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Supplying electric power to wearable IoT devices, particularly smart contact lenses (SCLs), is one of the main obstacles to widespread adoption and commercialization. In the present study, we have successfully designed, fabricated, and characterized semi-transparent, self-supported, and flexible single crystalline silicon solar cells using a single-sided micromachining procedure. Optical, mechanical, and electrical simulations, together with the practical measurements, verify the application of our developed solar cells to be mounted on a limited-footprint and flexible SCL. The 15 μm-thick silicon solar cells conformally fit on a dome-shaped contact lens (ROC = 8 mm) without any mechanical and electrical degradation. This homojunction photovoltaic device containing an array of micro-holes exhibits a

We demonstrate the implementation of a low-power, low-profile, varifocal liquid-crystal Fresnel lens stack suitable for tunable imaging in smart contact lenses. The lens stack consists of a high-order refractive-type liquid crystal Fresnel chamber, a voltage-controlled twisted nematic cell, a linear polarizer and a fixed offset lens. The lens stack has an aperture of 4 mm and thickness is ∼980 µm. The varifocal lens requires ∼2.5 VRMS for a maximum optical power change of ∼6.5 D consuming electrical power of ∼2.6 µW. The maximum RMS wavefront aberration error was 0.2 µm and the chromatic aberration was 0.008 D/nm. The average BRISQUE image quality score of the Fresnel lens was 35.23 compared to 57.23 for a curved LC lens of comparable power indicating a superior Fresnel imaging quality.

Presbyopia, an age-related ocular disorder, is characterized by the loss in the accommodative abilities of the human ocular system and afflicts more than 1.8 billion people world-wide. Conventional methods of correcting presbyopia fragment the field of vision, inherently resulting in significant vision impairment. We demonstrate the development, assembly and evaluation of autofocusing eyeglasses for restoration of accommodation without vision field loss. The adaptive optics eyeglasses consist of two variable-focus piezoelectric liquid lenses, a time-of-flight range sensor and low-power, dual microprocessor control electronics housed within an ergonomic frame. Patient-specific accommodation deficiency models were utilized to demonstrate a high-fidelity accommodative correction. Each accommodation correction calculation was performed in ~67 ms requiring 4.86 mJ of energy. The optical resolution of the system was 10.5 cycles/degree, featuring a restorative accommodative range of 4.3 D. This system can run for up to 19 hours between charge cycles and weighs ~132 g, allowing comfortable restoration of accommodative function, 12 pages, 13 figures

Objective: In this paper, we present a novel, low-profile, scleral-coil based, distance ranging system which is suitable for smart, accommodating contact lenses. Methods: We measure the induced emf between a set of four thin semi-circular coils patterned on flexible Kapton substrates that conform to the eyes’ sclera. This induced emf is a function of eye gaze angles. The system then determines the distance from the eyes to the desired object via the triangulation of these eye gaze angles Results : Experiments on eyeball simulated tissue gels indicate an accurate prediction of object distance in the 0.1-15 D range with a 0.15 D RMS error and object direction in the −15 to 15-degree arc with 0.4-degree RMS error, respectively. The energy required was determined to be as low as 20 μJ per range reading. Conclusion: Experimental data shows that our proposed new method of eye-tracking and distance ranging system can accurately predict eye-gaze angles and object-distance, whilst using only 20 μJ per range reading. Significance: The high-accuracy, low-profile and reduced energy requirements of the proposed eye-tracking technique, make it suitable for applications in the vast field of adaptive optics such as smart contact lenses and other low-power vision corrective applications.

This paper reports the development of a wireless pressure sensing coil system by embedding a capacitive micro sensor onto a wire. The coil system, consisting of an inductor (coil itself) and multiple capacitors (sensors), formed a passive LC telemetry configuration for wireless sensing. The capacitive sensor, utilizing the movements of a liquid in a sealed chamber for hydraulic amplification, enabled high capacitance changes and amplified signal outputs. The capacitive sensor also produced digitized signal outputs as the liquid movement crossed a finite number of the interdigitated electrodes. Such characteristics were modeled and confirmed by establishing an equivalent fluidic circuit. The capacitive sensor was fabricated by grafting and polishing a copper wire piece on a silicon wafer, then performing standard microfabrication on the polished wire surface and filling a liquid into a sensor chamber. The fabricated pressure sensing coil system demonstrated a pressure sensitivity of 11.8 kHz/mmHg under a clinical pressure range of 0~206.9 mmHg in an ex vivo test with a water flowing tube, meeting the requirements for wireless detection of vessel restenosis. The sensitivity corresponded to the capacitance changes of 0.052 fF/mmHg and liquid displacement of $0.39~\mu \text{m}$ /mmHg. The fabricated coil system held a dimension of 2.5 mm in diameter and 7.2 mm in length in the form of a wound wire (copper, $260~\mu \text{m}$ in diameter). The embedded capacitive sensor consisted of a hydraulic chamber of $400\times 100\times 1 2\,\,\mu \text{m}^{3}$ and a microchannel of $500\times 20\times 1 2\,\,\mu \text{m}^{3}$ . [2020-0364]

