DISCOVERY, DESIGN, DEVELOPMENT AND DELIVERY OF LANGEVIN’S QUARTZ SANDWICH TRANSDUCER
By Francis Duck, Retired.
Aim:
This poster will set out in detail the sequence of seven steps taken by Paul Langevin, from February 1917 to February 1918, to develop the first pulse-echo quartz transducer.
Method:
Original documents from French and English archives have been studied to reveal the genesis of Langevin’s piezoelectric ultrasonic transducers. Careful study of these texts and figures has allowed his process of transducer design to be demonstrated in detail for the first time.
Results:
Each design step was a necessary logical precursor for the subsequent one. (1) A quartz slice from the Curies’ apparatus was used to detect audible and then ultrasonic signals (February 1917). (2) A larger, 16mm thick, square slice was cut and demonstrated as a resonant receiver at 100 kHz (March/April). (3) A triplet transducer was used as emitter and receiver, demonstrating piezoelectric resonance at 60 kHz (June). (4) A resonant bilaminar transducer used a quartz slice glued to a steel plate (July): this encapsulated design was the basis for all British asdics transducers during WWI. (5) A mosaic replaced the single crystal, glued to the metal substrate, enabling the aperture to be increased (Aug/Sept). (6) A second steel plate was added to make a resonant half-wave thick encapsulated sandwich (Nov/Dec). (7) The final operational design, resonant at about 40 kHz, placed the sandwich in a watertight housing to allow air-backing. This was successfully tested for submarine detection in February 1918.
Conclusion:
Within 12 months, Langevin had converted his original idea of a piezoelectric transducer into a successful prototype operational device for underwater detection. In his patent, filed in September 1918, he identified medical ultrasonic applications as one possible future use. Langevin is correctly identified as ‘the originator of the science and art of modern ultrasonics’.