the number “y” for a function of one variable “x”.

Magnetic orientation field

What is a permanent magnet? It consists of a collection of atoms, each of which serves as a tiny magnet with a tiny magnetic field, and they are all aligned so that together they create a large magnetic field. The magnet is shown in Fig. 3, and in it every atom is directed upward. In this case, the orientation field Θ(x,t) tells us how far at time t the atom at point x has deviated from the vertical. Θ, in short, will be the angle between the magnet of each atom and the vertical. Animation in Fig. 3 shows a wave in a magnet in which the directions of the atomic magnets oscillate left and right. The graph Θ(x,t) is shown in green above the magnet; and again it looks exactly the same as on previous occasions.

Vector field

Suppose there is a large magnet in the corner of the room. And we walk around the room with a cord, to one end of which an iron nail is tied. We hold the second end of the lace in a horizontally extended hand.

Walking around the room, we will notice that in some area of the room the cord with a nail deviates from its vertical position towards the magnet.

The closer we get to the magnet, the more it attracts the nail. The more effort you need to make to hold the lace in your hand.

Such fields, like the field created by a magnet, are called force fields.

Force fields are vector fields, since the force distributed throughout the room and measured at various points in the room is a vector quantity.

Now we can assign to each point of the room not only the coordinates of the point, but also the vector F of the force acting on the nail at this point.

Let's make a table and write down in it the coordinates of each selected point in the room and the coordinates of the force vector with which the magnet acts on the nail at this point.

The force vector at each individual point will have its own characteristics - length and direction. Therefore, a table containing information about the force at each point in the room will contain 6 rows. Three lines are the coordinates of the point, and three lines are the coordinates of the vector.

Such a table defines a function, which mathematicians call for short “vector function”.

A vector function describing a vector field can be denoted as follows:

\(\large \overrightarrow{A \left( P \right)} \) – vector function. In more detail, you can write it this way:

\[\large \boxed{ \overrightarrow{A \left( P \right)} = A_{x}\left( x ; y ; z \right) \cdot \vec{i} + A_{y}\left( x ; y ; z \right) \cdot \vec{j} + A_{z}\left( x ; y ; z \right) \cdot \vec{k} }\]

\( A_{x}\left( x ; y ; z \right) ; A_{y}\left( x ; y ; z \right) ; A_{z}\left( x ; y ; z \right) \ ) are components (parts) of a vector function.

\( \vec{i} ; \vec{j} ; \vec{k} \) are unit vectors.

Usually such functions are not taught in school. But you now know that in addition to the usual scalar functions, there are vector functions.

From the record it is clear that a vector function differs from a scalar function in that it has three components (parts). Each component (part) depends on the three coordinates of the point P in space.

Strings

String values can contain any characters. The main limitation is the length.

Strings can be fixed or variable length. In the second case, the maximum possible size is usually set. The most common length limit for database strings is 255 characters.

The names of string field types may differ in different DBMSs. Most popular:

CHAR - fixed length up to 255 characters. If the string is smaller than the specified size, it will be padded with spaces.
VARCHAR, TINYTEXT - variable length up to 255 characters, an additional byte is spent to store the size.
TEXT, MEMO - variable length up to 65,535 characters.
MEDIUMTEXT - maximum 16,777,215 characters.
LONGTEXT - maximum 4,294,967,295 characters per line.

The string type of the database field allows you to store passwords, short descriptions, personal data, addresses, phone numbers, articles. No mathematical operations are performed with this information. Strings can be compared in lexicographical order.

Very large chunks of text can also be stored in BLOB fields, which are discussed below.

Possible integrity constraints: string length, mandatory, default value.

Which field is called stationary

Many processes occurring around us change over time. For example, the temperature at noon on a hot summer day will be higher than the temperature before sunset on the same day. In other words, the scalar quantity - the air temperature outside, and therefore its field, changes over time.

In contrast, the temperature field indoors will not change in winter. Of course, if the central heating radiators have the same temperature for a long time.

Quantities and processes that change over time are called non-stationary. And stable quantities that do not change over time are stationary.

If a field does not change over time, it is called stationary. And if it changes, then it is non-stationary.

The concept of quantum fields

In addition to the problem of the physical reality of elementary particles, it is necessary to study how they interact.

For example, two particles of mass interact through an attractive force - the gravitational force, since it is believed that everywhere there is a gravitational field that carries information about the mass, and makes the two particles move towards each other, which we call the “gravitational attractive force”.

In this context, the gravitational field is a field. But what is a field?

Can all fields be felt?

We can feel the temperature field due to the fact that our skin contains special receptors that can perceive the temperature of the environment.

However, not all fields can be felt by people. For example, we are immune to magnetic and electric fields because we do not have an organ capable of detecting their changes.

How then did we learn about electric and magnetic fields? We have found those who can sense these fields.

Some fish are able to detect changes in the electric field. For example, the electric stingray (Fig. 3) picks up electrical signals and thanks to this it is perfectly oriented. He has special organs for this, unlike humans. Individual stingrays are capable of generating electrical discharges of up to 200 volts.

Rice. 3. The electric stingray can sense the electric field

The electric eel (Fig. 4) can reach 2.5 meters in length. It is capable of not only capturing electric fields, but also generating powerful electrical discharges with voltages of up to 860 Volts and currents of up to 1 Ampere. Uses them mainly when hunting prey or escaping from other predators.

