@article{annayev_minhaj_adelegan_yamaner_dayton_oralkan_2024, title={Design and Fabrication of 1-D CMUT Arrays for Dual-Mode Dual-Frequency Acoustic Angiography Applications}, volume={71}, ISSN={["1525-8955"]}, url={https://doi.org/10.1109/TUFFC.2023.3342011}, DOI={10.1109/TUFFC.2023.3342011}, abstractNote={When microbubble contrast agents are excited at low frequencies (less than 5 MHz), they resonate and produce higher-order harmonics due to their nonlinear behavior. We propose a novel scheme with a capacitive micromachined ultrasonic transducer (CMUT) array to receive high-frequency microbubble harmonics in collapse mode and to transmit a low-frequency high-pressure pulse by releasing the CMUT plate from collapse and pull it back to collapse again in the same transmit-receive cycle. By patterning and etching the substrate to create glass spacers in the device cavity we can reliably operate the CMUT in collapse mode and receive high-frequency signals. Previously, we demonstrated a single-element CMUT with spacers operating in the described fashion. In this article, we present the design and fabrication of a dual-mode, dual-frequency 1-D CMUT array with 256 elements. We present two different insulating glass spacer designs in rectangular cells for the collapse mode. For the device with torus-shaped spacers, the 3 dB receive bandwidth is from 8 to 17 MHz, and the transmitted maximum peak-to-peak pressure from 32 elements at 4 mm focal depth was 2.12 MPa with a 1.21 MPa peak negative pressure, which corresponds to a mechanical index (MI) of 0.58 at 4.3 MHz. For the device with line-shaped spacers, the 3-dB receive bandwidth at 150 V dc bias extends from 10.9 to 19.2 MHz. By increasing the bias voltage to 180 V, the 3 dB bandwidth shifts, and extends from 11.7 to 20.4 MHz. The transmitting maximum peak-to-peak pressure with 32 elements at 4 mm was 2.06 MPa with a peak negative pressure of 1.19 MPa, which corresponds to an MI of 0.62 at 3.7 MHz.}, number={1}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Annayev, Muhammetgeldi and Minhaj, Tamzid Ibn and Adelegan, Oluwafemi J. and Yamaner, Feysel Yalcin and Dayton, Paul A. and Oralkan, Omer}, year={2024}, month={Jan}, pages={191–201} }
 @article{annayev_yamaner_oralkan_2022, title={A pre-charged CMUT structure with a built-in charge storage capacitor}, ISSN={["1948-5719"]}, DOI={10.1109/IUS54386.2022.9958201}, abstractNote={Pre-charging can eliminate the need for a DC bias in capacitive micromachined ultrasonic transducers (CMUTs) and enable energy transfer to implantables. Charging by Fowler-Nordheim (FN) tunneling through an oxide layer is challenging and requires a high electric field. We designed a pre-charged CMUT structure with a built-in charge storage capacitor. In this novel design, a floating electrode is formed between the top and bottom electrodes. Charge writing is achieved by directly contacting the floating electrode to the bottom electrode. The initial results show that the proposed structure can store electrical charges without leakage and it allows operation without a DC bias.}, journal={2022 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS)}, author={Annayev, Muhammetgeldi and Yamaner, F. Yalcin and Oralkan, Omer}, year={2022} }
 @article{zhao_annayev_oralkan_jia_2022, title={An Ultrasonic Energy Harvesting IC Providing Adjustable Bias Voltage for Pre-Charged CMUT}, volume={16}, ISSN={["1940-9990"]}, url={https://doi.org/10.1109/TBCAS.2022.3178581}, DOI={10.1109/TBCAS.2022.3178581}, abstractNote={Ultrasonic wireless power transmission (WPT) using pre-charged capacitive micromachined ultrasonic transducers (CMUT) is drawing great attention due to the easy integration of CMUT with CMOS techniques. Here, we present an integrated circuit (IC) that interfaces with a pre-charged CMUT device for ultrasonic energy harvesting. We implemented an adaptive high voltage charge pump (HVCP) in the proposed IC, which features low power, overvoltage stress (OVS) robustness, and a wide output range. The ultrasonic energy harvesting IC is fabricated in the 180 nm HV BCD process and occupies a 2 × 2.5 mm2 silicon area. The adaptive HVCP offers a 2× – 12× voltage conversion ratio (VCR), thereby