The performance and integration density of silicon integrated circuits (ICs) have progressed at an unprecedented pace in the past 60 years. While silicon ICs thrive at low‐power high‐performance ...computing, creating flexible and large‐area electronics using silicon remains a challenge. On the other hand, flexible and printed electronics use intrinsically flexible materials and printing techniques to manufacture compliant and large‐area electronics. Nonetheless, flexible electronics are not as efficient as silicon ICs for computation and signal communication. Flexible hybrid electronics (FHE) leverages the strengths of these two dissimilar technologies. It uses flexible and printed electronics where flexibility and scalability are required, i.e., for sensing and actuating, and silicon ICs for computation and communication purposes. Combining flexible electronics and silicon ICs yields a very powerful and versatile technology with a vast range of applications. Here, the fundamental building blocks of an FHE system, printed sensors and circuits, thinned silicon ICs, printed antennas, printed energy harvesting and storage modules, and printed displays, are discussed. Emerging application areas of FHE in wearable health, structural health, industrial, environmental, and agricultural sensing are reviewed. Overall, the recent progress, fabrication, application, and challenges, and an outlook, related to FHE are presented.
Flexible hybrid electronics (FHE) with applications in wearable health, structural health, and industrial, environmental, and agricultural sensing are reviewed. The recent progress, fabrication, application, and challenges, and an outlook, relating to FHE are presented with a focus on the fundamental building blocks of FHE systems: printed sensors and circuits, thinned silicon integrated circuits, printed antennas, printed energy harvesting and storage modules, and printed displays.
Pulse oximetry is a ubiquitous non-invasive medical sensing method for measuring pulse rate and arterial blood oxygenation. Conventional pulse oximeters use expensive optoelectronic components that ...restrict sensing locations to finger tips or ear lobes due to their rigid form and area-scaling complexity. In this work, we report a pulse oximeter sensor based on organic materials, which are compatible with flexible substrates. Green (532 nm) and red (626 nm) organic light-emitting diodes (OLEDs) are used with an organic photodiode (OPD) sensitive at the aforementioned wavelengths. The sensor's active layers are deposited from solution-processed materials via spin-coating and printing techniques. The all-organic optoelectronic oximeter sensor is interfaced with conventional electronics at 1 kHz and the acquired pulse rate and oxygenation are calibrated and compared with a commercially available oximeter. The organic sensor accurately measures pulse rate and oxygenation with errors of 1% and 2%, respectively.
A flexible organic reflectance oximeter array Khan, Yasser; Han, Donggeon; Pierre, Adrien ...
Proceedings of the National Academy of Sciences - PNAS,
11/2018, Letnik:
115, Številka:
47
Journal Article
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Transmission-mode pulse oximetry, the optical method for determining oxygen saturation in blood, is limited to only tissues that can be transilluminated, such as the earlobes and the fingers. The ...existing sensor configuration provides only singlepoint measurements, lacking 2D oxygenation mapping capability. Here, we demonstrate a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.
This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health ...monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98 mWh/cm(2) and demonstrates capacity retention of 90% at 3C discharge rate and ~99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.
The interfacing of soft and hard electronics is a key challenge for flexible hybrid electronics. Currently, a multisubstrate approach is employed, where soft and hard devices are fabricated or ...assembled on separate substrates, and bonded or interfaced using connectors; this hinders the flexibility of the device and is prone to interconnect issues. Here, a single substrate interfacing approach is reported, where soft devices, i.e., sensors, are directly printed on Kapton polyimide substrates that are widely used for fabricating flexible printed circuit boards (FPCBs). Utilizing a process flow compatible with the FPCB assembly process, a wearable sensor patch is fabricated composed of inkjet‐printed gold electrocardiography (ECG) electrodes and a stencil‐printed nickel oxide thermistor. The ECG electrodes provide 1 mVp–p ECG signal at 4.7 cm electrode spacing and the thermistor is highly sensitive at normal body temperatures, and demonstrates temperature coefficient, α ≈ –5.84% K–1 and material constant, β ≈ 4330 K. This sensor platform can be extended to a more sophisticated multisensor platform where sensors fabricated using solution processable functional inks can be interfaced to hard electronics for health and performance monitoring, as well as internet of things applications.