Rice. 4. The electric eel senses an electric field and can produce electrical impulses

The ability to detect changes in the electric field is called electroreception. It was found in some fish, amphibians and mammals - the platypus and echidna. It is used for hunting, communication and capturing the earth's magnetic field.

Migratory birds, such as cranes (Fig. 5), contain an organ capable of detecting changes in the Earth's magnetic field. Thanks to this, they orient themselves in space during flights to warmer climes.

Rice. 5. Migratory birds navigate by the Earth’s magnetic field

How can we detect the field without the help of animals?

To detect the electric field we will use an electric charge. Because the field acts with electric force on the charges placed in it.

And to detect the magnetic field, we can use a small magnet, or an iron object. Because the magnetic field will affect them.

The impact of the electric field on human life and health

An electric field is a low frequency wave that forms a charge on the human body and remains at a fairly shallow distance from its surface. Currents flowing in the human body can change the direction of their movement under the influence of fields with alternating electric current. It is for this reason that some people feel their hair move when they are near overhead AC power lines.

An electric field can cause irreparable harm to a person. Generally, negative effects of electricity occur when people regularly use mobile phones.

Another example of the possible observation of an electric field in everyday life is its occurrence near the displays of televisions with a kinescope. If you bring your hand to the screen of such a television receiver, the hairs on it seem to “stand up.” This phenomenon occurs precisely due to the influence of an electric field.

I also recommend watching the professor’s lecture on the topic “Electric Field”:

How are the fields indicated in the pictures?

Let's look at part of the world map. Let us pay attention to the fact that the areas of parts of the map are painted in different color shades (Fig. 6).

Rice. 6. Different elevation levels on the map are painted in different colors

Also, in one of the corners of the map you can see a multi-colored plate, similar to the one drawn on top of the map in the picture. A scale of heights and depths is drawn on it and, next to each shade, numbers are written indicating the height or depth in meters.

Note: Heights and depths on the ground are indicated using areas with different colors for clarity. The closer to red, the higher, and the closer to purple, the deeper.

Thin boundaries are drawn along the edges of the color areas; they limit areas that have the same height level. Such boundaries are called level lines.

Height or level is a scalar quantity. Therefore, we can say that with the help of colored areas and lines on their boundaries, a field is specified that describes the distribution of heights on the Earth's surface.

A scalar field can be represented using level lines.

Let us now recall the example with a magnet and a nail. At each point in the room you can draw a vector of the force with which the magnet attracts the iron nail (Fig. 7).

Rice. 7. Forces line up along certain lines, they are called field lines

The closer to the magnet, the greater the force of attraction, the longer the vectors. You can notice that the force vectors seem to be located along some lines. They are additionally shown as a dotted line in the figure. It can also be seen that these lines are curved.

Such lines along which the force vectors line up are called force lines. Force fields are vector.

Vector fields are represented using field lines. Force vectors are lined up along such lines. These lines have other names.

Electric charge

The concept of electric charge occupies a central place in the classical theory of electromagnetism. Electric charge in physics is a quantity that characterizes the ability of objects to enter into electrical interactions. It should be emphasized that bodies with like charges always repel, and bodies with opposite charges attract each other.

Electric charge

The fundamental characteristic of charge is its dual nature: charges can be both positive and negative. Thus, all charged bodies are conventionally divided by physicists into two subtypes, while all bodies of one subtype repel each other, but attract bodies from the second subtype. For example, if particle A repels particle B, but particle A attracts particle C, then particle B will also attract particle C.

Physicists still have not figured out why bodies have this global, universal and, upon closer examination, elementary property. However, the terms "negative charge" and "positive charge" are opposite manifestations of the same quality.

A charged particle is always born in pairs with a particle of opposite charge. For example, a pair of positively and negatively charged electrons (a positron and a negatron) is produced through the decay of a photon. During this process, there is no change in charge; in other words, the change in charge is zero before and after the “transformation” of the photon.

To understand what the essence of a given scalar quantity is and what electrical matter consists of, one should study two fundamental properties of electric charge: quantization and charge conservation.

Charge quantization principle

Even a novice physicist knows: in nature, electric charges consist of discrete charges that have a constant value, which is characterized as the charge of an electron and is denoted by the symbol e. For example, the positive charge of a positron and the negative charge of a negatron are equal in magnitude. Charge quantization is the natural equalization of the magnitudes of the charges of two oppositely charged particles. An important concept in quantization terminology is charge discreteness. According to the latest physical theories, the charge is quantized, that is, it has the property of discreteness: one charge consists of minimal portions of charges that cannot be further divided.

Charge conservation principle

This principle follows from the nature of the “birth” of two world bodies having opposite charges. This is a fundamental empirical law that has no contradictions in any of the studies done to date. Literally, the principle of conservation says: in a closed system, the electric charge, which also has another name - the algebraic sum of two unlike charges, remains constant.

Relationship between scalar and vector fields

A scalar field can be associated with a vector field. Let's return to the example of marking heights on a map (Fig. 6). We know that there are areas on the map where there are sharp changes in elevation. In such areas there are several gradations of color shades, and areas with different colors are located more often in such places.

To indicate sharp changes in height, they came up with the use of a special vector - the gradient vector. It describes how quickly a scalar quantity changes, such as height on a map of an area.

