@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{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{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} } @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 $\mu$m × 250 $\mu$m. The phase of each pulser output is individually programmable with a resolution of $1/f_{\mathrm{C}}/16$, where $f_{\mathrm{C}}$ is less than 10 MHz. This enables the fine granular control of a focus. The ASIC was fabricated in the TSMC 0.18-$\mu$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 ($\mathrm{I_{SPPA}}$) of 12.4 and 33.1 W/${\rm cm^{2}}$; and a 3-dB focal volume of 0.2 and 0.05 ${\rm mm^{3}}$—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} } @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{adelegan_coutant_wu_yamaner_oralkan_2021, title={Design and Fabrication of Wideband Air-Coupled Capacitive Micromachined Ultrasonic Transducers With Varying Width Annular-Ring and Spiral Cell Structures}, volume={68}, ISSN={["1525-8955"]}, url={https://doi.org/10.1109/TUFFC.2021.3076143}, DOI={10.1109/TUFFC.2021.3076143}, abstractNote={Air-coupled transducers with broad bandwidth are desired for many airborne applications, such as obstacle detection, haptic feedback, and flow metering. In this article, we present a design strategy and demonstrate a fabrication process for developing improved concentric annular- and novel spiral-shaped capacitive micromachined ultrasonic transducers (CMUTs) that can generate high output pressure and provide wide bandwidth in air. We explore the ability to implement complex geometries by photolithographic definition to improve the bandwidth of air-coupled CMUTs. The ring widths in the annular design were varied so that the device can be improved in terms of bandwidth when these rings resonate in parallel. Using the same ring width parameters for the spiral-shaped design but with a smoother transition between the ring widths along the spiral, the bandwidth of the spiral-shaped device is improved. With the reduced process complexity associated with the anodic-bonding-based fabrication process, a 25- $\mu \text{m}$ vibrating silicon plate was bonded to a borosilicate glass wafer with up to 15- $\mu \text{m}$ deep cavities. The fabricated devices show an atmospheric deflection profile that is in agreement with the FEM results to verify the vacuum sealing of the devices. The devices show a 3-dB fractional bandwidth (FBW) of 12% and 15% for spiral- and annular-shaped CMUTs, respectively. We measured a 127-dB sound pressure level at the surface of the transducers. The angular response of the fabricated CMUTs was also characterized. The results demonstrated in this article show the possibility of improving the bandwidth of air-coupled devices by exploring the flexibility in the design process associated with CMUT technology.}, number={8}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Adelegan, Oluwafemi Joel and Coutant, Zachary A. and Wu, Xun and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2021}, month={Aug}, pages={2749–2759} } @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} } @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{seok_mahmud_kumar_adelegan_yamaner_oralkan_2019, title={A Low-Power Wireless Multichannel Gas Sensing System Based on a Capacitive Micromachined Ultrasonic Transducer (CMUT) Array}, volume={6}, ISSN={["2327-4662"]}, url={https://doi.org/10.1109/JIOT.2018.2861330}, DOI={10.1109/JIOT.2018.2861330}, abstractNote={Detection of volatile organic compounds (VOCs), challenged by their diversity and similarity, is gaining much attention due to concerns about adverse health effects they cause, along with intensifying development efforts in wireless sensor nodes. Precise identification of volatiles may be subject to the sensitivity and selectivity of a sensor itself and the proximity of the sensor to the source, necessitating power-efficient and portable/wearable sensing systems. The metal-oxide sensors, commonly employed for detection of VOCs, are not power efficient, due to the required heating element, and lack the selectivity, thus reporting only the total VOC level. In this paper, we present a complete low-power wireless gas-sensing system based a capacitive micromachined ultrasonic transducer array, which is known to have several advantages such as high mass sensitivity, easy implementation of a multielement structure, and high selectivity upon polymer coating. We took a holistic approach to designing the sensing elements and the custom integrated circuit (IC) as well as to operating the system, resulting in a small self-contained sensor node (38-mm detect-weight diameter and 16-mm detect-weight height). The chemical-sensing capability of the system has been validated with ethanol, achieving 120-ppb limit-of-detection while the sensor array, including the IC and the power management unit, consuming 80- $\mu \text{W}$ average power with power cycling by actively taking measurements for 3 s detect-weight per minute. The presented system will eventually provide a ubiquitous tool to identify VOCs with the help of multivariate data analysis.