Compact Form Factor Research Articles

Towards Estimation of Tidal Volume and Respiratory Timings via Wearable-Patch-Based Impedance Pneumography in Ambulatory Settings.

Evaluating convenient, wearable multi-frequency impedance pneumography (IP)-based respiratory monitoring in ambulatory persons with novel electrode positioning. A wearable multi-frequency IP system was utilized to estimate tidal volume (TV) and respiratory timings in 14 healthy subjects. A 5.1 cm × 5.1 cm tetrapolar electrode array, affixed to the sternum, and a conventional thoracic electrode configuration were employed to measure the respective IP signals, patch and thoracic IP. Data collected during static postures-sitting and supine-and activities-walking and stair-stepping-were evaluated against a simultaneously-obtained spirometer (SP) volume signal. Across all measurements, estimated TV obtained from the patch and thoracic IP maintained a Pearson correlation coefficient (r) of 0.93 ± 0.05 and 0.95 ± 0.05 to the ground truth TV, respectively, with an associated root-mean-square error (RMSE) of 0.177 L and 0.129 L, respectively. Average respiration rates (RRs) were extracted from 30-second segments with mean-absolute-percentage errors (MAPEs) of 0.93% and 0.74% for patch and thoracic IP, respectively. Likewise, average inspiratory and expiratory timings were identified with MAPEs less than 6% and 4.5% for patch and thoracic IP, respectively. We demonstrated that patch IP performs comparably to traditional, cumbersome IP configurations. We also present for the first time, to the best of our knowledge, that IP can robustly estimate breath-by-breath TV and respiratory timings during ambulation. This work represents a notable step towards pervasive wearable ambulatory respiratory monitoring via the fusion of a compact chest-worn form factor and multi-frequency IP that can be readily adapted for holistic cardiopulmonary monitoring.

Entropy optimization of an additively manufactured heat exchanger with a dual stage Gifford-McMahon cryogenic refrigerator for hydrogen liquefaction

Small-scale hydrogen liquefaction has emerged as an approach to fuel small aircraft powered by fuel cells. However, limited research on the design and optimization of small-scale hydrogen liquefiers, specifically the heat exchangers, is available. This paper describes a minimum entropy design for a heat exchanger mounted on a dual stage Gifford-McMahon cryogenic refrigerator. To minimize entropy generation the heat exchanger utilizes a bifurcating flow structure with varying wall thickness. Numerical optimization indicates that the heat exchanger will generate half of the entropy of a single coiled tube, significantly reducing the required heat exchanger length by 91.4% and the thermal mass by 43.8%. The heat exchanger was 3D printed with an aluminum alloy and the interior coated with a ruthenium-based catalyst for ortho-parahydrogen conversion. Hydrogen entering the heat exchanger near 293 K and 653 kPa is cooled to 28.1 K and full ortho-parahydrogen conversion is assumed before entering the storage dewar. The resulting experimental tests indicate a potential to increase heat exchanger efficiency in a more compact form factor, as well as a promising future for additively manufactured components in cryogenics.

Thermal and driven noise in Brillouin lasers

Owing to their highly coherent emission and compact form factor, Brillouin lasers have been identified as a valuable asset for applications including portable atomic clocks, precision sensors, coherent microwave synthesis, and energy-efficient approaches to coherent communications. While the fundamental emission linewidth of these lasers can be very narrow, noise within dielectric materials leads to drift in the carrier frequency, posing vexing challenges for applications requiring ultrastable emission. A unified understanding of Brillouin laser performance may provide critical insights to reach new levels of frequency stability; however, existing noise models focus on only one or a few key noise sources, and do not capture the thermo-optic drift in the laser frequency produced by thermal fluctuations or absorbed power. Here, we develop a coupled-mode theory of Brillouin laser dynamics that accounts for dominant forms of noise in noncrystalline systems, capturing the salient features of the frequency and intensity noise for a variety of systems. As a result, theory and experiment can be directly compared to identify key sources of noise and the frequency bands they impact, revealing strategies to improve the performance of Brillouin lasers and pave the way for highly coherent sources of light on a chip.

Foveated imaging by polarization multiplexing for compact near‐eye displays

AbstractWe demonstrate a multi‐resolution foveated imaging system for virtual reality, which is enabled by a single display panel with polarization multiplexing to significantly increase the angular resolution without scarifying the frame rate. By using a polarization‐dependent cholesteric liquid crystal reflector, we have achieved a 4.4× higher resolution density while maintaining a compact form factor.