This vector is denoted as follows:

\[\large \boxed{ \overrightarrow{grad \left( h \right)} }\]

Note: Gradient, from the word gradation - it can be translated as variety, or variability. For example, gradations of brightness have different shades of gray. In school physics, the gradient vector is usually not considered.

The gradient is directed towards the greatest increase in the physical quantity. And the length of the gradient vector is equal to the speed at which the physical value increases. magnitude in this direction.

There are different elevation differences in different parts of the map, somewhere the height changes faster, and somewhere more slowly. This means that in different areas of the terrain the gradient vector will have different lengths.

And if a vector quantity is distributed in space, then they say that such a physical field is given. quantities.

Thus, we obtained two related fields - a scalar height field and a vector gradient field, which describes the rate of change in height in different areas of the terrain.

For example, when describing the electric field, we will use two quantities - scalar - the potential of the electrostatic field and vector - the electric field strength. These quantities are related to each other using a gradient vector.

Electrical capacitance, capacitor and electric field strength

The value C, equal to the charge q, which must be imparted to the conductor in order to increase its potential, is called electrical capacity.

Electrical capacitance describes the inertness of a charged substance that can conduct electric current, or, in other words, its resistance to an increase in potential. The formula that characterizes the principle of electrical capacity of the system:

The size and shape of the conductor determines the electrical capacitance value, as do the properties of the dielectric that separates the conductors. In physics, one type of system is important, concentrating the electric field in a certain place in space. It is called a “capacitor”, which, in turn, consists of conductors called plates.

This type of system is a conductor configuration that consists of two flat conducting plates located parallel to each other at a short distance and delimited by a dielectric layer.

Homogeneous and inhomogeneous fields

A field is homogeneous if at each point in space it has the same value of the distributed quantity.

For example, temperature at all points in space has the same value. Or, the electric field acts on a charge placed in it at all points in space with the same force.

Homogeneous force fields are depicted by straight lines, the distance between which does not change (Fig. 8a).

Rice. 8. Lines of homogeneous – a) and inhomogeneous – b) fields

Distributed charges can create uniform fields. The electric field existing between two charged parallel planes is uniform.

If at different points in space the field acts on the test charge with different forces, then the field is called inhomogeneous. The lines of inhomogeneous fields are curved and the distance between them changes (Fig. 8b).

A field is inhomogeneous if at different points in space it has different values of the distributed magnitude.

For example, the field of a magnet is a non-uniform field because the force of the magnet increases as it approaches it. The electric field around a point charge is also non-uniform, because the force on the test charge increases with decreasing distance to the charge that created the field.

The strength of the field can be determined from the lines of force. The denser the field lines are in any area, the greater the magnitude of the field in that area.

Potential energy of electric charge and potential fields

Charges fill the electric field. They move along some closed trajectories. The magnitude of the work of their forces is equal to zero, and therefore these forces (or force fields) are called potential. It is believed that some types of electric fields, in particular the electrostatic field, initially have the property of potentiality. This is a proven theory and does not require new research.

Potential energy

Thanks to the property of potentiality, physicists can judge that potential energy is inherent in each electric charge in a particular field. This principle can be clearly illustrated as follows: in space there is a specific point to which a specific charge can be moved, the value of the potential energy of which will be equal to zero.

Power lines

The concept of its field lines follows from the law of field potentiality. In reality, such objects do not exist in material form. It is a graphical tool that allows you to depict the electric field for visual schematic observation and research. By representing the density and number of lines, one can illustrate the direction of the field strength, as well as its magnitude.

Force field image

Examples of scalar fields

These are fields of distribution of scalar quantities - density, pressure, gravitational and electrostatic potentials, temperature, altitudes, etc.

Charge density field

When charges are distributed in three-dimensional space, we can talk about the density of such a distribution. Charge density is a scalar quantity. Its distribution defines a scalar field and is described by a scalar function.

Density field of bodies

If mass is distributed in space, then there is a mass distribution density. The body density is a scalar function; it defines a scalar field.

Sound wave pressure field

Let a sound wave be distributed in a gas or liquid. Sound waves are transverse waves. As the wave propagates in the gas or liquid, areas of condensation and rarefaction appear. Because the pressure fluctuates. It differs at different points in space. That is, it depends on the position of the point in space. When a scalar quantity, pressure, is distributed in space, its distribution is described by a scalar function. This function specifies a scalar field.

Gravitational potential field - distribution of potential energy

According to the law of universal gravitation, bodies with mass attract each other. And if there is interaction, then there is potential energy of such interaction. The distribution of potential energy is given by a scalar function; this function describes a scalar field and is called the gravitational potential.

Electric potential distribution field

Charges located at a certain distance attract or repel. This means that there is potential energy for their interaction. The energy distribution is described by the potential of a system of charged particles. Electric potential is a scalar function that describes a scalar field.

Types of physical fields of the human body. Their sources

IR radiation of the human body is measured by thermal imagers in the range of 3-10 microns, where it is maximum.

Acoustic fields

The range of self-acoustic radiation is limited on the long-wave side by mechanical vibrations of the surface of the human body (0.01 Hz), on the short-wave side by ultrasonic radiation, in particular, signals with a frequency of about 10 MHz were recorded from the human body.

