An Ultrasonic thickness gauge is a measuring instrument

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

 for the non-destructive investigation

Nondestructive testing

Nondestructive testing or Non-destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage....

 of a material's thickness using ultrasonic waves.

The first ultrasonic thickness gauge in the world was constructed by the Polish

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

 engineer Werner Sobek from Katowice

Katowice

Katowice is a city in Silesia in southern Poland, on the Kłodnica and Rawa rivers . Katowice is located in the Silesian Highlands, about north of the Silesian Beskids and about southeast of the Sudetes Mountains.It is the central district of the Upper Silesian Metropolis, with a population of 2...

, in year 1967. The ultrasonic thickness gauge measures the speed of propagation

Wave propagation

Wave propagation is any of the ways in which waves travel.With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves....

 of the ultrasonic waves in the given material, and then converts this speed to the thickness in millimetre

Millimetre

The millimetre is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length....

s, applying a suitable mathematical formula.