@article{ibn minhaj_annayev_adelegan_biliroğlu_yamaner_oralkan_2024, title={Design, Fabrication, and Characterization of Capacitive Micromachined Ultrasonic Transducers for Transcranial, Multifocus Neurostimulation}, volume={15}, ISSN={2072-666X}, url={http://dx.doi.org/10.3390/mi15091106}, DOI={10.3390/mi15091106}, abstractNote={In a recent study using 3-D fullwave simulations, it was shown for a nonhuman primate model that a helmet-shaped 3D array of 128 transducer elements can be assembled for neurostimulation in an optimized configuration with the accommodation of an imaging aperture. Considering all acoustic losses, according to this study, for a nonhuman primate skull, the assembly of the proposed transducers was projected to produce sufficient focusing gain in two different focal positions at deep and shallow brain regions, thus providing sufficient acoustic intensity at these distinct focal points for neural stimulation. This array also has the ability to focus on multiple additional brain regions. In the work presented here, we designed and fabricated a single 15 mm diameter capacitive micromachined ultrasonic transducer (CMUT) element operating at 800 kHz central frequency with a 480 kHz 3 dB bandwidth, capable of producing a 190 kPa peak negative pressure (PNP) on the surface. The corresponding projected transcranial spatial peak pulse average intensity (I}, number={9}, journal={Micromachines}, publisher={MDPI AG}, author={Ibn Minhaj, Tamzid and Annayev, Muhammetgeldi and Adelegan, Oluwafemi J. and Biliroğlu, Ali Önder and Yamaner, Feysel Yalçın and Oralkan, Ömer}, year={2024}, month={Aug}, pages={1106} }
 @article{annayev_biliroglu_sennik_yamaner_oralkan_2024, title={Fabrication of 32 x 32 2D CMUT Arrays on a Borosilicate Glass Substrate With Silicon-Through-Wafer Interconnects Using Non-Aligned and Aligned Anodic Bonding}, volume={8}, ISSN={["1941-0158"]}, url={https://doi.org/10.1109/JMEMS.2024.3440191}, DOI={10.1109/JMEMS.2024.3440191}, journal={JOURNAL OF MICROELECTROMECHANICAL SYSTEMS}, author={Annayev, Muhammetgeldi and Biliroglu, Ali Onder and Sennik, Erdem and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2024}, month={Aug} }
 @article{riley_roeder_zinke_weisend_eidum_pinton_biliroglu_yamaner_oralkan_connolly_2024, title={Activation of primate frontal eye fields with a CMUT phased array system}, volume={402}, ISSN={["1872-678X"]}, DOI={10.1016/j.jneumeth.2023.110009}, abstractNote={There are pushes toward non-invasive stimulation of neural tissues to prevent issues that arise from invasive brain recordings and stimulation. Transcranial Focused Ultrasound (TFUS) has been examined as a way to stimulate non-invasively, but previous studies have limitations in the application of TFUS. As a result, refinement is needed to improve stimulation results. We utilized a custom-built capacitive micromachined ultrasonic transducer (CMUT) that would send ultrasonic waves through skin and skull to targets located in the Frontal Eye Fields (FEF) region triangulated from co-registered MRI and CT scans while a non-human primate subject was performing a discrimination behavioral task. We observed that the stimulation immediately caused changes in the local field potential (LFP) signal that continued until stimulation ended, at which point there was higher voltage upon the cue for the animal to saccade. This co-incided with increases in activity in the alpha band during stimulation. The activity rebounded mid-way through our electrode-shank, indicating a specific point of stimulation along the shank. We observed different LFP signals for different stimulation targets, indicating the ability to"steer" the stimulation through the transducer. We also observed a bias in first saccades towards the opposite direction. In conclusion, we provide a new approach for non-invasive stimulation during performance of a behavioral task. With the ability to steer stimulation patterns and target using a large amount of transducers, the ability to provide non-invasive stimulation will be greatly improved for future clinical and research applications.}, journal={JOURNAL OF NEUROSCIENCE METHODS}, author={Riley, Mitchell R. and Roeder, Brent M. and Zinke, Wolf and Weisend, Michael P. and Eidum, Derek M. and Pinton, Gianmarco F. and Biliroglu, Ali O. and Yamaner, Feisal Y. and Oralkan, Omer and Connolly, Patrick M.}, year={2024}, month={Feb} }