In order of increasing frequency, the three acoustic field ranges include:

1) low-frequency vibrations (frequencies below 103 Hz);

2) cochlear acoustic emission (CAE) - radiation from the human ear (v ~ 103 Hz);

3) ultrasonic radiation (v ~ 1-10 MHz).

Sources of acoustic fields in different frequency ranges have different natures. Low-frequency radiation is created by physiological processes: respiratory movements, heartbeat, blood flow in blood vessels and some other processes accompanied by vibrations of the surface of the human body in the range of approximately 0.01 - 103 Hz. This radiation in the form of surface vibrations can be recorded by contact or non-contact methods, but it is almost impossible to measure it remotely using microphones. This is due to the fact that acoustic waves coming from deep in the body are almost completely reflected back from the “air-human body” interface and do not go out into the air from the human body. The reflection coefficient of sound waves is close to unity due to the fact that the density of human body tissue is close to the density of water, which is three orders of magnitude higher than the density of air.

All terrestrial vertebrates, however, have a special organ in which good acoustic coordination between the air and the liquid environment is achieved - this is the ear. The middle and inner ear provide almost lossless transmission of sound waves from the air to the receptor cells of the inner ear. Accordingly, in principle, the reverse process is also possible - transmission from the ear to the environment - and it was discovered experimentally using a microphone inserted into the ear canal.

The source of acoustic study of the megahertz range is thermal acoustic radiation - a complete analogue of the corresponding electromagnetic radiation. It arises as a result of the chaotic thermal movement of atoms and molecules of the human body. The intensity of these acoustic waves, like electromagnetic waves, is determined by the absolute temperature of the body. [4]

The nature of biomagnetic fields

Magnetic fields in a living organism can be caused by three reasons. First of all, these are ionic currents arising as a result of the electrical activity of cell membranes (mainly muscle and nerve cells). Another source of magnetic fields is tiny ferromagnetic particles that enter or are specially introduced into the body. These two sources create their own magnetic fields. In addition, when an external magnetic field is applied, inhomogeneities in the magnetic susceptibility of various organs appear, distorting the applied external field.

In the last two cases, the magnetic field is not accompanied by the appearance of an electric one, therefore, when studying the behavior of magnetic particles in the body and the magnetic properties of various organs, only magnetometric methods are applicable. Biocurrents, in addition to magnetic fields, also create a distribution of electrical potentials on the surface of the body. Registration of these potentials has long been used in research and clinical practice - this is electrocardiography, electroencephalography, etc. It would seem that their magnetic analogues, i.e. Magnetocardiography and magnetoencephalography, which record signals from the same electrical processes in the body, will provide almost similar information about the organs being studied. However, as follows from the theory of electromagnetism, the structure of the current source in an electrically conducting medium (organism) and the heterogeneity of this medium itself are reflected significantly differently in the distribution of magnetic and electric fields: (some types of bioelectrical activity manifest themselves predominantly in an electric field, giving a weak magnetic signal , others - on the contrary. Therefore, there are many processes the observation of which magnetographically is preferable.

Magitografiya does not require direct contact with the object, i.e. allows you to take measurements through a bandage or other obstacle. This is not only practically convenient, but also constitutes a fundamental advantage over electrical methods of data recording, since the places where electrodes are attached to the skin can be sources of slowly changing contact potentials. There are no such parasitic interferences with magnetographic methods, and therefore magnetography allows, in particular, to reliably study slowly occurring processes (today with a characteristic time of tens of minutes).

Magnetic fields quickly weaken with distance from the source of activity, as they are a consequence of relatively strong currents in the working organ itself, while surface potentials are determined by weaker and “smeared” currents in the skin. Therefore, magiitography is more convenient for precise determination (localization) of the bridge of bioelectrical activity.

And finally, the magnetic field induction as a vector is characterized not only by its absolute value, but also by its direction, which can also provide additional useful information.

It should not be assumed that electro- and magnetographic methods compete with each other. On the contrary, it is their combination that provides the most complete information about the processes under study. But for each method there are areas where the use of one of them is preferable. [1]

Magnetocardiography

The heart is the strongest source of electric and magnetic fields in the body, so magnetocardiography arose even before the advent of SQUIDS. But only SQUID magnetometers made it possible to obtain magnetocardiograms (MCG) of the same high quality as electrocardiograms. (ECG). In appearance, MCG and ECG signals are very similar, but disturbances in cardiac activity have somewhat different effects on the results of electrical and magnetic measurements. A number of laboratories around the world are currently in the process of accumulating relevant data, which will make it possible to systematize the features of the magnetic manifestations of various heart diseases.

As already mentioned, the advantages of magnetography are most clearly manifested when observing slowly changing and, especially, constant signals. Thus, it was magnetographically that detected constant “damage currents” that occur when a coronary artery is blocked (in experiments on dogs).

Another major success of magnetocardiography is the observation of MCG of the fetus in the mother’s body. The precise localization of the magnetic field in the source area made it possible to separate the fetal signals from the stronger signals of the maternal heart, while the electrical signals were largely mixed due to the spatial smearing of weak surface ECG currents.

Magitografiya allows you to solve another important problem in cardiology - determining blood flow in the heart. If a small external magnetic field is applied, the heart's periodic ejection of blood will produce an alternating magnetic signal, allowing the volume and speed of the moving fluid to be determined.

