Anuj Ashok - Academia.edu (original) (raw)

Papers by Anuj Ashok

arXiv (Cornell University), Nov 30, 2022

Photoacoustic image (PAI) quality improvement using a low frequency piezoelectric micromachined u... more Photoacoustic image (PAI) quality improvement using a low frequency piezoelectric micromachined ultrasound transducer (PMUT) having the fundamental resonant frequency ~ 1 MHz is being reported. Specifically, three different methods are implemented such asthe frame averaging, mathematically improved algorithms, and a hardware position accurate arrangement in order to obtain unparallel PAI image quality. Validation study has been conducted in both agar phantom and ex-vivo tissue samples. Measurable image quantifiers in the form of full width at half maximum (FWHM), signal to noise ratio (SNR), and contrast ratio (CR) are used to evaluate the improvement in the image quality. It is found that the FWHM increases by 34%, SNR by 23% and CR by 25%, suggesting the efficacy of the methods to achieve better photoacoustic images employing PMUT-based detector. The study demonstrates that the suggested methods of improvement could play a key role in a promising cost-effective PMUT-PAI system in future.

Nanotechnology

A novel methodology, based on wetting and electromigration, for transporting liquid metal, over l... more A novel methodology, based on wetting and electromigration, for transporting liquid metal, over long distances, at micro-and nano-scale using a stylus is reported. The mechanism is analogous to a dropper that uses ‘suction and release’ actions to ‘collect and dispense’ liquid. In our methodology, a stylus coated with a thin metal film acts like the dropper that collects liquid metal from a reservoir upon application of an electric current, holds the liquid metal via wetting while carrying the liquid metal over large distances away from the reservoir and drops it on the target location by reversing the direction of electric current. Essentially, the working principle of the technique relies on the directionality of electromigration force and adhesive force due to wetting. The working of the technique is demonstrated by using an Au-coated Si micropillar as the stylus, liquid Ga as the liquid metal to be transported, and a Kleindiek-based position micro-manipulator to traverse the styl...

IEEE Open Journal of Ultrasonics, Ferroelectrics, and Frequency Control

Data-over-sound is an emerging technology for digital communication which uses frequencies at the... more Data-over-sound is an emerging technology for digital communication which uses frequencies at the upper bounds of human hearing, usually between 15 kHz to 25 kHz. We report a successful development of Piezoelectric Micromachined Ultrasound Transducers (PMUTs) for low-power data-over-sound applications. Piezoelectric thin films used in PMUTs can have high residual tensile stresses ranging from 300 MPa to 1.5 GPa. These stresses have the effect of increasing the resonant frequencies of the transducers, making it a challenge to fabricate low frequency devices. Using the optimum dimensions by estimating the net residual stress in the fabricated diaphragms, transducers suitable for a frequency range of 17 kHz to 21 kHz were fabricated, capable of generating as much as 83 dB of sound pressure level at a distance of 5 cm in continuous operation.

2020 5th IEEE International Conference on Emerging Electronics (ICEE)

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained popularity in the past dec... more Piezoelectric micromachined ultrasound transducers (PMUTs) have gained popularity in the past decade as acoustic transmitters and receivers. As these devices usually operate at resonance, they can deliver large output sound pressures with very low power consumption. This paper explores the influence of the transmitter's packaging on the radiated acoustic field in air. We run simplified axisymmetric numerical models to observe the change in the acoustic field and directivity with respect to the device's package dimensions. The simulations demonstrate a notable change in the directivity of transmitter based on the size of the baffle. Experimental measurements are carried out to validate the simulations, which can prove useful in designing packages for transmitters to meet application specific requirements.

2022 IEEE 35th International Conference on Micro Electro Mechanical Systems Conference (MEMS), 2022

This paper presents a novel design of PMUTs with bossed diaphragms for frequencies near the upper... more This paper presents a novel design of PMUTs with bossed diaphragms for frequencies near the upper limits of human hearing. The dimensions of a central boss on a circular diaphragm were optimized to minimize resonance frequencies. The current design makes the devices 3x smaller than conventional PMUTs for the same frequencies, and the devices exhibit up to 5x higher quality factors. These devices have a higher mechanical impedance making them less sensitive to the operating media and are suitable for both air-coupled and liquid-coupled applications such as ranging, proximity sensing, level-sensing, and communication. With low operating voltages, these transducers have the potential to revolutionize how ultrasound is used in next generation wearables and IoT devices.

