Eye Tracking Simulation for a Magnetic-Based Contact Lens System

In this paper, we present a simulation of an eye motion tracking system. The system consists of a moving magnet and three static magnetic sensors, which implies the magnet embedded in a contact lens and sensors fixed on the spectacles in the application scenario. When the eye is moving, the changing relative position between sensors and magnet will result in different sensory outputs that encodes eye movement information. The simulation of eye movements and corresponding magnetic fields was carried out in MATLAB MathWorks software. After collecting the sensory output, artificial neural network was used to decode the signal and classify the direction of gaze. In total 30 different configurations were tested to determine which one gives the highest accuracy. The network prior to each configuration was trained and the output was compared to the actual position of the eye. It was found that the lens misplacement may cause a lot of issues and requires further investigation to lower its impact on the results. This could be fixed by introducing a calibration step. For all of the configurations, usually, the confusion occurred on the neighbouring classes. This could be due to poor design of the classes, where borders of the regions do not overlap, and cause a sudden change. Based on this simulation, better tracking method can be derived

Recent Advances on Implantable Wireless Sensor Networks

Implantable electronic devices are undergoing a miniaturization age, becoming more efficient and yet more powerful as well. Biomedical sensors are used to monitor a multitude of physiological parameters, such as glucose levels, blood pressure and neural activity. A group of sensors working together in the human body is the main component of a body area network, which is a wireless sensor network applied to the human body. In this chapter, applications of wireless biomedical sensors are presented, along with state-of-the-art communication and powering mechanisms of these devices. Furthermore, recent integration methods that allow the sensors to become smaller and more suitable for implantation are summarized. For individual sensors to become a body area network (BAN), they must form a network and work together. Issues that must be addressed when developing these networks are detailed and, finally, mobility methods for implanted sensors are presented

Wireless Power Transfer in Wearable Smart Contact Lenses [Open access]

In 2016, a smart contact lens was developed by Google company which aimed to directly implanting micro-smart lenses into the human eye to test blood sugar percentage by tears. However, small sizes implantable devices such as contact lens requires power transfer unit for continuously power supply. Thus, this project aims to design a power transfer unit with Inductively Coupled Power Transfer (ICPT) technology for smart contact lens which works under 2.45GHz to power an LED at load. The coil size is designed as 10mm inner diameter, 12mm outer diameter and 0.2mm wire width. Additionally, polydimethylsiloxane (PDMS) is used as the contact lens substrate. During the simulation, different eye models were built since the coil needs to be warped on top of lens and the eyeball, and under different conditions the S11 parameter is adjusted to around -10dB. The antenna is fabricated by technician in school, due to the technology restriction, the antenna was fabricated with unequal line width, which causes a resonate frequency shift to 900MHz with -8dB S11 value. To power an LED at load side, full-wave and half-wave rectifiers are built separately with different component values and send to fabrication. The antenna performance was tested under three conditions, in air, on human hand, and on water surface to imitate the liquid condition in human eye, but since the dielectric constant varies in each case, and for fabrication there is an extra circuit unit which effecting the copper coil numbers, the tested resonant frequency is not as desired values

Wireless Power Transfer in Wearable Smart Contact Lenses [Open access]

In 2016, a smart contact lens was developed by Google company which aimed to directly implanting micro-smart lenses into the human eye to test blood sugar percentage by tears. However, small sizes implantable devices such as contact lens requires power transfer unit for continuously power supply. Thus, this project aims to design a power transfer unit with Inductively Coupled Power Transfer (ICPT) technology for smart contact lens which works under 2.45GHz to power an LED at load. The coil size is designed as 10mm inner diameter, 12mm outer diameter and 0.2mm wire width. Additionally, polydimethylsiloxane (PDMS) is used as the contact lens substrate. During the simulation, different eye models were built since the coil needs to be warped on top of lens and the eyeball, and under different conditions the S11 parameter is adjusted to around -10dB. The antenna is fabricated by technician in school, due to the technology restriction, the antenna was fabricated with unequal line width, which causes a resonate frequency shift to 900MHz with -8dB S11 value. To power an LED at load side, full-wave and half-wave rectifiers are built separately with different component values and send to fabrication. The antenna performance was tested under three conditions, in air, on human hand, and on water surface to imitate the liquid condition in human eye, but since the dielectric constant varies in each case, and for fabrication there is an extra circuit unit which effecting the copper coil numbers, the tested resonant frequency is not as desired values

