Ultradźwięki

Please prepare the answers to the following questions.

1. What is a soundsoundsound wave?

2. List the properties of sounds.

3. What is the audibility area?

Do animals hear ultrasoundsultrasoundsultrasounds?

Some animals can hear ultrasoundsultrasoundsultrasounds and some animals even emit them and use as echolocation. Dogs, mice and rats can hear up to 40 kHz. On the other hand, dolphins and bats emit ultrasounds – echolocation.

How are the sounds generated?

Generation of ultrasound often takes place using variable voltage. This stimulates the quartz plate for resonance vibrations.

Describe the basic parameters associated with ultrasoundsultrasoundsultrasounds.

Ultrasounds parameters:

• The frequencyfrequencyfrequency of waves (f) is constant for a given generator and does not change when waves pass through different media.

• In the diagnostics, waves with frequencies of 1 to 15 MHz are used and in therapy the frequencyfrequencyfrequency range is from 0,8 MHz to 2,4 MHz.

• Ultrasonic waves velocity is different in various media: in the air it is ~ 340 $\frac{m}{s}$, in water 1500 $\frac{m}{s}$, in skull bones 3400 $\frac{m}{s}$, in fat tissue 1440 $\frac{m}{s}$, in muscles 1580 $\frac{m}{s}$.

• The ultrasonic wavelengthwavelengthwavelength depends on the frequency and speed of the wave spreading $\lambda =\frac{v}{f}$.

• The intensity of the wave decreases with the distance from the source, and the faster the higher the frequency, the shorter the wavelength.

Indicate the basic properties of ultrasounds.

Properties of ultrasoundsultrasoundsultrasounds

• Due to the low wavelength, ultrasounds are quickly suppressedsuppressedsuppressed in the air, but they spread very well in water.

• They strongly reflect on the border between two media.

• They can be easily and precisely focused, creating a thin beam (ray).

• High‑intensity ultrasounds can destroy or heat objects by which they are absorbed.

Application of ultrasounds.

UltrasoundsultrasoundsUltrasounds have found numerous applications in various areas of life.

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Prezentacja slajdów – własności i zastosowanie ultradźwięków. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).

Prezentacja slajdów – własności i zastosowanie ultradźwięków. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).

Zasób interaktywny dostępny pod adresem https://zpe.gov.pl/a/Dsci6ddoc

Ultrasonography (USG)

Ultrasonography (USG) is the most well‑known example of the application of ultrasounds in medicine. The wave is reflected on the border between two media. These media differ in their density and the speed of soundsoundsound propagation. Because various organs in the human body have different densities, the ultrasound wave is reflected partly from the media boundaries and it is recorded by the probe. The wave penetrates the body further and it is again partially reflected from the other border. The resulting reflected impulses are recorded and give an image of the internal structure of the human body.

Many people wonder why the gel lubricates the skin surface before ultrasonography is used. The reason for applying the gel is that in the air the wave spreads at a completely different speed than in the skin and would be very strongly reflected from the surface of the skin. The velocity of soundsoundsound spreading in the gel is similar to the speed obtained in the skin, the reflectionreflectionreflection is negligible and the wave can go deep into the body. It is worth noting that the frequencyfrequencyfrequency of vibrations while passing through different media does not change. However, the wavelength associated with the speed at which the wave propagates in a given environment changes.

What physical and physiological effects cause ultrasounds?

UltrasoundsultrasoundsUltrasounds create interesting physical and physiological effects: for example, liquids that do not mix with each other, subjected to ultrasounds, create emulsions (e.g. water and mercury) within a few minutes. A thermometer dipped in oil, in which ultrasonic waves propagate, cannot be touched by hand, because it is possible to scald under the influence of ultrasounds, even though the thermometer shows a low temperature. Ultrasounds kill microbes and some smaller animals, such as frogs and fish. It is worth to recall a certain curiosity of nature: bats respond to frequencies up to 100 kHz, and in addition they use ultrasounds to determine the position of the barrier. They send ultrasonic pulses with a frequency of 35 to 70 kHz and a duration of $\frac{1}{100}s$, and then they listen to impulses reflected from the barrier. From the time delay (similar to the usage of the radar), the bats assess the position of the barrier. Studying similar „apparatus” in living nature for their use in technology, is the subject of a new science - bionics.

Summary

Ultrasounds - soundsoundsound waves whose the frequencyfrequencyfrequency is too high for a man to hear. The frequency of 20 kHz is considered to be the upper limit of audible frequencies, at the same time the lower limit of ultrasound, although for many people the limit is much lower.

The frequency of 1 GHz is assumed to be the conventional upper limit of ultrasounds. Some animals, such as dogs, rats, dolphins, whales, hamsters or bats can emit and hear ultrasounds.

Thanks to the short wavelength ultrasounds allow to obtain detailed images of objects. The device that allows observation of deep sea is sonar. It is used to locate all objects submerged in water. Sonars were used in submarines.

UltrasoundsultrasoundsUltrasounds are also used in medicine. The image of internal organs can be obtained using a device that generates and registers ultrasound waves (ultrasound scannerultrasound scannerultrasound scanner).

Exercises

Glossary

Keywords

audibility of the soundaudibility of the soundaudibility of the sound

reflectionreflectionreflection

soundsoundsound

ultrasoundsultrasoundsultrasounds

wavelengthwavelengthwavelength