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1. mSAIL: milligram-scale multi-modal sensor platform for monarch butterfly migration tracking

   https://doi.org/10.1145/3447993.3483263  

   Lee, Inhee; Hsiao, Roger; Carichner, Gordy; Hsu, Chin-Wei; Yang, Mingyu; Shoouri, Sara; Ernst, Katherine; Carichner, Tess; Li, Yuyang; Lim, Jaechan; et al (October 2021, International Conference On Mobile Computing And Networking)

   Each fall, millions of monarch butterflies across the northern US and Canada migrate up to 4,000 km to overwinter in the exact same cluster of mountain peaks in central Mexico. To track monarchs precisely and study their navigation, a monarch tracker must obtain daily localization of the butterfly as it progresses on its 3-month journey. And, the tracker must perform this task while having a weight in the tens of milligram (mg) and measuring a few millimeters (mm) in size to avoid interfering with monarch's flight. This paper proposes mSAIL, 8 × 8 × 2.6 mm and 62 mg embedded system for monarch migration tracking, constructed using 8 prior custom-designed ICs providing solar energy harvesting, an ultra-low power processor, light/temperature sensors, power management, and a wireless transceiver, all integrated and 3D stacked on a micro PCB with an 8 × 8 mm printed antenna. The proposed system is designed to record and compress light and temperature data during the migration path while harvesting solar energy for energy autonomy, and wirelessly transmit the data at the overwintering site in Mexico, from which the daily location of the butterfly can be estimated using a deep learning-based localization algorithm. A 2-day trial experiment of mSAIL attached on a live butterfly in an outdoor botanical garden demonstrates the feasibility of individual butterfly localization and tracking. 

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2. Aeroelastic Characterization of Real and Artificial Monarch Butterfly Wings

   https://doi.org/10.2514/6.2020-2002  

   Twigg, Rachel; Sridhar, Madhu; Pohly, Jeremy A.; Hildebrandt, Nicholas; Kang, Chang-Kwon; Landrum, D Brian; Roh, Kyung-Ho; Salzwedel, Samantha (January 2020, AIAA Scitech 2020 Forum)

   The annual migration of monarch butterflies, Danaus plexippus, from their summer breeding grounds in North America to their overwintering sites in Mexico can span over 4000 kilometers. Little is known about the aerodynamic mechanism behind this extended flight. This study is motivated by the hypothesis that their flapping wing flight is enhanced by fluid-structure interactions. The objective of this study to quantify the aeroelastic performance of monarch butterfly wings and apply those values in the creation of an artificial wing with an end goal of creating a biomimetic micro-air vehicle. A micro-CT scan, force-deflection measurements, and a finite element solver on real monarch butterfly wings were used to determine the density and elastic modulus. These structural parameters were then used to create a monarch butterfly inspired artificial wing. A solidification process was used to adhere 3D printed vein structures to a membrane. The performance of the artificial butterfly wing was tested by measuring the lift at flapping frequencies between 6.3 and 14 Hz. Our results show that the elastic modulus of a real wing is 1.8 GPa along the span and 0.20 GPa along the chord, suggesting that the butterfly wing material is highly anisotropic. Real right forewings performed optimally at approximately 10 Hz, the flapping frequency of a live monarch butterfly, with a peak force of 4 mN. The artificial wing performed optimally at approximately 8 Hz with a peak force of 5 mN. 

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3. A Multi-Source Energy Harvesting System to Power Microcontrollers for Cryptography

   https://doi.org/10.1109/IECON.2018.8591833  

   Li, Jiayu; HoonHyun, Ji; SamHa, Dong (October 2018, IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)

   This paper presents a multi-source energy harvesting system for vibration, thermal, and solar energy from automobiles, which aims to power a micro controller (MCU) for cryptography. Each building block adopts a maximum power extraction scheme to match the unique characteristic of the energy source. Resistive impedance matching with a buck-boost converter is adopted for vibration and thermal energy harvesting, and maximum power point tracking for solar energy harvesting. The proposed system provides two regulated voltages, 3.3 V and 5 V, to power an MCU. An energy level indicator indicates the current energy level stored in the storage device. The MCU processes a cryptography algorithm accordingly based on the current energy level. The system is able to cold start, i.e., even if the storage device is drained completely, it can start. 

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4. Solar Harvesting through Multilayer Spectral Selective Iron Oxide and Porphyrin Transparent Thin Films for Photothermal Energy Generation

   https://doi.org/10.1002/adsu.202100006  

   Lyu, Mengyao; Lin, Jou; Krupczak, John; Shi, Donglu (March 2021, Advanced Sustainable Systems)

   Abstract A fundamental challenge in energy sustainability is efficient utilization of solar energy towards energy‐neutral systems. The current solar cell technologies have been most widely employed to achieve this goal, but are limited to a single‐layer 2D surface. To harvest solar light more efficiently, a multilayer system capable of harvesting solar light in a cuboid through transparent photothermal thin films of iron oxide and a porphyrin compound is developed. Analogous to a multilayer capacitor, an array of transparent, spectral selective, photothermal thin films allows white light to penetrate them, not only collecting photon energy in a 3D space, but generating sufficient heat on each layer with significantly increased total surface area. In this fashion, thermal energy is generated via a multilayer photothermal system that functions as an efficient solar collector, energy converter and generator with high energy density. A solar‐activated thermal energy generator that can produce heat without any power supply and reach a maximum temperature of 76.1 °C is constructed. With a constant incoming white light (0.4 W cm⁻²), the thermal energy generated can be amplified 12‐fold via multilayers. The multilayer system extends another dimension in solar harvesting and paves a new path to energy generation for the energy‐neutral system. 

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5. 3D Solar Harvesting and Energy Generation via Multilayers of Transparent Porphyrin and Iron Oxide Thin Films

   https://doi.org/10.3390/en16073173  

   Lin, Jou; Lyu, Mengyao; Shi, Donglu (April 2023, Energies)

   Photovoltaic solar cells have been extensively used for various applications and are considered one of the most efficient green energy sources. However, their 2D surface area solar harvesting has limitations, and there is an increasing need to explore the possibility of multiple layer solar harvest for enhanced energy density. To address this, we have developed spectral-selective transparent thin films based on porphyrin and iron oxide compounds that allow solar light to penetrate multiple layers, significantly increasing solar harvesting surface area and energy density. These thin films are designed as photovoltaic (PV) and photothermal (PT) panels that can convert photons into either electricity or thermal energy for various green energy applications, such as smart building skins and solar desalination. The advantages of this 3D solar harvesting system include enlarged solar light collecting surface area and increased energy density. The multilayer system transforms the current 2D to 3D solar harvesting, enabling efficient energy generation. This review discusses recent developments in the synthesis and characterization of PV and PT transparent thin films for solar harvesting and energy generation using multilayers. Major applications of the 3D solar harvesting system are reviewed, including thermal energy generation, multilayered DSSC PV system, and solar desalination. Some preliminary data on transparent multilayer DSSC PVs are presented. 

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