Browsing by Subject "Transducers"

Now showing 1 - 20 of 21

Open Access
Bandwidth, power and noise considerations in airborne cMUTs
(IEEE, 2009-09) Şenlik, Muhammed N.; Olcum, Selim; Köymen, Hayrettin; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (cMUTs) offer wider bandwidth in air due to their low mechanical impedances. The impedance mismatch between the air and transducer decreases with the smaller device dimensions increasing the bandwidth at the expense of the degradation in the transmit power and the receive sensitivity. In this work, the bandwidth of cMUT is optimized by increasing its radiation resistance. This is done by properly choosing the size of cMUT membranes and their placement within an array. This selection not only brings an improvement in the transmitted power when it is used as a transmitter, but also improves the noise figure when it is used as a receiver. A further improvement in the noise figure is possible when the cells are clustered and connected to separate receivers. ©2009 IEEE.
Open Access
Characterization and imaging with lamb wave lens at gigahertz frequencies
(IEEE, 1994-10-11) Bozkurt, Ayhan; Yaralıoğlu, Göksenin; Atalar, Abdullah; Köymen, Hayrettin; Kramer, K.
Lamb wave lenses with conical refracting surfaces are fabricated for use at 400 MHz and 1 GHz. The conical surfaces are ground and polished with mechanical means and they are sufficiently smooth for the frequencies of interest. The wide bandwidth of transducers allow frequency tuning necessary for Lamb wave lenses. The fabricated lenses show the expected V(Z) performance. At high frequencies the attenuation in the coupling medium can be very high, but due to the smaller wavelength the resolution is better and defocus distance can be reduced. Inherently higher leaky wave sensitivity of Lamb wave lens enables a good V(Z) characterization ability at higher frequencies as compared to the conventional spherical lens. Subsurface imaging with these Lamb wave lenses gives satisfactory results for layered structures. Chosen object has leaky wave modes within the angular coverage of the lens. The images exhibit a resolution close to the diffraction limit. Experimental V(Z) curves obtained with these lenses along with images are presented.
Open Access
Continuously tunable terahertz metamaterial employing magnetically actuated cantilevers
(Optical Society of American (OSA), 2011) Ozbey, B.; Aktas O.
Terahertz metamaterial structures that employ flexing microelectromechanical cantilevers for tuning the resonance frequency of an electric split-ring resonator are presented. The tuning cantilevers are coated with a magnetic thin-film and are actuated by an external magnetic field. The use of cantilevers enables continuous tuning of the resonance frequency over a large frequency range. The use of an externally applied magnetic field for actuation simplifies the metamaterial structure and its use for sensor or filter applications. A structure for minimizing the actuating field is derived. The dependence of the tunable bandwidth on frequency is discussed. © 2011 Optical Society of America.
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, Abdullah
Capacitive 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.
Open Access
Designing transmitting CMUT cells for airborne applications
(Institute of Electrical and Electronics Engineers Inc., 2014) Ünlügedik, A.; Taşdelen, A.; Atalar, Abdullah; Köymen, Hayrettin
We report a new mode of airborne operation for capacitive micromachined ultrasonic transducers (CMUT), in which the plate motion spans the entire gap without collapsing and the transducer is driven by a sinusoidal voltage without a dc bias. We present equivalent-circuit-based design fundamentals for an airborne CMUT cell and verify the design targets using fabricated CMUTs. The performance limits for silicon plates are derived. We experimentally obtain 78.9 dB//20 μPa@1 m source level at 73.7 kHz, with a CMUT cell of radius 2.05 mm driven by 71 V sinusoidal drive voltage at half the frequency. The measured quality factor is 120. We also study and discuss the interaction of the nonlinear transduction force and the nonlinearity of the plate compliance. © 1986-2012 IEEE.
Open Access
Developing a transducer based on localized surface plasmon resonance (LSPR) of gold nanostructures for nanobiosensor applications
(Trans Tech Publications, 2013) Turhan, Adil Burak; Ataman, D.; Çakmakyapan, S.; Mutlu, M.; Özbay, Ekmel; Vlachos, D. S.; Hristoforou, E.
In this work, we report the nanofabrication, optical characterization, and electromagnetic modeling of various nanostructure arrays for localized surface plasmon resonance (LSPR) based biosensing studies. Comparison of the experimental results and simulation outputs of various nanostructure arrays was made and a good correspondence was achieved.
