Function and harm of ultrasonic and infrasound

A series of mechanical, thermal, electromagnetic and chemical ultrasonic effects, including the following four effects:

① Mechanical effect. The mechanical action of ultrasonic wave can promote the emulsification and coagulation of liquid.

Liquefaction of glue and dispersion of solid. When a standing wave is formed in an ultrasonic fluid medium,

Due to the action of mechanical force, tiny particles suspended in the fluid condense at the nodes,

Form a periodic accumulation in space. Application of ultrasonic wave in piezoelectric materials and magnetostrictive materials

When propagating in materials, ultrasonic waves and

Induced magnetization (see dielectric physics and magnetostriction).

② Cavitation. When ultrasonic wave acts on liquid, it will produce a large number of small bubbles.

One reason is that the local tensile stress in the liquid forms negative pressure and the pressure decreases.

The gas initially dissolved in the liquid is supersaturated and escapes from the liquid into small bubbles.

Another reason is that the strong tensile stress "tears" the liquid into a cavity, which is called a void.

Change. The cavity is filled with liquid vapor or another gas dissolved in the liquid, and may even

It's vacuum. The small bubbles formed by cavitation will not change with the vibration of the surrounding medium.

Don't move, grow up or suddenly explode. When it bursts, the surrounding liquid will suddenly turn into bubbles.

High temperature and high pressure are generated, and shock waves are generated at the same time. Internal friction with cavitation

Friction will form charges and generate luminescence due to the discharge in bubbles. In liquid

Ultrasonic treatment technology is mostly related to cavitation.

③ Thermal effect. Because of the high frequency and high energy of ultrasound, when it is absorbed by the medium,

Will produce a significant thermal effect.

④ Chemical action. The action of ultrasound can promote or accelerate some chemical reactions.

Reaction. For example, pure distilled water generates hydrogen peroxide after ultrasonic treatment; dissolved nitrogen

Nitrous acid is produced after ultrasonic treatment of gas and water; The aqueous solution of dye is treated by ultrasonic wave.

Then it will change color or fade. These phenomena are always accompanied by cavitation. exceed

Sound waves can also accelerate the hydrolysis, decomposition and polymerization of many chemicals. ultrasound

Wave also has obvious influence on photochemical and electrochemical processes. Various amino acids and others

After ultrasonic treatment, the characteristic absorption band disappears and appears.

Uniform general absorption, which shows that cavitation has changed the molecular structure.

Ultrasonic application Ultrasonic effect has been widely used in practice, mainly in the following aspects.

Face:

① Ultrasonic examination. The wavelength of ultrasonic wave is shorter than ordinary sound wave, and its performance is better.

Directional, and can penetrate opaque substances, this characteristic has been widely used.

Ultrasonic flaw detection, thickness measurement, distance measurement, remote control and ultrasonic imaging technology.

Ultrasonic imaging is a technology that uses ultrasonic waves to present the internal image of opaque objects.

Ultrasonic waves emitted from the transducer are focused on an opaque sample through an acoustic lens, and the ultrasonic waves emitted from the transducer

Ultrasonic waves from the sample carry information of the irradiated part (such as reflection of sound waves,

The ability of absorption and scattering), through the acoustic lens on the piezoelectric receiver.

Electrical signals are input into the amplifier, and opaque samples can be visualized by using a scanning system.

Displayed on the screen. The device above is called an ultrasonic microscope. Ultrasonic imaging technology has

Widely used in medical examination and microelectronic device manufacturing.

Large scale integrated circuits are examined and used to display alloys in materials science.

Regions with different compositions and grain boundaries, etc.

Acoustic holography uses the interference principle of ultrasonic waves to record and reproduce opaque objects.

The principle of acoustic imaging technology for stereo images is basically the same as that of light wave holography.

Only the recording method is different (see hologram). Excited by the same ultrasonic signal source

Two transducers placed in liquid are excited to emit two coherent ultrasonic beams respectively.

Sound wave: one beam becomes an object wave after passing through the object under study, and the other beam is used as a reference.