}, number={1}, journal={IEEE INTERNET OF THINGS JOURNAL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Seok, Chunkyun and Mahmud, Marzana Mantasha and Kumar, Mohit and Adelegan, Oluwafemi Joel and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2019}, month={Feb}, pages={831–843} } @article{zhang_adelegan_yamaner_oralkan_2018, title={A Fast-Switching (1.35-mu s) Low-Control-Voltage (2.5-V) MEMS T/R Switch Monolithically Integrated With a Capacitive Micromachined Ultrasonic Transducer}, volume={27}, ISSN={["1941-0158"]}, url={https://doi.org/10.1109/JMEMS.2017.2781255}, DOI={10.1109/jmems.2017.2781255}, abstractNote={This paper describes the design and fabrication of an electrostatic microelectromechanical systems (MEMS) switch that can be co-fabricated on the same substrate with a capacitive micromachined ultrasonic transducer (CMUT) as a transmit/receive switch. The structure of the switch is modified from a single CMUT cell. An interrupted transmission line is defined across the center of the cell with control electrodes on both sides to pull a movable plate down. The plate has an insulation layer underneath, and a metal bump is formed on the insulation layer and aligned to the transmission line gap, so that the switch could be turned ON by pulling down the plate with electrostatic force and making the metal bump close the gap in the transmission line. The switch was designed using a finite-element model and fabricated on a glass substrate using anodic bonding. A static characterization was first performed on a switch test structure, which showed that the dc switching voltage was 68 V and the ON-resistance was 50 $\Omega $ . The RFin-to-RFout isolation was measured as approximately 66 dB and insertion loss was approximately 4.85 dB for the frequency range commonly used for medical ultrasound imaging. Then, we performed the dynamic characterization in immersion. By setting the dc bias at 67 V, we found that the switch could be operated with a control-voltage as low as 2.5 V. The switching and release times are related to the rise time and fall time of the control signal, respectively. The minimum switching time was measured as 1.34 $\mu \text{s}$ with a control signal rise time of 300 ns, and the minimum release time was measured as 80 ns with a control signal fall time of 20 ns. We further demonstrated that a 1-kHz control signal with the optimized rise and fall times can be used to conduct and block a sinusoidal signal with 1-MHz frequency and 300-mVpp amplitude, as well as unipolar pulses with 5-Vpp amplitude, 500-ns pulse width, and 2-kHz repetition rate. The presented MEMS switch could potentially eliminate the high-voltage process requirement for the on-chip front-end electronics of a CMUT-based ultrasound imaging system and thus improve the overall system efficiency. [2017-0225]}, number={2}, journal={JOURNAL OF MICROELECTROMECHANICAL SYSTEMS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Zhang, Xiao and Adelegan, Oluwafemi Joel and Yamaner, Feysel Yalcin and Oralkan, Omer}, year={2018}, month={Apr}, pages={190–200} } @inproceedings{zhang_zeshan_adelegan_yamaner_oralkan_2016, title={A MEMS T/R switch embedded in CMUT structure for ultrasound imaging frontends}, ISBN={9781467398978}, url={http://dx.doi.org/10.1109/ultsym.2016.7728635}, DOI={10.1109/ultsym.2016.7728635}, abstractNote={This paper describes a novel MEMS transmit/ receive (T/R) switch that could be embedded in the general structure of a capacitive micromachined ultrasonic transducer (CMUT). A MEMS switch and a CMUT element were fabricated side by side using an anodic-bonding-based fabrication process. The plates of the CMUT and the membrane-type switch were formed at the same step by anodic bonding. A single switch was tested in air for preliminary characterization. Vacuum-sealing of the switch cell was confirmed by an atmospheric deflection measurement. The switch was then biased at 59-V DC voltage and turned on and off by applying a 1-kHz, 5-Vpp square wave to the control terminal while a 1-MHz, 300-mVpp sinusoidal signal was applied at the RF input. The signal measured at the RF output demonstrates the basic switching behavior with a switch series resistance of 124 Ω. This work is important for the ultrasound imaging system efficiency and could significantly ease the high-voltage requirements of frontend circuits.}, booktitle={2016 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Zhang, Xiao and Zeshan, Arooba and Adelegan, Oluwafemi J. and Yamaner, F. Yalcin and Oralkan, Omer}, year={2016}, month={Sep} } @inproceedings{seok_mahmud_adelegan_zhang_oralkan_2016, title={A battery-operated wireless multichannel gas sensor system based on a capacitive micromachined ultrasonic transducer (CMUT) array}, DOI={10.1109/icsens.2016.7808803}, abstractNote={This paper reports on the design and implementation of a complete battery-operated wireless system for a mechanically resonant gas sensor based on a capacitive micromachined ultrasonic transducer (CMUT) array. A custom-designed front-end integrated circuit (IC) with eight inputs and a serial peripheral interface (SPI) was tightly integrated with a CMUT array. The power consumption of the front-end is 10 μW with a duty cycle of 1:60 corresponding to 1-s measurement time every minute. For the completeness of the system, a power management unit (PMU) was designed and interfaced with the described custom IC along with a wireless module. For multichannel operation, time-division multiplexing was adopted to minimize power consumption and prevent potential frequency locking between different channels. Multichannel wireless data acquisition with the described system was demonstrated by loading unfunctionalized sensor channels with humidity in human breath.