2021 IEEE International Ultrasonics Symposium (IUS), 2021

We report on the development of a novel technique for creating real-time frequency tuning in Piez... more We report on the development of a novel technique for creating real-time frequency tuning in Piezoelectric Micromachined Ultrasound Transducers (PMUTs). This technique employs controlled virtual added mass in a confined microfluidic environment as a switch to tune the resonant frequency of a PMUT. Using this technique, we could vary the frequency of a 500mumathrmm500\ \mu\mathrm{m}500mumathrmm circular PMUT from 489 kHz to 210 kHz, corresponding to a tuning range of 57%. This shows the potential of using such a technique in creating PMUTs with a wide range of frequency tuning.

2020 IEEE International Ultrasonics Symposium (IUS), 2020

Data-over-sound is an emerging technology for digital data communication which uses frequencies a... more Data-over-sound is an emerging technology for digital data communication which uses frequencies at the upper bounds of human hearing, usually between 15 kHz to 25 kHz. We report the successful development of Micromachined Piezoelectric Near-Ultrasound Transducers for low power data-over-sound applications. Lead zirconate titanate thin films used in Piezoelectric Micromachined Ultrasonic Transducers can have high residual tensile stresses ranging from 300 MPa to 1.5 GPa. These stresses raise the resonant frequencies of the transducers, making it a challenge to fabricate low frequency devices. Using the optimum dimensions by estimating the net residual stress inside the fabricated diaphragm, a low power transducer with a target frequency range of 17 kHz to 21 kHz was fabricated, capable of generating as much as 83 dB of sound pressure level at a distance of 5 cm for continuous operation.

2020 IEEE International Ultrasonics Symposium (IUS), 2020

A compact single cell piezoelectric micromachined ultrasound transducer (PMUT) with dual electrod... more A compact single cell piezoelectric micromachined ultrasound transducer (PMUT) with dual electrodes is designed, fabricated, and used to measure the density of a fluid mixture mimicking the range of human blood density variation. The sensor's novelty lies in its compactness enabled by on device sensing and actuation due to the dual electrodes. The active material used here is thin film PZT which is protected from the fluid environment with an appropriate coating. The results obtained show a linear response of the sensor output over the density range of interest with no appreciable degradation in the signal due to immersion in a fluid. The sensitivity of the sensor is 191 Hz/Kg/m3. These single cell PMUTs are, therefore, potential candidates for fluid density monitoring in industrial or biomedical applications.

Photons Plus Ultrasound: Imaging and Sensing 2021, 2021

2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers), 2021

We exhibit the design and fabrication of a linear array of single-celled dual-electrode piezoelec... more We exhibit the design and fabrication of a linear array of single-celled dual-electrode piezoelectric micromachined ultrasound transducers (PMUTs) and integrate them with a microfluidic channel. The integrated device forms an independent platform to sense the resonant peak shift in a reasonably low volume of fluids. We subsequently pitch on a novel technique of volumetric flow rate sensing based on resonant frequency shift, thereby demonstrating the PMUT-microfluidic integrated device's potentiality as a volumetric flow rate sensor. The sensitivity of the device to volume flow rate sensing is reported to be 537textms/mumathrml/texthr537\ \text{ms}/\mu \mathrm{l}/\text{hr}537textms/mumathrml/texthr.

Photons Plus Ultrasound: Imaging and Sensing 2020, 2020

Infant brain imaging is highly challenging but necessary for diagnosing various prevalent disorde... more Infant brain imaging is highly challenging but necessary for diagnosing various prevalent disorders including vascular malformations, encephalitis, and abusive head trauma. Conventional brain imaging technologies such as MRI, CT, and PET are not suitable for repeated use on neonates due to the use of ionizing radiation (CT and PET), need for patient transport, uncomfortable environment, high cost, and bulky equipment. A wearable photoacoustic imaging (PAI) hat can be an ideal candidate for this application. However, its practical realization suffers from many system design problems such as complex assembly, unviability of full-hat rotation around the neonatal head, ultrasound coupling, and requirements of <3,000 ultrasound data acquisition channels to cover the whole brain. Here, we present a modular photoacoustic imaging (PAI) hat solution that uses an innovative modular design approach, making it realizable by assembling individual working units while minimizing the challenges of back-end electronics. The modular photoacoustic hat consists of multiple PAI disc modules of 2 inches in diameter that conform to the shape of the local head surface and assembled on a hat to cover the whole neonatal brain. Each PAI disc is integrated with optical fibers for light excitation of brain tissue. For photoacoustic detection, the discs are either densely packed with ultrasound elements to eliminate the need for rotation or can have fewer ultrasound elements (usually in trapezoidal shape) on the rotating disc to overcome large number of data acquisition channels. In this article, we have demonstrated the design, integration and initial results of the proposed wearable PAI-hat.