 @article{sanders_biliroglu_newsome_adelegan_yamaner_dayton_oralkan_2022, title={A Handheld Imaging Probe for Acoustic Angiography With an Ultrawideband Capacitive Micromachined Ultrasonic Transducer (CMUT) Array}, volume={69}, ISSN={["1525-8955"]}, url={https://doi.org/10.1109/TUFFC.2022.3172566}, DOI={10.1109/TUFFC.2022.3172566}, abstractNote={This article presents an imaging probe with a 256-element ultrawideband (UWB) 1-D capacitive micromachined ultrasonic transducer (CMUT) array designed for acoustic angiography (AA). This array was fabricated on a borosilicate glass wafer with a reduced bottom electrode and an additional central plate mass to achieve the broad bandwidth. A custom 256-channel handheld probe was designed and implemented with integrated low-noise amplifiers and supporting power circuitry. This probe was used to characterize the UWB CMUT, which has a functional 3-dB frequency band from 3.5 to 23.5 MHz. A mechanical index (MI) of 0.33 was achieved at 3.5 MHz at a depth of 11 mm. These promising measurements are then combined to demonstrate AA. The use of alternate amplitude modulation (aAM) combined with a frequency analysis of the measured transmit signal demonstrates the suitability of the UWB CMUT for AA. This is achieved by measuring only a low level of unwanted high-frequency harmonics in both the transmit signal and the reconstructed image in the areas other than the contrast bubbles.}, number={7}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Sanders, Jean L. and Biliroglu, Ali Onder and Newsome, Isabel G. and Adelegan, Oluwafemi J. and Yamaner, Feysel Yalcin and Dayton, Paul A. and Oralkan, Omer}, year={2022}, month={Jul}, pages={2318–2330} }
 @article{belekov_bautista_annayev_adelegan_biliroglu_kierski_sanders_kemal_sennik_yamaner_et al._2022, title={Performance Assessment of Ultra-Wideband and Dual-Mode 1D CMUT Arrays for Acoustic Angiography}, ISSN={["1948-5719"]}, DOI={10.1109/IUS54386.2022.9958537}, abstractNote={In this work, we have demonstrated the imaging potential of 256-element ultra-wideband (UWB) and dual-mode CMUT 1D arrays for acoustic angiography through mechanical index measurements and in-vitro imaging experiments. We have designed a custom 256-channel imaging probe with integrated low-noise amplifiers and supporting power circuitry. To improve the elevational focusing, we mounted an acoustic lens on to the array. The acoustic characterization of the CMUT array was performed by a calibrated hydrophone, with which we measured sufficiently high mechanical indices (i.e., 0.79 MI for the UWB and 0.85 MI for the dual-mode array) at the focal spot at 15-mm depth. We conducted an imaging experiment with a tissue-mimicking phantom including a 0.2-mm-diameter cellulose tube, in which microbubbles and water flowed. We demonstrated a CTR of 62.12 ± 1.06 dB for the UWB array and a CTR of 59.69 ± 0.39 dB for the dual-mode array when microbubbles were flowing through the tube. These experiments presented a strong use case for the UWB and dual-mode CMUT arrays in acoustic angiography applications.}, journal={2022 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS)}, author={Belekov, Ermek and Bautista, Kathlyne J. and Annayev, Muhammetgeldi and Adelegan, Oluwafemi J. and Biliroglu, Ali O. and Kierski, Thomas M. and Sanders, Jean L. and Kemal, Remzi E. and Sennik, Erdem and Yamaner, Feysel Y. and et al.}, year={2022} }
