Jeffrey H. Lang

PURPOSE: The UmboMic is a recently developed middle ear microphone that functions by detecting the sound-induced motion of the umbo [1]. To prepare for a live animal study of the in vivo performance of the UmboMic, we developed the surgical implantation and fixation system in cadaveric sheep ears. METHODS: Temporal bones from seven female sheep were prepared for implantation of the UmboMic system. Fixation hardware for sheep was designed to secure the UmboMic sensor in position so that the sensing tip contacted the umbo in the middle-ear cavity and the non-sensing tail end was secured to the surrounding mastoid bone. First, pre-surgical micro-CT scans of the temporal bones and open-source software were used to simulate surgical drilling, and to virtually plan and fit the UmboMic fixation system. Then, in physical sheep temporal bones, sound-induced umbo motion was measured with a laser Doppler vibrometer as a preliminary step. After surgical implantation of the UmboMic system, the position of the UmboMic sensor was evaluated with microscopic visualization and post-surgical micro-CT. Implanted UmboMic sensor function in response to acoustic frequency sweeps to the external ear canal was measured in two specimens. RESULTS: Measurements of sheep temporal bone anatomical dimensions with micro-CT showed that the facial recess featured a mean maximum height of 2.36 mm, length of 12.2 mm, and depth from outer opening surface of facial recess to the umbo of 11.1 mm. The amplitude of umbo motion prior to UmboMic implantation was consistent with that previously reported by [2], with a displacement of ~ 14 nm/Pa up to a frequency of 5.5 kHz, followed by a gradual drop-off. When bench tested and implanted in sheep temporal bones, the UmboMic sensitivity was as predicted from [1], ~ 1-2 fC/nm. CONCLUSION: When implanted in sheep cadaveric ears, UmboMic performance was similar to previous measurements in fresh human cadaveric temporal bones. The method of simulating surgical drilling using micro-CT and simple open-source software is economical and broadly applicable in understanding the 3D biological anatomy and implantable device design and customization. The UmboMic implantation in cadaveric sheep ears was possible, and this study represents a step towards planned live animal studies.

Conventional power converters rely on magnetic components for energy storage, but these magnetics are often the bottleneck to achieving high power density, high efficiency, and light weight. Power converters that use piezoelectric components for energy storage are a promising alternative to magnetic-based converters, particularly for miniature, power-dense designs. One natural application for piezoelectrics is in isolated converters; due to their electromechanical nature, piezoelectric components can be used to create galvanically isolated converters without the use of magnetic components. Previously demonstrated isolated piezoelectric-resonator-based converters have performed well, but their topologies are best suited for modest conversion ratios. To reach a wider application space, this work presents two techniques for improving performance at high conversion ratios. The first is a new topology of isolated piezoelectric-based converter that operates with high efficiency for large variable conversion ratios greater than 2:1. The second is multi-cycle control, a method for modifying conventional switching sequences to reduce loss at higher conversion ratios. These techniques are demonstrated in a prototype that achieves significantly higher efficiency at large step-down than previous designs.

Foldable robots have been an active area of robotics research due to their high volume-to-mass ratio, easy packability, and shape adaptability. For locomotion, previously developed foldable robots have either embedded linear actuators in, or attached non-folding rotary motors to, their structure. Further, those actuators directly embedded in the structure of the folding medium all contributed to linear or folding motion, not to continuous rotary motion. On the macro-scale there has not yet been a folding continuous rotary actuator. This paper details the development and testing of the first macro-scale origami rotary motor that can be folded flat, and then unfurled to operate. Using corona discharge for torque production, the prototype motor achieved an expansion ratio of 2.5:1, reached a top speed of 1440 rpm when driven at -29 kV, and exhibited a maximum output torque over 0.15 mN m with an active component torque density of 0.04 Nm/kg.

Foldable robots have been an active area of robotics research due to their high volume-to-mass ratio, easy packability, and shape adaptability. For locomotion, previously developed foldable robots have either embedded linear actuators in, or attached non-folding rotary motors to, their structure. Further, those actuators directly embedded in the structure of the folding medium all contributed to linear or folding motion, not to continuous rotary motion. On the macro-scale there has not yet been a folding continuous rotary actuator. This paper details the development and testing of the first macro-scale origami rotary motor that can be folded flat, and then unfurled to operate. Using corona discharge for torque production, the prototype motor achieved an expansion ratio of 2.5:1, reached a top speed of 1440 rpm when driven at -29 kV, and exhibited a maximum output torque over 0.15 mN m with an active component torque density of 0.04 Nm/kg.