}, booktitle={2016 ieee sensors}, author={Seok, C. and Mahmud, M. M. and Adelegan, O. and Zhang, X. and Oralkan, Omer}, year={2016} } @inproceedings{zhang_adelegan_yamaner_oralkan_2016, title={CMUTs on glass with ITO bottom electrodes for improved transparency}, ISBN={9781467398978}, url={http://dx.doi.org/10.1109/ultsym.2016.7728671}, DOI={10.1109/ultsym.2016.7728671}, abstractNote={In this work, we fabricated capacitive micromachined ultrasonic transducers (CMUTs) on a glass substrate with indium tin oxide (ITO) bottom electrodes for improved transparency. A 2-μm vibrating silicon plate was formed by anodic bonding. The fabrication process requires three masks. The fabricated devices show approximately 300% improvement of optical transmission in the visible to NIR wavelength range (400 nm - 1000 nm) compared to the devices with chromium/gold (Cr/Au) bottom electrodes. The measured static surface profile confirmed that the fabricated devices are vacuum-sealed. The electrical input impedance measurement shows the device has a resonant frequency of 4.75 MHz at 30-V DC voltage. The series resistance of the device is ~1 kΩ, which is mainly due to the ITO bottom electrode connections. Using a full bottom electrode or using parallel connections to the pads could reduce the resistance. The main hurdle for the transparency at shorter wavelength range is the 2-μm silicon plate. The transfer-matrix model shows the transparency could be improved to -80% across the measured spectrum, if silicon is replaced with a more transparent plate material such as ITO or silicon nitride.}, booktitle={2016 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Zhang, Xiao and Adelegan, Oluwafemi and Yamaner, F. Yalcin and Oralkan, Omer}, year={2016}, month={Sep} } @inproceedings{howell_nag_mcknight_narsipur_adelegan_2015, title={A low-power wearable substance monitoring device}, DOI={10.1109/vcacs.2015.7439567}, abstractNote={Alcohol and illicit drug abuse has become a major problem in recent years. According to US Census, there are approximately 40 million teenagers between the age of 10-19, and 20% of them have used an illegal substance at least once in their lifetime. Therefore, by extrapolation, there are potentially 8 million drug abuse cases across the board. This opens up a major requirement for drug monitoring and devices capable of monitoring drug abusers or helping addicts recover. Previous research has shown that certain quantifiable physiological parameters become altered following illicit drug or alcohol consumption. A solution that addresses the problem of detecting drug abuse is the core focus of this research. Initial steps have been focused on developing a device in the form of a wrist-watch that is capable of measuring selected physiological parameters using commercially available sensors. An Android application with algorithms capable of determining if the user is under the influence of alcohol or drugs has been developed and tested.}, booktitle={2015 Virtual Conference on Application of Commercial Sensors}, author={Howell, J. and Nag, A. and McKnight, M. and Narsipur, S. and Adelegan, O.}, year={2015} } @inproceedings{zhang_yamanery_adelegan_oralkan_2015, title={Design of high-frequency broadband CMUT arrays}, ISBN={9781479981823}, ISSN={["1948-5719"]}, url={http://dx.doi.org/10.1109/ultsym.2015.0167}, DOI={10.1109/ultsym.2015.0167}, abstractNote={In this work we demonstrate a high-frequency (29-MHz) broadband (100% FBW) CMUT 1D array. The devices are fabricated using anodic bonding with only three photolithography steps. We also discuss the design guidelines for high-frequency broadband CMUTs using the simulations. A high fill factor and a thin plate are important for the broadband design. Small cell size is required for the increased center frequency. To improve the transducer sensitivity and to keep the collapse voltage low, the gap height should be small and a high-k dielectric insulation layer should be employed. The fabrication steps we report in this paper have good potential to meet the high-frequency broadband CMUT design requirements. So far we have demonstrated that we can define a 50-nm gap, bond to a post as narrow as 2 μm, and pattern a high-k dielectric layer on the bottom electrode.}, booktitle={2015 IEEE International Ultrasonics Symposium (IUS)}, publisher={IEEE}, author={Zhang, Xiao and Yamanery, F. Yalcin and Adelegan, Oluwafemi and Oralkan, Omer}, year={2015}, month={Oct} }