Touch-at-a-Distance: Pressure Microsensor Arrays for AUV Navigation

Inspired by the lateral-line organ in fish, the ultimate objective of this project continues to be the development of a passive system for AUVs that can detect, classify and locate underwater objects. The lateral line sensory organ in fish enables some species to form three-dimensional maps of their surroundings. The canal subsystem of that organ acts as an array of pressure sensors. Interpreting spatial pressure gradients allows fish to perform a variety of actions from schooling, to tracking prey, to recognizing nearby objects. Similarly, by measuring pressure variations on a vehicle surface, an engineered dense pressure-sensor array could enable the identification and location of obstacles during navigation. Our navigation system is based upon two key technologies: (1) large arrays of very small pressure sensors that can be mounted on the surface of an AUV, and (2) the pressure signal processing algorithms through which object detection, classification and location is implemented. Correspondingly, this project is organized during its early years around the development of these two key technologies

Bias-Flip Technique for Frequency Tuning of Piezo-Electric Energy Harvesting Devices

Devices that harvest electrical energy from mechanical vibrations have the problem that the frequency of the source vibration is often not matched to the resonant frequency of the energy harvesting device. Manufacturing tolerances make it difficult to match the Energy Harvesting Device (EHD) resonant frequency to the source vibration frequency, and the source vibration frequency may vary with time. Previous work has recognized that it is possible to tune the resonant frequency of an EHD using a tunable, reactive impedance at the output of the device. The present paper develops the theory of electrical tuning, and proposes the Bias-Flip (BF) technique, to implement this tunable, reactive impedance

Nominality Score Conditioned Time Series Anomaly Detection by Point/Sequential Reconstruction

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.Comment: NeurIPS 2023 (https://neurips.cc/virtual/2023/poster/70582

Development and application of distributed MEMS pressure sensor array for AUV object avoidance

A novel sensory system is being developed for AUVs to augment current sensory systems for navigation and operation in difficult environments. These environments are frequently cluttered and murky with substantial flow from currents or waves, frustrating sonar and vision systems while posing an increased risk to AUVs. In order to manage such situations, a better ability to locate and identify physical objects is needed. This gap could be filled by small low frequency pressure sensors distributed over the surface of the AUV in dense arrays.United States. National Oceanic and Atmospheric Administration (Grant NA06OAR4170019 Project R/RT-2/RCM-17

A Systematic Approach to Modeling Impedances and Current Distribution in Planar Magnetics

Planar magnetic components using printed-circuit-board windings are attractive due to their high repeatability, good thermal performance and usefulness for realizing intricate winding patterns. To enable higher system integration at high switching frequency, more sophisticated methods that can rapidly and accurately model planar magnetics are needed. This paper develops a lumped circuit model that captures the impact of skin and proximity effects on current distribution and electromagnetic fields in planar magnetics. This enables accurate predictions of impedances, losses, stored reactive energy and current sharing among parallel windings. This lumped model is also a circuit domain representation of electromagnetic interactions. It can be used to simulate circuits incorporating planar magnetics, to visualize the electromagnetic fields, and to extract parameters for magnetic models by simulations. The modeling results match with previous theories and finite-element-modeling results. A group of planar magnetic devices, including transformers and inductors with various winding patterns, are prototyped and measured to validate the proposed approach.Texas Instruments IncorporatedMassachusetts Institute of Technology. Center for Integrated Circuits and System

Lateral-Line Inspired MEMS-Array Pressure Sensing for Passive Underwater Navigation

This paper presents work toward the development of a novel MEMS sensing technology for AUVs. The proposed lateral line-inspired sensor system is a high-density array of pressure sensors for measuring hydrodynamic disturbances. By measuring pressure variations on a vehicle surface, a dense pressure sensor array will allow the AUV to detect, classify, and locate nearby obstacles and optimize its motion in unsteady environments. This approach is very similar to the canal lateral line system found in all fish, which allow them to function in dark or clouded environments. In order to lay the groundwork for developing the MEMS sensor and interpreting the pressure distributions, the paper also presents experiments demonstrating the discrimination between cylindrical obstacles of round and square cross sections with an array of off-the-shelf pressure sensors. Test objects with 5.1 cm and 7.6 cm diameters passed stationary sensors at 0.5 m/s and 0.75 m/s and with 1.3 and 5.1 mm separation. Hand chosen features and features chosen through a Principal Component Analysis are used to discriminate between object shapes under a variety of conditions. A classification error rate of under 2% is achieved across all velocities, sizes, and separations. These results lead to requirements for the density, sensitivity, and frequency response of the MEMS sensors, which fall well in the MEMS domain. The pressure sensor array proposed here consists of hundreds of MEMS pressure sensors with diameters near 1 mm spaced a few millimeters apart fabricated on etched silicon and Pyrex wafers; a fabrication process for producing the array is described. A strain-gauge pressure sensor is analyzed and shown to satisfy specifications as required by the results from the afore-mentioned experiments. The sensing element is a strain gauge mounted on a flexible diaphragm, which is a thin (20 µm) layer of silicon attached at the edges to a square silicon cavity 2000 µm wide on a side. A source voltage of 10 V produces a sensor with a sensitivity on the order of 1µV/Pa. Since the thermal noise voltage is near 0.7 µV, the pressure resolution of the sensors is on the order of 1 Pa.United States. National Oceanic and Atmospheric Administration (Grant NA06OAR4170019 Project R/RT-2/RMC-17

Controlled fabrication of nanoscale gaps using stiction

Utilizing stiction, a common failure mode in micro/nano electromechanical systems (M/NEMS), we propose a method for the controlled fabrication of nanometer-thin gaps between electrodes. In this approach, a single lithography step is used to pattern cantilevers that undergo lateral motion towards opposing stationary electrodes separated by a defined gap. Upon wet developing of the pattern, capillary forces induce cantilever deflection and collapse leading to permanent adhesion between the tip and an opposing support structure. The deflection consequently reduces the separation gap between the cantilever and the electrodes neighboring the point of stiction to dimensions smaller than originally patterned. Through nanoscale force control achieved by altering device design, we demonstrate the fabrication of nanogaps having controlled widths smaller than 15 nm. We further discuss optimization of these nanoscale gaps for applications in NEM and molecular devices.National Science Foundation (U.S.) (Center for Energy Efficient Electronics Science (E3S) Award ECCS-0939514)Natural Sciences and Engineering Research Council of Canad