Browsing by Subject "Integrated circuit modeling"
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Item Open Access Design and implementation of capacitive micromachined ultrasonic transducers for high power(IEEE, 2011) Yamaner F.Y.; Ölçüm, Selim; Bozkurt, A.; Köymen, Hayrettin; Atalar, AbdullahCapacitive micromachined ultrasonic transducers (CMUTs) have a strong potential to compete piezoelectric transducers in high power applications. In a CMUT, obtaining high port pressure competes with high particle velocity: a small gap is required for high electrostatic force while particle displacement is limited by the gap height. On the other hand, it is shown in [1] that CMUT array exhibits radiation impedance maxima over a relatively narrow frequency band. In this paper, we describe a design approach in which CMUT array elements resonate at the frequency of maximum impedance and have gap heights such that the generated electrostatic force in uncollapsed mode, can sustain particle displacement peak amplitude up to the gap height. The CMUT parameters are optimized for around 3 MHz of operation, using both a SPICE model and FEM. The optimized parameters require a thick membrane and low gap heights to get maximum displacement without collapsing membrane during the operation. We used anodic bonding process to fabricate CMUT arrays. A conductive 100 μm silicon wafer is bonded to a glass wafer. Before the bonding process, the silicon wafer is thermally oxidized to create an insulating layer which prevents break down in the operation. Then, the cavities are formed on the insulating layer by a wet etch. The gap height is set to 100 nm. Meanwhile, the glass wafer is dry etched by 120 nm and the etched area is filled by gold evaporation to create the bottom electrodes. The wafers are dipped into piranha solution and bonding process is done afterwards. The fabricated CMUTs are tested in an oil tank. To eliminate the DC voltage which may cause charging problem in the operation, we tried to drive the CMUT array with large continuous wave signals at half of the operating frequency. We observed 1MPa peak to peak pressure with -23 dB second harmonic at the surface of the array (Fig. 1). The proposed design further extends the operation of CMUTs. Observing low harmonic distortions at high output pressure levels, without any charging problem, make CMUT a big candidate for high power applications. © 2011 IEEE.Item Open Access A robust approach for the derivation of closed-form Green's functions(Institute of Electrical and Electronics Engineers, 1996-05) Aksun, M. I.Spatial-domain Green's functions for multilayer, planar geometries are cast into closed forms with two-level approximation of the spectral-domain representation of the Green's functions. This approach is very robust and much faster compared to the original one-level approximation. Moreover, it does not require the investigation of the spectral-domain behavior of the Green's functions in advance to decide on the parameters of the approximation technique, and it can be applied to any component of the dyadic Green's function with the same ease.