This letter presents an optical method of excitation for a 3-D fused silica dual-shell resonator. Modulated light from a 980-nm laser diode was directed at the rim of the hemispherical resonator, exciting the n = 2 wineglass mode. The displacement amplitudes were measured as a function of laser power. For a nonmetalized, pristine, fused silica resonator, displacements up to 3 nm were measured at an average laser power of 140 mW. Modeling of the opto-thermal and radiation pressure effects revealed distinct underlying mechanisms: thermal effects were predicted to dominate the response of a metal-coated resonator, while radiation pressure was predicted to primarily contribute to the excitation of the uncoated resonator. In experiments, a metal-coated resonator exhibited the largest displacement, but its quality factor was degraded and frequency shifted by 4800 ppm. In contrast, the uncoated resonator achieved substantial displacements while preserving its high quality factor of 1.5 million, and its frequency shifted by only 33 ppm. This method of excitation demonstrates the feasibility of nonmetalized optical actuation and offers a pathway for ultra-high quality factor opto-mechanical resonators and gyroscopes utilizing only optical means for excitation and detection.

Accurately localizing points of interest is vital for firefighters and first responders for effective surveying and rescue missions. Traditionally, firefighters rely on subjective visual descriptions transmitted via radios, leading to time-consuming and error-prone communication about their locations. This article presents an approach for far target detection (FTD) provided in terms of longitude, latitude, and altitude (LLA) coordinates in environments where GPS signals may not be available. Using LLA coordinates ensures concise communication among team members on their locations and provides a common coordinate reference system between outdoors/indoors. This article discusses the integration of three devices as a foundation for the FTD system. First, it uses zero-velocity-update (ZUPT)-aided inertial navigation systems (INS) via a foot-mounted inertial measurement unit (IMU) for personnel localization. Second, an augmented reality (AR) headset is employed to localize a handheld platform (HP) relative to the foot. Third, HP is used to determine the direction the firefighter is pointing at and to measure the distance to the objects. The system's performance was assessed through five experiments where a subject mapped a static point while walking a straight path demonstrating that the system is capable of achieving mapping precision within 2 [m] for distances on the order of 20 [m] from the target.

A fused silica toroidal ring gyroscope with highquality factor was designed, fabricated and characterized. The structure was designed to exploit thermoelastic properties of fused silica and, using a Femtosecond Laser Induced Chemical Etching (FLICE) fabrication process, devices with quality factors higher than 1 M were obtained. Despite fabrication process imperfections leading to sub-optimal symmetry, the obtained quality factors are, to the Authors best knowledge, the highest present in literature for resonant ring micro-structures.

The integration of Virtual Reality (VR) and Augmented Reality (AR) technologies into location-based services and applications necessitates precise navigation within an absolute geodetic reference frame, utilizing Latitude, Longitude, and Altitude (LLA) coordinates. Typically, VR/AR headsets establish a local Cartesian (XYZ) World Coordinate (WC) frame with an arbitrary initial origin and orientation. For accurate geodetic navigation, it is essential to align these devices to the True North (TN). This paper introduces an AR-based method for achieving the initial alignment of the WC frame relative to the geodetic frame. We developed an AR user interface (UI) to visually guide users to a known target with LLA coordinates, indirectly aligning the system to TN. Using a Magic Leap 2 (ML2) AR headset, we evaluated our approach against traditional magnetometer-based methods. Our experimental results demonstrated that our method reduces the Mean Angular Error (MAE) by a factor of $4\times$ and the standard deviation ( $\sigma$ ) by $5\times$ compared to traditional magnetometer methods. This improvement can eliminate the need for initial magnetometer calibration, offering a more efficient and robust solution for TN alignment in AR/VR applications.

Our innovative approach is to modify the Dual-Shell micro-Hemispherical Resonator Gyroscope (DSG) design [1] by using the inner and outer shells for electrostatic driving and sensing (Fig 3). Fem-to second Laser Induced Chemical Etching (FLICE) [2] is used to directly define the capacitive gap inside the bulk of the Fused Quartz material. With the pro-posed process, there is no need to separately fabricate electrodes, nor assemble the vibratory element with electrodes. The mean capacitance was measured to be 0.127pF and the highest quality factor of a released sample was measured to be 1.23 million before met-allization. Electrostatic actuation and detection of a DSG is demonstrated using the electrodes defined by the proposed process.

