Sergei Yakovlevich Sokolov (8.10.1897 —20.05.1957) was a Soviet physicist and a corresponding member of the USSR Academy of Sciences (1953). He was born in the village of Kryazhim, Saratov Governorate. He graduated from the Leningrad Electrotechnical Institute (1925), where he worked (head of a laboratory from 1926, and from 1931 professor and head of the department of electroacoustics).
His research concerned mainly ultrasonics. He established (1927) the ability of ultrasound to penetrate metals without appreciable absorption and applied this phenomenon to the detection of flaws in metals, thereby beginning ultrasonic imaging (ultrasonic flaw detection). In 1928 he stated the main ideas of ultrasonic flaw detection and described the experimental technique. He constructed the first ultrasonic flaw detector (an industrial model was made in 1937) and developed a number of designs of ultrasonic flaw detectors. He made a quartz vibrator for generating powerful ultrasonic oscillations (he obtained oscillations at a frequency of 106 Hz) and developed methods of detecting them. He put forward the idea of studying the structure of solids and phase transitions by an ultrasonic method. In 1942 he was awarded the USSR State Prize for the invention of the method of ultrasonic flaw detection.
He was a pioneer of sound imaging. He proposed (1935) methods of converting sound images into visible ones (by surface relief, by mechanical scanning, and with an electron-acoustic converter tube) and created sound-imaging equipment, which he called the ultrasonic microscope. In 1951 he was awarded the USSR State Prize for the invention (1948) of the ultrasonic microscope and for improving and introducing into industry the methods of ultrasonic flaw detection. He laid the foundations of acoustic holography.
He developed the first quartz sound analyser. He studied the diffraction of light by ultrasound. He put forward the idea of using the diffraction of light in an ultrasonic field in solid and liquid media to modulate a light beam.