Gary K. Fedder

Aerosol Jet (AJ) printing is a versatile additive manufacturing technique capable of producing high-resolution interconnects on both 2D and 3D substrates. The AJ process is complex and dynamic with many hidden and unobservable states that influence the machine performance, including aerosol particle diameter, aerosol carrier density, vial level, and ink deposition in the tube and nozzle. Despite its promising potential, the widespread adoption of AJ printing is limited by inconsistencies in print quality that often stem from variability in these hidden states. To address these challenges, we develop a digital twin model of the AJ process that offers real-time insights into the machine's operations. The digital twin is built around a physics-based macro-model created through simulation and experimentation. The states and parameters of the digital model are continuously updated using probabilistic sequential estimation techniques to closely align with real-time measurements extracted from the AJ system's sensor and video data. The result is a digital model of the AJ process that continuously evolves over a physical machine's lifecycle. The digital twin enables accurate monitoring of unobservable physical characteristics, detects and predicts anomalous behavior, and forecasts the effect of control adjustments. This work presents a comprehensive end-to-end digital twin framework that integrates customized computer vision techniques, physics-based macro-modeling, and advanced probabilistic estimation methods to construct an evolving digital representation of the AJ equipment and process. While the methodologies are customized for aerosol jet printing, the process for constructing the digital twin can be applied for other advanced manufacturing techniques.

The integration and fabrication of electrical circuits conformably onto 3D surfaces offer greater spatial efficiency, increased functionality, and improved performance in compact and tightly coupled electro-mechanical systems. However, existing 3D circuit prototyping workflows are often constrained by limited performance, insufficient generalizability or excessive manual effort and time requirements. In this paper, we present a framework that transforms 2D circuit design onto high-curvature 3D surfaces while preserving user-defined circuit characteristics and desired electrical parameters, such as trace length matching and resistance value target, allowing for the design of complex 3D circuitry using conventional 2D circuit design software that are intuitive for electrical engineers. The key contribution of this work is a two-stage processing algorithm that employs surface parameterization for 3D conformal circuit mapping followed by local distortion optimization for circuit parameter preservation. This method takes a 2D circuit design and a 3D CAD of the target surface as input, and then generates 3D circuit fabrication and process plans. We demonstrate the efficacy of our framework with a comparative analysis of circuit property preservation against other mapping approaches, both in simulation and in physical experiments, showing an 85% reduction in circuit deformation. We also demonstrate the potential of our framework through test case applications in aerospace and medical devices.

Neural Radiance Fields (NeRF) methods excel at 3D reconstruction from multiple 2D images, even those taken with unknown camera poses. However, they still miss the fine-detailed structures that matter in industrial inspection, e.g., detecting sub-micron defects on a production line or analyzing chips with Scanning Electron Microscopy (SEM). In these scenarios, the sensor resolution is fixed and compute budgets are tight, so the only way to expose fine structure is to add zoom-in images; yet, this breaks the multi-view consistency that pose-free NeRF training relies on. We propose Multi-Zoom Enhanced NeRF (MZEN), the first NeRF framework that natively handles multi-zoom image sets. MZEN (i) augments the pin-hole camera model with an explicit, learnable zoom scalar that scales the focal length, and (ii) introduces a novel pose strategy: wide-field images are solved first to establish a global metric frame, and zoom-in images are then pose-primed to the nearest wide-field counterpart via a zoom-consistent crop-and-match procedure before joint refinement. Across eight forward-facing scenes$\unicode{x2013}$synthetic TCAD models, real SEM of micro-structures, and BLEFF objects$\unicode{x2013}$MZEN consistently outperforms pose-free baselines and even high-resolution variants, boosting PSNR by up to $28 \%$, SSIM by $10 \%$, and reducing LPIPS by up to $222 \%$. MZEN, therefore, extends NeRF to real-world factory settings, preserving global accuracy while capturing the micron-level details essential for industrial inspection.

Electrical stimulation of neurons in the brain is used routinely in neuroscience and has numerous clinical applications. In contrast to invasive neural stimulation using invasive probes inserted in the brain, transcranial electrical stimulation (TES) is a safe and non-surgical neuromodulation modality. TES is generally performed using individually positioned large electrodes, which limits its precision and control. In this paper, we utilize high density surface electrode arrays to precisely control the location of TES in the human motor cortex. Current pulses of 100 µs duration and 50 to 150 mA amplitude were injected across electrodes chosen from within an array of 64 electrodes (7 mm pitch) placed above the motor cortex while recording high resolution electromyogrpahic (EMG) activity in the contralateral arm and hand muscles. Motor evoked potential (MEP) amplitude quantifies the changes in activity across the different muscles as a function of the stimulation electrode position. A map of motor responses to TES for six muscle groups in the arm is presented, showing that moving the injected electric field by sub-cm distances changes the activation profile of arm and hand muscles. This work demonstrates the potential of TES to elicit precisely controlled motor activity.Clinical relevance-Precision TES could replace invasive stimulation in some clinical applications, as well as improve the precision of intraoperative monitoring of muscle function.

Abstract A method for creating superhydrophobic surfaces is presented by aerosolizing polymer solutions into micrometer‐sized droplets and converting them into microgel particles during spatially controlled deposition using an aerosol jet printer. The polymer solutions are composed of marginally hydrophobic disulfide‐polydimethylsiloxane (DS‐PDMS) in three solvents with varying vapor pressures. The experiments, combined with an analytical model, demonstrate that solvents with high vapor pressures evaporate from the droplets during flight from the printer nozzle to the substrate. This evaporation increases the DS‐PDMS volume fraction in the droplets above the polymer gelation threshold. As a result, the droplets transform into microgel particles. This transformation leads to the formation of rough, superhydrophobic surfaces. Conversely, solvents with lower vapor pressures do not evaporate sufficiently, preventing DS‐PDMS volume fraction from reaching the gelation threshold. These droplets coalesce upon deposition, producing smooth surfaces with hydrophobicity similar to intrinsic DS‐PDMS. Heating the surfaces to 90 °C or above eliminates superhydrophobicity by de‐gelling the DS‐PDMS, allowing droplet coalescence. Potential applications of this method include droplet manipulation, microreactors for reactant mixing, water‐oil separation, and retardation of droplet evaporation.

