All About Sound, Vol. 4: Sonar and Ultrasound Quiz

Answer: Leonardo da Vinci

Da Vinci was interested in how sound moves through different materials including water. He began experimenting around 1490 when he inserted a tube into the water and was able to detect marine vessels by ear. Da Vinci wrote, "If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you."

Answer: Military due to World War I

The first sonar systems were developed in response to the Titanic disaster in 1912 but these systems were of limited practical use. Due to World War I, with the severity of the shipping losses, an agreement was reached among the allies that all their ideas for anti-submarine technology should be pooled.

Hence, the Anti-Submarine Division (ASD) of the British Royal Navy was created in 1917. Their work was undertaken in utmost secrecy. Ultimately, they were able to use quartz crystals to produce the first practical man-made underwater echolocation system which was referred to as ASDIC.

Answer: It was discovered by Galileo Galilei

French physicists Jacques and Pierre Curie (future husband of Marie Curie) discovered piezoelectricity in 1880. The effect occurs in certain solid materials including some crystals (such as quartz) and ceramics as well as bone and sugar.

One of the interesting properties of the piezoelectric effect is that it is reversible, meaning that materials exhibiting the direct piezoelectric effect (the generation of electric charge when stress is applied) also exhibit the reverse piezoelectric effect (deformation when an electric field is applied). If an alternating current is applied to a piezoelectric material, it will start to vibrate as it alternatingly contracts and expands, thereby emitting sound waves.

Answer: Navigation And Ranging

The term was coined in 1942 by Frederick Vinton (Ted) Hunt, director of the Harvard Underwater Sound Laboratory. The term was meant to be similar to RADAR (RAdio Detection And Ranging) and was accepted by the U. S. Navy. In 1948, NATO dropped the term ASDIC in favor of SONAR.

Answer: It is confined to the human range of hearing

The frequencies of sound used in sonar systems vary widely from infrasonic (below human hearing) to ultrasonic (above human hearing).

Passive sonar systems simply consist of sensors that pick up the noise produced by objects such as ships, submarines or marine creatures. The sound waves are analyzed to identify the object and determine its direction.

In active sonar systems, sound is generated and reflected back by a target object. The generator may be on a floating sonobuoy, attached to a vessel's hull, or suspended in the sea by a line lowered from a helicopter. Again, sensors pick up the reflected signal so it can be analyzed. Active sonar has the advantage of also measuring speed and distance but the disadvantage of producing a noise that lets others know you are there.

SODAR (which stands for SOnic Detection And Ranging), is a type of sonar used for atmospheric investigations such as measuring wind speed at various altitudes.

Answer: Clarity

Sonar is affected by many factors. The speed of sound is dependent upon the density of the medium it is traveling in. Temperature, pressure due to depth and salinity all affect density and therefore the speed of sound. As the speed of sound changes, the sound waves bend in their pathway due to refraction and therefore affect the determination of direction by sonar.

Refraction is more commonly associated with light waves which abruptly bend when the medium changes due to a change in the speed of light. The bending of light as it goes from air to glass and vice versa is the basis for optics. For sound, the bending is usually more continuous with gradual changes in temperature and pressure. However, density changes can be abrupt enough that the sound is refracted more dramatically. This can happen with thermoclines where there is a substantial change in temperature between layers in a body of water. Cunning submarine commanders can take advantage of this phenomenon.

Salinity, of course, changes depending upon the body of water you are in. There are also variations in salinity due to other factors such as the season and ice cover.

Clarity is an optical characteristic and not a direct factor for sound although the cause of reduced clarity can have an effect on sonar in certain situations. For example, the presence of solid particles in coastal waters decreases clarity and may reduce sound propagation, particularly at high frequencies.

Answer: It starts at 50,000 Hz

Ultrasound is defined as starting at the approximate maximum of the human hearing range and therefore starts at 20,000 Hz.

Ultrasound has a wide variety of industrial uses including cleaning, nondestructive testing, mixing, welding and sonochemistry.

Ultrasound can be used therapeutically to break up kidney stones as well as for strains, sprains and inflammation.

Ultrasonic humidifiers work because the vibrations propel microscopic water droplets into the air. The droplets then evaporate and add humidity to the air in the room. Nebulizers can also be ultrasonic and work on the same principles but are designed to deliver liquid medicine in the form of aerosols which are inhaled.

Answer: Birds

Interestingly, no bird species has been reported to be sensitive to ultrasound.

Dolphins use ultrasound for navigating, hunting and communicating. Bats use a complex set of ultrasonic sounds with calls of both constant frequencies and varying frequencies for echolocation. Many insects have good ultrasonic hearing, especially nocturnal insects listening for echolocating bats.

Answer: Whistle

Francis Galton invented the Galton whistle, an adjustable whistle that produced a range of ultrasonic pitches. He used the whistle to determine the hearing range of humans and animals. His work demonstrated that many animals respond to sound above the hearing range of humans.

Answer: The Doppler Effect

The Doppler Effect occurs when the source of sound is moving relatively towards or away from the receiver. When the source is moving toward the receiver, the pitch (frequency) of the sound increases. When the source is moving away from the receiver, the pitch decreases. When sound is reflected off a moving object, the frequency is also altered by the Doppler Effect. By measuring the change in frequency, the speed of an object can be calculated based upon the difference in frequency between a signal which is sent and the frequency of the signal when it is reflected back.

Doppler ultrasound is often used medically to measure blood flow. It works because ultrasound is reflected off red blood cells that are circulating in the bloodstream.