An Analytical Model for Bandwidth Enhancement of Air-Coupled Unsealed Helmholtz Structural CMUTs

Table 1

Material properties used in COMSOL (: the factor 0.6 is from [30]; others are the preset values/functions in COMSOL).

Parameter	Value/Preset function in COMSOL
Air: (used in cavity, holes, spherical air domain, PML)
Relative permittivity	1
Dynamic viscosity µair [Pa.s]	eta(T[1/K])
Heat capacity at constant pressure Cp [J/(kg.K)]	Cp(T[1/K])
Density ρair [kg/m^3]	rho(pA[1/Pa],T[1/K])
Thermal conductivity K [W/(m.K)]	k(T[1/K])
Bulk viscosity µb [Pa.s]	0.6eta(T[1/K])
Typical Wave Speed for PML [m/s]	343
Si: (used in membrane, support beam)
Young’s modulus Y [GPa]	170
Poisson ratio σ	0.28
Density ρSi [kg/m^3]	2329
Relative permittivity	11.7
SiO2: (used in insulator layer)
Young’s modulus [GPa]	70
Poisson ratio	0.17
Density [kg/m^3]	2200
Relative permittivity	4.2