Browsing by Subject "Capacitive micromachined ultrasonic transducers"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Open Access Batch-compatible micromanufacturing of a CMUT array for optoacoustic imaging of tissue-like phantoms(Bilkent University, 2021-08) Özyiğit, Doğu Kaan BuğraPhotoacoustic imaging (PAI), also named optoacoustic imaging, is a technol-ogy for medical imaging that relies on contrast data due to optical stimulation. Capacitive micromachined ultrasound transducers (CMUTs) are previously in-troduced for PAI applications. In this thesis, the provided CMUT array design has been partially micro-manufactured separately from electronics and a laser fiber light source while re-serving the necessary chip space for integration with electronics and laser fiber light source. Batch compatible wafer-scale microfabrication of CMUT arrays was done by a combination of novel as well as traditional MEMS microfabrication pro-cesses. CMUT array gaps, bottom electrodes, and insulation layer were formed on the Pyrex wafer using three separate photolithography masks. Anodic wafer bonding method is used for the formation of the top electrodes and top side of the gap heights of CMUT arrays. Process development for anodic wafer bonding between Pyrex wafers and SOI wafers has been done, where the Pyrex wafers have been previously processed with plasma etching, wet etching, metal stack de-position, insulation layer deposition, and insulation layer patterning, while SOI wafers have been used as received. Pyrex wafers and SOI wafers were anodically bonded to each other with developed anodic wafer bonding processes. After full completion of the micromanufacturing of the CMUT array chips, these CMUT ar-ray chips will be integrated with ASIC chips. Then, CMUT array chips and ASIC chips will be combined with a traditional printed circuit board (PCB). These in-tegrated CMUT array chips, ASIC chips, and PCB are going to be integrated with a fiber laser light source inside a mechanically robust hand-held probe that is planned to be used for optoacoustic imaging. The main goal of this CMUT array micromanufacturing study is to significantly contribute to the development of one of the necessary components for imaging of a tissue like-phantom using a hand-held imaging probe.Item Open Access Design charts to maximize the gain-bandwidth product of capacitive micromachined ultrasonic transducers(IEEE, 2005) Ölçüm, Selim; Şenlik, Muhammed Niyazi; Bayram, Can; Atalar, AbdullahIn this work we define a performance measure for capacitive micromachined ultrasonic transducers (cMUT) in the form of a gain-bandwidth product to investigate the conditions that optimize the gain and bandwidth with respect to device dimensions, electrode size and electrical termination resistance. For the transmit mode, we define the figure of merit as the pressure-bandwidth product. Fully-metallized membranes achieve a higher pressure-bandwidth product compared to partially metallized ones. It is shown that the bandwidth is not affected by the electrode size in the transmit mode. In the receive mode, we define the figure of merit as the gain-bandwidth product. We show in this case that the figure of merit can be maximized by optimizing the electrode radius. We present normalized charts for designing an optimum cMUT cell at the desired frequency with a given bandwidth for transmit or receive modes. The effect of spurious capacitance and liquid loading effect are considered. Design examples are given to clarify the use of these charts.Item Open Access Design, fabrication and operation of a very high intensity CMUT transmit array for beam steering applications(Bilkent University, 2020-12) Khan, Talha MasoodSeveral studies have reported airborne ultrasound transmission systems focused on achieving beamforming. However, beam steering and beamforming for capacitive micromachined ultrasonic transducers (CMUTs) at high intensity remains to be accomplished. CMUTs, like other ultrasonic transducers, incorporate a loss mechanism to obtain a wide bandwidth. They are restricted to a limited amount of plate swing due to the gap between the radiating plate and the bottom electrode, along with a high dc bias operation. CMUTs can be designed to produce high-intensity ultrasound by employing an unbiased operation. This mode of operation allows the plate to swing the entire gap without collapsing, thus enabling higher intensity. In this study, we use an equivalent circuit-based model to design unbiased CMUT arrays driven at half the mechanical frequency. This model is cross verified using finite element analysis (FEA). CMUT arrays are produced in multiple configurations using a customized microfabrication process that involves anodic wafer bonding, a single lithographic mask, and a shadow mask. We use impedance measurements to characterize the microfabricated devices. We experimentally obtained the highest reported intensity using a microfabricated 2×2 CMUT array driven at resonance in a pulsed configuration. This array is also capable of beam steering and beamforming at a high intensity such that it can steer the entire half-space. The beam obtained from the array is in excellent agreement with the theoretical predictions. The amplitude and phase compensation for the devices remain constant that makes these arrays attractive for applications involving park assist, gesture recognition, and tactile displays.Item Open Access Electrically unbiased and half frequency driven waterborne 16×16-element 