Compact multichannel imaging camera for wide-field imaging of diffused sources

We describe a multichannel camera operating in the visible to near-infrared wavelengths (450 to 900 nm) with an etendue of 0.08 cm2 sr that can be used to image extended sources across multiple optical bands, capable of 3σ detection of 20 Rayleigh signal in 120 s. It has an angular resolution of 0.1 deg and a 35 deg × 25 deg field of view, employing a charge-coupled device detector in a compact 1U CubeSat compatible form factor (10 × 10 × 8 cm3). The design uses commercial off-the-shelf components while offering versatility using a mosaic of bandpass filters to select different spectral channels to address a wide range of remote sensing needs. The specific implementation described here covers the application of the instrument to explore the neutral sodium and potassium atom density distribution in the atmospheres of the Earth or the Moon.

Microwave Flexible Electronics Directly Transformed from Foundry‐Produced, Multilayered Monolithic Integrated Circuits

AbstractMonolithic microwave integrated circuits hold a dominant position in telecom applications, especially in mobile devices with capabilities for wireless connectivity, due to high and repeatable performance, compact form factor, and low cost. With flexible electronic technologies forming the foundation for a rapidly growing wearable and implantable device segment, the need for flexible microwave electronics with levels of performance that match those of rigid counterparts has increased to unprecedented levels. Here, the fabrication processes for transforming a rigid form of foundry‐produced, multilayered monolithic microwave integrated circuit into a flexible format for amplification of radio frequency signals in the gigahertz level are described. The strategy involves a complete replacement of all rigid materials in the integrated circuit that do not provide any active electronic functionality with a soft, silicone elastomer to yield an overall structure that is mechanically compliant. Experimental studies indicate that the transformation process leads to a flexible silicon‐germanium‐based heterojunction bipolar transistor with a maximum oscillation frequency of 49 GHz and a 24 GHz amplifier with a small‐signal gain of 13.2 dB. This approach has potential uses across a diverse set of microwave devices and circuits, in a manner that could enable wireless connectivity using entirely flexible electronics.

Exploring efficacy of machine learning (artificial neural networks) for enhancing reliability of thermal energy storage platforms utilizing phase change materials

Thermal Energy Storage (TES) platforms mitigate the paucity between peaks in consumption and supply, i.e., they absorb thermal energy during periods of excess supply and release thermal energy during periods of deficit. Phase change materials (PCMs) have attracted significant attention over recent years due to their efficacy in improving performance and reliability of TES platforms. High latent heat values accruing from the use of PCMs enable improved storage densities which in turn yield devices with compact form factors for TES applications. Typically, inorganic PCMs afford higher latent heat values than organic PCMs, yet often at the detriment of compromised reliability. A crucial issue with inorganic PCMs is the higher degree of supercooling (also known as “subcooling”) required to initiate nucleation (which degrades their reliability, net energy storage capacity, and power rating of the TES platform). “Cold Finger Technique (CFT)” can be used to mitigate these issues where a small portion of the total mass of PCM in the TES platform is left in solid state (in order to facilitate the spontaneous nucleation). Therefore, reliability issues are ameliorated by using CFT but at a marginal cost to the net storage capacity while power rating of the TES remains almost unaffected. In this study, machine learning (ML) techniques were leveraged to exploit the capability of CFT more effectively. Temperature transients from PCM melting experiments are used to investigate the capability of this deep learning technique (i.e., using multi-layer perceptron model or “MLP”) in order to predict the required time to reach the designated melt-fraction of the PCM. The results show that the Artificial Neural Network (ANN) model designed and implemented in this study is capable of predicting the time required to reach pre-designated value of melt-fraction with outstanding accuracy (e.g., 90% melt-fraction or 95% melt-fraction, that is specified by the user). The mean error of the predictions is calculated and is expected to be less than 10 min, especially for an interval of 30 min before the TES platform reaches the desired value of the melt fraction (i.e., 90% melt-fraction) for a total time spanning 2∼3 h. However, this approach is more susceptible to the fidelity of the data-set utilized for training the ANN (MLP) algorithm.

