Browsing by Subject "Ultrasound"

Now showing 1 - 3 of 3

Open Access
Nonlinear modeling of an immersed transmitting capacitive micromachined ultrasonic transducer for harmonic balance analysis
(IEEE, 2010) Oguz, H. K.; Olcum, S.; Senlik, M. N.; Taş, V.; Atalar, Abdullah; Köymen, Hayrettin
Finite element method (FEM) is used for transient dynamic analysis of capacitive micromachined ultrasonic transducers (CMUT) and is particularly useful when the membranes are driven in the nonlinear regime. One major disadvantage of FEM is the excessive time required for simulation. Harmonic balance (HB) analysis, on the other hand, provides an accurate estimate of the steady-state response of nonlinear circuits very quickly. It is common to use Mason's equivalent circuit to model the mechanical section of CMUT. However, it is not appropriate to terminate Mason's mechanical LC section by a rigid piston's radiation impedance, especially for an immersed CMUT. We studied the membrane behavior using a transient FEM analysis and found out that for a wide range of harmonics around the series resonance, the membrane displacement can be modeled as a clamped radiator. We considered the root mean square of the velocity distribution on the membrane surface as the circuit variable rather than the average velocity. With this definition, the kinetic energy of the membrane mass is the same as that in the model. We derived the force and current equations for a clamped radiator and implemented them using a commercial HB simulator. We observed much better agreement between FEM and the proposed equivalent model, compared with the conventional model.
Open Access
Reflection of ultrasonic waves at a liquid–cubic–solid interface
(A I P Publishing, 1983-02) Atalar, Abdullah
The results of numerical calculations are presented for the reflection coefficient of sound waves incident on a liquid–cubic–solid interface. The reflection coefficient is calculated numerically for the (001) face of various cubic crystals. It is found that for certain orientations there is a null in the reflection coefficient. At this orientation all the power is coupled into a quasishear wave inside the solid. An explanation based on impedance theory is presented. The explanation given predicts that there might be reflection nulls for other liquid–solid interfaces where the solid is any anisotropic solid not just cubic.
Open Access
Silicon micromachined ultrasonic immersion transducers
(A I P Publishing LLC, 1996-12-09) Soh, H. T.; Ladabaum, I.; Atalar, Abdullah; Quate, C. F.; Khuri-Yakub, B. T.
Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signal‐to‐noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using siliconsurfacemicromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in high‐temperature environments and that arrays can be fabricated at lower cost.