Far-field RF energy transfer and harvesting

This chapter deals with radio frequency (RF) energy transfer over a distance. After explaining the differences between nonradiative and radiative RF energy transfer, the chapter gives definitions for transfer and harvesting. Nonradiative RF energy transfer is mostly employed in inductive systems, obeying the Qi standard. The chapter also identifies the subcomponents of an RF energy transfer system, and discusses the receiving rectifying antenna, commonly known as rectenna. Before discussing the rectenna results, the chapter discusses the complex conjugately matched antenna. After that, the transmission and propagation of RF signals is treated, followed by demonstration of some examples of far-field wireless RF energy transfer. It concludes that far-field RF energy transfer is feasible, but requires a careful co-design of the several subsystems that make up the whole far-field RF energy transfer system

Innovative micropower solutions for wireless autonomous sensor nodes

Low-power is one of the key demands for wireless autonomous sensor nodes. This demand has motivated industry and research institutes to work on various advanced systems that can efficiently deliver power to demanding applications. This paper deals with energy harvesters and energy storage systems as important building blocks for such sensor nodes. Energy harvesting is the process of converting unused ambient energy into usable electrical power. As these energy harvesting devices shrink in dimension, while still providing sufficient energy, they will be key enablers for autonomous wireless transducer systems. For such purposes, harvesting devices designed for a footprint of 1 cm(exp 2) and an average power harvesting level of 100 microwatt are being investigated. The power module will convert the highly irregular energy flow from the energy harvester further into regulated energy suitable to charge an energy storage device, e.g. battery or ultracapacitor, or to directly power the wireless autonomous sensor network modules. In such a module, the battery¿s basic task is to store energy obtained from the harvester and to release it to the load when needed. A complete wireless autonomous node has more functional blocks besides a micropower module. A sensor device will capture the required physical or chemical parameter. The Analog-to- Digital and signal processor will be used for transforming the measurements into (processed) digital information. A radio module will allow communication with external receivers. The focus in this paper will be on the micropower module, consisting of the harvester and the energy storage functions

Personalizing energy expenditure estimation using physiological signals normalization during activities of daily living

In this paper we propose a generic approach to reduce inter-individual variability of different physiological signals (HR, GSR and respiration) by automatically estimating normalization parameters (e.g. baseline and range). The proposed normalization procedure does not require a dedicated personal calibration during system setup. On the other hand, normalization parameters are estimated at system runtime from sedentary and low intensity activities of daily living (ADLs), such as lying and walking. When combined with activity-specific energy expenditure (EE) models, our normalization procedure improved EE estimation by 15 to 33% in a study group of 18 participants, compared to state of the art activity-specific EE models combining accelerometer and non-normalized physiological signals

Ultra low power wireless and energy harvesting technologies - An ideal combination

\u3cp\u3eRapid developments of energy harvesting in the past decade have significantly increased the efficiency of devices in converting ambient free energy into usable electrical energy, thus offering opportunities to design energy autonomous systems nowadays. To achieve such energy autonomous systems, a good understanding of the harvesting capability from the source side strongly motivates the design of ultra low power (ULP) systems. In this paper, we focus on wireless body area networks (WBAN) applications and show that ULP wireless is the key technology to enable wireless autonomous transducer solutions (WATS). We first show that the current energy harvesters cannot provide sufficient power for a typical wireless sensor node based on off the-shelf components. We then point out that the wireless module is the main component whose power consumption needs to be significantly reduced. To address this problem, we present a ULP wireless module that could satisfy the typical performance requirement of WBAN. Using this ULP wireless module, we demonstrate the feasibility of energy autonomous sensor nodes (i.e. WATS) with the current energy harvesting technology. Moreover, with this ULP module, we point out some new research trends on the miniaturization and cost reduction of energy harvesters. Therefore, we conclude that ultra low power wireless system is an ideal application for energy harvesting.\u3c/p\u3

Nanowire bonding with the scanning tunneling microscope

We have developed a reliable lithographic method to pattern thin gold films by locally exposing a thin layer of an electron beam resist with the tip of a scanning tunneling microscope (STM). The exposure of the resist layer is induced by applying a voltage difference of ca. -10V between the STM tip and the gold film on top of which the resist layer has been deposited with the Langmuir-Blodgett technique. Our resist material is omega-tricosenoic acid which acts as a negative resist. After development, the unexposed areas of the gold film can be removed via argon ion milling. We have been able to obtain continuous gold lines having a width down to 15 nm, the linewidth being determined by the exposure dose. When reducing the tunneling voltage <5 V, exposure of the Langmuir-Blodgett resist layer no longer occurs and one switches to the classical topographic imaging mode. This switching provides us with the unique possibility to attach electrical contacts to existing nanostructures. As a nice example of this nanowire bonding, gold contacts have been attached to individual multiwalled carbon nanotubes. We have made detailed measurements of the nanotube resistance as a function of temperature down to 10 mK and in magnetic fields up to 14 T. Al low temperatures a pronounced negative magnetoresistance is observed which is consistent with the two-dimensional weak electron localization occurring in the cylindrical graphite layers forming the nanotubes. The nanotubes also show reproducible fluctuations of the magnetoresistance which can be related to the Aharonov-Bohm effect in the nanotubes. (C) 1997 Elsevier Science B.V