A variable-volume cavity electromagnetic near-field simulator

A variable-volume cavity system capable of simulating complex electromagnetic fields by the simultaneous excitation of two independent cavity modes has been built and tested. As the physical dimensions of the cavity dictate the operating frequency ofthe device, in order to operate over a band of frequencies, its physical configuration must be mechanically adjustable. A novel mechanical design allows the cavity to be adjustable in size over a wide extreme. The cavity is formed by four movable walls, a stationary back wall, and a sixth wall, called a plunger, which is cut to size and whose location determines the length of the cavity. A structural framework supports the plates. The four movable walls allow the cross section of the cavity to be changed. They are positioned by the utilization of linear bearings, rack and pinion gears, shafting, and a chain-and- sprocket adjusting system. The plunger is attached to an all-thread bolt that is mounted between two pillow blocks. Although there are no inherent size limitations to the mechanical design, a prototype system has been built in which the cavity cross section can be adjusted from maximum dimensions of 609.6 mm x 609.6 mm to minimum dimensions of 152.4 mm x 152.4 mm, while the length is adjustable from 1219 mm to 304.8 mm. This cavity system is of sufficient size to irradiate a variety of biological objects, such as mice, cell samples, bacteria, and other microorganisms, as well as phantom scale models.