Wave. The object wave and reference wave are coherently superimposed on the liquid surface to form an acoustic hologram, which is generated by laser.

Using the diffraction generated when the laser is reflected on the acoustic hologram, the beam illuminates the acoustic hologram.

The reproduced image of the object obtained through the effect is usually observed in real time through the camera and TV set.

② Ultrasound therapy. Using the mechanical effect, cavitation effect and thermal effect of ultrasonic wave

Can be used for ultrasonic welding, drilling, solid crushing, emulsification,

Degassing, dust removal, boiler scale removal, cleaning, sterilization, chemical reaction promotion and sterilization.

Biological research and so on. , has been widely used in industry, mining, agriculture, medical and other departments.

Apply.

③ Basic research. After ultrasonic waves act on the medium, acoustic relaxation occurs in the medium.

Relaxation process, acoustic relaxation process is accompanied by the transfer of energy between various degrees of molecules.

Process, and shows the absorption of sound waves from a macro perspective (see sound waves). Through matter

The absorption law of ultrasonic wave can explore the characteristics and structure of matter, as well as the research in this respect.

It constitutes a branch of molecular acoustics.

The wavelength of ordinary sound waves is longer than the atomic spacing in solids. In this case,

Solid can be regarded as a continuous medium. However, for ultrasonic waves with frequencies above 10 12 Hz,

Wavelength can be compared with the atomic spacing in solids, which must be regarded as

It has a lattice structure with spatial periodicity. The energy of lattice vibration is quantized,

Called phonons (see solid state physics). The influence of ultrasound on solids can be summarized as follows.

Interaction of ultrasonic waves with thermal phonons, electrons, photons and various quasiparticles. correct

The generation, detection and propagation of ultrasonic waves in solid and quantum liquids are studied.

The study of sound phenomena in liquid helium constitutes a new field of modern acoustics.

Quantum acoustics.

& lt harm >:

The frequency of ultrasonic waves is as high as 20,000 Hz or more (more than 20,000 vibrations per second). Because of its high frequency, it has the following characteristics: (a) good directivity and almost linear propagation; (b) Strong penetration ability, which can penetrate many substances that cannot be penetrated by electromagnetic waves; (c) When propagating in the medium, it can generate great force, which can be used for cutting and drilling hard materials, and can also be used for cleaning and disinfection. We are familiar with the application of ultrasound, which is commonly used in hospitals. It emits ultrasonic waves into the human body, and judges whether there are abnormalities according to the changes of the transmission and reflection ability of human tissues to ultrasonic waves, such as pathological examination of human organs and calculus examination. It has the advantages of no harm to human body, simplicity and quickness.

Infrasound, also known as infrasound, is a low-frequency wave with a frequency below 20Hz. Many natural disasters, such as earthquakes, volcanic eruptions and tornadoes. And emits infrasound before infrasound occurs. Infrasound waves can cause harm to human body, causing symptoms such as headache, vomiting and dyspnea. In 1930s, an American physicist did an experiment: he brought an infrasound generator into the theater, turned it on quietly after the performance, and then sat in his box to observe the movement. I saw the audience sitting around the infrasound wave have a panic and puzzled expression, which quickly spread to the whole theater. Infrasound waves have the characteristics of wide source, long propagation and strong penetration. Scientists use it to predict typhoons and study the atmospheric structure. Militarily, infrasound waves can be used to detect nuclear explosions in the atmosphere, track missiles and so on.

1890, a sailboat named "Marpolo" suddenly disappeared mysteriously on the way from New Zealand to England. Twenty years later, it was found off the coast of Tierra del Fuego. Strangely, all the sails on the ship are intact. The handwriting in the captain's diary is still legible. Even those crew members who have been dead for many years are "in their positions" and maintain the "posture" when they were on the job;

At the beginning of 1948, a Dutch cargo ship passed through the Straits of Malacca and was caught in a storm. All the sailors died inexplicably. At the entrance to the Boradeli Cave in Hungary, three tourists suddenly fell to the ground and stopped breathing. ......

