Ultrasound

God gives us five senses to feel this world such as : sight, hearing, smell, taste and touch. We have ears to listen to the sound around us. Do you know that our ears can listen to the sound of some specific frequencies but not of all the frequencies. This is called audible sound and it ranges from 20 Hz to 20 KHz. The human ear cannot hear noises that are below or above this range. Sound greater than 20 KHz is known as ultrasound. Animals like moths, beetles, or bats use the ultrasound to communicate and detect obstructions in their way. There are a number of real life applications of the ultrasound. Let's learn more about ultrasound technology and its uses in detail.

Table of content

• Ultrasound
• Application of ultrasound
• Practice problems
• FAQs

Ultrasound

Ultrasounds are the sound waves with frequencies higher than what the human ear can detect. Simply put, an ultrasound is a sound that has a frequency higher than 20 kHz or 20,000 Hz, or higher than the highest audible frequency (i.e., 20 kHz). Although it is possible to produce ultrasound of frequencies up to a few gigahertz, we are unable to detect them. The physical characteristics of ultrasound are similar to the audible sound.

Fig: the sound with frequency ranges in log scale

Some living beings like bats use a variety of ultrasonic range (echolocation) mechanisms to locate their prey, and as a result, they are able to detect frequencies up to 200 kHz. Like dolphins, toothed whales produce ultrasounds that they utilise to find their way through the water and catch prey. The scientist uses the ultrasounds in a variety of fields, including medicine, communication, navigation, testing, cleaning, detection, ranging, and mixing. Lets see some of the applications of ultrasound.

Application of ultrasound

Ultrasound is used in various fields. Nowadays, the use of ultrasounds in everything from the medical field to military applications, has become standard practice in our life.

1. Applications of ultrasound in medical field

• Ultrasonography : Medical ultrasounds are diagnostic imaging procedures based on ultrasound imaging that are typically performed in hospitals and diagnostic clinics. Finding the affected place is made easier by obtaining an image of the body's interior structures, such as muscles, joints, and internal organs. With the aid of a probe, ultrasonic pulses are delivered to the tissue. Each sound that strikes a tissue reflects, and the sounds that reflect off of various tissues reflect at different angles, allowing us to distinguish between them. These audio echoes produced by these tissues are captured and shown to the professional as visuals.

• Lithotripsy : Originally, kidney stones had to be removed surgically, but with the use of ultrasonic waves, the stones can be broken down naturally without the need for any invasive surgery. In this way, the body is not seriously injured while high-energy waves that break the stones into dust or smaller sizes can be done which can pass through the body without damaging. These pieces can subsequently be removed from the body by the urinary tract.

• Echocardiography : To assess a patient's heart condition, specialists use echocardiography. In this procedure, ultrasound waves are used to obtain a picture of the heart utilising the methods of ultrasound detection and reflection from various locations from the heart.

2. Applications in engineering field

• UIT : To improve the mechanical and physical qualities of metals, ultrasounds are employed in a process called ultrasonic impact treatment (UIT). The procedure involves metal working. This method involves bombarding a metal item with ultrasonic waves. Such treatment can also refine the grains, reduce grain size, and produce controlled residual compressive stress. Stress corrosion cracking, corrosion fatigue, and other related problems have all been addressed with UIT.

• Cracks Detection : Large metallic components used to build large constructions like bridges and buildings. Ultrasounds can be used to detect cracks using sophisticated equipment. A skilled specialist uses analytic software to identify and categorise the defects in the components of these buildings by interpreting the ultrasonic waves.

3. Application in defence

• SONAR : SONAR stands for Sound Navigation and ranging. It is a tool used for communication, navigation, and detection below the surface of the sea. In this method, sound or ultrasound pulses are sent out, and the time it takes for them to bounce off a target item and return to the source is recorded. So, using SONAR, it is possible to effectively follow that object's motion and determine its exact location. Submarines under the ocean, lost ships, aircraft crashes, and explosive mines can all be found and tracked with its assistance.

