Data transmission and power supply for smart contact lens

The industry of wearable device is dramatically growing with the development of smart sensors, battery, and internet of things (IoT) in the stream of 4th industrial revolution. Among the wearable devices, smart contact lens has great potential to grow in the aspect of giving information to user directly. For collecting information, smart sensors can be used in noninvasive method to detect vital sign from the components in tear, intraocular pressure, and dangerous elements which are attached on the surface of contact lens. Also, computer vision can be used to get the information from the image taken by integrated camera on smart contact lens. From the previous researches on integration of sensor into smart contact lens, wireless power supply and communication were used to activate sensor and transfer the data with complex circuit and additional receiver. Lithium ion battery was integrated for giving power to smart contact lens in another research. However, wireless data transmission and power supply require high power consumption, additional antenna and external receiver. Furthermore, lithium ion battery requires additional electrolyte and has potential of explosion. In this thesis, direct electrochromic data transmission is suggested for smart contact lens instead of wireless communication. Prussian Blue (PB) is used for color change with voltage application, because it has electrochemical reaction with sodium and potassium ion in tear which shows clear color change between transparency and blue. Diverse signals are demonstrated by controlling the duration and magnitude of voltage application. Computer vision is used to detect the position and amount of color change for real-time application. For the safe power supply of smart contact lens, safe battery with self-recharging system is demonstrated. Prussian Blue analogues (PBAs) are safe battery materials which have electrochemical reaction with sodium and potassium ions in tear. This battery works in narrow voltage window without additional electrolyte which means removing the potential of explosion. Also, photodiode is integrated into system for charging the battery with solar energy. Furthermore, electrochemical kinetic energy harvesting is introduced as preliminary study for the energy harvesting using the flow of tear made by blinking. Voltage gap is induced on the surface of battery material and supercapacitor material by the flow of electrolyte, because the ways of attachment of ions on each material’s surface are different. Ions which are inserted into the structure of battery material maintain the original status under the flow of electrolyte, but ions which are attached on the surface of supercapacitor material are easily detached by the flow of electrolyte. This selective ion sweeping is characterized, and energy is harvested during 500 cycles without dramatic decrease of performance.Doctor of Philosoph

A comprehensive viscosity model for micro magnetic particle dispersed in silicone oil

Magnetorheological behavior of micro magnetic particle dispersed in silicone oil has been characterized by a multiplied form of phenomenological models taking the effect of shear rate, powder volume fraction, temperature and magnetic flux density. Magnetorheological fluid samples with seven different particle volume fraction were prepared by adding ferrite particles in silicone base oil and their shear viscosity of fluid samples were measured under three different temperatures (40 ??C, 70 ??C, and 110 ??C) and ten different magnetic flux density (0-100 mT). The fluid had an upper limit to the increase of viscosity under the effect of external magnetic field and the saturation values were dependent on the operating temperature, shear rate and volume fraction of magnetic powder. The rheological behaviors have been characterized by our developed model which can be very useful for the precise control of the magnetorheological fluid. ?? 2015 Elsevier B.V. All rights reserved

Thermally assisted alkali/zinc ion hybrid battery for high roundtrip efficiency

The growth of renewable energy generation has necessitated electric energy storage (EES) systems. Batteries are the most promising small-scale EES system, given their portability, quick response time, and high compatibility with electrical devices. We present a thermally assisted K/Zn ion hybrid battery for high roundtrip efficiency. The battery contains a copper hexacyanoferrate (CuHCFe) cathode and a zinc metal anode with a discharging voltage of 1.75 V in a K/Zn ion hybrid aqueous electrolyte. The battery's roundtrip efficiency improved by 2.1-4.5% when cycled between 10 and 30 °C. Its discharging voltage and temperature coefficient improved dramatically when the K ion was replaced with a Rb ion. The proposed thermally assisted battery cycle can be used with various conventional batteries to reduce EES energy loss during charge/discharge cycles.Ministry of Education (MOE)S.W.L. acknowledges the support by Academic Research Fund Tier 2 from the Ministry of Education, Singapore under ref. no. MOE2019-T2-1-122

