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1. Frequency selective wave beaming in nonreciprocal acoustic phased arrays

   https://doi.org/10.1038/s41598-020-77489-x  

   Adlakha, Revant ; Moghaddaszadeh, Mohammadreza ; Attarzadeh, Mohammad A. ; Aref, Amjad ; Nouh, Mostafa ( December 2020 , Scientific Reports)

   Acoustic phased arrays are capable of steering and focusing a beam of sound via selective coordination of the spatial distribution of phase angles between multiple sound emitters. Constrained by the principle of reciprocity, conventional phased arrays exhibit identical transmission and reception patterns which limit the scope of their operation. This work presents a controllable space–time acoustic phased array which breaks time-reversal symmetry, and enables phononic transition in both momentum and energy spaces. By leveraging a dynamic phase modulation, the proposed linear phased array is no longer bound by the acoustic reciprocity, and supports asymmetric transmission and reception patterns that can be tuned independently at multiple channels. A foundational framework is developed to characterize and interpret the emergent nonreciprocal phenomena and is later validated against benchmark numerical experiments. The new phased array selectively alters the directional and frequency content of the incident signal and imparts a frequency conversion between different wave fields, which is further analyzed as a function of the imposed modulation. The space–time acoustic phased array enables unprecedented control over sound waves in a variety of applications ranging from ultrasonic imaging to non-destructive testing and underwater SONAR telecommunication.
2. A perspective on the neuromorphic control of legged locomotion in past, present, and future insect-like robots

   https://doi.org/10.1088/2634-4386/acc04f  

   Szczecinski, Nicholas Stephen ; Goldsmith, Clarissa ; Nourse, William ; Quinn, Roger D. ( March 2023 , Neuromorphic Computing and Engineering)

   This article is a historical perspective on how the study of the neuromechanics of insects and other arthropods has inspired the construction, and especially the control, of hexapod robots. Many hexapod robots’ control systems share common features, including: 1. Direction of motor output of each joint (i.e., to flex or extend) in the leg is gated by an oscillatory or bistable gating mechanism; 2. The phasing between each joint is influenced by proprioceptive feedback from the periphery (e.g., joint angles, leg load) or central connections between joint controllers; and 3. Behavior can be directed (e.g., walking along a curved path) via low-dimensional, broadly-acting descending inputs to the network. These distributed control schemes are inspired by, and in some robots, closely mimic the organization of the nervous systems of insects, the natural hexapods, as well as crustaceans. Nearly a century of research has revealed organizational principles such as central pattern generators (CPGs), the role of proprioceptive feedback in control, and command neurons. These concepts have inspired the control systems of hexapod robots in the past, in which these structures were applied to robot controllers with neuromorphic (i.e., distributed) organization, but not neuromorphic computational units (i.e., neurons) or computational hardware (i.e., hardware-accelerated neurons). Presently, several hexapodmore »robots are controlled with neuromorphic computational units with or without neuromorphic organization, almost always without neuromorphic hardware. In the near future, we expect to see hexapod robots whose controllers include neuromorphic organization, computational units, and hardware. Such robots may exhibit the full mobility of their insect counterparts thanks to a “biology-first” approach to controller design. This perspective is not a comprehensive review of the neuroscientific literature but is meant to give a gentle introduction into the principles that underlie models and inspire neuromorphic robot controllers. Deeper reviews of particular topics from biology are suggested throughout.

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3. Measurement of oxygen consumption rates of human renal proximal tubule cells in an array of organ-on-chip devices to monitor drug-induced metabolic shifts

   https://doi.org/10.1038/s41378-022-00442-7  

   Kann, Samuel H. ; Shaughnessey, Erin M. ; Coppeta, Jonathan R. ; Azizgolshani, Hesham ; Isenberg, Brett C. ; Vedula, Else M. ; Zhang, Xin ; Charest, Joseph L. ( September 2022 , Microsystems & Nanoengineering)

