The Components of Sonar and Their Development
The history of sonar is tied directly to the invention and advances that have been made in sonar over the decades. The enhancement of the components of sonar equipment was needed to improve the function, usefulness, and accuracy dependent upon their many uses. Military and civilian uses of sonar created new challenges and needs. As in the case of many modern things, the inventions of war later became the gifts to mankind. The history of sonar parallels the history of electronic invention.
The original sonar type equipment, called passive sonar, was simply an underwater microphone or hydrophone. Materials which would convert liquid conducted sound waves into electricity were created. vacuum tube amplifiers raised the signal to a level which could drive carbon based magnetic coil headsets for human listening and interpretation.
Components of Sonar
The original components then were the underwater microphone or hydrophone and emitter, cabling, signal amplification and listening device or visual display. The microphones were limited in sensitivity secondary to early development of simply converting air based microphones to underwater use. Original equipment lost a lot of signal at the source because of materials needed to create a watertight, military device. After all, these were to be attached to the hull of a ship at sea.
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The very small electrical signal was carried over wires over some distance from its underwater microphone to the amplifier, usually near the command center of the ship. Microvolts or millivolts of signal were lost because of this wiring dilemma. This limitation actually existed for two reasons. First, it took time and experience with experimentation to realize the loss of signal and secondly, vacuum tube amplifiers limited the location of the equipment, which frequently needed repair. Later, a “sound room” was created near the bottom of the ship for some of the electronic equipment.
Improvements of Transducers
Major advances of materials, waterproofing, durability, and signal conversion led to significantly improved microphones for sonar wave reception. Beyond simple hydrophones, active sonar actually consists of a sound generation which is transmitted into the water, bouncing off underwater objects with reflected signals returning to the microphones. Considerable research allowed for discovery of frequencies, patterns, use of arrays, and creation of sonar emitters which were made specifically for each application. The tuning of the emitter/microphone combo created an incredibly efficient water interfaced device.
Early diagnostic X-rays were very toxic to humans. Evolution of components which reduced X-ray transmission led to safer radiography. With sonar, the injuries to sea life were lessened with the newer components.
Limitations of early electronic Equipment
Vacuum tubes were made of glass. They needed a heated filament to emit electrons which were then accelerated by high voltage and deflected like a gate in order to amplify signals. They were not considered “solid state” since a mechanical shock to them would frequently break the lighted filament or even break the glass. They also created a lot of heat which needed cooling and ventilation. Imagine having to stop the ship or fleet to change a vacuum tube under a hull with scuba divers, or to work inside the very bottom of the hull of a ship to repair a circuit. Even the resistors and capacitors were relatively unreliable. The amplification equipment had to be accessible for repairs and adjustment.
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Old resistors were carbon based or wire wound little heaters. They would literally burn out. Capacitors, which temporarily store and release electrical charges were frequently paper wrapped and would short out with vibration or water or just with the passage of time. Transformers, which act as inductors or which convert voltages in exchange for the opposite effect on electrical current, had rudimentary insulation and were very heavy and hot. They had the ability to actually burn up and set on fire because they had paper wrappings with fiber board amongst the numerous coils of wire.
These early electronic devices were plagued with drifting signals, lack of reliability and constantly needed re-tuning and adjustment. Mechanical and water damage as well as wear and tear over time created a maintenance nightmare. These problems were not the result of stupidity but simply a stage of electronic evolution which took time to improve. These inventors were actually geniuses.
The ‘Solid State’ Age
The sonar transducer (sound emitter and receiver package) had massive signal improvement with the development of ‘solid state’ electronics. The transistor was invented in 1947 by John Bardeen, Walter Brattan and William Shockley of Bell Labs, Murray Hill, New Jersey. They won the Nobel Prize for their invention. This device amplified electrical signals using germanium/silicon based materials. No more need for vacuum tubes with fragile heated filaments or heavy transformers. All the while, materials, especially plastics, revolutionized the production and reliability of the other sub-components. Circuit boards and chassis could handle considerably higher mechanical shock and hardly ever needed repair. Solid state refers to the lack of a glass and filament composition of the circuit.
Improvement of Signal Quality
As was discussed previously, signal losses from the microphone plagued the quality of reception. Preamplifiers were born. They were electrical circuits which amplified the microvolt or millivolts signals 1,000 to 1,000,000 times right at the source. Signal losses were markedly reduced as a result.
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The Human Element (Limitation)
Interpreting the data from underwater sound waves has always been a challenge. The use of headphones, speakers and green phosphor displays of sonar data was primitive. Computers and improved solid state microprocessors led to better signal filtering and display. Recently, microprocessor based digital signal processing allowed for such sophisticated analysis that even allows the U.S. Navy to identify the name of each ship in the sea by only its sonar “signature”
The history of sonar is an interesting compilation of the histories of each of its components and even the sub-components. Civilian technology has advanced because of military needs and developments. However, due to the mass production of consumer electronic devices, military equipment has certainly been helped by the improvements and reliability of civilian products.