This paper reports on the development of a monolithic capacitive accelerometer array system that has a designed full-scale range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 5~{\mathrm {\text {k}{g} }}$ </tex-math></inline-formula>, a bandwidth larger than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~{\mathrm {\text {k}\text {Hz} }}$ </tex-math></inline-formula>, with a minimum resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {5~\text {m}{g} }$ </tex-math></inline-formula> and a minimum bias instability of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {700~\mu {g} }$ </tex-math></inline-formula>. The resolution and full-scale range of the accelerometers correspond to a dynamic range of 120 dB that is on par with state-of-the-art low-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {{g} }$ </tex-math></inline-formula> accelerometers. High bandwidth and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {\text {k}{g} }$ </tex-math></inline-formula> detectability are achieved by the nano-gram proof mass and relatively stiff folded-flexure transducer design. High dynamic range with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {\text {k}{g} }$ </tex-math></inline-formula> input range is enabled by the hourglass-beam, interdigitated tapered comb-finger electrodes, and arrayed accelerometers. The accelerometer array design provides a potential path towards an emerging navigation through high-shock application.[2024-0091]

A miniature haptic stimulation device utilizes focused ultrasound to deliver a tactile haptic sensation to the finger. The 1-3 piezocomposite device has a 1 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> footprint, which is an order of magnitude smaller than other ultrasonic haptic devices and is a good candidate for wearable tactile rendering systems. The device focuses energy to a 1 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> voxel. The current prototype was validated with a small, preliminary human subject study and requires an average input voltage of 68.8 V to elicit tactile sensation. The sensory drive voltage threshold will decrease with future refinement of mechanical impedance matching and focusing.

This article presents a single-chip accelerometer with the best reported thermal noise and the lowest bias instability among state-of-the-art accelerometers with high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$ </tex-math></inline-formula> 1000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g$ </tex-math></inline-formula> ) sensing capability. Complete single-chip integration of microelectromechanical transducers, readout circuits, and environmental sensors is achieved by leveraging a CMOS-microelectromechanical systems (MEMS) approach. Simple equations are derived to estimate the gain degradation issue due to delay mismatch in chopper amplifiers. A coarse digital-to-time converter (CDTC) assisted chopper amplifier is introduced to suppress the gain degradation nonideality and potentially improve the energy efficiency. Measurements and simulations validate the accuracy of the predictions and efficacy of the CDTC-based signal-boosting technique. A fine digital-to-time converter (FDTC) assisted demodulation clock skew compensation technique is employed to further suppress the residual flicker noise in chopper amplifiers. Measurement results validate the preliminary investigation of the clock skew-induced residual flicker noise and prove the benefit of FDTC-assisted flicker noise reduction. Both low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g$ </tex-math></inline-formula> and high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g$ </tex-math></inline-formula> performance are characterized. Fabricated in a standard 180 nm CMOS process followed by post-CMOS processing, the accelerometer achieves 46.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu g/\surd $ </tex-math></inline-formula> Hz thermal noise, 472 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu g$ </tex-math></inline-formula> bias instability, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$ </tex-math></inline-formula> 1000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g$ </tex-math></inline-formula> full-scale (FS).

Transcranial electrical neuromodulation of the central nervous system is used as a non-invasive method to induce neural and behavioral responses, yet targeted non-invasive electrical stimulation of the brain with high spatial resolution remains elusive. This work demonstrates a focused, steerable, high-density epicranial current stimulation (HD-ECS) approach to evoke neural activity. Custom-designed high-density (HD) flexible surface electrode arrays are employed to apply high-resolution pulsed electric currents through skull to achieve localized stimulation of the intact mouse brain. The stimulation pattern is steered in real time without physical movement of the electrodes. Steerability and focality are validated at the behavioral, physiological, and cellular levels using motor evoked potentials (MEPs), intracortical recording, and c-fos immunostaining. Whisker movement is also demonstrated to further corroborate the selectivity and steerability. Safety characterization confirmed no significant tissue damage following repetitive stimulation. This method can be used to design novel therapeutics and implement next-generation brain interfaces.

Transcranial electrical stimulation (TES), a technique for stimulating the brain without surgical intervention, has potential applications for therapeutic interventions as well as brain-computer interfaces. One of the known limitations of conventional TES is that the stimulation volume is very large, due to the size and placement of electrodes typically used, which does not allow accurate targeting and results in large off-target activation. This work demonstrates a novel method for high resolution transcranial stimulation of motor cortex in mouse models using a flexible ultra-high-density electrode array. An electrode array was designed with ring-shaped electrodes having a hole in the middle, allowing simultaneous transcranial stimulation and intracortical recording using a commercial silicon neural probe. Intracortical recordings performed during transcranial stimulation, at both the stimulation target and at adjacent locations spaced at a 650 μm pitch, demonstrate the spatial localization of the evoked neural activity. Significant multi-unit activity was recorded at the center of the stimulation zone in the 15ms following stimulation, while low off-target activity is measured 650 μm away from the center. The locus of the stimulation was moved at four different locations in the cortex, with similar localized intracortical response obtained at all locations. Simultaneous stimulation of multiple sites was also demonstrated.