Scanning Angle Magnification with Compact Reflective Optics for Light Detection and Ranging

The function of lidar requests a large scanning angle for a wide field of view and a well calibrated collimation of the laser beam for distant sensing. Besides meeting the required functionality, the compact form factor of the whole optical system is also highly desirable for the ease of being installed in mobile systems. In corresponding to the currently developed phase array laser which can achieve beam scanning without mechanical movement but still with a small scanning angle, a compact optics consisting of only two reflective surfaces has been proposed to magnify the scanning angle of a laser beam up to seven times while keeping the divergence of the laser beam smaller than 8 mrad for some short distance applications. The prototype has been prepared and evaluated with the expected performance.

Waveguide-type Maxwellian near-eye display using a pin-mirror holographic optical element array.

We propose a novel, to the best of our knowledge, waveguide-type optical see-through Maxwellian near-eye display for augmented reality. A pin-mirror holographic optical element (HOE) array enables the Maxwellian view and eye-box replication. Virtual images with deep depth of field are presented by each pin-mirror HOE, alleviating the discrepancy between vergence and accommodation distance. The compact form factor is achieved by the thin waveguide and HOE couplers.

Toward 3D-Printed Inverse-Designed Metaoptics

Optical metasurfaces have been heralded as the platform to integrate multiple functionalities in a compact form-factor, potentially replacing bulky components. A central stepping stone towards realizing this promise is the demonstration of multifunctionality under several constraints (e.g. at multiple incident wavelengths and/or angles) in a single device -- an achievement being hampered by design limitations inherent to single-layer planar geometries. Here, we propose a general framework for the inverse design of volumetric 3D metaoptics via topology optimization, showing that even few-wavelength thick devices can achieve high-efficiency multifunctionality. We embody our framework in multiple closely-spaced patterned layers of a low-index polymer. We experimentally demonstrate our approach with an inverse-designed 3d-printed light concentrator working at five different non-paraxial angles of incidence. Our framework paves the way towards realizing multifunctional ultra-compact 3D nanophotonic devices.

Design of a Compact High Isolation 4-Element Wideband Patch Antenna Array for GNSS Applications

This work presents a compact (125 mm diameter) wideband four-element antenna array with a high isolation level for Global Navigation Satellite System (GNSS) anti-jamming applications. The array consists of four identical right hand circularly polarized (RHCP) single feed rectangular patch antennas that can cover BeiDou B1 band (1559.05 – 1563.15 MHz), GPS L1 band (1563 – 1587 MHz), Galileo E1 band (1559 – 1591 MHz), and GLONASS G1 band (1593 – 1610 MHz). The proposed array has a wide frequency bandwidth of 100 MHz (1.55 – 1.65 GHz) with an axial ratio of less than 3 dB. The patch antenna elements are designed on a substrate that has a high dielectric constant to achieve a compact size. The size of each patch element is only 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 32\times5.08$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . These patches are placed along the circumference of a circular aluminium ground plane of 125 mm diameter and 1.5 mm thickness in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> symmetrical arrangement. The edge-to-edge distance between the opposite patch elements is only 48 mm while for the adjacent elements the separation is only 27 mm. A microwave absorber material is employed to achieve an extremely low mutual coupling level over a wide frequency range (1.55 – 1.65 GHz) within a compact form factor. The proposed design achieves a mutual coupling of less than −20 dB within a compact overall form factor of 125 mm diameter over the entire band of interest. The simulated and measured results of reflection coefficient, mutual coupling, null steering, null depth, and radiation pattern show that the proposed antenna array is an excellent choice for multiband GNSS applications.

Strong and Smart

Miele reveals how it’s engineering team has improved the performance and usability of the Scout RX robotic vacuum cleaner while keeping a compact form factor, enabling it to clean even in the hardest to reach places

Holographic techniques for augmented reality and virtual reality near-eye displays

Near-eye displays are the main platform devices for many augmented reality (AR) and virtual reality (VR) applications. As a wearable device, a near-eye display should have a compact form factor and be lightweight. Furthermore, a large field of view and sufficient eyebox are crucial for immersive viewing conditions. Natural three-dimensional (3D) image presentation with proper focus cues is another requirement that enables a comfortable viewing experience and natural user interaction. Finally, in the case of AR, the device should allow for an optical see-through view of the real world. Conventional bulk optics and two-dimensional display panels exhibit clear limitations when implementing these requirements. Holographic techniques have been applied to near-eye displays in various aspects to overcome the limitations of conventional optics. The wavefront reconstruction capability of holographic techniques has been extensively exploited to develop optical see-through 3D holographic near-eye displays of glass-like form factors. In this article, the application of holographic techniques to AR and VR near-eye displays is reviewed. Various applications are introduced, such as static holographic optical components and dynamic holographic display devices. Current issues and recent progress are also reviewed, providing a comprehensive overview of holographic techniques that are applied to AR and VR near-eye displays.

