Underwater Acoustics: Period (1938 – 1945)

 

Underwater Acoustics (1938 – 1945)

 
Around 1935, the Measurement Building was already researching ferromagnetic materials and magnetostriction: the shortening or lengthening of material in a magnetic field [1]. Moreover, commercial developments such as an underwater telephone for surface ships [2] and a “noise direction device” (periphone) from Atlas Werke A.G. [3] for underwater navigation did not go unnoticed by the Navy and the Measurement Building.

A periphone is a device for detecting extra-ship sounds; a distinction is made between passive listening (noise levels; navigation), determining distance and direction (active), telephony, and telegraphy.

In 1936, the Navy commissioned an Atlas Werke A.G. to install a “noise tracking device” (periphone) for experiments in submarine O-16.[7] In 1939, noise tracking devices (“periphone installations”) were built into the submarines O-19 and O-20. Museum Waalsdorp possesses Atlas Werke documentation of the periphone installation and its components. [8]

On April 5, 1938, the Defence Commission for Physical Armament received a (very secret) assignment from the Dutch Department of Defence for research into underwater acoustics with periphones and for studying underwater noise reception. The construction of periphones was started expeditiously. An excerpt from the monthly lab reports available at the Museum between September 1938 and 1940 follows here:

• In 1938, four periphones were first built by the laboratory. Three periphones were made of layers of nickel-tin and one was made of layers of magnetostrictive nickel and monel.

  

• In October 1938, one of the periphones with 490 layers of 0.2 mm thick nickel-tin plates measuring 70 by 240 mm was used for tests. It had four 25 x 40 mm holes. A copper wire with 40 windings ran through each hole. The wires were connected serially. Under dry conditions, five resonant frequencies were measured. Strong resonant frequencies were at 7.8 and 43 kHz which relates to the 240 and 70 mm sizes, respectively. The measurements showed that this periphone has a completely different character from the O-16’s Atlas Werke noise locator device.
• A month later, experiments were carried out with two periphones of different dimensions. The experimental resonant frequencies matched the theoretically calculated values.

  

   

  

• Underwater experiments were carried out at the Measurement Building. The packet of nickel plates was impregnated to prevent the penetration of water. Clamps were used to reduce the damping between the plates.
  Work was also performed on signal processing. Using a crystal microphone as an ‘antenna’ for the acoustic energy, a high-frequency amplifier stage (34 kHz) followed by a low-frequency stage (1 kHz), a signal was derived that could be displayed on a Braun tube (cathode ray tube). A special circuit (drawings available) was used to provide the transmitting periphone with acoustic pulses. Received reflections became visible as deflections of the beam on the cathode ray tube. The time since the start of the pulse provided a measure of the distance from the reflector.
• In early 1939, with trial and error, work was carried out to insulate the nickel plates and waterproof the whole package (paper, lacquer, paper with bakelite lacquer, rubber). The plate voltage device (PSA) was also modified in terms of its construction to make the volume control of the amplifier crackle-free.
• In May 1939, tests with a receiving periphone were conducted from a jetty in the Kleine Poel of the Westeinderplas. The transmitting periphone was mounted to a motor sloop. Detection took place at a distance of 1 km during which the amplification of the receiver had to be greatly reduced.
  The receiver was then moved to the water tower. The receiver easily received the transmitted telephony signal along the entire length of the lake (5.75 km). Next, reflection tests were carried out. The results showed unexpected effects such as closeby reflections (turned out to be the bottom) and reduced signal strength (water penetrating the device through leaking screw holes).
• Another improvement on the receiver side was the replacement of the low-pass filter up to 1150 Hz with a bandpass filter 910-1050 Hz to suppress hum and interference from the aggregate
• In July 1939, tests were performed from a Rijkswaterstaat jetty at Hoek van Holland. The results were highly variable. The equipment proved uncontrollable. Did something malfunction in the electronic equipment? In the afternoon, the setup suddenly worked flawlessly. The same effect occurred the following day. In the afternoon, the system suddenly worked properly. The good operation appeared to coincide with the turning of the tide, the time when the water current is almost zero. Conclusion: the source of the disturbance was the eddies in the flowing water through the jetty poles!
  Rijkswaterstaat advised finding still water for the tests in the 5-metre-deep Kanaal door Voorne near the former hamlet of Nieuwesluis.

  

• In September 1939, reflection tests were made in the Kanaal door Voorne from the Wellebrug‘s bridge keeper’s house. Despite some noise interference problems, reflections from the raft bridges were visible at 2.5, 4 and 7 kilometres on the Braun tube. Similarly, the lock gate on the other side at 1.8 kilometres was visible.

