Steven A. Hackworth

A Wearable Electronic System for Objective Dietary Assessment

Dietary reporting by individuals is subject to error (1–3). Therefore, a research program has been initiated to develop a small electronic device to record food intake automatically. This device, which contains a miniature camera, a microphone, and several other sensors, can be worn on a lanyard around the neck. It collects visual data immediately in front of the participant and stores them on a memory card in the device. The data are transferred regularly to the dietitian’s computer for further processing and analysis. The device is designed to be almost completely passive to the participant, and thus hopefully will not intrude on or alter the participant’s eating activities. In addition to this function, in the future the device will have other functions, such as the measurement of physical activity, human behavior, and environmental exposure (e.g., pollutants).

Relay Effect of Wireless Power Transfer Using Strongly Coupled Magnetic Resonances

Wireless power transfer using strongly coupled electromagnetic resonators is a recently explored technology. Although this technology is able to transmit electrical energy over a much longer distance than traditional near field methods, in some applications, its effective distance is still insufficient. In this paper, we investigate a relay effect to extend the energy transfer distance. Theoretical analysis is performed based on a set of coupled-mode equations. Experiments are conducted to confirm the theoretical results and demonstrate the effectiveness of the relay approach. Our results show that the efficiency of power transfer can be improved significantly using one or more relay resonators. This approach significantly improves the performance of the present two-resonator system and allows a curved path in space to be defined for wireless power transfer using smaller resonators.

In vitro and in vivo studies on wireless powering of medical sensors and implantable devices

This paper investigates wireless electricity (witricity) and its application to medical sensors and implantable devices. Several coupling scenarios of resonators are analyzed theoretically. In vitro experiments are conducted in open air and through an agar phantom of the human head. An in vivo animal experiment is also carried out. Our studies indicate that witricity is a suitable tool for providing wireless power to a variety of medical sensors and implanted devices.

Wireless energy transfer platform for medical sensors and implantable devices

Witricity is a newly developed technique for wireless energy transfer. This paper presents a frequency adjustable witricity system to power medical sensors and implantable devices. New witricity resonators are designed for both energy transmission and reception. A prototype platform is described, including an RF power source, two resonators with new structures, and inductively coupled input and output stages. In vitro experiments, both in open air and using a human head phantom consisting of simulated tissues, are employed to verify the feasibility of this platform. An animal model is utilized to evaluate in vivo energy transfer within the body of a laboratory pig. Our experiments indicate that witricity is an effective new tool for providing a variety of medical sensors and devices with power.

The relay effect on wireless power transfer using witricity

Witricity is a recent technology for wireless power transfer over a limited distance. In this paper, we investigate a relay effect to extend the distance. The concept of magnetic resonance in strongly coupled regime with more than two resonators is presented. Theoretical analysis is performed based on a set of differential equations and experiments are conducted to demonstrate its effectiveness. Our results show that the efficiency of power transfer can be improved significantly using one or more relay resonators. This approach enhances the performance of the present two-resonator witricity systems and allows transmitting power over a longer range, following a curved path, and using smaller resonators.

Wireless power transfer system design for implanted and worn devices

Witricity, a highly efficient wireless power transfer method using mid-range resonant coupling, was reported in recent literature. Based on this method, we present a wireless power transfer scheme using thin film resonant cells for medical applications. The thin film cells, consisting of a tape coil in the exterior layer and conductive strips in the interior layer separated by an insulation layer, are made light and flexible to provide comfort for users during wear. The wireless power transfer scheme presented displays great potential for delivering energy to implantable and worn devices, with range much larger than the current technology for powering implantable devices.

Modeling and simulation of a thin film power transfer cell for medical devices and implants

Recently, a highly efficient method to transmit power wirelessly using mid-range resonant coupling was reported. Based on this method, we present a multilayer thin film design of power transfer cells for medical applications. Consisting of a tape coil in the exterior layer and strips in the interior layer separated by an insulation layer, these cells have an equivalent structure of multiple inductors and capacitors, forming several resonant frequencies. In order to verify these frequencies, a mesh current analysis is performed computationally. Our experiments show that this analysis is accurate. The results of this study are useful for the design of high-performance thin film cells for wireless power transfer.

Transcutaneous battery recharging by volume conduction and its circuit modeling.

Many implantable devices require large capacity batteries implanted in the body. Transcutaneous battery recharging can effectively maintain the longevity of these implants. Based on this consideration we have developed a transcutaneous battery recharging circuit unit which takes advantages of skin volume conduction. This unit is able to pass 2.8 mA from the outside to the inside of pig skin with a current transmitting efficiency of 27%. Theoretical analysis and experiments have validated that this battery recharging technology is an effective approach. In this research we have constructed an x-type equivalent circuit model of skin volume conduction for battery recharging. The parameters of the x-type equivalent circuit can be easily measured and used to evaluate the battery charging system characteristics, such as the rechargeable prerequisite and the current transmitting efficiency limitation. We have analyzed the transcutaneous current transmitting efficiency by applying the x-type equivalent circuit model and discussed approaches for enhancing current transmitting efficiency

How to Pass Information and Deliver Energy to a Network of Implantable Devices within the Human Body

It has been envisioned that a body network can be built to collect data from, and transport information to, implanted miniature devices at multiple sites within the human body. Currently, two problems of utmost importance remain unsolved: 1) how to link information between a pair of implants at a distance? and 2) how to provide electric power to these implants allowing them to function and communicate? In this paper, we present new solutions to these problems by minimizing the intra-body communication distances. We show that, based on a study of human anatomy, the maximum distance from the body surface to the deepest point inside the body is approximately 15 cm. This finding provides an upper bound for the lengths of communication pathways required to reach the bodys interior. We also show that these pathways do not have to cross any joins within the body. In order to implement the envisioned body network, we present the design of a new device, called an energy pad. This small-size, lightweight device can easily interface with the skin to perform data communication with, and supply power to, miniature implants.

Wireless energy delivery and data communication for biomedical sensors and implantable devices

In this paper, we present a wireless power transfer and communication method for biomedical sensors and implants by taking advantage of recently developed witricity technology. New witricity resonator and system designs are described and evaluated by performing both in vitro and in vivo experiments. When compared to the current designs, these new witricity designs demonstrate much improved performances for wireless energy delivery to and data communication with biomedical sensors and implantable devices from outside the human body, providing a higher efficiency and a longer transmission distance.