We propose a photonic crystal nanocavity design with self-similar electromagnetic boundary conditions, achieving ultrasmall mode volume (V_{eff}). The electric energy density of a cavity mode can be maximized in the air or dielectric region, depending on the choice of boundary conditions. We illustrate the design concept with a silicon-air one-dimensional photon crystal cavity that reaches an ultrasmall mode volume of V_{eff}∼7.01×10^{-5}λ^{3} at λ∼1550  nm. We show that the extreme light concentration in our design can enable ultrastrong Kerr nonlinearities, even at the single-photon level. These features open new directions in cavity quantum electrodynamics, spectroscopy, and quantum nonlinear optics.

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Self-Similar Nanocavity Design with Ultrasmall Mode Volume for Single-Photon Nonlinearities.

Electrical impedance tomography (EIT) uses electrical stimulation and measurement at the body surface to image the electrical properties of internal tissues. It has the advantage of noninvasiveness and high temporal resolution but suffers from poor spatial resolution and sensitivity to electrode movement and contact quality. EIT can be useful to applications, where there are conductive contrasts between tissues, fluids, or gasses, such as imaging of cancerous or ischemic tissue or functional monitoring of breathing, blood flow, gastric motility, and neural activity. The past decade has seen clinical application and commercial activity using EIT for ventilation monitoring. Interpretation of EIT-based measures is complex, and this review paper focuses on describing the image interpretation “pathway.” We review this pathway, from Tissue Electrical Properties , EIT Electrodes & Hardware , Sensitivity , Image Reconstruction , Image Processing to EIT Measures . The relationship is discussed between the clinically relevant parameters and the reconstructed properties. An overview is given of areas of EIT application and of our perspectives for research and development.

Electrical Impedance Tomography: Tissue Properties to Image Measures

Recently, omnidirectional wireless power transfer systems have been studied intensely due to their improved flexibility when compared with their planar counterparts. In this paper, a novel wireless charging bowl with multiple transmitter coils is proposed to power portable devices. The bowl-shaped transmitter coil is optimized to provide sufficiently strong and nearly uniform omnidirectional field distribution. Inside the bowl, a planar receiver coil can be charged with free-positioning and arbitrary orientation. This unique benefit is particularly attractive for low-power portable devices. In the experiment, the proposed transmitter coils are built and operated at 6.78 MHz. The magnetic field is measured to verify the uniform and omnidirectional magnetic field distribution. The coil to coil efficiency is 85% to 95%. A complete system including the inverter and rectifier stage is implemented. When charging a 5W smart phone receiver, the overall efficiency varies within a range from 68–80% for any possible position.

Transmitter Coils Design for Free-Positioning Omnidirectional Wireless Power Transfer System

In recent years, the increasing number of wearable devices on human has been witnessed as a trend. These devices can serve for many purposes: personal entertainment, communication, emergency mission, health care supervision, delivery, etc. Sharing information among the devices scattered across the human body requires a body area network (BAN) and body sensor network (BSN). However, implementation of the BAN/BSN with the conventional wireless technologies cannot give optimal result. It is mainly because the high requirements of light weight, miniature, energy efficiency, security, and less electromagnetic interference greatly limit the resources available for the communication modules. The newly developed intra-body communication (IBC) can alleviate most of the mentioned problems. This technique, which employs the human body as a communication channel, could be an innovative networking method for sensors and devices on the human body. In order to encourage the research and development of the IBC, the authors are favorable to lay a better and more formal theoretical foundation on IBC. They propose a multilayer mathematical model using volume conductor theory for galvanic coupling IBC on a human limb with consideration on the inhomogeneous properties of human tissue. By introducing and checking with quasi-static approximation criteria, Maxwell's equations are decoupled and capacitance effect is included to the governing equation for further improvement. Finally, the accuracy and potential of the model are examined from both in vitro and in vivo experimental results.

Quasi-Static Modeling of Human Limb for Intra-Body Communications With Experiments

Metaphotonics : An emerging field with opportunities and challenges

Quasistatic models provide intermediate levels of electromagnetic theory in between statics and the full set of Maxwell’s equations. Quasistatics is easier than general electrodynamics and in some ways more similar to statics, but exhibits more interesting physics and more important applications than statics. Quasistatics is frequently used in electromagnetic modeling, and the pedagogical potential of electromagnetic simulations gives additional support for the importance of quasistatics. Quasistatics is introduced in a way that fits into the standard textbook presentations of electrodynamics.

https://www.if.ufrj.br/~dore/Fis3/Electromagnetics_from_a_quasistatic_perspective.pdf

Jonas Larsson

Papers

Electromagnetics from a quasistatic perspective