 @article{seok_adelegan_biliroglu_yamaner_oralkan_2021, title={A Wearable Ultrasonic Neurostimulator-Part II: A 2D CMUT Phased Array System With a Flip-Chip Bonded ASIC}, volume={15}, ISSN={["1940-9990"]}, url={https://doi.org/10.1109/TBCAS.2021.3105064}, DOI={10.1109/TBCAS.2021.3105064}, abstractNote={A 2D ultrasonic array is the ultimate form of a focused ultrasonic system, which enables electronically focusing beams in a 3D space. A 2D array is also a versatile tool for various applications such as 3D imaging, high-intensity focused ultrasound, particle manipulation, and pattern generation. However, building a 2D system involves complicated technologies: fabricating a 2D transducer array, developing a pitch-matched ASIC, and interconnecting the transducer and the ASIC. Previously, we successfully demonstrated 2D capacitive micromachined ultrasonic transducer (CMUT) arrays using various fabrication technologies. In this paper, we present a 2D ultrasonic transmit phased array based on a 32 × 32 CMUT array flip-chip bonded to a pitch-matched pulser ASIC for ultrasonic neuromodulation. The ASIC consists of 32 × 32 unipolar high-voltage (HV) pulsers, each of which occupies an area of 250 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m × 250 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m. The phase of each pulser output is individually programmable with a resolution of <inline-formula><tex-math notation="LaTeX">$1/f_{\mathrm{C}}/16$</tex-math></inline-formula>, where <inline-formula><tex-math notation="LaTeX">$f_{\mathrm{C}}$</tex-math></inline-formula> is less than 10 MHz. This enables the fine granular control of a focus. The ASIC was fabricated in the TSMC 0.18-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m HV BCD process within an area of 9.8 mm × 9.8 mm, followed by a wafer-level solder bumping process. After flip-chip bonding an ASIC and a CMUT array, we identified shorted elements in the CMUT array using the built-in test function in the ASIC, which took approximately 9 minutes to scan the entire 32 × 32 array. A compact-form-factor wireless neural stimulator system—only requiring a connected 15-V DC power supply—was also developed, integrating a power management unit, a clock generator, and a Bluetooth Low-Energy enabled microcontroller. The focusing and steering capability of the system in a 3D space is demonstrated, while achieving a spatial-peak pulse-average intensity (<inline-formula><tex-math notation="LaTeX">$\mathrm{I_{SPPA}}$</tex-math></inline-formula>) of 12.4 and 33.1 W/<inline-formula><tex-math notation="LaTeX">${\rm cm^{2}}$</tex-math></inline-formula>; and a 3-dB focal volume of 0.2 and 0.05 <inline-formula><tex-math notation="LaTeX">${\rm mm^{3}}$</tex-math></inline-formula>—at a depth of 5 mm—at 2 and 3.4 MHz, respectively. We also characterized transmission of ultrasound through a mouse skull and compensated the phase distortion due to the skull by using the programmable phase-delay function in the ASIC, achieving 10% improvement in pressure and a tighter focus. Finally, we demonstrated a ultrasonic arbitrary pattern generation on a 5 mm × 5 mm plane at a depth of 5 mm.}, number={4}, journal={IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Seok, Chunkyun and Adelegan, Oluwafemi Joel and Biliroglu, Ali Onder and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2021}, month={Aug}, pages={705–718} }
 @misc{minhaj_adelegan_biliroglu_annayev_coutant_yamaner_oralkan_2021, title={Design and Fabrication of Single-Element CMUTs for Forming a Transcranial Array for Focused Beam Applications}, ISSN={["1948-5719"]}, url={http://dx.doi.org/10.1109/IUS52206.2021.9593499}, DOI={10.1109/IUS52206.2021.9593499}, abstractNote={Focused ultrasound (FUS) offers numerous applications, including ablative therapies and transcranial neural stimulation. Prototypes of high-intensity FUS transducer arrays have been fabricated with the aid of rapid prototyping using piezoelectric (lead zirconate titanate, PZT) elements. However, piezoelectric transducer elements used in this process are manufactured through convoluted process steps, contain harmful element lead (Pb), and require matching layers for effective operation, which adds to the complexity and cost of the overall process. With capacitive micromachined ultrasonic transducer (CMUT) technology, such transducers can be fabricated in a substantially simplified microfabrication process. We have previously reported a three-mask process for fabricating vacuum-sealed CMUTs using anodic bonding. In this work, we designed CMUTs aiming at achieving a negative peak pressure (on the transducer surface) up to 400 kPa at 750-kHz center frequency which is required for the intended transcranial application. Later, we fabricated the designed single-element CMUT transducers and completed the initial characterization.}, journal={2021 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Minhaj, Tamzid Ibn and Adelegan, Oluwafemi J. and Biliroglu, Ali Onder and Annayev, Muhammetgeldi and Coutant, Zachary A. and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2021}, month={Sep}, pages={1–3} }