Electrostatically actuated mesh reflectors are a promising technology for space-based sensing and communication antennas. Key advantages over current passive mesh reflectors include the ability to correct surface distortions (e.g., from manufacturing defects and environmental disturbances) and to achieve beam steering and beam shaping via dynamic adjustment of the reflector surface. Implementation of an electrostatically actuated mesh requires a method for determining optimal control voltages that achieve a desired reflector shape. This work demonstrates such an inverse method using a simplified numerical model of a linear isotropic elastic membrane subject to nonlinear electrostatic pressure. The model is used to determine the number of electrodes required to achieve a desired surface error. A prototype reflector, consisting of a 0.5-m diameter gold mesh and 9 electrodes, is constructed and various reflector shapes, including non-axisymmetric ones, are produced and refined using an open-loop controller based on the method. Before refinement, the experimentally measured RMS surface error is within 840μm of the target shape. The method is also shown to be useful for fine-tuning the shape; with only 3 iterations of surface refinement, the RMS error is reduced to within 231 μm. The experimentally characterized surface error proves that the method can adapt to unmodeled mechanics, achieving the desired shape precision for operation at 35 GHz Ka-band. Full-wave electromagnetic simulations of the target and experimental reflector surfaces were performed, and it was found that the fine-tuned surfaces had sufficient surface precision for convergence of the main lobe of the antenna pattern. This work demonstrates both the viability of, and method for achieving, shape control of an electrostatically actuated reflector.

We report a nanoelectromechanical (NEM) switch fabricated entirely through the bottom-up assembly of low-dimensional materials, comprising graphene, self-assembled molecular spacers and Au nanowires. The device works by electrostatically compressing the molecular spacer, thereby modulating the tunneling current through it. By leveraging the atomically smooth interfaces inherent to low-dimensional materials, we demonstrate that this device can operate without shorting for more than 7000 cycles while demonstrating a low actuation voltage.

Miniaturization of power converters is limited by the inherently diminished performance of magnetic components at small sizes. Piezoelectric components offer an alternative energy storage mechanism that provides high power density and efficiency, particularly at small sizes. This work extends the development of power converters based on piezoelectric resonators by presenting a novel method for developing isolated dc-dc piezoelectric-resonator-based converters. This class of converters achieves full resonant soft switching and capacitor soft charging without the use of any magnetic components. An example hardware prototype experimentally demonstrates peak efficiencies above 95% for conversion ratios between 0.6 and 0.9. In addition, this design achieves a piezoelectric component power density of 209 W/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>, the highest recorded in an isolated piezoelectric-based topology.

A large mechanical sensitivity can be achieved by a mechanically tunable quantum tunneling barrier. The tunneling resistance across the nanometer-sized gap can be changed by several orders of magnitude through a sub-angstrom-scale displacement. Here, we demonstrate the performance of a strain sensor formed from pre-stretched Platinum (Pt) on PDMS, where perturbation of the thickness of the nanogap cracks due to strain change the resistance of the device. A gauge factor >500 is realized in a device that is mechanically stabilized by self-assembled monolayer (SAM). Then, we extend the application of the nanogap based strain sensor to temperature and infrared detection. Fabricated proof-of-concept metal/SAM/metal suspended bolometers yield a temperature coefficient of resistance (TCR) between -0.006 K-1 and - 0.085 K-1, and theoretical predictions show that with further optimization the TCRs could be improve to as much as -2.7 K-1, which is more than one order of magnitude better than the state-of-the-art VOx bolometers. Furthermore, this work quantifies the 50 Hz to 10 kHz noise performance of suspended metal/nanogap/metal bolometers and compares the noise spectrum of devices with and without SAM, as well as 10 nm Pt channel vs. 30 nm Pt channel devices. Finally, early stage 830 nm optical measurements show that the device sensitivity of a 10nm Pt / air nanogap / 10 nm Pt peaks at low bias (< 1V, <20 pA) and that the 3dB point of the sensor extends past 10 kHz. The experimental results of this work suggest that nanogap-based sensor architectures exhibit a high sensitivity and may also enable fast response time detectors.