More recently, a new direction in magnetocardiography has emerged, which is similar to the neuromagnetic measurements discussed below - high-resolution PMC. Its essence lies in a more “closer” study of those intervals of the cardiac cycle when the muscle is calm: at this time, weak magnetic signals that accompany nerve impulses propagating in the heart can be measured. An interesting feature was identified - these systems remain unchanged for approximately 20 cycles, then slightly change shape, again maintaining it for the next 5-10 cycles, etc. It probably contains some information about the nervous processes in the heart. [1]

Neuromagnetic fields

During the functioning of the brain, the basis of which is still largely mysterious, both electric and magnetic fields arise. The strongest signals are generated by spontaneous rhythmic brain activity. Using electroencephalography, these rhythms were classified and a correspondence was established between them and the functional state of the brain (wakefulness, different phases of sleep) or pathological manifestations (for example, an epileptic seizure).

Research has shown that electro- and magnetoencephalograms (EEG and MEG) can be very different. In cardiography, the ECG and MCG signals are very similar. Therefore, the use of SQUID magnetometers is especially promising in brain research.

However, the difference in EEG and MEG is by no means necessary. So, in the alpha rhythm, i.e. oscillations with a frequency of 8-12 Hz, characteristic of a awake person with his eyes closed and

in a quiet state, magnetic and electric fields appear synchronously, i.e. a subject with a greater electrical alpha signal produces a greater magnetic signal. However, such a clear connection was absent in patients with rhythmic activity disorders.

When comparing electro- and magnetoencephalograms, it should be taken into account that, unlike other organs, the brain is almost entirely surrounded by the bone tissue of the skull, and its electrical conductivity is much less than that of the skin and the brain itself. In addition, the natural openings of the skull complicate the paths of electrical current, resulting in the pattern of potentials on the surface of the human head representing a complex superposition of the spatial distributions of signals from fairly distant sources within the brain. The magnetic sensor reacts mainly to stronger currents in the very region of bioelectrical activity, which is also very important, oriented in a certain way relative to the receiving coil of the SQUID magnetometer. This makes magnetographic methods preferable because the greatest research and diagnostic interest is in studying signals from a specific source within the brain - without interference created by other types of activity. Thus, studies of the brain in people suffering from epileptic seizures have shown that magnetography can accurately detect the focus of pathological activity, while the EEG of some patients did not record a spectrum characteristic of epilepsy.

But the advantages of magnetic recording are most clearly manifested in studies of brain responses to various influences through the senses.

A number of laboratories around the world are conducting research on magnetic signals accompanying the brain's responses to tactile, sound and visual stimulation. Already the first results showed that these so-called evoked magnetic fields (EMFs) of the brain have a relatively simple structure and from them it is possible to determine the location of the source of bioelectrical activity in the cerebral cortex. Some HFMF sources can be quite well represented in the form of a current dipole. In response to visual stimulation, a current dipole appears in the occipital part of the head, and in response to auditory stimulation, in the temporal part. In response to stimulation of the little finger of the right hand, a dipole appears perpendicular to the central sulcus of the left hemisphere. This dipole is located in the projection zone of sensitive receptors of various parts of the body, and precisely in the place where, as neurosurgical studies have shown, the “representation” of the little finger is located. With the help of magnetography, it becomes possible, without surgical intervention, to very accurately identify the place in the cerebral cortex where information from the senses arrives and is processed. EEG does not allow such precise determination of the position of the source of bioelectrical activity in the brain.

The comparative simplicity of a number of VMPs makes it possible to conduct reliable neurophysiological experiments with them. For example, magnetic fields in the brain caused by the reaction of a grating of dark and light stripes periodically appearing on an oscilloscope screen were studied. This type of stimulation is very common in studies of visual perception, and its use is associated with modern theoretical ideas about image perception. It turned out that the amplitude of the magnetic signal in this case is greater than, for example, when using a simple flash. By periodically (from eight to twenty times per second) presenting such a grating, one can use the phase lag of the magnetic response to determine the time it takes for the signal to travel along the nerve pathways from the eye to a certain area of the cerebral cortex.

As has been established, the passage of a signal is not a passive process.

In this case, sequential processing of information is carried out in various parts of the brain, and by the time of this “active” delay (t) one can, to one degree or another, judge the nature of this processing.

For most subjects, the delay time for both hemispheres of the brain is the same, but for some people the difference in reaction time between the right and left hemispheres reached 0.1 s! This fact, apparently, may have clinical value, for example, for the early diagnosis of sclerosis.

Accurate measurement of the position of the area of nervous activity that accompanies irritation of a particular sensory organ makes it possible to construct maps of the activity of the cerebral cortex: “somatotopic” for touch, “tonotopic” for hearing, “retinotopic” for vision.

Such maps can serve as the basis for understanding the processes of processing information entering the brain and setting up more complex neurophysiological experiments based on the results obtained. Moreover, studies can be carried out on completely healthy people without any surgical intervention or significant inconvenience for the subject.

Magnetography makes it possible to study processes not only in the cerebral cortex, but also in the deep structures of the brain and not only responses to stimulation of the sensory organs, but also more complex processes.