This paper presents non-metallized dual-shell hemispherical resonator gyroscope (DSG) operation. The study addresses three key challenges: non-metallized driving, sensing, and tuning. Non-metallized driving is achieved using indirect piezoelectric excitation (IPE) with atomic layer deposited lead hafnate titanate (ALD PHT) on the outer shell. Sensing is accomplished using two commercial, benchtop laser doppler vibrometers (LDVs) to probe the drive and sense wineglass antinodes, serving as a prototype of future all-optical detection with interferometers implemented using Photonic Integrated Circuits (PIC). Tuning is performed through laser ablation trimming, reducing the frequency split from 50-60 Hz as-fabricated to under 1 Hz, the lowest being 0.39Hz. The paper demonstrates successful non-metallized gyroscope operation with a scale factor of 0.02 mV/(deg/s). This approach shows promise for achieving unparalleled HRG performance by eliminating metallization-induced energy losses.

We report a two-fold increase in quality factor offused silica Dual-Shell Gyroscopes (DSG) by implementing a low-stress anchor topology. Although these complex 3D resonators are dynamically balanced in-plane, they can still experience unbalanced out-of-plane stresses at the anchor, leading to energy loss. Through a parametric study, we demonstrate that a hemitoroidal shell topology significantly reduces the out-of-plane stress component, resulting in lower anchor loss compared to conventional hemispherical design topology. A total of 33 resonators across three different topologies were fabricated and experimentally characterized. Resonators employing the low-stress anchor design achieved quality factors exceeding 3 million in the n=2 mode - representing a two-fold increase over previously reported values.

We present a fast and precise laser-based digital manufacturing process for glasses. The process is based on a 3-dimensional Femtosecond Laser-Induced Chemical Etching (FLICE) capable of building Micro-Electro-Mechanical Systems (MEMS) from a single piece of transparent dielectric material, such as glass. For the first time, we demonstrated manufacturing of devices with over 200 mu m in thickness and over 15:1 Aspect Ratio (AR) using Fused Quartz (FQ) as the structural material. In the proposed process, Hydrofluoric acid (HF) erosion of FQ wafer surfaces was utilized to expose the openings of the laser-inscribed micro-trenches for the subsequence wet etching. It eliminated the laser surface damage (e.g., cracks, subsurface damage, material deformation, etc.) and material redeposition due to low fluence laser initiation caused by impurities on FQ wafer surfaces. To illustrate this new capability, we designed, manufactured, and demonstrated a micro Disk Resonator Gyroscope (DRG) with over 1 M in quality factor. Our results demonstrate a potential for the process to become an alternative to commonly used plasma etching techniques for machining MEMS from quartz, Pyrex, and other transparent materials.

In this article, we propose an approach to enhance zero-velocity-update (ZUPT)-aided inertial navigation systems (INSs) with a time series support vector machine (SVM) forecaster algorithm. The approach is based on the inclusion in ZUPT algorithm the time correlation of velocity threshold values based on classification of 19 distinct pedestrian activities determined from a foot-mounted inertial measurement unit. The classification enhances the traditional ZUPT-aided INS by first optimizing the threshold in the detector called stance hypothesis optimal detection and second adjusting zero-velocity measurement variances for each categorized locomotion type. Experimental validation involved three subjects, each conducting 10 trials of indoor navigation, encompassing activities, such as walking, fast walking, jogging, running, sprinting, walking backward, jogging backward, and sidestepping, over a nearly 100 [m] path. The trained time series SVM classifier achieved a 90.04% average classification accuracy, resulting in an improvement in navigation accuracy by a factor of 250 as compared to a standalone INS and by a factor of 3 as compared to a traditional ZUPT-aided INS solution. Comparable improvements in the vertical drift of the navigation solution have been also demonstrated.

Anchor losses significantly limit the quality factor (Q) in MEMS resonators such as gyroscopes. This work demonstrates a zero-energy diamagnetic levitation scheme for a Dual-Shell Resonator Gyroscope (DSG), using a custom 3D-printed NdFeB magnet and pyrolytic graphite stabilizers for passive, contactless support. Stable levitation of a similar to 1.1 g mass is achieved with a 3.8-4.4 mT magnetic field and -71 mu T/mm gradient, while integrated coils enable PID-controlled height adjustment (similar to 750 mu m range) at similar to 1.9 mW. Under AC drive near 20 kHz, out-of-vacuum vibration amplitudes remain limited by air damping, but simulations predict significantly larger resonant responses in vacuum. This compact, low-power approach offers a promising avenue for high-Q inertial sensing.