A wearable sensor patch is fabricated by directly interfacing inkjet‐printed gold electrocardiography electrodes and a stencil‐printed nickel oxide thermistor to silicon integrated circuits. This direct printing technique, which is fully compatible with flexible printed circuit board assembly process, is promising for health and performance monitoring, as well as internet of things applications.
Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents ...electrodes from reacting with biological fluids and living tissues. Therefore, flexible gold electrodes are ideal for bioimpedance and biopotential measurements such as bioimpedance tomography, electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). However, a manufacturing process to fabricate gold electrode arrays on plastic substrates is still elusive. In this work, a fabrication and low‐temperature sintering (≈200 °C) technique is demonstrated to fabricate gold electrodes. At low‐temperature sintering conditions, lines of different widths demonstrate different sintering speeds. Therefore, the sintering condition is targeted toward the widest feature in the design layout. Manufactured electrodes show minimum feature size of 62 μm and conductivity values of 5 × 10 6 S m−1. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode‐to‐electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet‐printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.
Fabrication of inkjet‐printed flexible gold electrode arrays on plastic substrates is described, with a special focus on laser‐cut freestanding electrodes, low‐temperature sintering, and the methodology used for impedance mapping on conformal surfaces. Taking advantage of low‐cost and large‐area manufacturing techniques, these electrically reproducible and mechanically robust electrode arrays are promising for novel wearable biomedical sensing.
Solution‐processibility is one of the distinguished traits of organic light‐emitting diodes (OLEDs) compared to existing solid‐state LED technologies. It allows new opportunities which can simplify ...the fabrication and potentially reduce the cost of manufacturing process. Emission area patterning is one of the crucial fabrication steps and it usually involves subtractive methods, such as photolithography or etching. Here, printing techniques are used to pattern the emission area of blade‐coated OLED layers. The print qualities of a number of printing schemes are characterized and compared. Spray coating and screen printing are used to deposit dielectrics with desired patterns on the OLED layers. At luminance of 1000 cd m−2 the OLEDs patterned using spray‐coated and screen‐printed dielectric show current density of 8.2 and 10.1 mA cm−2, external quantum efficiency (EQE) of 2.1% and 2.1%, and luminous efficacy of 5.5 and 6.3 lm W−1, respectively. The OLED characteristics and features of each printing scheme in depositing the dielectric layer are discussed. The printing methods are further applied to demonstrate displays with complex shapes and a seven‐segment display.
The emission area of organic light‐emitting diode (OLED) is patterned by printed dielectrics using various printing schemes. The dielectric layers deposited via spray coating and screen printing are characterized in terms of their print quality using various concentrations of inks. Then, these patterning techniques are used to create OLED with a logo and a seven‐segment display.
A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of ...material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light‐emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface‐energy‐patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near‐infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs.
Blade‐coated polymer light‐emitting diodes (PLEDs) with different colors are successfully demonstrated on one substrate using surface energy patterning (SEP). SEP is further utilized to fabricate two PLEDs with different colors on one substrate. The PLEDs are used to perform photoplethysmogram measurements with a silicon photodiode. With the multicolor PLEDs, pulse and oxygenation measurements are successfully demonstrated.
Purpose: To assess pre-clerkship and clerkship medical student performance in an ophthalmology Objective Standardized Clinical Examination (OSCE) station. Methods: One hundred pre-clerkship medical ...students and 98 clerkship medical students were included in this study. The OSCE station consisted of a common ocular complaint - blurry vision with decreased visual acuity - and students were asked to take an appropriate history, provide two or three differential diagnoses to explain the symptoms, and perform a basic ophthalmic examination. Results: Generally, clerks performed better than pre-clerks in the history taking (P < 0.01) and ophthalmic examination (P < 0.05) sections, with few specific exceptions. In the history-taking section, more pre-clerkship students asked about patient age and past medical history (P < 0.00001) and for the ophthalmic examination, more pre-clerkship students performed the anterior segment examination (P < 0.01). Interestingly, more pre-clerkship students were also able to provide two or three differential diagnoses (P < 0.05), specifically diabetic retinopathy (P < 0.00001) and hypertensive retinopathy (P < 0.00001). Conclusion: The performance of both groups was generally satisfactory; however, many students in both groups had scores that were unsatisfactory. Notably, pre-clerks also outperformed clerks in certain areas, which emphasizes the importance of revisiting ophthalmology content through clerkship. Awareness of such knowledge can allow medical educators to incorporate focused programs into the curriculum.
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