In this work, we study airborne CMUT cells with vacuum gap where silicon plate is operated both in elastically linear and nonlinear regimes. We report the results of a new mode of operation where the plate center swings the entire gap. The plate is kept in elastically linear region in this mode. Very large pressure levels are obtained at relatively low drive voltage levels. The operation is very efficient but the bandwidth is less than 1%. We considered operating the silicon membrane in elastically nonlinear region for larger bandwidth without sacrificing efficiency. This is achieved by employing the stiffening effect due to the atmospheric pressure. We derived the new model of the CMUT, where the membrane profile deviates from linear profile as a function of the differential static pressure on it. We present the force, the compliance models and the static analysis of stiffened CMUT cells in this work.