Computation of shift in oscillation frequency in the cavity resonator caused by anisotropicity and inhomogeneity of the permittivityPragya Shilpi, Dharmendra Upadhyay and Harish ParthasarathyEur. Phys. J. Plus, 135 1 (2020) 59DOI: https://doi.org/10.1140/epjp/s13360-019-00089-w