The above tragedy has aroused widespread concern among scientists, and many scientists have also conducted long-term research on the cause of death of crew members. As for the tragedy at the beginning of this article, how did the crew die? Did you die of skyfire or lightning? No, because there are no signs of burning on the ship; Did you die by the pirate's sword? Don't! The remains of the victims showed signs of fighting before their death; Did you die of hunger and thirst? Not really! There was enough food and fresh water on board. As for the second and third tragedies mentioned above, is it suicide or homicide? What was the cause of death? Who is the murderer? The test results showed that no scars were found on all the victims and there were no signs of poisoning. Obviously, the theory of murder or suicide is no longer valid. So, did the sudden attack of cardiovascular and cerebrovascular diseases such as He Yi kill them? The autopsy report of the forensic doctor shows that the deceased were all strong before his death!

After repeated investigations, it was finally found that the "murderer" who caused the above tragedy was a kind of infrasound that people didn't know much about. Infrasound is a kind of sound wave that vibrates very little every second and can't be heard by human ears. The frequency of infrasound is very low, generally below 20 MHz, but the wavelength is very long and the propagation distance is very long. It travels farther than ordinary sound waves, light waves and radio waves. Such as frequency below 6544. Can spread to thousands or even tens of thousands of kilometers away. 1960, a major earthquake occurred in Chile, South America, and infrasound waves generated during the earthquake spread to all corners of the world! 196 1 year, the Soviet union conducted a nuclear explosion in the arctic circle, and the infrasound waves produced actually turned around the earth for five times before disappearing!

Infrasound waves have strong penetrating power, which can not only penetrate the atmosphere, seawater and soil, but also penetrate solid reinforced concrete buildings, even tanks, warships, submarines and airplanes. Infrasound can not only cause dizziness, irritability, tinnitus, nausea, palpitation, blurred vision, dysphagia, stomachache, liver dysfunction, numbness of limbs, but also damage the brain and nervous system.

Why can infrasound cause death?

It turns out that the natural vibration frequency of human internal organs is similar to infrasound frequency (0.0 1 ~ 20 Hz). If the external infrasound frequency is close to or the same as the vibration frequency of internal organs, it will cause "* * * vibration" of human internal organs, thus causing a series of symptoms such as dizziness, irritability, tinnitus and nausea. It is mentioned above, especially when the natural vibration frequency of human abdominal cavity and chest cavity is close to the external infrasound. It is more likely to cause * * * vibration of human internal organs, resulting in damage to human internal organs and death. The tragedy that happened in the Straits of Malacca mentioned at the beginning is because the cargo ship happened to encounter a storm at sea when approaching the Straits. The storm rubs against the waves, producing infrasound waves. Infrasound waves make people's heart and other internal organs vibrate and beat violently, leading to blood vessel rupture and eventually death.

Although infrasound is invisible, it is always produced, threatening the safety of human beings. In nature, such as solar magnetic storm, strait roar, thunder and lightning, sudden change of air pressure; In the factory, mechanical shock and friction; Military atomic bomb, hydrogen bomb explosion test, etc. Can produce infrasound waves.

Due to the strong penetration of infrasound, the International Maritime Rescue Organization has set up "infrasound positioning stations" on some islands far from the mainland to monitor the tidal ocean surface. Once a ship or plane is wrecked and attached to the sea, its position can be quickly determined and rescue can be carried out.

In recent years, some countries have devoted themselves to the development of infrasonic weapons-infrasonic bombs, which are still in the development stage, but scientists predict that; As long as the infrasonic bomb explodes, in an instant, everyone on the ground in Fiona Fang for more than ten kilometers will be killed, and no one will be spared. Infrasound weapons can penetrate 15 cm of concrete and tank steel plates. Even if people hide in bomb shelters or get into the "belly" of tanks, they are still doomed to be disabled. Infrasound bombs, like neutron bombs, only kill creatures and do not destroy buildings. But compared with the two,