Objective: We present the "UmboMic," a prototype piezoelectric cantilever microphone designed for future use with totally-implantable cochlear implants. Methods: The UmboMic sensor is made from polyvinylidene difluoride (PVDF) because of its low Young's modulus and biocompatibility. The sensor is designed to fit in the middle ear and measure the motion of the underside of the eardrum at the umbo. To maximize its performance, we developed a low noise charge amplifier in tandem with the UmboMic sensor. This paper presents the performance of the UmboMic sensor and amplifier in fresh cadaveric human temporal bones. Results: When tested in human temporal bones, the UmboMic apparatus achieves an equivalent input noise of 32.3 dB SPL over the frequency range 100 Hz to 7 kHz, good linearity, and a flat frequency response to within 10 dB from about 100 Hz to 6 kHz. Conclusion: These results demonstrate the feasibility of a PVDF-based microphone when paired with a low-noise amplifier. The reported UmboMic apparatus is comparable in performance to a conventional hearing aid microphone. Significance: The proof-of-concept UmboMic apparatus is a promising step towards creating a totally-implantable cochlear implant. A completely internal system would enhance the quality of life of cochlear implant users.

Increasing the size of radio frequency (RF) reflectors in space can enhance gain and spatial resolution in applications such as space-based communication and remote sensing. The size of current passive deployable reflectors is limited by a tradeoff between diameter and surface precision, which causes RF performance to degrade as size increases. A promising approach to overcome this tradeoff is to combine in-space manufacturing, which enables large structures, with distributed embedded actuation, which enables precise control over the reflector surface. Here we demonstrate a reflector antenna system that integrates these two technologies, using a candidate in-space manufacturing process, termed “Bend-Forming,” with embedded electrostatic actuators. We design and fabricate a 1-m-diam prototype of an electrostatically actuated X-band reflector with a knitted gold-molybdenum mesh as the reflector surface, carbon-fiber-reinforced plastic booms as electrodes, and a truss support structure fabricated with Bend-Forming. We characterize the RF performance of this reflector, successfully demonstrating i) control over a wide range of focal lengths by suppressing a pull-in instability and ii) beam steering over an angular range of 4.2° via asymmetric electrostatic actuation. This work lays the foundation for future space communication and remote sensing technologies, offering a scalable solution to enhance RF performance through in-space manufacturing and precision control.

Sheep have been proposed as a large-animal model for studying cochlear implantation. However, prior sheep studies report that the facial nerve (FN) obscures the round window membrane (RWM), requiring FN sacrifice or a retrofacial opening to access the middle-ear cavity posterior to the FN for cochlear implantation. We investigated surgical access to the RWM in Hampshire sheep compared to Suffolk-Dorset sheep and the feasibility of Hampshire sheep for cochlear implantation via a facial recess approach. Sixteen temporal bones from cadaveric sheep heads (ten Hampshire and six Suffolk-Dorset) were dissected to gain surgical access to the RWM via an extended facial recess approach. RWM visibility was graded using St. Thomas’ Hospital (STH) classification. Cochlear implant (CI) electrode array insertion was performed in two Hampshire specimens. Micro-CT scans were obtained for each temporal bone, with confirmation of appropriate electrode array placement and segmentation of the inner ear structures. Visibility of the RWM on average was 83% in Hampshire specimens and 59% in Suffolk-Dorset specimens (p = 0.0262). Hampshire RWM visibility was Type I (100% visibility) for three specimens and Type IIa (> 50% visibility) for seven specimens. Suffolk-Dorset RWM visibility was Type IIa for four specimens and Type IIb (< 50% visibility) for two specimens. FN appeared to course more anterolaterally in Suffolk-Dorset specimens. Micro-CT confirmed appropriate CI electrode array placement in the scala tympani without apparent basilar membrane rupture. Hampshire sheep appear to be a suitable large-animal model for CI electrode insertion via an extended facial recess approach without sacrificing the FN. In this small sample, Hampshire specimens had improved RWM visibility compared to Suffolk-Dorset. Thus, Hampshire sheep may be superior to other breeds for ease of cochlear implantation, with FN and facial recess anatomy more similar to humans.

electromechanical models are crucial in the design and control of motors and actuators. Modeling, identification, drive, and current control loop of a limited-rotation actuator with magnetic restoration is presented. New nonlinear and linearized electromechanical models are developed for the design of the drive as well as small and large signal controls of the actuator. To attain a higher accuracy and an efficient design, and the eddy-currents in the laminations and magnet are modeled. This involves analytically solving 1-D and 2-D diffusion equations, leading to the derivation of a lumped-element circuit for system-level analyses, such as control system design. Additionally, the study analyzes and incorporates the impact of pre-sliding friction. The actuator is prototyped, and the paper delves into the identification of the model, presenting a procedure for parameter extraction. A close agreement is observed between the results obtained from the model, finite element analysis, and experimental results. The superiority of the proposed model over previous approaches is highlighted. Part II of the paper is dedicated to the drive circuit, the current control, as well as linear and nonlinear position control system designs.