Microfluidics, BioMEMS, and Medical Microsystems XIX, 2021

We report the development of an opto-acousto-fluidic platform by combining an illumination source... more We report the development of an opto-acousto-fluidic platform by combining an illumination source in the form of a pulsed laser, a microfluidic channel, and an ultrasound transducer to detect photoacoustic signals generated from the fluid sample inside the channel. We study the effect of the channel dimensions on the emitted acoustic signals using methylene blue solution, a dye of immense interest in processing industry, as a target fluid and select an appropriate channel for further studies. We vary the concentration of the methylene blue dye and collect the corresponding photoacoustic signals. We find that the measured acoustic signal strength varies linearly with the increasing dye concentration, thus making this measurement scheme a potential dye concentration detector. This is a significant finding as it paves the way for developing a miniaturized photoacoustic detector for onsite sensing of dye concentration and perhaps even an online monitoring system which will be radical departure for current analysis methods using bench top bulky and expensive analytical tools.

Journal of Microelectromechanical Systems, 2021

We demonstrate the design, fabrication and use of a dual electrode PMUT (Piezoelectric Micromachi... more We demonstrate the design, fabrication and use of a dual electrode PMUT (Piezoelectric Micromachined Ultrasound Transducer) integrated with a microfluidic channel as a fluid density sensor in both static and dynamic density-change conditions. The dual electrode configuration makes the PMUT resonator a self-contained resonant peak-shift sensor and the microfluidic integration makes this system a versatile fluid density sensing platform that can be used with extremely low volumes of fluids in various industrial and healthcare applications. The density measurements carried out here under flowing fluid conditions demonstrate the potential of this system as a real-time fluid density monitoring system. We include results of density measurements in the range of 1020-1090 kg/m 3 that corresponds to the human blood density variation generally due to the change in its hemoglobin content. The sensitivity of the sensor-26.3 Hz/(kg/m 3)-is good enough to reliably detect even 1% change in the hemoglobin content of the human blood. Thus, this system could potentially be used also as a hemoglobin measurement sensor in healthcare applications.

arXiv (Cornell University), Nov 30, 2022

Photoacoustic image (PAI) quality improvement using a low frequency piezoelectric micromachined u... more Photoacoustic image (PAI) quality improvement using a low frequency piezoelectric micromachined ultrasound transducer (PMUT) having the fundamental resonant frequency ~ 1 MHz is being reported. Specifically, three different methods are implemented such asthe frame averaging, mathematically improved algorithms, and a hardware position accurate arrangement in order to obtain unparallel PAI image quality. Validation study has been conducted in both agar phantom and ex-vivo tissue samples. Measurable image quantifiers in the form of full width at half maximum (FWHM), signal to noise ratio (SNR), and contrast ratio (CR) are used to evaluate the improvement in the image quality. It is found that the FWHM increases by 34%, SNR by 23% and CR by 25%, suggesting the efficacy of the methods to achieve better photoacoustic images employing PMUT-based detector. The study demonstrates that the suggested methods of improvement could play a key role in a promising cost-effective PMUT-PAI system in future.

Nanotechnology

A novel methodology, based on wetting and electromigration, for transporting liquid metal, over l... more A novel methodology, based on wetting and electromigration, for transporting liquid metal, over long distances, at micro-and nano-scale using a stylus is reported. The mechanism is analogous to a dropper that uses ‘suction and release’ actions to ‘collect and dispense’ liquid. In our methodology, a stylus coated with a thin metal film acts like the dropper that collects liquid metal from a reservoir upon application of an electric current, holds the liquid metal via wetting while carrying the liquid metal over large distances away from the reservoir and drops it on the target location by reversing the direction of electric current. Essentially, the working principle of the technique relies on the directionality of electromigration force and adhesive force due to wetting. The working of the technique is demonstrated by using an Au-coated Si micropillar as the stylus, liquid Ga as the liquid metal to be transported, and a Kleindiek-based position micro-manipulator to traverse the styl...

