Browsing by Subject "Array"

Now showing 1 - 8 of 8

Open Access
Acoustical tuning of CMUT receiver arrays
(IEEE, 2016) Taşdelen, Akif Sinan; Atalar, Abdullah; Enhoş, Kerem; Köymen, Hayrettin
Cell placement in an element and structural modifications on the array baffle significantly change the bandwidth, band shape and signal to noise ratio of a CMUT receiver array. In this paper, optimum receiver performance tailoring by means of cell placement, cell size variation and use of dummy cells in the array elements is discussed. The performance of the array is modified acoustically at the acoustic port of the elements.
Open Access
Batch-compatible micromanufacturing of a CMUT array for optoacoustic imaging of tissue-like phantoms
(2021-08) Özyiğit, Doğu Kaan Buğra
Photoacoustic 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.
Open Access
Design, fabrication and operation of a very high intensity CMUT transmit array for beam steering applications
(2020-12) Khan, Talha Masood
Several 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.
Open Access
Designing, fabrication and post- fabrication characterization of half-frequency driven 16 x 16 waterborne transmit CMUT array
(2021-02) Abhoo, Yusuph Abubakar
Capacitive Micromachined Ultrasonic Transducers (CMUT) are micro-scaled electromechanical devices which are used to either transmit or receive pressure signals and applicable for various purposes such as ultrasonic sensor, medical imaging, accurate biometric sensing and parametric speakers. For transmitting CMUT transducer, different sizes and array configurations are used to intensify the transmission power depending on the application. The half-frequency driven waterborne transmitting CMUT array designed in this work is to be used for high resolution volumetric medical imaging purpose. This was accomplished by a design which prioritizes maximizing the power output, achieving a directive radiation pattern with low sidelobes which maximizes the beamformable region. In this work, the issues with steering of the focused beam are also resolved to achieve a focused steerable beam. This work is an advancement from the earlier designed half-frequency driven airborne transmit CMUT to improve power output, introduce the beamforming and focused transmission capabilities and be applicable for high resolution volumetric medical imaging purpose. To improve the power output, the design was made to compensate for the static depression. Compensating for static depression was achieved by designing to operate the CMUT without DC bias voltage which allows for full-gap swing and giving output signal of twice the input frequency. This property allows the cell to produce high power output with low voltage levels but also brings the advantage of operating the cell with very high voltages without collapsing. The CMUT was chosen to be operating at 7.5 MHz and be driven by Digital Phased Array System (DiPhAS) which allowed to have maximum of 256 channels which for volumetric transmission meant a maximum of 16 x 16 array. Since the radiation pattern and Rayleigh distance are both the functions of radius, frequency and the pitch, the design optimization was found while considering all the above preferences simultaneously. The cells’ radii were determined to be 80 µm, the plate thickness was 15 µm, the gap height was found to be 117 nm and the pitch was 192 µm. The array designing was carried out using the large-signal equivalent circuit model and the radiation impedance matrix phenomenon. The simulations showed that with this design, the maximized Rayleigh distance was 45.3 mm and the sidelobe of -17.4 dB. In simulations, very high pressure outputs were achievable with individual cells up to 425 kPa per cell with 150 VPP input while up to 1.5 MPa was emitted by the array plane wave transmission with only 10 VPP input and almost doubles when the transmitted beam was focused at zero degrees. Fabrication was done by the wafer boding and flip-chip bonding techniques where the whole process required only two lithography masks. After fabrication, the tests were performed to identify the yield of the transducer was 18.75% of the array then impedance analysis was done to characterize the functional cells and resonance frequency drift. The transducer was cased in a water-tight manner and the waterborne transmission were done with individual cells to characterize and compare the performance with the design simulations which were in the range of agreement achieving an average of 1625 Pa per cell. The functional cells were then used for plane wave transmission with 10 VPP and the output pressure of 397 kPa was achieved at resonance frequency. The measurement results showed that the design could further be improved by compensating the active area to improve the yield for better results and be able to use it for high resolution 3D medical imaging.