In part II, an op-amp-based drive is proposed and designed. Subsequently, a very accurate model for the drive circuit and the current loop is developed as a simulation platform, while its simplified version is derived, tailored for efficient design purposes. Through a comprehensive evaluation, the accuracy and efficacy of both the actuator and drive circuit modeling is scrutinized, showcasing their superiorities over existing approaches. The importance of eddy current modeling is underscored. Also, the effectiveness of the designed current loop and its practical trade-offs are engineered and discussed. Then, three DSP-based position control techniques are implemented: pole placement with voltage drive, pole placement with current drive, and nonlinear control with feed linearization. Both full-order and reduced-order observers are leveraged to estimate the unmeasured states. The performance of control designs across various applications are evaluated through indices such as rise time, overshoot, steady-state error, and large-signal tracking in the step response as well as bandwidth, robustness, phase margin, sensitivity, disturbance rejection, and noise rejection in the frequency domain. The distinctive features of implemented control strategy are compared, offering a nuanced discussion of their respective advantages and drawbacks, shedding light on their potential applications.

This paper investigates and compares the performance of three-phase inverters against sets of single-phase full-bridge inverters in motor drive applications. Comparisons are made for a common semiconductor device area and rms phase current ripple, and the regions of the design space in which each topology is advantageous are identified. It is found that separate full-bridge inverters are preferable for designs in which switching losses are dominant, whereas three-phase inverters are preferable for designs in which conduction losses are dominant. This result suggests that individual phase drive is desirable in applications requiring high switching frequencies, as in high-speed, low-inductance machines. A 10-kW system is constructed to enable experimental comparisons. The experimental results conducted at 3.6 kW validate analytical and simulation findings.

Magnetics are key components of conventional power converters, but they are often the bottleneck to achieving high power density due to their size, weight, and poor performance at small sizes. Piezoelectric devices, when operated in their inductive regime, can serve a purpose similar to that of magnetic components and offer favorable scaling properties as components are miniaturized. Several sources have demonstrated the viability of piezoelectric-based power converters, but selection of the optimal material and component size is limited by a lack of data on the performance of these materials at high drive levels. This work aims to fill that gap by collecting data to examine the variation in resonator quality factor across a range of drive levels for multiple resonator sizes, frequencies, and materials. By normalizing the collected data, material trends are derived that can predict resonator losses under high drive levels, offering more insight into realistic converter operation than the currently available small-signal data sheet values. Based on these trends, implications for converter efficiency and selection of material and dimensions are discussed.

This article studies the impact of intrinsic nonlinearities on the system-level performance of piezoelectric vibration energy harvesters. The study focuses on harvester operation involving realistic large accelerations at the frequency of its designed linear resonance. It is experimentally observed that two intrinsic nonlinearities are required for nonlinear modeling, namely a mechanical (Duffing) nonlinearity and a piezoelectric-coupling nonlinearity. One goal of this article is to develop a modeling and analysis framework that enables the study of these nonlinearities as they interact with realistic interface circuits. Another goal is to use the framework for benchmarking performance differences between linear harvesters and their nonlinear counterparts. To these ends, this article: 1) presents an accurate equivalent circuit model of piezoelectric vibration energy harvesting (PVEH) systems that captures the aforementioned intrinsic nonlinearities; 2) demonstrates model validity over varying levels of nonlinearity (induced by varying vibration acceleration) through ac-input–ac-output experiments; and 3) employs harmonic balance analysis to study the impact of each nonlinearity on optimized system output power and voltage with optimal load–impedance tuning. Key findings of this article are: 1) both nonlinearities reduce maximum output power at resonance despite optimal tuning and 2) nonlinearities cause additional terminal voltage build-up under tuning for optimal power. Practical voltage constraints on the interface electronics limit the tuning range due to voltage buildup, further degrading output power. For both reasons, a purposely designed linear piezoelectric vibration energy harvester is a better choice vis-a-vis its nonlinear counterpart for applications targeting maximum output power at nominal linear resonance frequency even in the presence of large accelerations.