Open Access
Electrically unbiased driven airborne capacitive micromachined ultrasonic transducer design
(IEEE, 2012) Ünlügedik, Aslı; Atalar, Abdullah; Kocabaş, Coşkun; Oğuz, H. Kağan; Köymen, Hayrettin
We present a design method for airborne capacitive micromachined ultrasonic transducers (CMUT). We use an equivalent lumped element circuit to model both electrical and mechanical properties of CMUT and analyze it in frequency domain using harmonic balance approach. We use this method to design CMUTs for large transmitted power generation at low drive voltage amplitude. We determine the dimensions of an airborne CMUT using the proposed method that works at 30 kHz with 5 mm radius, 240 μm membrane thickness and 11.8 μm effective gap height. The CMUT is designed such that an atmospheric depression of 70% of effective gap height is maintained. © 2012 IEEE.
Open Access
Experimental characterization of capacitive micromachined ultrasonic transducers
(IEEE, 2007) Ölçüm, Selim; Atalar, Abdullah; Köymen, Hayrettin; Oğuz, Kağan; Şenlik, Muhammed N.
In this paper, capacitive micromachined ultrasonic transducers are fabricated using a sacrificial surface micromachining process. A testing procedure has been established in order to measure the absolute transmit and receive sensitivity spectra of the fabricated devices. The experiments are performed in oil. Pulse-echo experiments are performed and the results are compared to the pitch-catch measurements using calibrated transducers.
Open Access
Frequency optimization in high intensity focused ultrasound
(IEEE, 2014-09) Yetik, H.; Arıyurek, Cemre; Bozkurt, A.; Ergun, A. S.
In high intensity focused ultrasound (HIFU) the choice of transducer frequency depends on the target depth and tissue type. At high frequencies attenuation does not permit enough acoustical power to be transmitted to the target whereas at low frequencies the transmitted power is not absorbed efficiently. Hence, there exists an optimum frequency at which the power deposited at the target is maximum. In this study, we verified this relation experimentally using MR compatible focused transducers, ex-vivo tissue samples and magnetic resonance (MR) thermometry. © 2014 IEEE.
Open Access
Harmonic cantilevers for nanomechanical sensing of elastic properties
(IEEE, 2003-06) Şahin, O.; Yaralıoğlu, G.; Grow, R.; Zappe, S. F.; Atalar, Abdullah; Quate, C.; Solgaard, O.
We present a micromachined scanning probe cantilever, in which a specific higher order flexural mode is designed to be resonant at an exact integer multiple of the fundamental resonance frequency. We have demonstrated that such cantilevers enable sensing of nonlinear mechanical interactions between the atomically sharp tip at the free end of the cantilever and a surface with unknown mechanical properties in tapping-mode atomic force microscopy.
Open Access
Nanomechanical motion transducers for miniaturized mechanical systems
(MDPI AG, 2017) Kouh, T.; Hanay, M. S.; Ekinci, K. L.
Reliable operation of a miniaturized mechanical system requires that nanomechanical motion be transduced into electrical signals (and vice versa) with high fidelity and in a robust manner. Progress in transducer technologies is expected to impact numerous emerging and future applications of micro- and, especially, nanoelectromechanical systems (MEMS and NEMS); furthermore, high-precision measurements of nanomechanical motion are broadly used to study fundamental phenomena in physics and biology. Therefore, development of nanomechanical motion transducers with high sensitivity and bandwidth has been a central research thrust in the fields of MEMS and NEMS. Here, we will review recent progress in this rapidly-advancing area.
Open Access
Optimization and tunability of deep subwavelength resonators for metamaterial applications: complete enhanced transmission through a subwavelength aperture
(Optical Society of American (OSA), 2009) Alici, K.B.; Bilotti F.; Vegni L.; Özbay, Ekmel
In the present work, we studied particle candidates for metamaterial applications, especially in terms of their electrical size and resonance strength. The analyzed particles can be easily produced via planar fabrication techniques. The electrical size of multi-split ring resonators, spiral resonators, and multi-spiral resonators are reported as a function of the particle side length and substrate permittivity. The study is continued by demonstrating the scalability of the particles to higher frequencies and the proposition of the optimized particle for antenna, absorber, and superlens applications: a multi-spiral resonator with ë/30 electrical size operating at 0.810 GHz. We explain a method for tuning the resonance frequency of the multi-split structures. Finally, we demonstrate that by inserting deep subwavelength resonators into periodically arranged subwavelength apertures, complete transmission enhancement can be obtained at the magnetic resonance frequency. © 2009 Optical Society of America.
