P2P-5 Radiation Impedance and Equivalent Circuit for Immersed CMUT Array Element

Abstract

Abstract-In this paper, we present equivalent circuit for immersed capacitive micromachined ultrasonic transducers (cMUT), based on an accurate parametric model. We also present an accurate approximation for the radiation impedance cMUT. We develop a design approach for immersed cMUTs using the equivalent circuit. We demonstrate that the equivalent circuit predicts the performance of a cMUT array element composed of many cells in parallel. We investigate the applicability of the equivalent circuit in designing cMUT array elements.

Radiation impedance of an array of circular capacitive micromachined ultrasonic transducers

“…8(a). 4 For k p a = 2.15, it is seen that there is a dip in the radiation resistance near ka = 0.54k p a = 1.16 (or kd = 2.1 × 1.16 = 2.4) corresponding to the antisymmetric mode as determined from FEM simulations, which is not predicted by (15). The velocity profiles of the cells showing the excitation of antisymmetric mode at this frequency can be seen in Fig.…”

“…For example, at f = 100 kHz, this maximum for an airborne cMUT array is reached when d = 4.05 mm giving a = 1.7 mm. If the cMUT cell is made of a silicon membrane, then its thickness needs to be 69 µm [15] to have a mechanical resonance at 100 kHz. as shown in Fig.…”

“…This is most pronounced for the array with N = 7, because all the outer cells experience antisymmetric loading from the neighboring cells. To investigate this effect, the radiation impedance of an array made of cells with d = 2.1a, k p a = 2.15 and 3.7 as determined by FEM simulations and calculated using (15) are plotted in Fig. 8(a).…”

“…In [14], the radiation impedance of an array is modeled with lumped circuit elements. In [15], the radiation impedance is calculated by subtracting the mechanical impedance of the membrane from the input mechanical impedance as computed by a finite element simulation. In [16], cMUT is modeled with a modal expansion-based method, and the radiation impedance is calculated using that method.…”