Towards a Smart Contact Lens

Talya T. Weinshel1, Volker J. Sorger2

1Department of Biomedical Engineering 2Department of Electrical and Computer Engineering

George Washington University, Washington, DC, 20052, USA

I. INTRODUCTION The goal of this work is to develop a wearable head-up

display (Fig. 1). Our research will set a path the way towards functional microsystems that will superimpose information, via light, over a person’s field of view. In doing so, it overcomes the enigma of augmented reality, a known grand challenge for engineering today. With the ability to actualize augmented reality (AR), advancements in numerous applications will unfold. Incorporation of AR could be seen in various area, such as education, training, navigation, and cross-cultural communication. It could not only revolutionize human-machine-interface, but they could also bridge the gap between patients and healthcare professionals. Such

functionality and advancement in these areas will improve the standard of living and expand nanotechnology. Lastly, this profound innovative technology could be used in numerous fields of research: bodily motion, fluid flow, material deformation, and transportation of chemicals across biological or synthetic barriers, such as membranes or other media. This research project requires the integration of biomedical, electrical, and mechanical engineering and nanotechnology.

II. METHOD AND APPROACH

The antenna, interconnects, and other electrical components were designed and fabricated directly onto the polyethylene terephthalate (PET) substrate (Fig. 2., all parameters are in mm). The first deposition method was done through the use of the high vacuum magnetron sputtering machine (CVC) in a nanomanufacturing clean room, but the alternative deposition method of electron beam physical vapor deposition, proved more successful.

Fig. 2. CAD File of Antenna Fig. 3. Vacuum Molding Apparatus

The antenna was designed using a numerical mode solver

and fabricated using shadow mask deposition, with the goal of reducing the electrical conductivity and thereby improving the antenna capturing efficiency. With the end purpose of the antenna to receive RF data, the target was to drive an array of nano (n)-LEDs onto the lens in order to demonstrate the CL’s power consumption and delivery capabilities. The nLEDs will be etched out from an epitaxially-grown film (III-V and nitride-based) provided by a collaborator, and aligned with the on-lens integrated circuit. Once the nLEDs can be driven, it is necessary to ensure that the emission is focused on the human’s retina. In order to converge the light onto the retina from the nLEDs, we will utilize a 2-dimensional Fresnel lens (FL) design (FDTD simulation for optimization) by varying the optical refractive index of a passivation layer (SU8) on top of the nLED. Beam-steering to align the emission onto the human’s fovea is realized by applying a selective voltage to the FL, which allows to reduce the nLED power output. Aligning the emission onto the fovea is necessary since the vast majority of a human’s cone receptors reside, enables one to perceive color. The observation of images can be created by bypassing the physical object and focusing light onto specific receptors in an eye. FL’s were fabricated using electron-beam-lithography (EBL) and subsequent development. The FL fabrication will be the last step, before the molding process begins. Note the FL shaping layer synergistically acts as a passivation layer and bio-compatibility protection film. Before and after applying the epoxy, numerous tests were run to observe the CL’s viability to drive the nLEDs.

Up to this point the nanofabrication process was done with a flat PET film. To form the hemispherical lens shape, a temperature molding process will be applied to the PET where it will be heated to its glass transition temperature and then vacuum formed to the mold of the intended shape. An apparatus was designed and assembled to accomplish this manufacturing process (Fig. 3.).

III. RESULTS

Fig. 1. Smart contact lens worn and schematic.

This research project is currently in the stage of obtaining results. However, an S-11 parameter test was conducted to determine the resonance frequencies of the antenna (Fig 4.). While we were unable to directly measure the S-11 of our ideal sized antenna, we were able to measure the S-11 of two scaled up versions of the antenna. Based on the resonance frequencies found for the two larger antennas (4 cm and 6 cm in diameter), we can extrapolate that the ideal frequency of our 1 cm diameter antenna will be around the targeted 2.4 GHz. Through further calculations we determined that the radiation and reception efficiencies of the RF loop antenna to be 37.56% and 0.1%-1%, respectively. Although these values may seem inadequate, given the number of restraints and limitations these results are decent. Based off of these figures, it can be believed that the ideal incoming signal harvested will deliver 100mW of power.

Fig. 3. S11 Parameter Test Results

Based on the average amount of light entering the human eye during the day, we have calculated estimates on how much optical power is needed for an LED to be seen and how much energy this would require. In order to do such calculations, it was necessary to compute the photon energy at VIS, which we estimated to be about 2-3eV = 4x10-19W. Next, it was determined that during the daytime, the number of photons that hits a photoreceptor every second is 104. Additionally, the minimum optical intensity per code is on the magnitude of fW.

IV. CONCLUSIONS

Once the study is complete, one such conclusion we want to be able to make is that the antenna successfully delivers data and drives power toward the versatile contact lens, which resulted in the illumination of nLEDs. With the results obtained thus far, we anticipate that with the current design of the model, the CL will successfully drive an nLED. In addition, we want to be able to demonstrate how micron-scale metal interconnects can be incorporated onto a thin flexible plastic substrate, how the structure can be encapsulated in a biocompatible polymer, and how the encapsulated structure can be micro-molded and polished into the shape of a contact lens. To learn more about Prof. Sorger’s research visit us at:

sorger.seas.gwu.edu