It is quite possible to create a set of, say, a hundred sensitive elements that simultaneously record magnetic fields at different points around a person’s head. Processing this data on a computer will give a picture of the distribution of field sources throughout the entire volume of the brain. Such a system is in many ways similar to the already existing systems of computed x-ray tomography and NMR introscopy, of which the first gives a complete picture of the distribution of substance density in the brain based on the reconstruction of X-ray absorption data, and the second gives a picture of the distribution of certain chemical substances obtained by nuclear magnetic resonance. . Magnetic methods promise the future of building a three-dimensional picture of the electrical activity of the brain.

Magnetic studies of the brain have actually been carried out for only a few years, but already the first results have shown great promise of the method. Biomagnetism proved to be not only an important part of biological science, but also provided the basis for the development of other applications, ultrasensitive magnetometry.

Along with the transistor and the laser, the brainchild of quantum mechanics, the SQUID once again demonstrates how practical this amazing science, which seemed so abstract in the past, has become. [1]

Infrared radiation

The most vivid information about the distribution of temperatures and the surface of the human body and its changes over time is provided by the method of dynamic infrared thermal imaging. In technical terms, this is a complete analogue of television, only the sensor measures not the optical radiation reflected from the object, which is seen by the human eye, as in television, but its own infrared radiation, invisible to the eye. A thermal imager consists of a scanner that measures thermal radiation in the wavelength range from 3 to 10 microns, a device for data collection and a computer for image processing. Thermal radiation from different parts of the body is sequentially, using oscillating mirrors, projected onto one infrared radiation receiver, cooled with liquid nitrogen. Thermal imagers transmit 16 frames per second. The sensitivity of a thermal imager when measuring one frame is about 0.1 K, but it can be dramatically increased by using a computer for image processing.

Human acoustic fields

The surface of the human body continuously vibrates. These vibrations carry information about many processes inside the body: respiratory movements, heartbeats and the temperature of internal organs.

Low frequency mechanical vibrations

with a frequency below several kilohertz provide information about the functioning of the lungs, heart, and nervous system. The movements of the surface of the human body can be recorded using remote or contact sensors, depending on the task being solved. For example, phonocardiography uses microphones placed on the surface of the body to measure the acoustic noise produced by the heart. Electrical signals from the sensors are amplified and sent to a recording device or computer, and based on their shape and size, conclusions are drawn about the movements of certain parts of the body.

Cochlear acoustic emissions.

Sounds can be emitted from the ear of animals and humans - this phenomenon is called cochlear acoustic emission, since their source is localized in the cochlea (cochlea) of the hearing organ. These sounds can be recorded by a microphone placed in the ear canal. A number of types of cochlear acoustic emission have been discovered, among which the so-called spontaneous emission and acoustic echo stand out.

Spontaneous emission is the spontaneous, continuous emission of sound from a person's ears. The sound pressure level reaches 20 dB, i.e. 10 times higher than the threshold value of 2 • 10 5 Pa, which the human ear is capable of perceiving at a frequency of 1 kHz. Emission frequencies differ from person to person and lie in the range of 0.5-5 kHz; the radiation is highly monochromatic. Emission is observed on average in 25% of men and 50% of women. Spontaneous emission has nothing to do with “ringing in the ears,” a subjective sensation of purely nervous origin.

Cochlear acoustic emission is associated with the activity of the so-called outer hair cells located in the organ of Corti of the cochlea. In response to the incoming sound wave, they change their size and cause mechanical vibrations in the inner ear, which are capable of propagating in the opposite direction and exiting through the middle ear. The biophysical mechanism of rapid changes in cell geometry is still unclear; its speed is a hundred times higher than that of muscles.

Of all the types of cochlear acoustic emission, the phenomenon of acoustic echo—the emission of sounds from the ear some time after a short sound signal is applied to the ear—has so far found application in medicine. It is used to diagnose hearing in newborns in the first few days of life, when conventional audiometric methods cannot be used. The absence of echo is an alarming symptom not only of deafness, but also of lesions of other parts of the central nervous system often associated with it. Early diagnosis allows you to take active measures from the first days of life and significantly reduce the adverse consequences of this disease.

Acoustic radiation in the ultrasonic range.

The human body is a source of thermal acoustic radiation with different frequencies. Typically, acoustic waves come from deep within the body, are reflected from its surface and go back, but a piezoelectric sensor in contact with the body can register them. The peculiarity of acoustic waves propagating in the human body is that the higher the frequency, the more they attenuate. Therefore, only thermal ultrasonic waves of the megahertz range with frequencies no higher than 0.5 - 10 MHz can reach from the depths of the human body from distances of 1 - 10 cm. The intensity of these waves is proportional to the absolute temperature of the body. To measure the intensity of thermal acoustic radiation, a device is used - an acoustothermometer. Using this device, you can, for example, measure the body temperature of a person immersed in water.

A significant area of application of acoustothermography will be the measurement of deep temperature in oncology, during procedures involving the heating of tumors deep in the body using various methods: ultra-high and ultra-high frequencies, ultrasound, laser radiation. Acoustothermography is potentially the only non-invasive method that can provide high spatial resolution in an acceptable measurement time of about one minute. [4]

Conclusion

Human physical fields are currently one of the branches of medical and biological physics. Its most important application is the study of the state of various human organs using passive recording of electromagnetic or acoustic radiation directly from this organ or from any other parts of the body connected to the organ under study by nervous or humoral connections.

