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The technical name for one expansion and one compression of the medium, passing through a fixed point, is Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum cycle. Thus, a vibration rate of 50 cycles per second produces 50 expansions and 50 compressions each second at a given point. The term frequency designates the number of cycles per unit of time that a sound wave vibrates. One cycle per second is called a hertz and is abbreviated Hz. Other useful units of scale in ultrasonics are kilohertz (kHz), 1,000 Hz; and megahertz (MHz), meaning 1,000,000 Hz or 1,000 kHz.

Most people can only hear frequencies of sound that fall between about 16 and 16,000 Hz. Ultrasonics is concerned with sound waves with frequencies greater than the human hearing range. Some insects can produce ultrasound with frequencies as high as 40 kHz. Small animals such as cats and dogs hear frequencies of up to 30 kHz, and bats are known to detect Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum of up to 100 Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum. Sound waves of several megahertz frequency are common in various technological applications such as medical imaging.

A sound wave that causes compressions and expansions of the molecules in the medium surrounding it as it propagates is called a longitudinal wave. The distance from one compression to the next is known as the wavelength of the sound wave. Sound waves with long wavelengths pass over small objects in much the Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum way Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum ocean waves pass over small objects.

Sound waves with short wavelengths, on the other hand, tend to be diffracted or scattered by objects comparable to them in size. The mbti estj velocity of a sound wave is obtained by multiplying the frequency of the sound wave by its wavelength. Thus, if the wavelength and frequency of the sound wave in a given medium are known, its velocity can also be calculated.

The sound velocities in a variety of materials are shown in Table 1. Since ultrasonic waves have high frequencies, they have short wavelengths. As a result, ultrasonic waves can be focused in narrow, straight beams. In order to duplicate Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum frequencies, humans have harnessed the electrical properties of materials. When a specially cut piezoelectric quartz crystal is compressed, the crystal becomes electrically charged and an electric current is generated: the greater jim johnson pressure, the greater the electric current.

If the crystal is suddenly stretched rather than beingcompressed, the direction of the current will reverse itself. Alternately compressing and stretching the crystal has the effect of producing an alternating current. It follows that by applying an alternating current that matches the natural frequency of the crystal, the crystal can be made to expand and contract with the alternating current.

When such a current is applied to the crystal, ultrasonic waves are produced. Depending on which way the crystal is cut, the waves can be focused along the direction of ultrasound propagation or at right angles to the direction of propagation.

Waves that travel along the direction of propagation are called longitudinal waves; as noted above, these waves travel in what is dna direction in which molecules in the surrounding medium move back and forth.

Waves that travel at right angles to the propagation direction are called transverse waves; the molecules in the surrounding medium move up and down with respect to the direction that the waves propagate. Ultrasound waves can also propagate as surface waves; in this case, molecules in the surrounding medium experience up-and-down motion as well as expanding and contracting motion. In most applications, ultrasonic waves are generated by a transducer that includes a piezoelectric crystal that converts electrical energy (electric current) to mechanical energy (sound waves).

These sound wavesare reflected and return to the transducer as echoes and are converted back to electrical signals by the same transducer or Diphtheria and Tetanus Toxoids (Diphtheria and Tetanus)- Multum a separate one.

Alternately, one can generate ultrasonic waves by means of magnetostriction (from magneto, meaning magnetic, and strictio, meaning drawing together. Ultrasound may also be produced by a whistle or siren-type generator. In this method, gas or liquid streams are passed through a resonant cavity or reflector with the result that ultrasonic vibrations characteristic of the particular gas or liquid are produced. There are literally dozens of ways that people have already found to make use of ultrasound.

The technique is used in a process called ultrasonic scrubbing, by which particulate matter is coagulated in smokestacks before it pollutes the atmosphere. Coagulation has also been used at airports to disperse fog and mist.

The water droplets are propelled into a chamber where they are mixed with air, and a mist of air and water leaves the humidifier and enters the shanghai johnson to be humidified.

Two liquids that do not ordinarily mix, i. Such mixtures are called dispersions. With this technique, alloys of aluminum and lead, iron and lead, and aluminum and cadmium can be mixed as liquids-and kept mixed-until they solidify.

This technique is known as ultrasonic dispersion. It is also used to produce stable and consistent photographic emulsions. Ultrasonic waves can be used to break up fat globules in milk, so that the fat mixes with the milk (homogenization).

In addition, pasteurization, the removal of harmful bacteria and microorganisms, is sometimes done ultrasonically.



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