Open Access
Electrically unbiased and half frequency driven waterborne 16×16-element 2-D phased array CMUT
(2019-08) Enhoş, Kerem
Capacitive 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.
Open Access
High Power CMUTs: design and experimental verification
(IEEE, 2012) Yamaner, F. Y.; Olcum, S.; Oguz, H. K.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with piezoelectric transducers in high-power applications. As the output pressures increase, nonlinearity of CMUT must be reconsidered and optimization is required to reduce harmonic distortions. In this paper, we describe a design approach in which uncollapsed CMUT array elements are sized so as to operate at the maximum radiation impedance and have gap heights such that the generated electrostatic force can sustain a plate displacement with full swing at the given drive amplitude. The proposed design enables high output pressures and low harmonic distortions at the output. An equivalent circuit model of the array is used that accurately simulates the uncollapsed mode of operation. The model facilities the design of CMUT parameters for high-pressure output, without the intensive need for computationally involved FEM tools. The optimized design requires a relatively thick plate compared with a conventional CMUT plate. Thus, we used a silicon wafer as the CMUT plate. The fabrication process involves an anodic bonding process for bonding the silicon plate with the glass substrate. To eliminate the bias voltage, which may cause charging problems, the CMUT array is driven with large continuous wave signals at half of the resonant frequency. The fabricated arrays are tested in an oil tank by applying a 125-V peak 5-cycle burst sinusoidal signal at 1.44 MHz. The applied voltage is increased until the plate is about to touch the bottom electrode to get the maximum peak displacement. The observed pressure is about 1.8 MPa with −28 dBc second harmonic at the surface of the array.
Open Access
Transmitting CMUT arrays without a DC bias
(IEEE Computer Society, 2019) Enhoş, Kerem; Taşdelen, Akif Sinan; Yılmaz, Mehmet; Atalar, Abdullah; Köymen, Hayrettin
This study focuses on design, simulation, fabrication and measurement of transmitting CMUT arrays with unbiased mode of operation. We presented a design procedure considering the radiation pattern, Rayleigh distance and the parameters of the large signal equivalent circuit, which can be applied for different operation frequencies and applications. Large signal equivalent circuit model is used for lumped-element simulations. Harmonic balance and transient analyses are carried out with Gaussian enveloped tone burst, sinusoidal and pulse width modulation (PWM) signals with different duty cycles. Outputs of these simulations are fed in beamforming toolboxes for further verification. According to the design specifications transmitting CMUT arrays are fabricated. Corresponding experimental impedance measurements are conducted.
Open Access
A triple-band antenna array for next-generation wireless and satellite-based applications
(Cambridge University Press, 2016) Razzaqi, A. A.; Khawaja, B. A.; Ramzan M.; Zafar, M. J.; Nasir, S. A.; Mustaqim, M.; Tarar, M. A.; Tauqeer, T.
In this paper, a triple-band 1 × 2 and 1 × 4 microstrip patch antenna array for next-generation wireless and satellite-based applications are presented. The targeted frequency bands are 3.6, 5.2 and 6.7 GHz, respectively. Simple design procedures and optimization techniques are discussed to achieve better antenna performance. The antenna is designed and simulated using Agilent ADS Momentum using FR4 substrate (r = 4.2 and h = 1.66 mm). The main patch of the antenna is designed for 3.6 GHz operation. A hybrid feed technique is used for antenna arrays with quarter-wave transformer-based network to match the impedance from the feed-point to the antenna to 50. The antenna is optimized to resonate at triple-bands by using two symmetrical slits. The single-element triple-band antenna is fabricated and characterized, and a comparison between the simulated and measured antenna is presented. The achieved simulated impedance bandwidths/gains for the 1 × 2 array are 1.67%/7.75, 1.06%/7.7, and 1.65%/9.4 dBi and for 1 × 4 array are 1.67%/10.2, 1.45%/8.2, and 1.05%/10 dBi for 3.6, 5.2, and 6.7 GHz bands, respectively, which are very practical. These antenna arrays can also be used for advanced antenna beam-steering systems. Copyright © Cambridge University Press and the European Microwave Association 2014.