providing a wide bias voltage range of 4 V–44 V for the pre-charged CMUT. Moreover, a VCR tunning finite state machine (FSM) implemented in the proposed IC can dynamically adjust the VCR to stabilize the HVCP output (i.e., the pre-charged CMUT bias voltage) to a target voltage in a closed-loop manner. Such a closed-loop control mechanism improves the tolerance of the proposed IC to the received power variation caused by misalignments, amount of transmitted power change, and/or load variation. Besides, the proposed ultrasonic energy harvesting IC has an average power consumption of 35 μW–554 μW corresponding to the HVCP output from 4 V–44 V. The CMUT device with a local surface acoustic intensity of 3.78 mW/mm2, which is well below the FDA limit for power flux (7.2 mW/mm2), can deliver sufficient power to the IC.}, number={5}, journal={IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS}, author={Zhao, Linran and Annayev, Muhammetgeldi and Oralkan, Omer and Jia, Yaoyao}, year={2022}, month={Oct}, pages={842–851} }
 @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{annayev_adelegan_yamaner_dayton_oralkan_2021, title={Design and Fabrication of 1D CMUT Arrays for Dual-Mode Acoustic Angiography Applications - Preliminary Results}, ISSN={["1948-5719"]}, DOI={10.1109/IUS52206.2021.9593432}, abstractNote={When microbubble contrast agents are excited at low frequencies (less than 5 MHz), they resonate and produce higher order harmonics due to their non-linear behavior. We propose a novel scheme with a capacitive micromachined ultrasonic transducer (CMUT) array to receive high-frequency microbubble harmonics in collapse mode and to transmit a low-frequency high-pressure pulse by releasing the CMUT plate from collapse and pull it back to collapse again in the same transmit-receive cycle. By patterning and etching the substrate to create glass spacers in the device cavity we can operate the CMUT in collapse mode and receive high-frequency signals. Finite element model simulation results show that the fabricated devices can transmit at low frequency (< 5 MHz) and receive echoes at high frequency (> 15 MHz), which are verified by experimental results.}, journal={INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS 2021)}, author={Annayev, Muhammetgeldi and Adelegan, Oluwafemi J. and Yamaner, F. Yalcin and Dayton, Paul A. and Oralkan, Omer}, year={2021} }
 @article{ibn 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"]}, 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={INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS 2021)}, author={Ibn Minhaj, Tamzid and Adelegan, Oluwafemi J. and Biliroglu, Ali Onder and Annayev, Muhammetgeldi and Coutant, Zachary A. and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2021} }
 @article{annayev_adelegan_yamaner_oralkan_2021, title={Design of Pre-Charged CMUTs with a Metal Floating Gate}, ISSN={["1948-5719"]}, DOI={10.1109/IUS52206.2021.9593593}, abstractNote={Capacitive micromachined ultrasonic transducers (CMUTs) require a DC bias voltage for efficient operation. Precharged CMUTs can eliminate the requirement of DC bias voltage, thus ease the design of frontend circuitry for transmit/receive operation. We used a metal floating gate structure to trap charges instead of an oxide-nitride interface or a silicon floating island. Because the potential barrier height for metal-oxide interface is much higher than oxide-nitride and oxide-silicon barrier heights, it is possible to retain trapped charge without leakage. Also we do not expect any charge leakage on the metal-nitride side because of the vacuum gap. We used an anodic bonding based process and formed the floating metal under the silicon plate where the metal is sandwiched between silicon dioxide and silicon nitride layers. Initial results show that the proposed structure can store electrical charges to allow operation without a DC bias. The CMUTs fabricated using the described approach will be primarily used as an ultrasound-powered implantable biomedical device.}, journal={INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS 2021)}, author={Annayev, Muhammetgeldi and Adelegan, Oluwafemi J. and Yamaner, F. Yalcin and Oralkan, Omer}, year={2021} }