An electrochromic alarm system for smart contact lenses

Wearable devices are becoming essential tools for mandatory daily health checks. The technology permits the sounding of alarms in response to critical conditions and as part of a continuous, real-time smart healthcare system. Among wearable devices, the smart contact lens is a pivotal technology, as it permits vital-sign monitoring through lachrymation and an augmented visual reality that can be used for the provision of information. Past research regarding smart contact lenses has relied on wireless communication for data transmission, which has necessitated the use of additional receivers. Furthermore, no research has thus far been published that deals with the provision of information through image visualization on the contact lens. Here, we describe an electrochromic alarm system that operates via electrochemical reactions with ions in tears and achieves data transmission and the provision of information. The system was shown to function in harsh conditions and with limbed space and thickness. It was able to maintain contact with tears as a result of its curved shape. The voltage and duration of the potential applied to our electrochromic system were controlled in a way that achieved a broad range of color changes and frequencies. Furthermore, diverse patterns were demonstrated by controlling the duration of the applied voltage, and words were visualized via telecommunication with Morse code. We believe that the electrochromic alarm system reported here is able to be integrated into smart contact lens while extending the possibilities of data transmission and information provision for the users

The effect of electrolyte type on the Li ion intercalation in copper hexacyanoferrate

Copper hexacyanoferrate (CuHCFe) is proved to be a potential cathode for potassium ion and sodium ion storage in aqueous system recently. However, its ability for lithium ion storage has not been well studied. Here, we synthesized CuHCFe by a low-cost and scalable co-precipitation method, and its electrochemical behavior as the cathode for lithium ion storage was investigated both in aqueous and organic systems. The CuHCFe electrode shows larger capacity and better rate capability in organic system compared with the performance in aqueous system. In addition, the capacity has 88% retention after 500 cycles. We further analyzed the strain generated during lithium ion intercalation by ex-situ X-ray diffraction (XRD) method in both types of electrolyte. The lattice of CuHCFe shows shrinkage with ion intercalation in both systems. The measured strains are 0.70% and 0.83% in aqueous and organic system, respectively. The results indicate that the large open framework and small strain are the essential factors for the promising electrochemical performance.ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio

Copper hexacyanoferrate thin film deposition and its application to a new method for diffusion coefficient measurement

The use of Prussian blue analogues (PBA) materials in electrochemical energy storage and harvesting has gained much interest, necessitating the further clarification of their electrochemical characteristics. However, there is no well-defined technique for manufacturing PBA-based microelectrochemical devices because the PBA film deposition method has not been well studied. In this study, we developed the following deposition method for growing copper hexacyanoferrate (CuHCFe) thin film: copper thin film is immersed into a potassium hexacyanoferrate solution, following which the redox reaction induces the spontaneous deposition of CuHCFe thin film on the copper thin film. The film grown via this method showed compatibility with conventional photolithography processes, and the micropattern of the CuHCFe thin film was successfully defined by a lift-off process. A microelectrochemical device based on the CuHCFe thin film was fabricated via micropatterning, and the sodium ion diffusivity in CuHCFe was measured. The presented thin film deposition method can deposit PBAs on any surface, including insulating substrates, and it can extend the utilization of PBA thin films to various applications.National Research Foundation (NRF)Published versionThis research was funded by the National Research Foundation, Prime Minister’s Office, Singapore under its NRF-ANR Joint Programme (grant number Award No. NRF2019-NRF-ANR052 KineHarvest), the Ministry of Trade, Industry and Energy/Korea Institute of Energy Technology Evaluation and Planning (MOTIE/KETEP) (20194010000100), and KU-KIST School Project

Selective Ion Sweeping on Prussian Blue Analogue Nanoparticles and Activated Carbon for Electrochemical Kinetic Energy Harvesting

Kinetic energy is an ideal energy source for powering wearable devices or internet of things (IoTs) because of its abundant availability. Currently, most kinetic energy harvesting systems are based on friction or deformation, which require high-frequency motion or high material durability for sustainable energy harvesting. Here, we introduce selective ion sweeping in a hybrid cell consisting of an ionadsorbing activated carbon and an ion-hosting Prussian blue analogue nanoparticle for electrochemical kinetic energy harvesting. The flow of electrolyte induced by kinetic motion of the cell causes ion sweeping only on the surface of the supercapacitor and induces current flow between the supercapacitor and the battery electrode. This method exhibits 24.9 mu W cm(-2) as maximum power of system with 34 Omega load in half-cell test, which is several thousand times smaller than the load used in conventional methods. In a long-term test with full cell, this method supplies a continuous current flow similar to 6 mu A cm(-2) at the flow of 40 mL min(-1) for 500 cycles without performance decay. The prototype of the hybrid cell demonstrated kinetic energy harvesting from bare hand press with the various flow speeds from 0.41 to 1.39 cm s(-1) as well as walking, running, and door closing, which are representative examples of low-frequency kinetic motions in daily life. We believe that the simple structure of the hybrid cell will enable power supply to various applications from miniaturized systems (e.g., IoTs and wearables) to large-scale systems (e.g., ocean wave energy harvesting)