One of the major reasons that totally implantable cochlear microphones are not readily available is the lack of good implantable microphones. An implantable microphone has the potential to provide a range of benefits over external microphones for cochlear implant users including the filtering ability of the outer ear, cosmetics, and usability in all situations. This paper presents results from experiments in human cadaveric ears of a piezofilm microphone concept under development as a possible component of a future implantable microphone system for use with cochlear implants. This microphone is referred to here as a drum microphone (DrumMic) that senses the robust and predictable motion of the umbo, the tip of the malleus. The performance was measured by five DrumMics inserted in four different human cadaveric temporal bones. Sensitivity, linearity, bandwidth, and equivalent input noise were measured during these experiments using a sound stimulus and measurement setup. The sensitivity of the DrumMics was found to be tightly clustered across different microphones and ears despite differences in umbo and middle ear anatomy. The DrumMics were shown to behave linearly across a large dynamic range (46 dB SPL to 100 dB SPL) across a wide bandwidth (100 Hz to 8 kHz). The equivalent input noise (over a bandwidth of 0.1–10 kHz) of the DrumMic and amplifier referenced to the ear canal was measured to be about 54 dB SPL in the temporal bone experiment and estimated to be 46 dB SPL after accounting for the pressure gain of the outer ear. The results demonstrate that the DrumMic behaves robustly across ears and fabrication. The equivalent input noise performance (related to the lowest level of sound measurable) was shown to approach that of commercial hearing aid microphones. To advance this demonstration of the DrumMic concept to a future prototype implantable in humans, work on encapsulation, biocompatibility, and connectorization will be required.

Objective: We present the "UmboMic," a prototype piezoelectric cantilever microphone designed for future use with totally-implantable cochlear implants. Methods: The UmboMic sensor is made from polyvinylidene difluoride (PVDF) because of its low Young's modulus and biocompatibility. The sensor is designed to fit in the middle ear and measure the motion of the underside of the eardrum at the umbo. To maximize its performance, we developed a low noise charge amplifier in tandem with the UmboMic sensor. This paper presents the performance of the UmboMic sensor and amplifier in fresh cadaveric human temporal bones. Results: When tested in human temporal bones, the UmboMic apparatus achieves an equivalent input noise of 32.3 dB SPL over the frequency range 100 Hz to 7 kHz, good linearity, and a flat frequency response to within 10 dB from about 100 Hz to 6 kHz. Conclusion: These results demonstrate the feasibility of a PVDF-based microphone when paired with a low-noise amplifier. The reported UmboMic apparatus is comparable in performance to a conventional hearing aid microphone. Significance: The proof-of-concept UmboMic apparatus is a promising step towards creating a totally-implantable cochlear implant. A completely internal system would enhance the quality of life of cochlear implant users.

Purpose: One of the major reasons that totally implantable cochlear microphones are not readily available is the lack of good implantable microphones. An implantable microphone has the potential to provide a range of benefits over external microphones for cochlear implant users including the filtering ability of the outer ear, cosmetics, and usability in all situations. This paper presents results from experiments in human cadaveric ears of a piezofilm microphone concept under development as a possible component of a future implantable microphone system for use with cochlear implants. This microphone is referred to here as a drum microphone (DrumMic) that senses the robust and predictable motion of the umbo, the tip of the malleus. Methods: The performance was measured of five DrumMics inserted in four different human cadaveric temporal bones. Sensitivity, linearity, bandwidth, and equivalent input noise were measured during these experiments using a sound stimulus and measurement setup. Results: The sensitivity of the DrumMics was found to be tightly clustered across different microphones and ears despite differences in umbo and middle ear anatomy. The DrumMics were shown to behave linearly across a large dynamic range (46 dB SPL to 100 dB SPL) across a wide bandwidth (100 Hz to 8 kHz). The equivalent input noise (0.1-10 kHz) of the DrumMic and amplifier referenced to the ear canal was measured to be 54 dB SPL and estimated to be 46 dB SPL after accounting for the pressure gain of the outer ear. Conclusion: The results demonstrate that the DrumMic behaves robustly across ears and fabrication. The equivalent input noise performance was shown to approach that of commercial hearing aid microphones. To advance this demonstration of the DrumMic concept to a future prototype implantable in humans, work on encapsulation, biocompatibility, connectorization will be required.

