Reflection Coefficient of Liquid Foams with a Layer Thickness of about 100 mm in the Range of 38-52 GHz

This experimental study is devoted to the issues of electromagnetic waves propagation of the millimeter range in complex media such as liquid foam structures by studying the reflection of waves in the range of $38-52 \mathrm{GHz}$ from the foam layer on a metal surface. The experimental setup, calibration method and measurements for a significant time of the foam structure’s existence (around 4 hours) are described. The measurements were performed using a multi-frequency method with processing of the results using the fast Fourier transform. The measuring setup in the form of a measuring and computing complex provided a speed of measurements and processing of the results significantly higher than the rate of foam layer decay. A special foam generator was used to form the foam layer with a thickness of 100 mm and foam bubbles less than 1.5 mm in size and spherical in shape. The obtained reflection coefficient results were within -54 dB at the beginning of the measurements and $-19,2 \mathrm{~dB}$ at the end of 4 hours, which demonstrates the suitability of the studied waterbased foam structures for solving the problems of practical masking of metal objects in the millimeter range of electromagnetic waves.