Contact measurements of the electric field currently find the greatest application in medicine: in cardiography and electroencephalography. With the help of which it is possible to identify pathologies of the heart and brain.

And magnetocardiograms (MCGs) are of the same high quality as electrocardiograms. Magnetography makes it possible to study processes not only in the cerebral cortex, but also in the deep structures of the brain and not only responses to stimulation of the sensory organs, but also more complex processes. By changing magnetic fields, one can judge the physiological state of muscles, internal organs, skin, and eyes.

Microwave radiometry can currently diagnose malignant tumors of various organs: breast, brain, lungs, metastases, as well as the functional state of the cerebral cortex.

Infrared thermal imaging is a way to evaluate skin blood flow in different areas of the body. By recording the size of areas with reduced temperature, it is possible to determine the severity of the disease, as well as the effectiveness of therapeutic measures. Infrared thermal imaging is used to monitor the development of Raynaud's disease.

Optical glow is not associated with the presence of dirt on the skin and depends on the functional state of the patient, decreasing at rest and increasing with increasing activity.

Acoustic vibrations carry information about many processes inside the body: respiratory movements, heartbeats and the temperature of internal organs.

Low frequency mechanical vibrations

used to measure acoustic noise generated by the heart.

The acoustic echo phenomenon is used to diagnose the hearing of newborns in the first few days of life, when it is impossible to use conventional audiometric methods.

Using an acoustothermometer device, you can, for example, measure the body temperature of a person immersed in water. A significant area of application of acoustothermography will be the measurement of deep temperature in oncology, during procedures involving the heating of tumors deep in the body using various methods: ultra-high and ultra-high frequencies, ultrasound, laser radiation.

Thus, to summarize, we can say that the study of changes in human physical fields is very important for the diagnosis of many diseases.

Bibliography

1. Godik E.E., Gulyaev Yu.V. Physical fields of humans and animals // In the world of science. - 1990. - No. 5. — P.75-83.

2. Gulyaev Yu.V., Godik E.E., Petrov A.V., Taratorin A.M. On the possibilities of remote functional diagnostics of biological objects using their own infrared radiation // Dokl. Academy of Sciences of the USSR. - 1984. - T.277, - No. 6. — P.1486-1491

3. Miroshnikov M.M. Theoretical foundations of optical-electronic devices, 1983.

4. Antonov V.F., Chernysh A.M., Voznesensky S.A., Kozlova E.K., 2000.

Introduction

Around any body there are various physical fields determined by the processes occurring inside it. In this sense, humans are no exception. The physical fields that the body generates during its functioning are called the human body’s own physical fields. [4]

Numerous physical methods for studying the human body, using registration of a person’s own physical fields, make it possible to obtain information about processes in the body that cannot be obtained by other means.

Scientists are not interested in the physical fields of biological objects themselves, but in the possibility of transferring information related to the functioning of internal organs through these channels. The study of the physical fields of biological objects is methodologically very close to passive remote sensing of the Earth, atmosphere, etc. Much experience has been accumulated in the use of such methods. There is no need to explain how important information they provide about the structure and functioning of an object. Due to the non-stationary nature of biological objects, it is necessary to record signals through many channels simultaneously, including electrophysiological control. To obtain the spatial structure of the field in each channel, it is necessary to use matrix or scanning antennas. The equipment must be fast enough to be able to record signals dynamically, i.e. faster than the state of the object changes. Almost all channels require careful shielding from interference.

The task is not to develop fundamentally new equipment, but to use modern remote sensing technology to study biological objects and, most importantly, to create a methodology for such research. [1]

Since a biological object is a complex receiving system, the problem of studying physical fields arises. The solution to this problem is possible only on the basis of close cooperation between physiologists, biophysicists, psychologists, doctors, as well as specialists from industry organizations developing measuring equipment.

The problem of systematic research of the physical fields of biological objects was posed at the Institute of Radio Engineering and Electronics of the Russian Academy of Sciences by Yu.V. Gulyaev and E.E. A year old.

Types of physical fields of the human body. Their sources

There are electromagnetic and acoustic fields around a person (the gravitational field and elementary particles remain beyond the scope of our consideration).

We can distinguish the main 4 ranges of electromagnetic radiation and 3 ranges of acoustic radiation in which research is currently being conducted. [4]

Electromagnetic fields

The range of its own electromagnetic radiation is limited on the short wavelength side by optical radiation; shorter wavelength radiation - including x-rays and γ-quanta - has not been recorded. On the long wave side, the range can be limited to radio waves with a length of about 60 cm. In order of increasing frequency, the four ranges of the electromagnetic field, presented in Fig. 12.1, include:

1) low-frequency electric (E) and magnetic (B) fields (frequencies below 103 Hz);

2) radio waves of ultra-high frequencies (microwave) (frequencies 109 - 1010 Hz and wavelength outside the body 3-60 cm);

3) infrared (IR) radiation (frequency 1014 Hz, wavelength 3-10 µm);

4) optical radiation (frequency 1015 Hz, wavelength about 0.5 μm).