This paper presents analytical modeling and design of a high-acceleration, low-vibration slotless double-sided linear motor with an arbitrary Halbach array for lithography machines used in semiconductor manufacturing technology. Amperian current and magnetic charge models of permanent magnets are integrated into a hybrid approach to develop comprehensive analytical modeling. Unlike conventional methods that treat magnets as sources for Poisson's equations, the solution is reduced to Laplace's equations, with magnets being represented as boundary conditions. The magnetic fields and potentials within distinct regions, along with machine quantities such as shear stress, force-angle characteristics, torque profile, attraction force, misalignment force, and back-EMF, are derived, comprehensively analyzed, and compared to FEM results for accuracy validation. In addition, two models based on Poisson's equations in terms of scalar and vector potentials are derived, compared, and analyzed. Finally, design optimization and sensitivity analysis of a linear stage for lithography applications are discussed.

In part II, an op-amp-based drive is proposed and designed. Subsequently, a very accurate model for the drive circuit and the current loop is developed as a simulation platform, while its simplified version is derived, tailored for efficient design purposes. Through a comprehensive evaluation, the accuracy and efficacy of both the actuator and drive circuit modeling is scrutinized, showcasing their superiorities over existing approaches. The importance of eddy current modeling is underscored. Also, the effectiveness of the designed current loop and its practical trade-offs are engineered and discussed. Then, three DSP-based position control techniques are implemented: pole placement with voltage drive, pole placement with current drive, and nonlinear control with feed linearization. Both full-order and reduced-order observers are leveraged to estimate the unmeasured states. The performance of control designs across various applications are evaluated through indices such as rise time, overshoot, steady-state error, and large-signal tracking in the step response as well as bandwidth, robustness, phase margin, sensitivity, disturbance rejection, and noise rejection in the frequency domain. The distinctive features of implemented control strategy are compared, offering a nuanced discussion of their respective advantages and drawbacks, shedding light on their potential applications.

Electromechanical models are crucial in the design and control of motors and actuators. Modeling, identification, drive, and current control loop of a limited-rotation actuator with magnetic restoration is presented. New nonlinear and linearized electromechanical models are developed for the design of the drive as well as small and large signal controls of the actuator. To attain a higher accuracy and an efficient design, and the eddy-currents in the laminations and magnet are modeled. This involves analytically solving 1-D and 2-D diffusion equations, leading to the derivation of a lumped-element circuit for system-level analyses, such as control system design. Additionally, the study analyzes and incorporates the impact of pre-sliding friction. The actuator is prototyped, and the paper delves into the identification of the model, presenting a procedure for parameter extraction. A close agreement is observed between the results obtained from the model, finite element analysis, and experimental results. The superiority of the proposed model over previous approaches is highlighted. Part II of the paper is dedicated to the drive circuit, the current control, as well as linear and nonlinear position control system designs.

Time series anomaly detection is challenging due to the complexity and variety of patterns that can occur. One major difficulty arises from modeling time-dependent relationships to find contextual anomalies while maintaining detection accuracy for point anomalies. In this paper, we propose a framework for unsupervised time series anomaly detection that utilizes point-based and sequence-based reconstruction models. The point-based model attempts to quantify point anomalies, and the sequence-based model attempts to quantify both point and contextual anomalies. Under the formulation that the observed time point is a two-stage deviated value from a nominal time point, we introduce a nominality score calculated from the ratio of a combined value of the reconstruction errors. We derive an induced anomaly score by further integrating the nominality score and anomaly score, then theoretically prove the superiority of the induced anomaly score over the original anomaly score under certain conditions. Extensive studies conducted on several public datasets show that the proposed framework outperforms most state-of-the-art baselines for time series anomaly detection.

