Ultrasound
- We know that a vibrating body produces sound in a medium.
- The normal human ear is not able to detect sounds of all frequencies.
- The sound with frequencies below the lower limit of the human range of audibility is known as infrasonic. If we could hear infrasound, we would hear the vibrations of a pendulum.
- The sound with frequencies above the upper limit of the human range of audibility is known as Ultrasound. Our ears also cannot hear very high-frequency sounds known as ultrasound.
- Generally, we classify ultrasound as those having frequencies above 20,000 Hz.
- The range of frequencies of sound that a person can hear is called the range of audibility or the audible frequency range. Different animals can hear different ranges of frequencies.
Applications of Ultrasound
- Ultrasounds, which are high-frequency sound waves, can propagate along well-defined straight paths.
- Ultrasounds are used extensively in industries and for medical diagnostic (imaging) purposes because of their high penetrating power.
Industrial Applications
- Cleansing: Ultrasound is commonly used to clean many objects, even in hard-to-reach places, including jewelry, dental and surgical instruments, and mechanical instruments. In this process, objects to be cleaned are placed in a cleaning solution, and ultrasonic waves are sent into the solution. Due to its high frequency, dust, grease, and contamination particles are detached and dropped. The objects thus get thoroughly cleansed.
- Quality control: Ultrasound has higher penetrating power due to its very high frequency. Thus, ultrasounds are also used to detect cracks, cavities, and flaws in metal and concrete blocks. These invisible cracks or cavities inside the blocks reduce the strength of the structure. Ultrasound waves pass through the metal block, and detectors are used to detect the transmitted waves. If there is any defect, the ultrasound will be reflected, indicating the presence of the defect.
- Sound navigation and ranging (SONAR): SONAR is extensively used in marine applications. Due to their high frequencies, ultrasound waves can travel greater distances. In this method, the transmitter sends out ultrasound pulses and measures the time it takes for the pulses to reflect off a distant object and return to the source or transducer. The position of that object can be identified, and its movement can be tracked. This technique is used to measure the depth of sea beds, locate and track submarines at sea, and locate explosive mines below the surface of the water.
Medical Applications
- Ultrasonography: It is a technique that uses an instrument called an ultrasound scanner. This scanner uses high-frequency sound waves to obtain images of the internal organs of the human body and to examine the fetus during pregnancy. A sonologist visualizes the organs of the patient, such as the liver, gallbladder, uterus, kidney, etc. It helps the doctor to identify abnormalities, such as stones in the gallbladder and kidney, or tumors and abnormalities in different organs. In this technique, the sound waves penetrate the body and hit a boundary between tissues, e.g., between fluid and soft tissue, bone and soft tissue, and get reflected from an area where their tissue density changes. The instrument calculates the distance from the probe to the tissue or organ boundaries using the speed of sound in tissue and the time of the return of each echo. These pulses are then converted into electrical signals used to create two-dimensional images of the organ.1
- Echocardiography: Echocardiography is a painless and non-invasive medical imaging procedure. A transmitter sends out pulses of very high frequency. The transducer is positioned on the chest at specific locations and angles, and the pulses move across the skin and other body tissues to the heart tissues, where the pulses bounce or echo off the heart structures. These pulses are then transmitted to a computer to create moving images of the heart walls and valves. The image produced is called an echocardiogram.