This paper presents a navigation environment, NEV-ERLOST, specifically designed for firefighters and first responders to localize and navigate in indoor environments. Challenging indoor conditions demand safe, accurate, and high-precision navigation solutions. NEVERLOST addresses two primary technical challenges: 1) real-time position tracking using foot-mounted IMU, and 2) optimal route planning to targets. The framework addresses these challenges through a dual-interface platform, that leverages Augmented Reality (AR) with a Magic Leap 2 (ML2) to overlay navigational information onto the real-world view of firefighters. The dual-interface platform facilitates coordination between firefighters and fire commanders: commanders handle strategic planning, including target selection and mission oversight on a digital map, while firefighters navigate indoor environments, and communicate their indoor position in real-time. An experimental evaluation was conducted in a multi-floor indoor setting demonstrating a navigation error of 0.74 meters over a 141.84-meter trajectory.

We propose and demonstrate photonic integrated readout of vibrational modes of fused-silica dual-shell resonators designed for MEMS gyroscopes. We detect vibrational mode frequencies near 25.8KHz and measure nano-displacements with <5% error, matching conventional tabletop measurements.

This paper proposes a Simultaneous Localization And Mapping (SLAM) approach, utilizing a combination of foot-mounted Inertial Measurement Units (IMU), foot-mounted Ultra-WideBand (UWB), and environment-deployed UWBs, referred to as the UWB-Foot-SLAM. The proposed approach first leverages a Zero-velocity-UPdaTe (ZUPT)-aided Inertial Navigation System (INS) to map unknown UWB beacons deployed in an environment during navigation and then utilizes the localized beacons to bound position error propagation. An experimental testbed was developed, and we conducted two experiments to validate the performance of the proposed UWB-Foot-SLAM. Experimental results in the first experiment, which involved a pedestrian walking for 3 minutes and deploying two beacons, showed that the UWB beacons' positions estimated by the proposed UWB-Foot-SLAM had displacement errors of 0.28 [m] and 0.22 [m]. In the second experiment, a pedestrian traveled for 25 minutes in a large multi-floor indoor environment and deployed four beacons. The positions of the pedestrian estimated by ZUPT-aided INS had horizontal and vertical Loop-Closure Errors (LCEs) of 11 [m] and 4.5 [m], respectively. When our proposed UWB-Foot-SLAM was used, the LCEs were reduced to 1.49 [m] and 1 [m], respectively, and the covariances associated with the pedestrian position states were bounded after operating for 155 [s].

We report on optimization of the inertial measurement unit (IMU) mounting position for zero velocity update (ZUPT)-aided inertial navigation systems (INS) in firefighter crawling scenarios. In this study, we considered four IMU mounting positions: (1) on the heel of the foot, (2) inside the knee, (3) outside the knee, and (4) embedded in the center of the supporting knee-pad. We focused on two methods of crawling maneuvers commonly used for performing tasks in firefighting scenarios, described as hand/knee crawling and “duck” crawling. Two performance metrics were considered: stability of the IMU during stance phase and the stance phase duration. We concluded that the optimal mounting position is in the center of the knee under the experimental conditions. This finding is supported by ten navigation trials performed over a 42.6m straight line for each of the four mounting positions and two crawling maneuvers. A circular error probable (CEP) on the order of 0.8m was demonstrated for the center-knee placement of the IMU.

This paper presents a simplified model for predicting navigation uncertainty of a pedestrian. The model simulates trajectories of a person's foot, and these trajectories are then used to generate simulated IMU readings. Eight different noise errors are considered for both the simulated accelerometer and gyroscope readings, including white noise, bias instability, random walk, scale factor error, misalignment, turn-on bias, limited full-scale range, and limited bandwidth. We conducted a series of pedestrian walking experiments to validate the proposed model. The experimental results showed that the position Root-Mean-Square-Errors (RMSEs) in the simulations and in the experiments had a discrepancy of 6% for about 40 [m] of walk. The model also predicted the bounds of the vertical position drift, which matched the trend of estimated vertical position uncertainties in the experiments. We concluded that the model could predict, with sufficient accuracy, the navigation uncertainty for foot-mounted IMU-based systems, and we suggested future research to enhance the model with additional details of foot motion to further improve the prediction accuracy.