2-D phased array CMUT(Bilkent University, 2019-08) Enhoş, KeremCapacitive micromachined ultrasonic transducers (CMUT) are typically used as arrays consisting of separate cells or interconnected sub arrays, and these cells have several operation modes. Design procedure and measurements have been previously presented for an airborne CMUT cell without a DC bias. In unbiased mode, the plate motion spans the entire gap without collapsing. The frequency of sinusoidal electrical input signal is half of the resulting acoustical output signal. A large plate swing can be obtained at low excitation voltages using the entire remaining gap. In this work, a design procedure of arrays with unbiased operation mode is derived. Designs are validated by means of simulations and measurements on fabricated CMUTs. The problems associated with beamforming are resolved. Use of this operation mode in an array configuration enables larger acoustical power output. A better transmitted signal waveform definition is obtained when pulse width modulation (PWM) is employed. In the design process of CMUTs, large-signal equivalent circuit model is used. In order to have volumetric transmission, a 16×16 (256 elements) phased array configuration is chosen. A design procedure is presented considering the radiation pattern, Rayleigh distance and the parameters of the lumped-element model. This procedure is applied for designing two arrays, with resonance frequencies at 7.5 MHz and at 18.5 MHz. Harmonic balance and transient analyses are carried out with Gaussian enveloped tone burst, transient sinusoidal and PWM signals with different duty cycles. Outputs of these simulations are fed in beamforming toolboxes for further verification. Corresponding experimental measurements are conducted on an ultrasound measurement system. The dimensions of the CMUT elements in the array are determined as 80 μm element radius, 15 μm plate thickness, and 171 nm effective gap height at 7.5 MHz, where the center-to-center inter-element pitch is set at 192 μm. The array is designed such that it has maximum Rayleigh distance of 45.3 mm, while having a maximum sidelobe level of −17.4 dB. According to these specifications, CMUT array is manufactured using wafer scale batch compatible production. Only two lithography masks, which require conventional photolithography steps, are used in production. The vibrating plate is constructed with anodic wafer bonding and the fabricated CMUT array chip is integrated to PCB with flip-chip bonding. Measurements are conducted for this novel device by integrating the CMUT array chip manufactured with MEMS techniques and conventional macro scale manufactured PCB by using impedance analyser.Item 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.Item Open Access Improved performance of cMUT with nonuniform membranes(IEEE, 2005-09) Şenlik, Muhammed N.; Olcum, Selim; Atalar, AbdullahWhen capacitive micromachined ultrasonic transducers are immersed in water, the bandwidth of the device is limited by the membrane's second resonance frequency. At this frequency no mechanical power to immersion medium can be transferred. We present a membrane shape to shift the second resonance frequency to a higher value. The structure consists of a very thin membrane at the outer rim with a rigid mass at the center. The stiffness of the central region moves the second resonance to a higher frequency. This membrane configuration is shown to work better in terms of gain and bandwidth as compared to conventional uniform membranes in both transmission and reception. © 2005 IEEE.Item Open Access A new detection method for capacitive micromachine ultrasonic transducers(IEEE, 2001) Ergun, A. S.; Temelkuran, B.; Özbay, Ekmel; Atalar, AbdullahCapacitive micromachine ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They consist of many small circular membranes that are connected in parallel. In this work, we report a new detection method for cMUTs. We model the membranes as capacitors and the interconnections between the membranes as inductors. This kind of LC network is called an artificial transmission line. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial line at a high RF frequency (in the gigahertz range), the vibrations of the membranes can be detected in a very sensitive manner. For the devices we measured, we calculated the minimum detectable displacement to be in the order of 10 -5 Å/√Hz with a possible improvement to 10 -7 Å/√Hz.Item Open Access A new signal detection method for capacitive micromachined ultrasonic transducers(Bilkent University, 1999) Ergun, Arif SanlıCapacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They are constructed by integrating many small circular membranes in parallel. In this thesis, we demonstrate a new signal detection method for cMUT’s. We model the membranes as capacitors, and the interconnection lines between the membranes as inductors. The resulting circuit is an artificial transmission line with a certain electrical length. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial transmission line using a high RF frequency (in the GHz range), the vibrations of the membranes can be detected in a very sensitive manner. Typically, the improvement over the conventional method is two orders of magnitude. For the devices we measured we observed a minimum detectable displacement in the order of 10"^ A/V^.Item 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, HayrettinIn 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.