This choice of ranges is determined not by the technical capabilities of modern electronics, but by the characteristics of biological objects and assessments of the information content of various ranges for medicine. The characteristic parameters of various electromagnetic fields created by the human body are given in Table 12.1

The sources of electromagnetic fields are different in different frequency ranges. Low-frequency fields are created mainly during the course of physiological processes accompanied by electrical activity of organs: intestines (~1 min), heart (characteristic process time of the order of 1 s), brain (-0.1 s), nerve fibers (-10 ms). The spectrum of frequencies corresponding to these processes is limited from above by values not exceeding ~1 kHz.

In the microwave and IR ranges, the source of physical fields is thermal electromagnetic radiation.

To estimate the intensity of electromagnetic radiation at different wavelengths, the human body, as a radiator, can be modeled with sufficient accuracy by a completely black body, which, as is known, absorbs all radiation incident on it and therefore has maximum emissivity.

Emissivity

body - the amount of energy emitted by a unit surface of a body per unit time in a unit wavelength interval in all directions - depends on the wavelength
X
and the absolute temperature of the body T.

IR radiation of the human body is measured by thermal imagers in the range of 3-10 microns, where it is maximum.

Acoustic fields

In order of increasing frequency, the three acoustic field ranges include:

1) low-frequency vibrations (frequencies below 103 Hz);

2) cochlear acoustic emission (CAE) - radiation from the human ear (v ~ 103 Hz);

3) ultrasonic radiation (v ~ 1-10 MHz).

The source of acoustic study of the megahertz range is thermal acoustic radiation - a complete analogue of the corresponding electromagnetic radiation. It arose

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Examples of vector fields

These are fields of distribution of vector quantities - forces, velocities, etc.

Gravitational force field

The force of universal gravitation is a vector, which means the field describing the gravitational attraction of bodies will be vector.

Fluid flow velocity field

When a fluid flows, some parts of the fluid move faster than others. This means that the speeds of the liquid particles differ. The distribution of flow particle velocities can be described by a field. Velocity is a vector, which means that the field of fluid flow velocities is a vector field.

Field of Coulomb forces

We know that charges at rest attract or repel due to Coulomb forces. The forces of such interaction are distributed in space and set the field. This is an electrostatic field, it is a vector field of tension.

Magnetic force field

Moving charges interact due to magnetic fields. Magnetic field induction describes how the force of interaction changes in space. Therefore, the magnetic field induction is a vector function that specifies the vector magnetic field.

Note: Essentially, magnetic field induction is the force exerted on a moving charge by other moving charges.

Electric field strength

Electric field strength is the second most important term in the theory of electricity after electric charge. If a natural scientist knows everything about at least these two concepts, he will be able to conduct simple experiments with electricity and support them with knowledge from an elementary physics course.

Tension is the force acting on a single static charge. Based on generally accepted standards, we can say that the electric field strength is denoted by the symbol E. It is worth noting that the intensity is a vector quantity, and the electric charge is a scalar quantity.

Article - magnetic field strength.

Electric field strength

conclusions

All quantities we measure can be divided into scalar ones, which have no direction, and vector ones, which have a direction.
The field of a physical quantity is said to be given when this quantity is distributed in space.
Not only scalar quantities, but also vector quantities can be distributed in space.
If a scalar quantity is distributed in space, then the field is called scalar, and if it is a vector quantity, then the field is called vector.
A field is stationary if it does not change over time. And if it changes, then the field is non-stationary.
People may not sense all fields. But the field can be detected using bodies or instruments sensitive to these fields. For example, an electric field can be detected by its effect on charges.
It is convenient to depict fields in the figures using special lines. It is convenient to denote scalar fields using level lines.
Vector fields are depicted using lines along which vectors distributed in space are directed. Such lines are called lines of force, field strength lines, field induction lines.
Vector and scalar fields can be linked. To do this, you can use a special vector - the gradient vector.
A homogeneous field at every point in space has the same distributed value. Homogeneous force fields are depicted by straight lines, the distance between which is maintained.
A non-uniform field at different points in space has different values of the distributed magnitude. Inhomogeneous fields are depicted by curved lines, the distance between them varies.
The denser the field lines are in any area, the greater its value in that area.

Ordinary fields describing ordinary things

The field Z(x,t) can represent many different physical quantities.
For example: • The height of a rope stretched across a room. • The height of the water in the river. • Density of the crystal or gas. • Position of atoms in a magnet. • Wind speed. • Temperature, density or air pressure. In any of these cases, there is a field Z(x,t): height field, density field, orientation field, wind field, temperature field. Its value as a function of space and time tells us the height, density, orientation, wind speed or temperature of some medium - a rope, a river, a crystal, a gas, a magnet, air - in all places at any given time. His equation of motion shows how Z(x,t) could in principle behave. It also shows how to predict the behavior of Z(x,t) in the future, if we know exactly its behavior in the present and past.

In each example there is a field and a medium, and we should not confuse the field with the medium. The field simply describes and characterizes one of the many properties of the corresponding environment. Completely different media can have very similar behaving fields with very similar waves - we will see this later.

Let me once again clarify a point that often causes misunderstanding. In general, the field may have nothing to do with physical distance in space. Yes, in articles 3 and 4 I used the example of an ox on a rope to illustrate what Z(x,t) could be because it is nice and intuitive. I also often plotted Z(x,t) for waves. This may give you the false impression that Z(x,t) is always associated with waves that cause a physical object (such as a rope) to move a distance Z in a direction perpendicular to the x axis. But this is not so, as three of our four examples will demonstrate to us.