This paper describes a powerful, yet simple, procedure how to acquire a current approaching the lower bound of quality factor $Q$ . This optimal current can be determined for an arbitrarily shaped electrically small radiator made of a perfect conductor. Quality factor $Q$ is evaluated by Vandenbosch’s relations yielding stored electromagnetic energy as a function of the source current density. All calculations are based on a matrix representation of the integro-differential operators. This approach simplifies the entire development and results in a straightforward numerical evaluation. The optimal current is represented in a basis of modal currents suitable for solving the optimization problem so that the minimum is approached by either one mode tuned to the resonance, or, by two properly combined modes. An overview of which modes should be selected and how they should be combined is provided and results concerning rectangular plate, spherical shell, capped dipole antenna, and fractal shapes of varying geometrical complexity are presented. The reduction of quality factor $Q$ and the $G / Q$ ratio are studied and, thanks to the modal decomposition, the physical interpretation of the results is discussed in conjunction with the limitations of the proposed procedure.

Optimal Composition of Modal Currents for Minimal Quality Factor $Q$

Human Body Communication (HBC) has emerged as an alternative to radio wave communication for connecting low power, miniaturized wearable and implantable devices in, on and around the human body which uses the human body as the communication channel. Previous studies characterizing the human body channel has reported widely varying channel response much of which has been attributed to the variation in measurement setup. This calls for the development of a unifying bio physical model of HBC supported by in depth analysis and an understanding of the effect of excitation, termination modality on HBC measurements. This paper characterizes the human body channel up to 1MHz frequency to evaluate it as a medium for broadband communication. A lumped bio physical model of HBC is developed, supported by experimental validations that provides insight into some of the key discrepancies found in previous studies. Voltage loss measurements are carried out both with an oscilloscope and a miniaturized wearable prototype to capture the effects of non common ground. Results show that the channel loss is strongly dependent on the termination impedance at the receiver end, with up to 4dB variation in average loss for different termination in an oscilloscope and an additional 9 dB channel loss with wearable prototype compared to an oscilloscope measurement. The measured channel response with capacitive termination reduces low frequency loss and allows flat band transfer function down to 13 KHz, establishing the human body as a broadband communication channel. Analysis of the measured results and the simulation model shows that (1) high impedance (2) capacitive termination should be used at the receiver end for accurate voltage mode loss measurements of the HBC channel at low frequencies.

BioPhysical Modeling, Characterization and Optimization of Electro-Quasistatic Human Body Communication

We present the first real-time technique to synthesize full-bandwidth sounds for 2D virtual wind instruments. A novel interactive wave solver is proposed that synthesizes audio at 128,000Hz on commodity graphics cards. Simulating the wave equation captures the resonant and radiative properties of the instrument body automatically. We show that a variety of existing non-linear excitation mechanisms such as reed or lips can be successfully coupled to the instrument's 2D wave field. Virtual musical performances can be created by mapping user inputs to control geometric features of the instrument body, such as tone holes, and modifying parameters of the excitation model, such as blowing pressure. Field visualizations are also produced. Our technique promotes experimentation by providing instant audio-visual feedback from interactive virtual designs. To allow artifact-free audio despite dynamic geometric modification, we present a novel time-varying Perfectly Matched Layer formulation that yields smooth, natural-sounding transitions between notes. We find that visco-thermal wall losses are crucial for musical sound in 2D simulations and propose a practical approximation. Weak non-linearity at high amplitudes is incorporated to improve the sound quality of brass instruments.

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Aerophones in flatland: interactive wave simulation of wind instruments

In this paper, we investigate the use of fat tissue as a communication channel between in-body, implanted devices at R-band frequencies (1.7–2.6 GHz). The proposed fat channel is based on an anatomical model of the human body. We propose a novel probe that is optimized to efficiently radiate the R-band frequencies into the fat tissue. We use our probe to evaluate the path loss of the fat channel by studying the channel transmission coefficient over the R-band frequencies. We conduct extensive simulation studies and validate our results by experimentation on phantom and ex-vivo porcine tissue, with good agreement between simulations and experiments. We demonstrate a performance comparison between the fat channel and similar waveguide structures. Our characterization of the fat channel reveals propagation path loss of ∼0.7 dB and ∼1.9 dB per cm for phantom and ex-vivo porcine tissue, respectively. These results demonstrate that fat tissue can be used as a communication channel for high data rate intra-body networks.

Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies

For loudspeaker horns, the throat acoustic impedance and the far field directional characteristics are important measures of performance. Both quantities depend greatly on the shape of the horn, and the acoustical conditions at the mouth of the horn. The Mode Matching Method (MMM) is a semianalytical method for the simulation of sound propagation in ducts, and is the method used as the fundamental building block in this work. In previous work using this method, the horn has usually been assumed to be mounted in an infinite baffle, a condition that is not realistic for most real-world applications. Most horns are usually mounted in finite baffles or cabinets, or placed close to reflecting surfaces or in rooms. This work has therefore focused on extending the MMM to new cases closer to real-world applications. For horns without baffle, or with finite baffles or flanges, two methods have been explored; one for axisymmetric horns based on the solution for a semi-infinite unflanged duct, and one for general geometries based on edge diffraction. For horns near infinite reflecting surfaces, a method has been derived to compute the modal mutual radiation impedance. For the final radiation condition, a horn mounted in the wall of a room, two methods have been explored, where in both cases analytical expressions for radiation impedance and radiated pressure are found for shoebox shaped rooms. Experimental verification of some of the cases mentioned above is provided. The MMM is restricted to certain cross-sectional geometries; round and rectangular geometries are treated in this work. In many practical cases a rectangular horn is connected to a circular loudspeaker, and in order to simulate this and similar configuration, a method has been developed to interface the MMM with the Boundary Element Method. By modifying the MMM, it has also been possible to simulate radiation from concave structures like loudspeaker diaphragms. Using this approach it is also possible to simulate concave reflectors, as long as the source is not outside of the cavity. A final application of the MMM in this work, is the use of the method to compute the transfer function and resonance frequencies of non-shoebox shaped rooms. While the shape of the room is still somewhat restricted compared to Finite Element Method simulations, a wide range of rooms can be simulated.

Extensions to the Mode Matching Method for Horn Loudspeaker Simulation

We present an approach to design from scratch planar microwave antennas for the purpose of ultra-wideband (UWB) near-field sensing. Up to about 120 000 design variables associated with square grids on planar substrates are subject to design, and a numerical optimization algorithm decides, after around 200 iterations, for each edge in the grid whether it should consist of metal or a dielectric. The antenna layouts produced with this approach show UWB impedance matching properties and near-field coupling coefficients that are flat over a much wider frequency range than a standard UWB antenna. The properties of the optimized antennas are successfully cross-verified with a commercial software and, for one of the designs, also validated experimentally. We demonstrate that an antenna optimized in this way shows a high sensitivity when used for near-field detection of a phantom with dielectric properties representative of muscle tissue.

Topology Optimization of Planar Antennas for Wideband Near-Field Coupling

Acoustic boundary layers as boundary conditions

The human body can act as a medium for the transmission of electromagnetic waves in the wireless body sensor networks context. However, there are transmission losses in biological tissues due to the presence of water and salts. This Letter focuses on lateral intra-body microwave communication through different biological tissue layers and demonstrates the effect of the tissue thicknesses by comparing signal coupling in the channel. For this work, the authors utilise the R-band frequencies since it overlaps the industrial, scientific and medical radio (ISM) band. The channel model in human tissues is proposed based on electromagnetic simulations, validated using equivalent phantom and ex-vivo measurements. The phantom and ex-vivo measurements are compared with simulation modelling. The results show that electromagnetic communication is feasible in the adipose tissue layer with a low attenuation of ∼2 dB per 20 mm for phantom measurements and 4 dB per 20 mm for ex-vivo measurements at 2 GHz. Since the dielectric losses of human adipose tissues are almost half of ex-vivo tissue, an attenuation of around 3 dB per 20 mm is expected. The results show that human adipose tissue can be used as an intra-body communication channel.

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Intra-body microwave communication through adipose tissue

This paper explores high data rate microwave communication through fat tissue in order to address the wide bandwidth requirements of intrabody area networks. We have designed and carried out experiments on an IEEE 802.15.4-based WBAN prototype by measuring the performance of the fat tissue channel in terms of data packet reception with respect to tissue length and power transmission. This paper proposes and demonstrates a high data rate communication channel through fat tissue using phantom and ex-vivo environments. Here, we achieve a data packet reception of approximately 96% in both environments. The results also show that the received signal strength drops by ∼1 dBm per 10 mm in phantom and ∼2 dBm per 10 mm in ex-vivo . The phantom and ex-vivo experimentations validated our approach for high data rate communication through fat tissue for intrabody network applications. The proposed method opens up new opportunities for further research in fat channel communication. This study will contribute to the successful development of high bandwidth wireless intrabody networks that support high data rate implanted, ingested, injected, or worn devices.

/pdf/data-packet-transmission-through-fat-tissue-for-wireless-2z1ry2ro6s.pdf

Daniel Noreland

Papers

Topology Optimization of Planar Antennas for Wideband Near-Field Coupling

Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies

Acoustic boundary layers as boundary conditions

Intra-body microwave communication through adipose tissue

Data Packet Transmission Through Fat Tissue for Wireless IntraBody Networks