Smart, adaptive contact lenses (SCLs) are amongst the most anticipated, next-generation, standalone medical devices. SCLs require the integration of thin microelectronic components, tunable lenses, and micro-power sources onto a common non-planar substrate. Here, we report a miniaturized, sliding metal-air electrochemical micro-battery driven by natural eye blinking motion that can be integrated with an SCL platform as a source of electrical energy. The metal-air battery (3⋅8 mm2) consists of a Mg anode and a Pt cathode. The electrolyte of the battery is the eye-tear liquid and is introduced to the battery structure during the natural eye-blinking cycle, which activates the battery. The open-circuit voltage across the eye-tear activated metal-air battery (ETMAB) was measured to be 2.2 V and the maximum specific capacity of 3561 mA h g−1 was obtained at a discharge current density of 5 mA·cm−2. Impedance matching analysis exhibits the maximum generated power density of 1.3 mW·cm−2 at the load of 740 Ω.

Using high-performance LC (E7) filled microfabricated refractive Fresnel chambers, we experimentally demonstrate a thin low-profile adaptive optical system with high analog tunability (2.1 D) that can be integrated with an adaptive contact-lens system.

Wearable eye tracking devices have broad uses in medicine, psychology, augmented & virtual reality and consumer market research. Most mobile eye trackers available today utilize infrared imaging of the pupil and corneal reflections with video cameras. This tracking method requires sophisticated real-time processing of video signals consuming substantial electrical power. This method is thus unsuitable for light weight wearables such as adaptive smart eyeglasses for correction of presbyopia. In this paper we present a low-profile, low-power (7.7 mJ/sample) digital eye tracker oculometer based on infrared sclera tracking. The system is implemented using eight, 24-bit infrared proximity sensors and synchronous infrared LEDs. The pupil location is determined from 32 reflected pulsed light measurements independent of ambient illumination. The digital oculometer is 3.1 mm thick and weighs ~3 g. The tracker mounts adjacent to the tunable lenses in the smart eyeglasses frame. The eye tracker showed a pointing error of 1.3 degrees rms over a vertical and horizontal range of 30 degrees when tested by an observer.

This paper reports a novel method for detecting ethylene by using KMn04/polyimide composite thin-films as the analyte-sensitive layer in a capacitive MEMS ethylene sensor which requires zero-DC power for reliable operation. The technique utilizes a MEMS parallel-plate capacitor with the thin-film as a dielectric layer. Exposure of ethylene to the KMnO 4 molecules embedded within the polyimide matrix results in oxidation of ethylene into CO 2 and H 2 0, which induces swelling of the thin-film and also changes its dielectric-constant. This leads to a change in device capacitance. Preliminary results indicate a nearly reversible linear decrease of sensor capacitance of ~1 - 14 pF when exposed to ethylene concentrations ranging from 130 - 1000 ppm, yielding a normalized capacitance sensitivity of ~3.74×10−6/ppm. Selectivity tests revealed a favorable response towards ethylene compared to gases such as hexanal, indole, pentane, acetone, and IPA.

Polyimide and PDMS are the most common materials used in the packaging of flexible electronics. Silicon dioxide being photolithographically patternable, can be used to selectively bond polyimide (PI) to PDMS to realize flexible microsystems integrating fluidic and electronic components. In this work, we characterize the plasma bond strength of polyimide (Kapton) to PDMS with thin-film SiO 2 as an intermediate bonding layer. Peel strengths of samples prepared with different types of deposition methods – sputtering, plasma-enhanced chemical vapor deposition (PECVD), and atomic layer deposition (ALD) were evaluated. The measured forces (normalized to the width of the bonded area), required to separate the PDMS and Kapton films, either due to adhesive or cohesive failures, were 174-860 N/m, 79-179 N/m, and 7-12 N/m for samples bonded with sputtered, PECVD and ALD oxide, respectively. The strength of the sputtered oxide bond is comparable to the strength of the best chemical adhesive method available.