This article proposes a generalized UltraWideBand (UWB)-Zero-velocity-UPdaTe (ZUPT)-simultaneous localization and mapping (SLAM) algorithm, a SLAM approach, utilizing a combination of foot-mounted localization systems integrating inertial measurement units (IMUs), UWB modules, barometers, and dynamically-deployed beacons incorporating UWB, IMUs, and reference barometers. The proposed approach leverages a ZUPT-aided Inertial Navigation System augmented with self-contained sensor fusion techniques to map unknown UWB beacons dynamically deployed in an environment during navigation and then utilizes the localized beacons to bound position error propagation. An experimental testbed was developed, and we conducted two series of experiments to validate the performance of the proposed approach. The first experiment involved high-accuracy motion capture cameras in generating ground truth, and the results showed that the proposed approach estimated positions of UWB beacons with a maximum localization error of 0.36 m, when deployed during the first 15 and 20 s of the navigation. In the second experiment, a pedestrian traveled for around 3.5 km in 1 h in a large multifloor indoor environment and deployed seven beacons, during the first 63, 151, 290, 399, 517, 585, and 786 s of the experiment. The proposed generalized UWB-ZUPT-SLAM had a 3-D mean absolute error of 0.48 m in this experiment, equivalent to 0.013% traveling distance.

This paper presents a prioritizable Inertial Measurement Unit (IMU) array, referred to as the Prio-IMU, which is a systematic approach to mitigate the problem of insufficient sensor's Full-Scale Range (FSR) and bandwidth, in the case of foot-mounted Inertial Navigation Systems (INS). The Prio-IMU integrates multiple IMUs with different sensor characteristics, aligns all the sensor measurements to a universal coordinate frame, and prioritizes the usage of each integrated sensor based on different scenarios. We developed a Prio-IMU prototype integrating two IMUs (ICM-20948 and ICM-20649) and a 3-axis accelerometer (ADXL375) and conducted a series of pedestrian navigation experiments involving walking and running. We observed that during the heel-strike phases of running activity, accelerometer and gyroscope measurements as large as 70 [gravity (g)] and 2600 [degree per second (dps)] could be picked up by the developed Prio-IMU prototype. The experimental results showed that the navigation accuracy of the Zero-velocity-UPdaTe (ZUPT)-aided INS using the proposed Prio-IMU was improved by 79% and 82% along the horizontal and vertical directions, as compared to the case of using a single IMU.

Hemispherical resonator gyroscopes (HRGs) fabricated out of fused silica (FS) offer high quality-factor ( $Q$ -factor) properties making the sensors suitable for high-precision gyroscope operation. In this configuration, metal-coating is typically required for electrical conductivity to allow for capacitive actuation and detection of motion. Such method of transduction is relatively simple, but reduces the $Q$ -factor of FS HRGs. To eliminate the metallization and preserve the high $Q$ -factor for FS hemispherical resonator dual-shell gyroscopes (DSGs), an indirect excitation method is designed and demonstrated in this letter. The DSG contains a central stem, an inner device shell as the sensing element, and an outer packaging cap shell. The proposed method utilizes the mechanical coupling between the sensing element and the cap shell. The energy induced by deformation of the cap shell transfers to the inner device shell and excites it at the resonance, thus allowing for gyro operation. In this letter, the method was realized using a lead zirconate titanate (PZT) layer deposited on the cap shell, and the mechanical $Q$ -factor as high as 2.3 million was measured. Using the indirect excitation method, for the first time, gyroscope operation was demonstrated on DSG architectures.

We report on the design, implementation, and demonstration of a miniaturized Inertial Navigation platform. The platform, with a total volume of 7.1 $cm^{3}$ (excluding battery and case), includes the Inertial Measurement Unit (IMU), chip-scale barometer, magnetometer, as well as a powerful computational engine for signal processing and execution of the navigation algorithm. The sensors are integrated using separate PCBs with castellated edges forming the connections with the main board allowing some flexibility in sensor selection. The platform is small enough for integration in the sole of a shoe, which is an optimal location for implementation of Zero Velocity Update (ZUPT) algorithms for prolonged self-contained navigation. The navigation solution is performed using an Extended Kalman Filter (EKF) framework with an update rate of 500 Hz. A series of indoor walking experiments were conducted to verify the navigation accuracy of the platform which showed error 0.53% of the trajectory length for a 125 m, 2.75-minute duration walk including flat planes, stairs, and an elevator ride.