Electronic – What device/component from the early 1940’s can listen to only a specific narrow range of acoustic frequencies

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This website briefly describes the development of the first active acoustic homing torpedo of the US Navy:

Investigation of the use of echo-ranging equipment or an "active" homing torpedo system was initiated under the auspices of NDRC in 1941 at the G.E. Co. Research Laboratory, Schenectady, N.Y. Active homing differs from passive homing in that, with active homing, the torpedo steers on the basis of the signal returned by the target through reflection of the torpedo's own transmitted signal. In mid-1942, G.E. began development of the first active homing torpedo, Torpedo Mk 32, which was physically similar to Mine Mk 24 (figure 17).

By mid-1944, the program had progressed through the successful prototype stage… About ten units were completed when World War II ended, and the project was deactivated until 1951 when Torpedo Mk 32 Mod 2 was produced in quantity by the Philco Corp. of Philadelphia, Pa.

So basically, an active homing torpedo needs to send out its own ping and listen for that specific echo, rather than other noise on other frequencies. AFAIK, all active homing systems choose a high frequency, sounding like a high ping, because all large ship screws make very low frequency noise.

Anyway, my question is what kind of electronic device can listen to only a narrow set of acoustic frequencies? It has to be a device that existed in the early 1940's.

Best Answer

Sonar history lesson: -

In 1906, American naval architect Lewis Nixon invented the first sonar-like listening device to detect icebergs. During World War I (1914-18), a need to detect submarines increased interest in sonar. French physicist Paul Langévin constructed the first sonar set to detect submarines in 1915. At first, these sonar sets could only "listen" to returning signals. By 1918, Britain and the United States had built sonar sets that could send out, as well as receive, sound signals. The U.S. military began using the term "sonar" during World War II. As with radar, new military applications for sonar are constantly being developed. For example, in the early 2000's, the U.S. Navy introduced a sonar system to help clear military mines.

Text above taken from here. Use of resonant circuits whether mechanical or aided by electrical filters was well-known throughout the 20th century.

US patent 609,154 made in 1898 describes the use of matched tuned circuits used in a radio transmitter and receiver. I think Tesla may have made an earlier patent regards the use of tuning. Tuning/resonance was therefore a fairly open-book since the start of the 20th century.

Piezo electricity: -

The word ‘piezo’ is derived from the Greek word for pressure. The piezoelectric effect was discovered by Jacques and Pierre Curie in 1880. They found that pressure applied to a quartz crystal creates an electric charge in the crystal, a phenomenon they referred to as the (direct) piezoelectric effect. Later they also verified that an electric field applied to the crystal leads to a deformation of the material: the inverse piezoelectric effect. In the subsequent century, research has been performed into the development of materials with improved piezoelectric properties, enabling commercial utilization of the piezoelectric phenomenon.

Taken from here. Making a mechanical movement resonate has been known about far longer than just the 20th century - think tuning forks and pendulums etc..

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