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  1. Abstract

    Dielectric metasurfaces, composed of planar arrays of subwavelength dielectric structures that collectively mimic the operation of conventional bulk optical elements, have revolutionized the field of optics by their potential in constructing high-efficiency and multi-functional optoelectronic systems on chip. The performance of a dielectric metasurface is largely determined by its constituent material, which is highly desired to have a high refractive index, low optical loss and wide bandgap, and at the same time, be fabrication friendly. Here, we present a new material platform based on tantalum pentoxide (Ta2O5) for implementing high-performance dielectric metasurface optics over the ultraviolet and visible spectral region. This wide-bandgap dielectric, exhibiting a high refractive index exceeding 2.1 and negligible extinction coefficient across a broad spectrum, can be easily deposited over large areas with good quality using straightforward physical vapor deposition, and patterned into high-aspect-ratio subwavelength nanostructures through commonly-available fluorine-gas-based reactive ion etching. We implement a series of high-efficiency ultraviolet and visible metasurfaces with representative light-field modulation functionalities including polarization-independent high-numerical-aperture lensing, spin-selective hologram projection, and vivid structural color generation, and the devices exhibit operational efficiencies up to 80%. Our work overcomes limitations faced by scalability of commonly-employed metasurface dielectrics and their operation into the visible and ultraviolet spectral range, and provides a novel route towards realization of high-performance, robust and foundry-manufacturable metasurface optics.

     
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    Free, publicly-accessible full text available December 1, 2025
  2. Abstract

    Two-dimensional (2D) superlattices, formed by stacking sublattices of 2D materials, have emerged as a powerful platform for tailoring and enhancing material properties beyond their intrinsic characteristics. However, conventional synthesis methods are limited to pristine 2D material sublattices, posing a significant practical challenge when it comes to stacking chemically modified sublattices. Here we report a chemical synthesis method that overcomes this challenge by creating a unique 2D graphene superlattice, stacking graphene sublattices with monodisperse, nanometer-sized, square-shaped pores and strategically doped elements at the pore edges. The resulting graphene superlattice exhibits remarkable correlations between quantum phases at both the electron and phonon levels, leading to diverse functionalities, such as electromagnetic shielding, energy harvesting, optoelectronics, and thermoelectrics. Overall, our findings not only provide chemical design principles for synthesizing and understanding functional 2D superlattices but also expand their enhanced functionality and extensive application potential compared to their pristine counterparts.

     
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    Free, publicly-accessible full text available December 1, 2025
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  5. Free, publicly-accessible full text available November 17, 2024
  6. C-Auth is a novel authentication method for smart glasses that explores the feasibility of authenticating users using the facial contour lines from the nose and cheeks captured by a down-facing camera in the middle of the glasses. To evaluate the system, we conducted a user study with 20 participants in three sessions on different days. Our system correctly authenticates the target participant versus the other 19 participants (attackers) with a true positive rate of 98.0% (SD: 2.96%) and a false positive rate of 4.97% (2.88 %) across all three days. We conclude by discussing current limitations, challenges, and potential future applications for C-Auth. 
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    Free, publicly-accessible full text available October 8, 2024
  7. We present HPSpeech, a silent speech interface for commodity headphones. HPSpeech utilizes the existing speakers of the headphones to emit inaudible acoustic signals. The movements of the temporomandibular joint (TMJ) during speech modify the reflection pattern of these signals, which are captured by a microphone positioned inside the headphones. To evaluate the performance of HPSpeech, we tested it on two headphones with a total of 18 participants. The results demonstrated that HPSpeech successfully recognized 8 popular silent speech commands for controlling the music player with an accuracy over 90%. While our tests use modified commodity hardware (both with and without active noise cancellation), our results show that sensing the movement of the TMJ could be as simple as a firmware update for ANC headsets which already include a microphone inside the hear cup. This leaves us to believe that this technique has great potential for rapid deployment in the near future. We further discuss the challenges that need to be addressed before deploying HPSpeech at scale. 
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    Free, publicly-accessible full text available October 8, 2024
  8. Free, publicly-accessible full text available August 1, 2024
  9. In this paper, we introduce PoseSonic, an intelligent acoustic sensing solution for smartglasses that estimates upper body poses. Our system only requires two pairs of microphones and speakers on the hinges of the eyeglasses to emit FMCW-encoded inaudible acoustic signals and receive reflected signals for body pose estimation. Using a customized deep learning model, PoseSonic estimates the 3D positions of 9 body joints including the shoulders, elbows, wrists, hips, and nose. We adopt a cross-modal supervision strategy to train our model using synchronized RGB video frames as ground truth. We conducted in-lab and semi-in-the-wild user studies with 22 participants to evaluate PoseSonic, and our user-independent model achieved a mean per joint position error of 6.17 cm in the lab setting and 14.12 cm in semi-in-the-wild setting when predicting the 9 body joint positions in 3D. Our further studies show that the performance was not significantly impacted by different surroundings or when the devices were remounted or by real-world environmental noise. Finally, we discuss the opportunities, challenges, and limitations of deploying PoseSonic in real-world applications.

     
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    Free, publicly-accessible full text available September 27, 2024