4. Cleaning 

• The electronic components of big machines and spiral tubes etc. are difficult to clean. These gadgets use ultrasonic waves to clean things. The object to be cleaned is submerged in a solution containing the proper cleaning agent while being subjected to ultrasonic waves. The filth and grease separate from the surface as a result of the creation of these high-frequency waves. The production of these high-frequency waves causes the dirt and dust to separate from the surface.

5. Echolocation 

• Echolocation is the method of identifying objects in space by using sound waves and echoes. Bats use echolocation to navigate across their environment and detect obstacles or find food at night. The mouth and nose of bats both produce ultrasound-frequency sound waves. Echoes are created when these sound waves hit nearby objects and reflect. The bats then find these echoes, which aids them in determining the size, form, and proximity of the object. Ultrasonic echolocation is now frequently employed in assembly-line sorting and counting of objects as well as in traffic control applications.

Practice problems

Q1. Ultrasonic waves are used by SONAR (sound navigation and ranging) devices to find and detect underwater objects. The interval between the creation of a probe wave and the receiving of its echo following reflection from an adversarial submarine is found to be 50.0 s. How far away is the enemy submarine? (Speed of sound in water is 1450 m/s)

A. Given, transmission to receiving, the lag time t_lag = 50.0 s
So, time take to reach the the submarine $t=\frac{1}{2}\times 50.0 s=25 s$
The speed of sound in water, $v=1450 m/s$
The distance of the enemy marine is , $d=v\times t$

$$\begin{gathered} d=1450\times 25 \\ d=36250 km \\ d=36.25 km \end{gathered}$$

Hence enemy marine is 36.25 km away.

Q2. An ultrasound wave of wavelength of 0.5 cm is transmitting in the air with the speed of 330 m/s. What is the frequency of the ultrasound wave?

A. Given =0.5 cm=0.005 m

v = 330 m/s

The frequency of the wave can be find as,

$$\begin{gathered} v=f\times \lambda \\ 330=f\times 0.005 \\ f=66000 Hz \\ f=66 kHz \end{gathered}$$

The frequency of the ultrasound wave is 66 kHz.

Q3. What is ultrasound ?

A. A sound wave with a frequency greater than 20 kHz is referred to as an ultrasound. These are sound waves that are louder than the human's upper auditory range.

Q4 What are the applications of ultrasound sensors?

A. Since ultrasound sensors can cover a large area from a single location, they are frequently employed as automated door openers. The door is opened when the ultrasonic sensors recognise footsteps. Detecting robbers, criminals, and invaders is another application for ultrasonic sensors. There are many military and medical uses for ultrasound sensors, including the development of non-contact sensors that can seek the target from a distance and then hit the target.

Q5. How is ultrasound used in therapies ?

A. Ultrasound is used in many therapeutic applications which are very helpful. Hard deposits or tissue are broken apart using the high power of ultrasound. This aids in assessing the elasticity of tissue and speeds up the effects of medications where they are needed. Cells or microscopic particles are frequently sorted using ultrasounds for scientific purposes.

FAQs

Q1. What is the upper limit of the audible sound?

A. Audible sound ranges from 20 Hz to 20 KHz. So the upper limit of audible sound is 20,000 Hz. Beyond this a human can not listen to the sound.

Q2. What is echolocation?

A. The process of finding items using the reflected sound is called echolocation. It is primarily used by animals like dolphins and bats.

Q3. Name the animal which can direct the ultrasound.

A. Animals like cats and dogs, whales, bats, and dolphins can detect the ultrasound.

Q4. What are the medical uses of ultrasound?

A. In the medical field ultrasound is used in Ultrasonography, Lithotripsy, Echocardiography and various therapies.

Q5. What is an ultrasonic flowmeter ?

A. In order to measure the flow rate of a liquid, ultrasonic flowmeters are used. In this process the reflection of ultrasound from a flowing liquid results in a calibrated Doppler shift. This approach is frequently used to measure arteries' blood flow in medical industries.