   Measurement of cell metabolism in moderate-throughput to high-throughput organ-on-chip (OOC) systems would expand the range of data collected for studying drug effects or disease in physiologically relevant tissue models. However, current measurement approaches rely on fluorescent imaging or colorimetric assays that are focused on endpoints, require labels or added substrates, and lack real-time data. Here, we integrated optical-based oxygen sensors in a high-throughput OOC platform and developed an approach for monitoring cell metabolic activity in an array of membrane bilayer devices. Each membrane bilayer device supported a culture of human renal proximal tubule epithelial cells on a porous membrane suspended between two microchannels and exposed to controlled, unidirectional perfusion and physiologically relevant shear stress for several days. For the first time, we measured changes in oxygen in a membrane bilayer format and used a finite element analysis model to estimate cell oxygen consumption rates (OCRs), allowing comparison with OCRs from other cell culture systems. Finally, we demonstrated label-free detection of metabolic shifts in human renal proximal tubule cells following exposure to FCCP, a drug known for increasing cell oxygen consumption, as well as oligomycin and antimycin A, drugs known for decreasing cell oxygen consumption. The capability to measure cellmore »OCRs and detect metabolic shifts in an array of membrane bilayer devices contained within an industry standard microtiter plate format will be valuable for analyzing flow-responsive and physiologically complex tissues during drug development and disease research.

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4. MEMS-in-the-lens architecture for a miniature high-NA laser scanning microscope

   https://doi.org/10.1038/s41377-019-0167-5  

   Liu, Tianbo ; Rajadhyaksha, Milind ; Dickensheets, David L. ( June 2019 , Light: Science & Applications)

   Laser scanning microscopes can be miniaturized for in vivo imaging by substituting optical microelectromechanical system (MEMS) devices in place of larger components. The emergence of multifunctional active optical devices can support further miniaturization beyond direct component replacement because those active devices enable diffraction-limited performance using simpler optical system designs. In this paper, we propose a catadioptric microscope objective lens that features an integrated MEMS device for performing biaxial scanning, axial focus adjustment, and control of spherical aberration. The MEMS-in-the-lens architecture incorporates a reflective MEMS scanner between a low-numerical-aperture back lens group and an aplanatic hyperhemisphere front refractive element to support high-numerical-aperture imaging. We implemented this new optical system using a recently developed hybrid polymer/silicon MEMS three-dimensional scan mirror that features an annular aperture that allows it to be coaxially aligned within the objective lens without the need for a beam splitter. The optical performance of the active catadioptric system is simulated and imaging of hard targets and human cheek cells is demonstrated with a confocal microscope that is based on the new objective lens design.
5. Fabrication of Fresnel lens arrays by a rapid non-isothermal imprinting process

   https://doi.org/10.1364/AO.412763  

   Shu, Yang ; Zhou, Wenchen ; Zhou, Zhixiong ; Yi, Allen Y. ( January 2021 , Applied Optics)

   Fresnel lens arrays are widely employed in concentrator photovoltaics, photonic devices, and integral imaging systems. In this study, a rapid non-isothermal imprinting process for Fresnel lens arrays was proposed. In this process, a heated mold with microstructures was momentarily pressed onto a thermoplastic polymer surface that was initially kept at room temperature. The microstructures of the mold can be copied completely to the polymer substrate by imprinting consecutively until a continuous surface Fresnel lens array is obtained. Different from more traditional molding processes, the substrate does not need to be heated and cooled repeatedly in the replicating process. In addition, the imprinting process is carried out at room temperature, which can greatly reduce the thermal cycle time and energy consumption. Generally speaking, the material flow and stress distribution of the substrate need to be monitored so that the microlenses with a high precision surface finish can be produced in the non-isothermal imprinting process. To verify this, the finite element method (FEM) model for the non-isothermal process was established, and the feasibility of this process was analyzed. A hexagonal continuous surface Fresnel lens array was then fabricated, and its geometrical contour and imaging performance were tested. The experimental results showed this newmore »process could be an effective and low-cost optical fabrication technology for high-quality production of Fresnel lens arrays.

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