Power-free contact lens for glucose sensing

Recent advances in wearable devices have enabled noninvasive monitoring for healthcare applications. Smart contact lenses have gained substantial attention for medical diagnosis through the analysis of vital signs in tear fluids. However, previous studies have mostly focused on designs embedded with electronic devices or antennas for wireless transmission, which are power-intensive and require external receivers around the ocular system. Here, the study reports a power-free smart contact lens for noninvasive glucose sensing according to the color changes of multiple electrochromic electrodes to achieve direct data transmission without the external wireless system. The device detects various glucose concentrations, from the ordinary range (0.16–0.5 mm) to abnormally high concentrations (0.9 mm). The multi-electrode design exhibits acceptable accuracy, with a correlation coefficient r = 0.99543 to the controlled sample and allowed low-glucose detections with concentrations down to 0.05 mm. The device shows good reproducibility, with standard deviations of determined glucose levels of 0.0462 and 0.025 for four continuous cycles and for an interval of several days, respectively. It is believed that the reported smart contact lens has the potential for daily health monitoring by ordinary users without a power supply and external devices. Its simple electronics-free structure will allow for immediate application to the market with cost-effective manufacturing.National Research Foundation (NRF)Submitted/Accepted versionS.W.L. acknowledges the support by the National Research Foundation, Prime Minister’s Office, Singapore under its NRF-ANR Joint Pro-gramme (NRF2019-NRF-ANR052 KineHarvest)

Tear-based aqueous batteries for smart contact lenses enabled by Prussian blue analogue nanocomposites

Batteries for contact lenses fabricated by conventional methods could cause severe damage to the eyes if broken. Herein, we present flexible aqueous batteries that operate in tears and provide a safe power supply to smart contact lenses. Nanocomposite flexible electrodes of carbon nanotubes and Prussian blue analogue nanoparticles for cathode and anode were embedded in UV-polymerized hydrogel as not only a soft contact lens but also an ion-permeable separator. The battery exhibited a discharging capacity of 155 μAh in an aqueous electrolyte of 0.15 M Na-ions and 0.02 M K-ions, equivalent to the ionic concentration of tears. The power supply was enough to operate a low-power static random-access memory. In addition, we verified the mechanical stability, biocompatibility and compatibility with a contact lens cleaning solution. It could ultimately enable a safe power supply for smart contact lenses without risk of injury due to the leakage or breakage of the battery.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)S.W.L. acknowledges the support by Academic Research Fund Tier 2 from the Ministry of Education, Singapore under ref. no. MOE2018-T2-1-045. T.-H.B. acknowledges the support by the National Research Foundation of Korea (NRF) grant funded by the Korea government MSIT (reference number: NRF-2020R1F1A1064853). W.Z. acknowledges the support by the Singapore Ministry of Education (MOE) Academic Research Fund Tier 1 (W. Zhao, 2018-T1-002-098) and Nanyang Technological University Start-up Grant (W. Zhao)

Efficient Low-Grade Heat Harvesting Enabled by Tuning the Hydration Entropy in an Electrochemical System

Harvesting of low-grade heat (<100 degrees C) is promising, but its application is hampered by a lack of efficient and low-cost systems. The thermally regenerative electrochemical cycle (TREC) is a potential alternative system with high energy-conversion efficiency. Here, the temperature coefficient (alpha), which is a key factor in a TREC, is studied by tuning the hydration entropy of the electrochemical reaction. The change of alpha in copper hexacyanoferrate (CuHCFe) with intercalation of different monovalent cations (Na+, K+, Rb+, and Cs+) and a larger alpha value of -1.004 mV K-1 being found in the Rb+ system are observed. With a view to practical application, a full cell is constructed for low-grade heat harvesting. The resultant eta(e) is 4.34% when TREC operates between 10 and 50 degrees C, which further reaches 6.21% when 50% heat recuperation is considered. This efficiency equals to 50% of the Carnot efficiency, which is thought to be the highest eta(e) reported for low-grade heat harvesting systems. This study provides a fundamental understanding of the mechanisms governing the TREC, and the demonstrated efficient system paves the way for low-grade heat harvesting