  

• A sea trial was then conducted aboard the submarine NLHMS O 20 with the minesweeper NLHMS Jan van Brakel as the target ship. The periphone received sound reflections up to 1,200 metres. This led to requests for periphone equipment for the Dutch submarines.
• The research developments are presented to the Commission for Physical Armament.
• For follow-up tests, the minesweeper HNLMS M2 stationed at Hoek van Holland was made available to the Measurement Building by the Royal Navy. Using a scissor construction of rods, tests were carried out to a depth of 3.5 metres. In parallel to the tests, the Measurement Building’s electrical engineers were improving the electrical transmission and reception equipment. The back-and-forth sailing pilot ship and other passing-by ships were good targets. The test results left much to be desired although ship reflections were sometimes detected over 2 kilometres.
• In December 1939, the transmitted beam was found to be 23 degrees in the horizontal plane and very low in the vertical. Great for detecting submarines but poor for detecting sea mines. Theoretical calculations were performed to determine which design parameters (dimensions, frequency) would have to be changed to detect sea mines up to 200 metres forward of the ship’s bow with a 40-metre ‘guarded channel’.
• Other tests assessed how well the periphone would be usable for noise detection of ship propeller noise. The receiver was tuned to 23 kHz with a 300- or 3000 Hz bandwidth. This worked quite well.
• On 13 December 1939, see mine detection trials took place at Hellevoetsluis.
• On 29 December 1939, the joint meeting with Navy representatives defined the requirements for operational periphones to be built as:
  1. Periphones are to be deployable for detection and distance measuring of targets, not for underwater telephony and/or telegraphy.
  2. Received signals to be made visible on a Braun tube and audible through headphones.
  3. The transmitter is to operate at 30 kHz with a horizontal beam of +/- 20 degrees and vertically +/- 60 degrees.
  4. The transmitter consists of a Colpitt (ed. should be Colpitts) oscillator, an ‘intermediate amplifier’ and an output stage (preferably not push-pull when Philips can supply a PB2/500).
  5. The receiver should have an HF stage, a mixing stage and three LF stages (about 1 kHz).
  6. An on/off switchable bandpass filter is needed for noise detection between the 1^st and 2^nd LF stages.
  7. The pulse duration of the transmit pulses is to be adjustable with a mechanical relay.

  It is decided that the Department of Defence will purchase 50 kg of nickel in sheet form from NV Philips to manufacture two periphone transmitters. The Naval Radio Service will build the 30 and 50 kHz receivers [the Museum still has mechanical and electrical construction drawings dated 22 January 1940 prepared for this purpose]. The systems must be ready by 1 April 1940. Arrangements must be made with the Naval Dockyard to prepare for attaching the periphones to various types of Navy ships for trials and how and where to install the electronic equipment. Mine detection has priority in this regard.

• In January 1940, work continued on the mine-detection periphone (50 KHz) where the transmission pulses are given automatically. The nickel plating is ordered.
• In February 1940, the transmitter design was adapted to fit the PB 2/500 tube;  the relay circuit was delivered.
• In March 1940, a report on possible countermeasures against the effectiveness of enemy periphones was delivered.
• In April 1940, the mine periphone and its newly designed plate voltage device were tested.

The German invasion and subsequent Dutch capitulation in May 1940 halted the work of the Measurement Building for the Navy.

Drawings from March 1941 show that some work did continue in 1940-1941 on a sea mine detection device equipped with a 45.4 kHz transceiver.

 

Publications [9-11] show that during the first years of the war, research was also carried out on magnetostrictive materials and measuring deviations from the earth’s magnetic field (the laboratory was then part of the PTT organisation). Those studies were potentially of interest to the rest of the PTT. This research laid a good foundation for the transducer developments by TNO after World War II.
 
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References

1. ir. J. Piket, Magnetostrictie, Serie Electriciteitsgeleidingen, De Ingenieur No. 28, Electrotechniek 9, 1936.
2. Unterwasserschall-Telegraphie: Spezialgerät für schnellfahrende Oberflächenschiffe, Electroacustic GmbH, Kiel, 1936.
3. Periphone, Atlas Werke A.G., Bremen, 1935.
4. Onderwater-luister-inrichting,  Atlas Werke A.G., Bremen, 1935.
5. Unterwasserschall-Gruppenhorchanlage,  Atlas Werke A.G., Bremen, 1935.
6. Über die Hörwelle von Unterwasser-schallsignalen, Bremen, 1935.
7. Onderwaterpeilinrichting (multispot) voor ontvangstinstallatie voor nautische doeleinden Hr.Ms. O 16. Atlas Werke A.G., Bremen, 1936, No. 315 H. [Technical drawings can be found in the archives of the Museum]
8. Perifoon-installatie voor de Hr.Ms. “O 19” en “O 20”, Atlas Werke A.G., Bremen, 1939, No. 514 H. [Technical drawings can be found in the archives of the Museum]
9. Mulders, C.E. (1942). Apparaat voor het meten van zeer zeer kleine plaatselijke variaties van een magneetveld. Physica Vol IX No. 8.
10. Mulders, C.E. (1942). Magnetostrictie. Tijdschrift van het Nederlandsch Radiogenootschap, Vol X-2, November 1942, No. 8. 
11. Dijl, B. van (1942). Opwekking en voortplanting van ultra sonore signalen in water. Tijdschrift van het Nederlandsch Radiogenootschap, Vol X-2, December 1942, No. 10.

 
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