Open Access
Optimization of the gain-bandwidth product of capacitive micromachined ultrasonic transducers
(IEEE, 2005-12) Olcum, S.; Senlik, M. N.; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (cMUT) have large bandwidths, but they typically have low conversion efficiencies. This paper defines a performance measure in the form of a gain-bandwidth product and investigates the conditions in which this performance measure is maximized. A Mason model corrected with finite-element simulations is used for the purpose of optimizing parameters. There are different performance measures for transducers operating in transmit, receive, or pulse-echo modes. Basic parameters of the transducer are optimized for those operating modes. Optimized values for a cMUT with silicon nitride membrane and immersed in water are given. The effect of including an electrical matching network is considered. In particular, the effect of a shunt inductor in the gain-bandwidth product is investigated. Design tools are introduced, which are used to determine optimal dimensions of cMUTs with the specified frequency or gain response.
Open Access
Optimizing CMUT geometry for high power
(IEEE, 2010) Yamaner F.Y.; Olcum, Selim; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (CMUTs) have demonstratedvarious advantages over piezoelectric transducers. However, current CMUT designsproduce low output pressures with high harmonic distortions. Optimizing thetransducer parameters requires an iterative solution and is too time consumingusing finite element (FEM) modelling tools. In this work, we present a method ofdesigning high output pressure CMUTs with relatively low distortion. We analyzethe behavior of a membrane under high voltage continuous wave operation using anonlinear electrical circuit model. The radiation impedance of an array ofCMUTs is accurately represented using an RLC circuit in the model. The maximummembrane swing without collapse is targeted in the transmit mode. Using SPICEsimulation of the parametric circuit model, we design the CMUT cell withoptimized parameters such as the membrane radius (a), thickness (tm),insulator thickness (ti) and gap height (tg). The modelalso predicts the amount of second harmonic at the output. To verify theaccuracy of the results, we built a FEM model with the same CMUT parameters. Thedesign starts by choosing ti for the given input voltage level.First, a is selected for the maximum radiation resistance of the array at theoperating frequency. Second, tm is found for the resonance at theinput frequency. Third, tg is chosen for the maximum membrane swing.Under this condition, a frequency shift in the resonant frequency occurs. Secondand third steps are repeated until convergence. This method results in a CMUTarray with a high output power and with low distortion. © 2010 IEEE.
Open Access
Parametric nonlinear lumped element model for circular CMUTs in collapsed mode
(2014) Aydoǧdu, E.; Ozgurluk, A.; Atalar, Abdullah; Köymen, Hayrettin
We present a parametric equivalent circuit model for a circular CMUT in collapsed mode. First, we calculate the collapsed membrane deflection, utilizing the exact electrical force distribution in the analytical formulation of membrane deflection. Then we develop a lumped element model of collapsed membrane operation. The radiation impedance for collapsed mode is also included in the model. The model is merged with the uncollapsed mode model to obtain a simulation tool that handles all CMUT behavior, in transmit or receive. Large- and small-signal operation of a single CMUT can be fully simulated for any excitation regime. The results are in good agreement with FEM simulations. © 2014 IEEE.
Open Access
Radiation impedance of an array of circular capacitive micromachined ultrasonic transducers
(IEEE, 2010) Senlik, M. N.; Olcum, S.; Köymen, Hayrettin; Atalar, Abdullah
The radiation impedance of a capacitive micromachined ultrasonic transducer (cMUT) with a circular membrane is calculated analytically using its velocity profile for the frequencies up to its parallel resonance frequency for both the immersion and the airborne applications. The results are verified by finite element simulations. The work is extended to calculate the radiation impedance of an array of cMUT cells positioned in a hexagonal pattern. A higher radiation resistance improves the bandwidth as well as the efficiency of the cMUT. The radiation resistance is determined to be a strong function of the cell spacing. It is shown that a center-to-center cell spacing of 1.25 wavelengths maximizes the radiation resistance, if the membranes are not too thin. It is also found that excitation of nonsymmetric modes may reduce the radiation resistance in immersion applications.
