The radiation impedance seen by a single circular CMUT cell in the absence of any neighboring cells is shown in figure as a function of *ka*, where *k* is the wavenumber in the immersion medium and *a* is the radius of the top plate. The radiation impedance shown is normalized with respect to *Sρ _{0}c_{0}* where

*S*is the area of the top plate of the CMUT cell,

*ρ*is the density and

_{0}*c*is the sound velocity of the immersion medium.

_{0 }In the equations below

*Z*: normalized complex radiation impedance*k*: wavenumber in the immersion medium*k*: wavenumber of the second order circularly symmetric mode of the CMUT top plate_{p}*a*: radius of the CMUT top plate

**Mutual Impedance between two neighboring CMUT cells**

The mutual impedance (normalized with respect to *Sρ _{0}c_{0}*) between two circular CMUT cells with a center-to-center distance of

*d*:

*Z*=(sin *kd* +j cos *kd*)/(*kd*)