The small-signal equivalent circuit of an uncollapsed CMUT cell is given in the figure. The parameters on the acoustic side are dependent on the lumped variable used to represent the velocity or force in the acoustic side. The equivalent circuit shows the parameters with *rms* variables. The velocity of the top plate is represented by an spatial *rms* velocity averaged over the area of the top plate (current in the acoustic side).

Parameters of the circular CMUT cell (all in MKS units)

*a*: Radius of the cell*t*: gap height of the cell_{g}*t*: thickness of the insulator_{i}*t*: thickness of the top plate_{m}- ε
_{r}: relative permitivity of the insulator *P*: Ambient pressure_{0}*Y*: Young’s modulus of the top plate_{0}- σ : Poisson’s ratio of the top plate
- ρ : density of the top plate
- V
_{DC}: DC bias voltage at the electrical port

Parameters in the equivalent circuit may be found using the equations given below.

*t*is the effective gap height: Eq (1)_{ge}*V*is the collapse voltage in the absence of ambient pressure: Eq (3)_{r}*C*represents the compliance of the top plate: Eq (4)_{Rm}*L*is due to mass of the top plate: Eq (5)_{Rm}*X*is the deflection of the top plate at its center: Eq (6)_{P}*n*is the turns ratio of electromechanical transformer: Eq (7)_{R}*C*is the input electrical capacitance including the effect of top plate deflection: Eq (9)_{0d}*C*arises from the spring-softening effect: Eq (11)_{RS}

Refer to the paper by Koymen, et.al for details.