Open Access
Radiation impedance of an array of circular capacitive micromachined ultrasonic transducers in collapsed state
(IEEE, 2011-10) Özgürlük, Alper; Atalar, Abdullah; Köymen, Hayrettin; Olcum, Selim
Radiation impedance is one of the important parameters in designing efficient and wideband capacitive micro-machined ultrasonic transducer (CMUT) arrays. It determines how much acoustical power is generated in the surrounding medium given the membrane motion. Recently, considerable effort has been put to characterize the radiation impedance of CMUT arrays in conventional uncollapsed regime. However, the radiation impedance of an array of CMUT cells in collapsed state has not yet been investigated. To calculate the array radiation impedance in collapse mode, we first calculate the radiation impedance of a single cell CMUT. For the array case, the mutual impedances between the neighboring cells must also be taken into account.We consider an array of 7, 19, 37, and 61 cells placed in a hexagonal pattern and try to determine the radiation impedance for different degrees of collapse. We find that in the collapsed case the peak radiation resistance value is reached at higher kd values, where k is the wavenumber and d is the center to center cell spacing, compared to the uncollapsed regime.
Open Access
Radiation impedance of collapsed capacitive micromachined ultrasonic transducers
(Institute of Electrical and Electronics Engineers, 2012) Ozgurluk, A.; Atalar, Abdullah; Köymen, Hayrettin; Olçum, S.
The radiation impedance of a capacitive micromachined ultrasonic transducer (CMUT) array is a critical parameter to achieve high performance. In this paper, we present a calculation of the radiation impedance of collapsed, clamped, circular CMUTs both analytically and using finite element method (FEM) simulations. First, we model the radiation impedance of a single collapsed CMUT cell analytically by expressing its velocity profile as a linear combination of special functions for which the generated pressures are known. For an array of collapsed CMUT cells, the mutual impedance between the cells is also taken into account. The radiation impedances for arrays of 7, 19, 37, and 61 circular collapsed CMUT cells for different contact radii are calculated both analytically and by FEM simulations. The radiation resistance of an array reaches a plateau and maintains this level for a wide frequency range. The variation of radiation reactance with respect to frequency indicates an inductance-like behavior in the same frequency range. We find that the peak radiation resistance value is reached at higher kd values in the collapsed case as compared with the uncollapsed case, where k is the wavenumber and d is the center-to-center distance between two neighboring CMUT cells.
Open Access
Transmission enhancement through deep subwavelength apertures using connected split ring resonators
(Optical Society of American (OSA), 2010) Ates, D.; Cakmak, A.O.; Colak, E.; Zhao, R.; Soukoulis, C.M.; Özbay, Ekmel
We report astonishingly high transmission enhancement factors through a subwavelength aperture at microwave frequencies by placing connected split ring resonators in the vicinity of the aperture. We carried out numerical simulations that are consistent with our experimental conclusions. We experimentally show higher than 70,000-fold extraordinary transmission through a deep subwavelength aperture with an electrical size of λ/31xλ/12 (width x length), in terms of the operational wavelength. We discuss the physical origins of the phenomenon. Our numerical results predict that even more improvements of the enhancement factors are attainable. Theoretically, the approach opens up the possibility for achieving very large enhancement factors by overcoming the physical limitations and thereby minimizes the dependence on the aperture geometries. © 2010 Optical Society of America.
Open Access
Wafer bonded capacitive micromachined underwater transducers
(IEEE, 2009-09) Olcum, Selim; Oǧuz, Kaan; Şenlik, Muhammed N.; Yamaner F. Y.; Bozkurt, A.; Atalar, Abdullah; Köymen, Hayrettin
In this work we have designed, fabricated and tested CMUTs as underwater transducers. Single CMUT membranes with three different radii and 380 microns of thickness are fabricated for the demonstration of an underwater CMUT element. The active area of the transducer is fabricated on top of a 3″ silicon wafer. The silicon wafer is bonded to a gold electrode coated glass substrate wafer 10 cm in diameter. Thermally grown silicon oxide layer is used as the insulation layer between membrane and substrate electrodes. Electrical contacts and insulation are made by epoxy layers. Single CMUT elements are tested in air and in water. Approximately 40% bandwidth is achieved around 25 KHz with a single underwater CMUT cell. Radiated pressure field due to second harmonic generation when the CMUTs are driven with high sinusoidal voltages is measured. ©2009 IEEE.