Electronic contact lens: a platform for wireless health monitoring applications

Electronic contact lenses can be used for non‐invasively monitoring vital human signs and medical parameters. However, maintaining a secure communications connection and a self‐sustainable power source are still looming challenges. This paper demonstrates a proof of concept electronic contact lens that includes a spiral antenna with its wireless circuit unit for data telemetry, a rectifier circuit for power conditioning and a micro light emitting diode (µLED) as a load. The spiral antenna with its rectifying circuit was designed considering operation in the Industrial, Scientific and Medical (ISM) band of 2.4 GHz. The spiral coil with an inner diameter of 10 mm, an outer diameter of 12 mm and a wire width of 0.2 mm was fabricated on a donut‐shaped flexible polyimide substarte. For biocompatibility purposes, Polyimide was used as the contact lens substrate and polydimethylsiloxane (PDMS) was used for encapsulation. A 3D‐printed eye model was developed for accurately shaping the curvature of the PDMS‐encapsulated contact lens. The reflection coefficient (S11) of the fabricated antenna was tested in different conditions and on an eye model to mimic the liquid condition of the human eye. In a wide range of conditions, a minimum of ‐20 dB reflection coefficient (S11) was obtained. The maximum antenna gain was ‐28 dBi and the contact lens satisfied the electromagnetic exposure safety limit of 1.6 W/kg for 1 g of tissue mass. We also determined the wavelength dependence of the electronic contact lens on different lens thicknesses. Our results showed that the lens is transmissive in the visible part of the spectrum

Wireless communication and power harvesting in wearable contact lens sensors

The human eye contains multiple biomarkers related to various diseases, making electronic contact lens an ideal non-invasive platform for their diagnosis and treatment. Recent advances in technology have enabled the monitoring and diagnosis of glaucoma from Intraocular Pressure (IOP) detection, diabetes from glucose concentration detections, and other biosensors for pH and temperature sensing. Different sensor designs have led to distinct power transfer techniques, among which inductively coupled power transfer is considered most favourable for electronic contact lenses power delivery applications. Therefore, loop antenna, spiral shape antenna, and antenna with nanomaterials such as graphene and hybrid silver nanofibers have been explored under Industrial, Scientific, and Medical (ISM) frequency bands for both Wireless Power Transfer (WPT) and data communication. Notably, spiral antennas are also considered as the component of IOP sensing using capacitive sensors to detect the changes in frequency caused by pressure. This article reviews the state-of-the-art technologies in electronic contact lens sensors and their power delivery techniques. Herein, diverse sensing methods, materials, and power transfer techniques and the promising future trends and challenges in electronic contact lenses have been presented

Inductively Coupled CMOS Power Receiver For Embedded Microsensors

Inductively coupled power transfer can extend the lifetime of embedded microsensors that save costs, energy, and lives. To expand the microsensors' functionality, the transferred power needs to be maximized. Plus, the power receiver needs to handle wide coupling variations in real applications. Therefore, the objective of this research is to design a power receiver that outputs the highest power for the widest coupling range. This research proposes a switched resonant half-bridge power stage that adjusts both energy transfer frequency and duration so the output power is maximally high. A maximum power point (MPP) theory is also developed to predict the optimal settings of the power stage with 98.6% accuracy. Finally, this research addresses the system integration challenges such as synchronization and over-voltage protection. The fabricated self-synchronized prototype outputs up to 89% of the available power across 0.067%~7.9% coupling range. The output power (in percentage of available power) and coupling range are 1.3× and 13× higher than the comparable state of the arts.Ph.D

Battery-less near field communications (nfc) sensors for internet of things (iot) applications