Purpose Sheep are used as a large-animal model for otology research and can be used to study implantable hearing devices. However, a method for temporal bone extraction in sheep, which enables various experiments, has not been described, and literature on middle ear access is limited. We describe a method for temporal bone extraction and an extended facial recess surgical approach to the middle ear in sheep. Methods Ten temporal bones from five Hampshire sheep head cadavers were extracted using an oscillating saw. After craniotomy and removal of the brain, a coronal cut was made at the posterior aspect of the orbit followed by a midsagittal cut of the occipital bone and disarticulation of the atlanto-occipital joint. Temporal bones were surgically prepared with an extended facial recess approach. Micro-CT scans of each temporal bone were obtained, and anatomic dimensions were measured. Results Temporal bone extraction was successful in 10/10 temporal bones. Extended facial recess approach exposed the malleus, incus, stapes, and round window while preserving the facial nerve, with the following surgical considerations: minimally pneumatized mastoid; tegmen (superior limit of mastoid cavity) is low-lying and sits below temporal artery; chorda tympani sacrificed to optimize middle ear exposure; incus buttress does not obscure view of middle ear. Distance between the superior aspect of external auditory canal and tegmen was 2.7 (SD 0.9) mm. Conclusion We identified anatomic landmarks for temporal bone extraction and describe an extended facial recess approach in sheep that exposes the ossicles and round window. This approach is feasible for studying implantable hearing devices.

Piezoelectric transformers (PTs) are a promising energy storage alternative to magnetics for power converter miniaturization. PTs offer galvanic isolation and voltage transformation like traditional magnetic transformers, but with superior power scaling properties at small size scales. Despite these advantages, most magnetic-less PT-based dc-dc converter designs have limited efficiencies and power densities. In this paper, we present a design framework for PTs that enables high efficiency and energy handling density at a nominal operating point, while maintaining high-efficiency converter behaviors such as zero voltage switching (ZVS). We illustrate this design process in the context of dc-dc power conversion, and the result suggests that significant gains in PT performance are possible with existing materials using these design strategies.

View Video Presentation: https://doi.org/10.2514/6.2023-4161.vid This paper presents the design and optimization of a 1-MW inverter for a high-speed, high-specific-power motor drive. The proposed inverter consists of ten 100-kW inverter sets distributed around the periphery of the machine to drive ten separate sets of three-phase open-ended windings. Each inverter set consists of three single-phase full-bridge inverters each of which drives an open-ended phase winding. The use of three single-phase full-bridge inverters for each inverter set yields an improved specific power as compared to either the three-phase bridge inverter or the active neutral-point clamped (ANPC) inverter in the target application. The proposed inverter system is co-designed and co-optimized with a 1-MW permanent magnet machine and associated thermal management system. Experimental results demonstrating the performance of a 100-kW inverter set are provided. The air-cooled inverter set operates at 720 Vdc, 73.5 Aac,rms per phase and 80 kHz device switching frequency, and achieves 53.4 kW/kg specific power and > 98% efficiency.

View Video Presentation: https://doi.org/10.2514/6.2023-4157.vid While continued propulsion system and turbomachinery improvements are necessary, they are not sufficient to address the 2050 aviation sustainability goals. Without intervention aviation will emit a cumulative total of over 20 billion tons of CO2 by then. An ambitious target is to achieve a net-zero economy by 2050. The step change achievements needed to address the climate grand challenge are unconventional aircraft configurations with integrated and distributed propulsion systems, thermal management of high power-density rotating machinery, advanced high temperature materials, reduced, but safe, engineering and operability margins for improved performance, alternative energy carriers, smart and flexible fuel systems, and key enabling technology demonstrations. Independent of the energy carrier (battery, SAF, H2, NH3), MW class electrical machines will play a key role in greening aviation. To address the climate and sustainability grand challenge, a high specific power fully air-cooled 1MW electrical machine is being developed, conceived to advance electrified aviation but also suitable for other ground-based applications. One application is integration in an aero-engine as a motor-drive for turbo-electric propulsion. The emphasis of this project is on risk mitigation experiments and technology demonstration of a 1 MW integrated motor drive with performance estimates exceeding the NASA 2030 goals.

View Video Presentation: https://doi.org/10.2514/6.2023-4158.vid This paper presents the detailed design and manufacturing of a1-MW, air-cooled, outer-rotor, Halbach-array PMSM for aircraft propulsion. Component level risk mitigation experiments have validated the highest risk elements of the design including stator core loss, structural stability, winding insulation, and permanent magnet field strength. Two manufacturing processes for Fe-Co-V stator cores are compared through core loss and B-H curve measurements. A conventional lamination bonding process is shown to increase core loss by 20%. A novel approach to modelling Halbach array rotors is introduced and validated with experimental data and FEA. A modular single-phase winding pattern is introduced to improve robustness and enable single phase inverter drives. Full power testing is planned using two prototype machines connected through one shaft, with one acting as a motor and the other as a generator.