IEEE Open Journal of Ultrasonics, Ferroelectrics, and Frequency Control

Data-over-sound is an emerging technology for digital communication which uses frequencies at the... more Data-over-sound is an emerging technology for digital communication which uses frequencies at the upper bounds of human hearing, usually between 15 kHz to 25 kHz. We report a successful development of Piezoelectric Micromachined Ultrasound Transducers (PMUTs) for low-power data-over-sound applications. Piezoelectric thin films used in PMUTs can have high residual tensile stresses ranging from 300 MPa to 1.5 GPa. These stresses have the effect of increasing the resonant frequencies of the transducers, making it a challenge to fabricate low frequency devices. Using the optimum dimensions by estimating the net residual stress in the fabricated diaphragms, transducers suitable for a frequency range of 17 kHz to 21 kHz were fabricated, capable of generating as much as 83 dB of sound pressure level at a distance of 5 cm in continuous operation.

2020 5th IEEE International Conference on Emerging Electronics (ICEE)

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained popularity in the past dec... more Piezoelectric micromachined ultrasound transducers (PMUTs) have gained popularity in the past decade as acoustic transmitters and receivers. As these devices usually operate at resonance, they can deliver large output sound pressures with very low power consumption. This paper explores the influence of the transmitter's packaging on the radiated acoustic field in air. We run simplified axisymmetric numerical models to observe the change in the acoustic field and directivity with respect to the device's package dimensions. The simulations demonstrate a notable change in the directivity of transmitter based on the size of the baffle. Experimental measurements are carried out to validate the simulations, which can prove useful in designing packages for transmitters to meet application specific requirements.

2022 IEEE 35th International Conference on Micro Electro Mechanical Systems Conference (MEMS), 2022

This paper presents a novel design of PMUTs with bossed diaphragms for frequencies near the upper... more This paper presents a novel design of PMUTs with bossed diaphragms for frequencies near the upper limits of human hearing. The dimensions of a central boss on a circular diaphragm were optimized to minimize resonance frequencies. The current design makes the devices 3x smaller than conventional PMUTs for the same frequencies, and the devices exhibit up to 5x higher quality factors. These devices have a higher mechanical impedance making them less sensitive to the operating media and are suitable for both air-coupled and liquid-coupled applications such as ranging, proximity sensing, level-sensing, and communication. With low operating voltages, these transducers have the potential to revolutionize how ultrasound is used in next generation wearables and IoT devices.

2021 IEEE International Ultrasonics Symposium (IUS), 2021

We report on the development of a novel technique for creating real-time frequency tuning in Piez... more We report on the development of a novel technique for creating real-time frequency tuning in Piezoelectric Micromachined Ultrasound Transducers (PMUTs). This technique employs controlled virtual added mass in a confined microfluidic environment as a switch to tune the resonant frequency of a PMUT. Using this technique, we could vary the frequency of a 500mumathrmm500\ \mu\mathrm{m}500mumathrmm circular PMUT from 489 kHz to 210 kHz, corresponding to a tuning range of 57%. This shows the potential of using such a technique in creating PMUTs with a wide range of frequency tuning.

2020 IEEE International Ultrasonics Symposium (IUS), 2020

Data-over-sound is an emerging technology for digital data communication which uses frequencies a... more Data-over-sound is an emerging technology for digital data communication which uses frequencies at the upper bounds of human hearing, usually between 15 kHz to 25 kHz. We report the successful development of Micromachined Piezoelectric Near-Ultrasound Transducers for low power data-over-sound applications. Lead zirconate titanate thin films used in Piezoelectric Micromachined Ultrasonic Transducers can have high residual tensile stresses ranging from 300 MPa to 1.5 GPa. These stresses raise the resonant frequencies of the transducers, making it a challenge to fabricate low frequency devices. Using the optimum dimensions by estimating the net residual stress inside the fabricated diaphragm, a low power transducer with a target frequency range of 17 kHz to 21 kHz was fabricated, capable of generating as much as 83 dB of sound pressure level at a distance of 5 cm for continuous operation.

2020 IEEE International Ultrasonics Symposium (IUS), 2020

A compact single cell piezoelectric micromachined ultrasound transducer (PMUT) with dual electrod... more A compact single cell piezoelectric micromachined ultrasound transducer (PMUT) with dual electrodes is designed, fabricated, and used to measure the density of a fluid mixture mimicking the range of human blood density variation. The sensor's novelty lies in its compactness enabled by on device sensing and actuation due to the dual electrodes. The active material used here is thin film PZT which is protected from the fluid environment with an appropriate coating. The results obtained show a linear response of the sensor output over the density range of interest with no appreciable degradation in the signal due to immersion in a fluid. The sensitivity of the sensor is 191 Hz/Kg/m3. These single cell PMUTs are, therefore, potential candidates for fluid density monitoring in industrial or biomedical applications.