L’ implementació de la tecnologia de comunicació de camp proper (NFC) en els telèfons intel·ligents no para de créixer degut a l’ús d’aquesta per fer pagaments, això, junt amb el fet de poder aprofitar l’energia generada pel mòbil no només per la comunicació, sinó també per transmetre energia, el baix cost dels xips NFC, i el fet de que els telèfons tinguin connectivitat amb internet, possibilita i fa molt interesant el disseny d’etiquetes sense bateria incorporant-hi sensors i poder enviar la informació al núvol, dins del creixent escenari de l’internet de les coses (IoT). La present Tesi estudia la viabilitat d’aquests sensors, analitzant la màxima distància entre lector i sensor per proveir la potència necessària, presenta tècniques per augmentar el rang d’operació, i analitza els efectes de certs materials quan aquests estan propers a les antenes. Diversos sensors han estat dissenyats i analitzats i son presentats en aquest treball. Aquests son: Una etiqueta que mesura la humitat de la terra, la temperatura i la humitat relativa de l’aire per controlar les condicions de plantes. Un sensor per detectar la humitat en bolquers, imprès en material flexible que s’adapta a la forma del bolquer. Dues aplicacions, una per estimació de pH i una altre per avaluar el grau de maduració de fruites, basats en un sensor de color. I, per últim, s’estudia la viabilitat de sensors en implants per aplicacions mèdiques, analitzant l’efecte del cos i proposant un sistema per augmentar la profunditat a la que aquests es poden llegir utilitzant un telèfon mòbil. Tots aquests sensors poden ser alimentats i llegits per qualsevol dispositiu que disposin de connexió NFC.La implementación de la tecnología de comunicaciones de campo cercano (NFC) en los teléfonos inteligentes no para de crecer debido al uso de esta para llevar a cabo pagos, esto, junto con el hecho de poder aprovechar la energía generada por el móvil no sólo para la comunicación, sino también para transmitir energía, el bajo coste de los chips NFC, i el hecho que los teléfonos tengan conectividad a internet, posibilita y hace muy interesante el diseño de etiquetas sin batería que incorporen sensores i poder enviar la información a la nube, enmarcado en el creciente escenario del internet de las cosas (IoT). La presente Tesis estudia la viabilidad de estos sensores, analizando la máxima distancia entre lector i sensor para proveer la potencia necesaria, presenta técnicas para aumentar el rango de operación, y analiza los efectos de ciertos materiales cuando estos están cerca de las antenas. Varios sensores han sido diseñados y analizados y son presentados en este trabajo. Estos son: Una etiqueta que mide la humedad de la tierra, la temperatura y la humedad relativa del aire para controlar las condiciones de plantas. Un sensor para detectar la humedad en pañales, impreso en material flexible que se adapta a la forma del pañal. Dos aplicaciones, una para estimación de pH y otra para evaluar el grado de maduración de frutas, basados en un sensor de color. Y, por último, se estudia la viabilidad de sensores en implantes para aplicaciones médicas, analizando el efecto del cuerpo y proponiendo un sistema para aumentar la profundidad a la que estos se pueden leer usando un teléfono móvil. Todos estos sensores pueden ser alimentados y leídos por cualquier dispositivo que disponga de conexión NFC.The implementation of near field communication (NFC) technology into smartphones grows rapidly due the use of this technology as a payment system. This, altogether with the fact that the energy generated by the phone can be used not only to communicate but for power transfer as well, the low-cost of the NFC chips, and the fact that the smartphones have connectivity to internet, makes possible and very interesting the design of battery-less sensing tags which information can be sent to the cloud, within the growing internet of things (IoT) scenario. This Thesis studies the feasibility of these sensors, analysing the maximum distance between reader and sensor to provide the necessary power, presents techniques to increase the range of operation, and analyses the effects of certain materials when they are near to the antennas. Several sensors have been designed and analysed and are presented in this work. These are: a tag that measures the soil moisture, the temperature and the relative humidity of the air to control the conditions of plants. A moisture sensor for diapers, printed on flexible material that adapts to the diaper shape. Two applications, one for pH estimation and another for assessing the degree of fruit ripening, based on a colour sensor. And finally, the feasibility of sensors in implants for medical applications is studied, analysing the effect of the body and proposing a system to increase the depth at which they can be read using a mobile phone. All of these sensors can be powered and read by any NFC enabled device