 @article{adelegan_coutant_minhaj_seok_biliroglu_yamaner_oralkan_2021, title={Fabrication of 32 x 32 2D Capacitive Micromachined Ultrasonic Transducer (CMUT) Arrays on a Borosilicate Glass Substrate With Silicon-Through-Wafer Interconnects Using Sacrificial Release Process}, volume={30}, ISSN={["1941-0158"]}, url={https://doi.org/10.1109/JMEMS.2021.3111304}, DOI={10.1109/JMEMS.2021.3111304}, abstractNote={Close integration of transducer arrays with supporting electronic circuits is essential in achieving efficient and compact ultrasound systems. An integral part of hybrid integration of 2D CMUT array to CMOS electronics is the introduction of through-glass-via (TGV) interconnects in glass substrates as an integral part of the 2D CMUT array fabrication. Micro-cracks around via locations, via discontinuity, and poor coplanarity between the vias and glass substrate are some of the challenges with laser-drilled, paste-filled copper-through-glass-via (Cu-TGV) interconnects. This study provides a detailed fabrication process for making $32\times 32$ -element 2D CMUT arrays on a composite glass substrate incorporating silicon-through-glass vias (Si-TGV) as interconnects using sacrificial release approach. On one column of a fabricated 2D CMUT array, we measured a mean resonant frequency of 5.6 MHz in air and an average device capacitance of 1.5 pF. With the introduction of a buried top electrode in the device structure, we achieved a collapse voltage of 93 V, which is considerably lower than the collapse voltage measured in our previously demonstrated 2D CMUT arrays with top electrode on top of the nitride plate. The fabricated array is flip-chip bonded on a custom-designed driving integrated circuit to demonstrate the complete system operation. We measured a peak-to-peak pressure of 1.82 MPa at 3.4 MHz, and 5 mm from the array surface in a 0.33 mm focal spot size. [2021-0101]}, number={6}, journal={JOURNAL OF MICROELECTROMECHANICAL SYSTEMS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Adelegan, Oluwafemi J. and Coutant, Zachary A. and Minhaj, Tamzid Ibn and Seok, Chunkyun and Biliroglu, Ali Onder and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2021}, month={Dec}, pages={968–979} }
 @article{sanders_biliroglu_wu_adelegan_yamaner_oralkan_2021, title={A Row-Column (RC) Addressed 2-D Capacitive Micromachined Ultrasonic Transducer (CMUT) Array on a Glass Substrate}, volume={68}, ISSN={["1525-8955"]}, url={https://doi.org/10.1109/TUFFC.2020.3014780}, DOI={10.1109/TUFFC.2020.3014780}, abstractNote={This article presents a row-column (RC) capacitive micromachined ultrasonic transducer (CMUT) array fabricated using anodic bonding on a borosilicate glass substrate. This is shown to reduce the bottom electrode-to-substrate capacitive coupling. This subsequently improves the relative response of the elements when top or bottom electrodes are used as the “signal” (active) electrode. This results in a more uniform performance for the two cases. Measured capacitance and resonant frequency, pulse-echo signal amplitude, and frequency response are presented to support this. Biasing configurations with varying ac and dc arrangements are applied and subsequently explored. Setting the net dc bias voltage across an off element to zero is found to be most effective to minimize spurious transmission. To achieve this, a custom switching circuit was designed and implemented. This circuit was also used to obtain orthogonal B-mode cross-sectional images of a rotationally asymmetric target.}, number={3}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Sanders, Jean L. and Biliroglu, Ali Onder and Wu, Xun and Adelegan, Oluwafemi J. and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2021}, month={Mar}, pages={767–776} }