This paper reports the development of a high-sensitivity gas sensor and the demonstration of selectively detecting green leaf volatiles (GLV, here hexanal) released from damaged plant leaves. The developed sensor is a conductivity sensor that utilized a 5.2-nm gap as the key detection site between electrodes. The gap was coated with with customized molecular probes toward binding to hexanal. The fabricated sensor demonstrated the detection of a GLV, hexanal, from the collected gas samples from damaged plant leaves, sorghum. Gas samples were collected into a tedlar bag from a glass jar containing damaged sorghum leaves. When exposed to hexanal concentrations from 77.7 to 5181.3 ppm, it produced output signal changes in resistance by 1.64~4.45 times. The sensor response time was measured as 41.6 min at a hexanal concentration of 77.7 ppm.

We present the fabrication and experimental results of a flexible electrostatic energy harvester chip suitable for a smart contact lens application. The harvester consists of a variable area liquid capacitor formed between a hydrophobic film on the flex substrate and the rolling meniscus of a non-wetting eye tear drop. The harvester was tested under tear sliding motion emulating eyelid blinking. The 2×10 mm2 harvester generated 1.36 µJ of energy per blink and average power of 0.265 µW when pre-charged at 6 V and driven at typical blinking velocity conditions.

Power generation for the Internet of Things (IoT), particularly wearable electronics, is a significant challenge and a subject of great interest in the field of photovoltaics research. Here, we have designed and fabricated single crystalline silicon solar cells using a single-sided micromachining process. Preliminary results indicate that the solar cell is flexible and ~50% transparent. Furthermore, the open-circuit voltage and the short-circuit current density of the fabricated device under indoor light with the power density of 2 mW.cm-2 are 0.4 V and 110 µA.cm-2, respectively. The fabricated solar cells have been specifically designed to conformally fit on the commercial contact lenses.

We report the electrical detection of captured gases through measurement of the quantum tunneling characteristics of gas-mediated molecular junctions formed across nanogaps. The gas-sensing nanogap device consists of a pair of vertically stacked gold electrodes separated by an insulating 6 nm spacer (~1.5 nm of sputtered α-Si and ~4.5 nm ALD SiO2), which is notched ~10 nm into the stack between the gold electrodes. The exposed gold surface is functionalized with a self-assembled monolayer (SAM) of conjugated thiol linker molecules. When the device is exposed to a target gas (1,5-diaminopentane), the SAM layer electrostatically captures the target gas molecules, forming a molecular bridge across the nanogap. The gas capture lowers the barrier potential for electron tunneling across the notched edge region, from ~5 eV to ~0.9 eV and establishes additional conducting paths for charge transport between the gold electrodes, leading to a substantial decrease in junction resistance. We demonstrated an output resistance change of >108 times upon exposure to 80 ppm diamine target gas as well as ultralow standby power consumption of

The paper reports the fabrication and testing results of a graphene-based thermal conductivity detector (TCD) by taking advantages of ultra low mass, large surface area and high thermal conductivity of a multilayer graphene (MLG) for low power gas detection. The fabricated TCD consists of a transferred and thus suspended MLG across a micro channel where target gases flow through. The sophisticated transfer process was successfully performed to construct a relatively large free-standing MLG membrane with a footprint of 75x3,600 um2. The fabricated TCD, when connected to a micro gas chromatography (μGC) column, demonstrated the chromatographic detection of pentane, hexane and heptane gases with a limit of detection (LOD) of 4760 ppm of pentane, while consuming only 26 mW.

We are reporting the fabrication and test of ultrathin, flexible semi-transparent single-crystal solar cells using a silicon undercut microfabrication techniques suitable for powering up exposed biomedical microsystems. The resulting cells are 15 micrometers thick. The solar cells provide a short circuit current density of 0.54 mA cm-2 and the open circuit voltage of 340 mV under low indoor lighting (13 mW.cm-2) conditions achieving an average light transmission of ~25%.

By stacking multiple thin and flexible LC based lenses, we experimentally demonstrate a low-power adaptive optical system with enhanced focusing tunability that is suitable for integration with a smart contact lens system.