A Miniaturized 256-Channel Neural Recording Interface With Area-Efficient Hybrid Integration of Flexible Probes and CMOS Integrated Circuits.

We report a miniaturized, minimally invasive high-density neural recording interface that occupies only a 1.53 mm2 footprint for hybrid integration of a flexible probe and a 256-channel integrated circuit chip. To achieve such a compact form factor, we developed a custom flip-chip bonding technique using anisotropic conductive film and analog circuit-under-pad in a tiny pitch of 75 μm. To enhance signal-to-noise ratios, we applied a reference-replica topology that can provide the matched input impedance for signal and reference paths in low-noise aimpliers (LNAs). The analog front-end (AFE) consists of LNAs, buffers, programmable gain amplifiers, 10b ADCs, a reference generator, a digital controller, and serial-peripheral interfaces (SPIs). The AFE consumes 51.92 μW from 1.2 V and 1.8 V supplies in an area of 0.0161 mm2 per channel, implemented in a 180 nm CMOS process. The AFE shows > 60 dB mid-band CMRR, 6.32 μVrms input-referred noise from 0.5 Hz to 10 kHz, and 48 MΩ input impedance at 1 kHz. The fabricated AFE chip was directly flip-chip bonded with a 256-channel flexible polyimide neural probe and assembled in a tiny head-stage PCB. Full functionalities of the fabricated 256-channel interface were validated in both in vitro and in vivo experiments, demonstrating the presented hybrid neural recording interface is suitable for various neuroscience studies in the quest of large scale, miniaturized recording systems.

Programmable linear random-access memory and its in-memory computing circuits and systems based on flash memory

The neural network inference chips based on novel non-volatile memories and compute-in-memory architectures have exhibited significant advantages in terms of power consumption, computation speed and storage density, making them a widely-attractive candidate for IoT and edge computing applications. In this paper, we introduced the design and implementation of an in-memory computing SoC chip based on modified floating-gate transistor devices named PLRAM. In order to achieve highly-efficient inference computation under constrained resources, this system combines a series of techniques from the device, circuit and system perspectives, including: new devices with 7 bit/cell storage capability, self-adaptive write of data, compensation of circuits mismatch and model deployment techniques based on training residual models. These new techniques helped the system to achieve superb overall performance, including compact form factor, energy efficiency above 10 TOPS/W and computation accuracy of roughly 95%. It has been successfully used in low-power, low-cost products for keyword-spotting applications.

Compact User-Specific Reconfigurable Intelligent Surfaces for Uplink Transmission

Large-scale antenna arrays employed by the base station (BS) constitute an essential next-generation communications technique. However, due to the constraints of size, cost, and power consumption, it is usually considered unrealistic to use a large-scale antenna array at the user side. Inspired by the emerging technique of reconfigurable intelligent surfaces (RIS), we firstly propose the concept of user-specific RIS (US-RIS) for facilitating the employment of a large-scale antenna array at the user side in a cost- and energy-efficient way. In contrast to the existing employments of RIS, which belong to the family of base-station-specific RISs (BSS-RISs), the US-RIS concept by definition facilitates the employment of RIS at the user side for the first time. This is achieved by conceiving a multi-layer structure to realize a compact form-factor. Furthermore, our theoretical results demonstrate that, in contrast to the existing single-layer structure, where only the phase of the signal reflected from RIS can be adjusted, the amplitude of the signal penetrating multi-layer US-RIS can also be partially controlled, which brings about a new degree of freedom (DoF) for beamformer design that can be beneficially exploited for performance enhancement. In addition, based on the proposed multi-layer US-RIS, we formulate the signal-to-noise ratio (SNR) maximization problem of US-RIS-aided communications. Due to the non-convexity of the problem introduced by this multi-layer structure, we propose a multi-layer transmit beamformer design relying on an iterative algorithm for finding the optimal solution by alternately updating each variable. Finally, our simulation results verify the superiority of the proposed multi-layer US-RIS as a compact realization of a large-scale antenna array at the user side for uplink transmission.

CMOS-Based Electrokinetic Microfluidics With Multi-Modal Cellular and Bio-Molecular Sensing for End-to-End Point-of-Care System.