Flight is an energetically expensive task. While aerial insects can effortlessly fly through natural environments, achieving power autonomous flights in insect-scale robots remains a major challenge. In prior works, we developed soft-actuated insect-scale aerial robots that demonstrated unique capabilities such as in-flight collision recovery and somersaults. However, the soft dielectric elastomer actuators (DEAs) have low efficiency (< 20%) and require a high driving voltage (>600 V). These properties represent formidable obstacles for soft aerial robots to achieve power autonomous flights. In this work, we developed a 127 mg boost circuit that can convert a 7.7 V DC input into a 600 V and 400 Hz output for driving a 120 mg DEA. It has an equivalent capacitance and resistance of 20 nF and 5 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{k}\Omega$</tex> , respectively. The DEA is assembled into a 158 mg aerial robot, which can demonstrate liftoff while carrying the boost circuit as a payload. Although the robot remains tethered to an off-board power supply, this result represents a first step towards achieving power autonomy in soft aerial robots.

Abstract Switched reluctance machines offer a robust structure, inexpensive maintenance, and a low‐cost drive. However, they can suffer from low mean torque, low torque density, and high noise. Techniques such as offering the stator poles at each phase in the shape of a C core, adding several teeth to the two poles of each C‐core, and embedding permanent magnets to overcome these deficiencies are presented. Permanent magnets are embedded into the structure to create a hybrid excitation that provides a higher torque density. The C‐core stator modules of the stator are toothed to improve the torque. The radial forces on the shaft are balanced. The design procedure, operating principles, and performance trade‐offs are explained. Also, a magnetic equivalent circuit model is introduced. The model provides continuous relationships over the operating regions and incorporates core saturation and accurate flux tubes to attain high precision. Finite element models are also employed in the analysis and design process. The motor is prototyped, and experimental results are extracted, closely matching those obtained with the model and finite‐element analysis.

A state observer driven by measurements of phase voltages and currents for estimating the angular orientation of a rotor of a synchronous motor such as a variable reluctance motor (VRM). Phase voltages and currents are detected and serve as inputs to a state observer. The state observer includes a mathematical model of the electromechanical operation of the synchronous motor. The characteristics of the state observer are selected so that the observer estimates converge to the actual rotor angular orientation and velocity, winding phase flux linkages or currents.

View Video Presentation: https://doi.org/10.2514/6.2023-1302.vid We present a novel electrostatic thin-shell structure concept capable of actively controlling the shape of large area systems with minimal mass overhead and complexity. It consists of an assembly of collapsible thin-shell cells for which the cross-section follows the classical Collapsible Tubular Mast (CTM) architecture. Two conductive electrodes are added to the top and bottom flanges of the cell. An electrostatic force develops between top and bottom electrodes upon voltage application, which flattens the cross-section and causes the cell to expand longitudinally. When multiple layers of these cells are bonded to each other, the controlled differential expansion of each layer can be harnessed to cause global bending.

View Video Presentation: https://doi.org/10.2514/6.2023-0756.vid Large reflectors in space (>30 m diameter) can enable advances in communications, remote sensing, and astronomy, by enabling antennas with increased gain, resolution, and bandwidth. However, modern deployable reflectors exhibit a decrease in performance as their diameter increases, due to fabrication errors, slewing, and disturbances on orbit, such as thermal distortion, which decrease surface precision. A potential solution to achieve larger apertures with high precision is to combine in-space manufacturing (ISM) with active control. Herein we demonstrate a reflector concept which combines a candidate ISM process called Bend-Forming with electrostatic actuation to achieve closed-loop control of the reflector surface. We design and fabricate a 1-meter diameter prototype of an electrostatically actuated X-band reflector, using a knitted gold-molybdenum mesh as the reflector surface, carbon fiber-reinforced plastic booms as electrodes, and a truss support structure fabricated with Bend-Forming, a deformation process for constructing trusses from wire feedstock. To characterize the performance of this prototype, we measure its radiation patterns at X-band in an RF anechoic chamber. We successfully demonstrate 1) the stabilization of a pull-in instability with closed-loop control, and 2) beam steering of up to 4.2 degrees with asymmetric electrostatic actuation. Our reflector prototype highlights the opportunities of implementing electrostatically-actuated reflector antennas in space.