FlexPower: Integration of Flexible Segmented Li-ion Batteries (Battlet) with Flexible Wireless Charging Technology for Wearable Devices

The proliferation of wearable devices has been significantly hindered by limitations of reliable flexible power solutions. To address this challenge, this dissertation introduces the concept of a flexible Li-ion battery, featuring a partitioned cathode and anode electrode array coated on flexible composite current collectors, which is referred to as the “battlet”. Ionic liquid Lithium bis(fluorosulfonyl)imide (LiFSI) with 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI) is used as liquid electrolytes to address the flammability concern. The mechanism of mechanical failure during bending, the fabrication of partitioned electrodes, a comparison of the ionic liquid and organic electrolyte, and electrochemical performance is discussed in this work. Results show that this approach can reduce the crack propagation of the electrodes under mechanical distortion, thus improving electrochemical stability. The full cell battery achieves a 0.7 mAh/cm² capacity density and can withstand around 1000 bending cycles at a 5 mm bending radius.Additionally, using a flexible Fan-Out Wafer-Level Packaging (FOWLP) platform, FlexTrateTM, a flexible wireless charger is designed using resonant magnetic coupling. The wireless charger can withstand up to 5 mm bending radius and can deliver a constant 3.3 V output voltage and 3.9 mW peak power. The flexible wireless charger, along with the flexible battlet battery, serves as a fully wireless power solution for wearables that we call FlexPower. To integrate the FlexPower with flexible electronics, this dissertation also discusses a 2D and a 3D flexible integration approach based on FlexTrateTM. As a demonstration of the 2D approach, the FlexPower is integrated with a UV microLED display array consisting of 33 microLEDs. The power consumption of the LED array is 3 mW, and the flexible battery, with a capacity of 4.6 mWh, can power the microLEDs for more than 1.5 hours. For the 3D integration, the dissertation explores the development of flexible interconnects on the front and back sides of FlexTrateTM. A through-glass via die is used to facilitate interconnection between both sides. A detailed experimental study of the SF6/O2 plasma PDMS dry-etch method for backside contact opening, interconnect performance, and reliability is also addressed. This work represents, to the best of our knowledge, the first demonstration of a flexible battery integrated with a flexible wireless charger powering flexible µLED arrays for wearable applications

Switching the current through molecular wires

The influence of Gaussian laser pulses on the transport through molecular wires is investigated within a tight-binding model for spinless electrons including correlation. Motivated by the phenomenon of coherent destruction of tunneling for monochromatic laser fields, situations are studied in which the maximum amplitude of the electric field fulfills the conditions for the destructive quantum effect. It is shown that, as for monochromatic laser pulses, the average current through the wire can be suppressed. For parameters of the model, which do not show a net current without any optical field, a Gaussian laser pulse can establish a temporary current. In addition, the effect of electron correlation on the current is investigated.Comment: 8 pages, 6 figure

A model analysis of climate and CO2 controls on tree growth and carbon allocation in a semi-arid woodland

Many studies have failed to show an increase in the radial growth of trees in response to increasing atmospheric CO2 concentration [CO2] despite the expected enhancement of photosynthetic rates and water-use efficiency at high [CO2]. A global light use efficiency model of photosynthesis, coupled with a generic carbon allocation and tree-growth model based on mass balance and tree geometry principles, was used to simulate annual ring-width variations for the gymnosperm Callitris columellaris in the semi-arid Great Western Woodlands, Western Australia, over the past 100 years. Parameter values for the tree-growth model were derived from independent observations except for sapwood specific respiration rate, fine-root turnover time, fine-root specific respiration rate and the ratio of fine-root mass to foliage area (ζ), which were calibrated to the ring-width measurements by Bayesian optimization. This procedure imposed a strong constraint on ζ. Modelled and observed ring-widths showed quantitatively similar, positive responses to total annual photosynthetically active radiation and soil moisture, and similar negative responses to vapour pressure deficit. The model also produced enhanced radial growth in response to increasing [CO2] during recent decades, but the data do not show this. Recalibration in moving 30-year time windows produced temporal shifts in the estimated values of ζ, including an increase by ca 12% since the 1960s, and eliminated the [CO2]-induced increase in radial growth. The potential effect of CO2 on ring-width was thus shown to be small compared to effects of climate variability even in this semi-arid climate. It could be counteracted in the model by a modest allocation shift, as has been observed in field experiments with raised [CO2]

Visual modeling of dynamic gestures using 3D appearance and motion features

We present a novel 3-D gesture recognition scheme that combines the 3-D appearance of the hand and the motion dynamics of the gesture to classify manipulative and controlling gestures. Our method does not directly track the hand. Instead, we take an object-centered approach that efficiently computes 3-D appearance using a region-based coarse stereo matching algorithm. Motion cues are captured by differentiating the appearance feature with respect to time. An unsupervised learning scheme is carried out to capture the cluster structure of these features. Then, the image sequence of a gesture is converted to a series of symbols that indicate the cluster identities of each image pair. Two schemes, i.e., forward HMMs and neural networks, are used to model the dynamics of the gestures. We implemented a real-time system and performed gesture recognition experiments to analyze the performance with different combinations of the appearance and motion features. The system achieves recognition accuracy of over 96 % using both the appearance and motion cues.