The importance of point-of-care (POC) bio-molecular diagnostics capable of rapid analysis has become abundantly evident after the outbreak of the Covid-19 pandemic. While sensing interfaces for both protein and nucleic-acid based assays have been demonstrated with chip-scale systems, sample preparation in compact form factor has often been a major bottleneck in enabling end-to-end POC diagnostics. Miniaturization of an end-to-end system requires addressing the front-end sample processing, without which, the goal for low-cost POC diagnostics remain elusive. In this paper, we address bulk fluid processing with AC-osmotic based electrokinetic fluid flows that can be fully controlled, processed and automated by CMOS ICs, fabricated in TSMC 65 nm LP process. Here, we combine bulk fluid flow control with bio-molecular sensing, cell manipulation, cytometry, and separation-all of which are controlled with silicon chips for an all-in-one bio-sensing device. We show CMOS controlled pneumatic-free bulk fluid flow with fluid velocities reaching up to 160 μm/s within a microfluidic channel of 100 × 50 μm 2 of cross-sectional area. We incorporate electrode arrays to allow precise control and focused cell flows ( ±2 μm precision) for robust cytometry, and for subsequent separation. We also incorporate a 16-element impedance spectroscopy receiver array for cell and label-free protein sensing. The massive scalability of CMOS-driven microfluidics, manipulation, and sensing can lead to a new design space and a new class of miniaturized sensing technologies.

Waveguide-type see-through dual focus near-eye display with a polarization grating.

Waveguide-type near-eye displays have useful properties such as compact form factor, lightweight and see-through capability. Conventional systems, however, support only a single image plane fixed at a certain distance, which may induce eye fatigue due to the vergence-accommodation conflict. In this paper, we propose a waveguide-type near-eye display with two image planes using a polarization grating. Two images with orthogonal polarizations propagate within the waveguide with different total internal reflection angles and form virtual images at different distances. The use of the polarization grating and two pairs of holographic optical elements enables dual image plane formation by a single waveguide with high transparency for the real scene. Optical experiments confirm the principle of the proposed optical system.

Computational design and optimization of electro-physiological sensors

Electro-physiological sensing devices are becoming increasingly common in diverse applications. However, designing such sensors in compact form factors and for high-quality signal acquisition is a challenging task even for experts, is typically done using heuristics, and requires extensive training. Our work proposes a computational approach for designing multi-modal electro-physiological sensors. By employing an optimization-based approach alongside an integrated predictive model for multiple modalities, compact sensors can be created which offer an optimal trade-off between high signal quality and small device size. The task is assisted by a graphical tool that allows to easily specify design preferences and to visually analyze the generated designs in real-time, enabling designer-in-the-loop optimization. Experimental results show high quantitative agreement between the prediction of the optimizer and experimentally collected physiological data. They demonstrate that generated designs can achieve an optimal balance between the size of the sensor and its signal acquisition capability, outperforming expert generated solutions.

Design and control of the first foldable single-actuator rotary wing micro aerial vehicle

The monocopter is a type of micro aerial vehicle largely inspired from the flight of botanical samaras (Acer palmatum). A large section of its fuselage forms the single wing where all its useful aerodynamic forces are generated, making it achieve a highly efficient mode of flight. However, compared to a multi-rotor of similar weight, monocopters can be large and cumbersome for transport, mainly due to their large and rigid wing structure. In this work, a monocopter with a foldable, semi-rigid wing is proposed and its resulting flight performance is studied. The wing is non-rigid when not in flight and relies on centrifugal forces to become straightened during flight. The wing construction uses a special technique for its lightweight and semi-rigid design, and together with a purpose-designed autopilot board, the entire craft can be folded into a compact pocketable form factor, decreasing its footprint by 69%. Furthermore, the proposed craft accomplishes a controllable flight in 5 degrees of freedom by using only one thrust unit. It achieves altitude control by regulating the force generated from the thrust unit throughout multiple rotations. Lateral control is achieved by pulsing the thrust unit at specific instances during each cycle of rotation. A closed-loop feedback control is achieved using a motion-captured camera system, where a hybrid proportional stabilizer controller and proportional-integral position controller are applied. Waypoint tracking, trajectory tracking and flight time tests were performed and analyzed. Overall, the vehicle weighs 69 g, achieves a maximum lateral speed of about 2.37 m s−1, an average power draw of 9.78 W and a flight time of 16 min with its semi-rigid wing.