Reference article: Metaxas, A.C. and Meredith, R.J. (1993) Multimode oven applicators. In Industrial Microwave Heating ed. Peregrinus, P. pp. 130-150. London, UK: Institute of Electrical & Electronics Engineer.
A rectangular waveguide (7.2 x 3.4 cm) was connected to another identical adapter through a brass waveguide straight section. Two empty borosilicate glass spheres (4 mm outer diameter) were introduced into the test tubes and held to the bottom by a coiled, thin walled teflon tube (0.9 mm diameter x 50 mm). For comparison purpose, test tubes filled with water were placed in a commercial multimode oven (34.5 x 34 x 23 cm internal capacity) with a nominal working power of 750 W at 2.45 GHz. The samples immersed into the boiling water were heated for the same time intervals as the samples in the waveguide.