Abstract: This paper based on two dimensional motion equations of circular piezoceramic disks, and separate the variables we can attain the equation set which depends on axial variable z only, then according to the boundary conditions solved this equation set with adjoint method to obtain the vibrational frequency spectrum which is relative to the radial expansive frequencies. Conversely from the basic frequency of thickness vibrations we could calculate the spectrum of radial expansive vibrations. From the results of calculation by this method, we can see that the radial and axial vibration spectrum of circular piezoceramic disks are influenced by each other as well as dependence to their dielectric, piezoelectric and elastic constans. That is so called "Coupling" relations.
In order to examine the correctness of this method, the author calculated an example. Although the results of calculation is not very coincide with measurements, but is better than that of onedimensional theory. Here the errors in material parameters are important factor to cause mistakes.