Measurement of microwave radiation pressure on thin metal fibers

The pressure of electromagnetic radiation in the optical range is widely used to hold microparticles in a given place and control their movement. This is possible by focusing the laser radiation into an area with the dimension of several micrometers. The intensity of radiation in this area is large and sufficient to retain micro-particles in the laser beam and manipulate them. Nowadays, intensive research is underway on the use of microwave and terahertz radiation and the possibility of applying radiation pressure in these ranges. But in the microwave range, the focal spot dimension is much larger than in the optical one. Therefore, control of the objects whose dimensions are comparable to those of the focal spot using the radiation pressure requires very high power. For the objects with small dimensions, a small amount of radiation energy falls on them, and the acting force decreases. However, it is known that thin conductive fibers interact very strongly with microwave radiation. This can be used to levitate short thin metal fibers (vibrators), hold them in predicted place and control their position in space. The paper describes the measurements of the pressure of microwave radiation with a wavelength of 8 mm on thin copper fibers. Torsional balance is used for this purpose. In the metal case on a suspension from a tungsten fiber with a diameter of 8 microns there is located the rocker arm with 50 mm length with receiving elements in the form of system of copper fibers with a diameter of 300 microns and 15 mm length. Microwave radiation was directed to one of the receiving elements using a horn. The calibration of torsion balance, the measurement process, and the evaluation of the resulting error are described. The measurements gave the value of the efficiency factor of the radiation pressure Qpr = 4.86. This agrees satisfactorily with the results of calculations Qpr = 5.39. The difference is 10%.