Floyd Alburn Firestone (1898–1986) was an acoustical physicist, who in 1940 while a professor at the University of Michigan invented the first practical ultrasonic testing method and apparatus. He was granted US Patent 2,280,226 for the invention in 1942. Manufactured by Sperry Corporation, the testing device was known variously as the Firestone-Sperry Reflectoscope, the Sperry Ultrasonic Reflectoscope, the Sperry Reflectoscope and sometimes also just as a Supersonic Reflectoscope, the name Firestone had originally coined for the instrument. The technology is not just used in quality control in factories to reject defective parts before shipment, but also revolutionized transportation safety. For example, ultrasonic testing is used for safety maintenance inspection of railroad cars, particularly axles and wheels, aircraft, particularly fuselages, and other transportation vessels for material fatigue. Dr. Firestone’s ultrasonic pulse echo technique for metal defect testing was also later applied in medical diagnosis, giving birth to the field of Echocardiography and to the field of Medical Ultrasonography, generally. Dr. Firestone was the editor of the Journal of the Acoustical Society of America from 1939-1957. Among Firestone’s many other inventions in his field are in a single year an “automatic device for the minute inspection of flaws”, “a new and useful improvement in hook-up of electrical apparatus”, and “[a] device for measuring noise”, and, even, later a “musical typewriter”.
In 1933 Firestone proposed an alternative to the mechanical-electrical analogy of James Clerk Maxwell in which force is made the analogy of voltage (the impedance analogy). Firestone's analogy (now called the mobility analogy) makes force the analogy of current. In this work he introduced the concept of "through" and "across" variables and demonstrated that there were analogies for these variables in other energy domains, making it possible to treat a complex system as a unified whole in analysis. Firestone's analogy became popular amongst mechanical filter designers because it has the property of preserving network topologies when transforming between the mechanical and electrical domains.
- Firestone, Floyd A (1933). "A new analogy between mechanical and electrical system elements". The Journal of the Acoustical Society of America. 4 (3): 249–267. doi:10.1121/1.1915605.
- Firestone, Floyd A. (1946). The Supersonic Reflectoscope, An instrument for inspecting the interior of solid parts by means of sound waves. Journal of the Acoustical Society of America, 17(3), 287-299,  Full Article
- Ancestry .com-Freepages
- Beyer, R.T. (1999). Sounds of our times: 200 years of acoustics. New York, New York: Springer-Verlag, pp. 246-247.
- Fahr, A., Ph.D. (2014). Aeronautical Applications of Non-destructive Testing. Lancaster, Pennsylvania: DEStech Publications, Inc., p. 150
- Singh, S; Goyal, A (2007). "The origin of echocardiography: a tribute to Inge Edler". Tex Heart Inst J. 34 (4): 431–8. PMC 2170493. PMID 18172524.
- Levine, H. III. (2010). Medical Imaging. Santa Barbara, California: ABC-CLIO, LLC., p. 62
- Nicholson, M. & Fleming J. E. E. (2013). Imaging and Imaging the Fetus: The Development of Obstetrics Ultrasound. Baltimore, Maryland: Johns Hopkins University Press.
- Proceedings of the Board of Regents. (1929). Ann Arbor, Michigan: University of Michigan, p. 452
- Staff (1948). "Machine types simplified music". Popular Science. 153 (2): 143.
- Bishop, Robert H., Mechatronics: An Introduction, CRC Press, 2005 ISBN 1420037242, p. 8-2.
- Smith, Malcolm C., "Synthesis of mechanical networks: the inerter", IEEE Transactions on Automatic Control, vol. 47, iss. 10, pp. 1648–1662, October 2002