Photons Plus Ultrasound: Imaging and Sensing 2021, 2021

2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers), 2021

We exhibit the design and fabrication of a linear array of single-celled dual-electrode piezoelec... more We exhibit the design and fabrication of a linear array of single-celled dual-electrode piezoelectric micromachined ultrasound transducers (PMUTs) and integrate them with a microfluidic channel. The integrated device forms an independent platform to sense the resonant peak shift in a reasonably low volume of fluids. We subsequently pitch on a novel technique of volumetric flow rate sensing based on resonant frequency shift, thereby demonstrating the PMUT-microfluidic integrated device's potentiality as a volumetric flow rate sensor. The sensitivity of the device to volume flow rate sensing is reported to be 537textms/mumathrml/texthr537\ \text{ms}/\mu \mathrm{l}/\text{hr}537textms/mumathrml/texthr.

Photons Plus Ultrasound: Imaging and Sensing 2020, 2020

Infant brain imaging is highly challenging but necessary for diagnosing various prevalent disorde... more Infant brain imaging is highly challenging but necessary for diagnosing various prevalent disorders including vascular malformations, encephalitis, and abusive head trauma. Conventional brain imaging technologies such as MRI, CT, and PET are not suitable for repeated use on neonates due to the use of ionizing radiation (CT and PET), need for patient transport, uncomfortable environment, high cost, and bulky equipment. A wearable photoacoustic imaging (PAI) hat can be an ideal candidate for this application. However, its practical realization suffers from many system design problems such as complex assembly, unviability of full-hat rotation around the neonatal head, ultrasound coupling, and requirements of <3,000 ultrasound data acquisition channels to cover the whole brain. Here, we present a modular photoacoustic imaging (PAI) hat solution that uses an innovative modular design approach, making it realizable by assembling individual working units while minimizing the challenges of back-end electronics. The modular photoacoustic hat consists of multiple PAI disc modules of 2 inches in diameter that conform to the shape of the local head surface and assembled on a hat to cover the whole neonatal brain. Each PAI disc is integrated with optical fibers for light excitation of brain tissue. For photoacoustic detection, the discs are either densely packed with ultrasound elements to eliminate the need for rotation or can have fewer ultrasound elements (usually in trapezoidal shape) on the rotating disc to overcome large number of data acquisition channels. In this article, we have demonstrated the design, integration and initial results of the proposed wearable PAI-hat.

Microfluidics, BioMEMS, and Medical Microsystems XIX, 2021

We report the development of an opto-acousto-fluidic platform by combining an illumination source... more We report the development of an opto-acousto-fluidic platform by combining an illumination source in the form of a pulsed laser, a microfluidic channel, and an ultrasound transducer to detect photoacoustic signals generated from the fluid sample inside the channel. We study the effect of the channel dimensions on the emitted acoustic signals using methylene blue solution, a dye of immense interest in processing industry, as a target fluid and select an appropriate channel for further studies. We vary the concentration of the methylene blue dye and collect the corresponding photoacoustic signals. We find that the measured acoustic signal strength varies linearly with the increasing dye concentration, thus making this measurement scheme a potential dye concentration detector. This is a significant finding as it paves the way for developing a miniaturized photoacoustic detector for onsite sensing of dye concentration and perhaps even an online monitoring system which will be radical departure for current analysis methods using bench top bulky and expensive analytical tools.

Journal of Microelectromechanical Systems, 2021

We demonstrate the design, fabrication and use of a dual electrode PMUT (Piezoelectric Micromachi... more We demonstrate the design, fabrication and use of a dual electrode PMUT (Piezoelectric Micromachined Ultrasound Transducer) integrated with a microfluidic channel as a fluid density sensor in both static and dynamic density-change conditions. The dual electrode configuration makes the PMUT resonator a self-contained resonant peak-shift sensor and the microfluidic integration makes this system a versatile fluid density sensing platform that can be used with extremely low volumes of fluids in various industrial and healthcare applications. The density measurements carried out here under flowing fluid conditions demonstrate the potential of this system as a real-time fluid density monitoring system. We include results of density measurements in the range of 1020-1090 kg/m 3 that corresponds to the human blood density variation generally due to the change in its hemoglobin content. The sensitivity of the sensor-26.3 Hz/(kg/m 3)-is good enough to reliably detect even 1% change in the hemoglobin content of the human blood. Thus, this system could potentially be used also as a hemoglobin measurement sensor in healthcare applications.