Spatial In-Body Channel Characterization Using an Accurate UWB Phantom

"(c) 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works."Ultra-wideband (UWB) systems have emerged as a possible solution for future wireless in-body communications. However, in-body channel characterization is complex. Animal experimentation is usually restricted. Furthermore, software simulations can be expensive and imply a high computational cost. Synthetic chemical solutions, known as phantoms, can be used to solve this issue. However, achieving a reliable UWB phantom can be challenging since UWB systems use a large bandwidth and the relative permittivity of human tissues are frequency dependent. In this paper, a measurement campaign within 3.1-8.5 GHz using a new UWB phantom is performed. Currently, this phantom achieves the best known approximation to the permittivity of human muscle in the whole UWB band. Measurements were performed in different spatial positions, in order to also investigate the diversity of the in-body channel in the spatial domain. Two experimental in-body to in-body (IB2IB) and in-body to on-body (IB2OB) scenarios are considered. From the measurements, new path loss models are obtained. Besides, the correlation in transmission and reception is computed for both scenarios. Our results show a highly uncorrelated channel in transmission for the IB2IB scenario at all locations. Nevertheless, for the IB2OB scenario, the correlation varies depending on the position of the receiver and transmitter.This work was supported by the Ministerio de Economia y Competitividad, Spain, under Grant TEC2014-60258-C2-1-R and Grant TEC2014-56469-REDT and by the European FEDER Funds.Andreu Estellés, C.; Castelló Palacios, S.; García Pardo, C.; Fornés Leal, A.; Vallés Lluch, A.; Cardona Marcet, N. (2016). Spatial In-Body Channel Characterization Using an Accurate UWB Phantom. IEEE Transactions on Microwave Theory and Techniques. 64(11):3995-4002. doi:10.1109/TMTT.2016.2609409S39954002641

UWB Path Loss Models for Ingestible Devices

[EN] Currently, some medical devices such as the Wireless Capsule Endoscopy (WCE) are used for data transmission from inside to outside the body. Nevertheless, for certain applications such as WCE, the data rates offered by current medical frequency bands can result insufficient. Ultra Wideband (UWB) frequency band has become an interesting solution for this. However, to date, there is not a formal channel path loss model for the UWB frequency band in the gastrointestinal (GI) scenario due to the huge differences between the proposed studies. There are three main methodologies to characterize the propagation channel, software simulations and experimental measurements either in phantom or in in vivo animals. Previous works do not compare all the methodologies or present some disagreements with the literature. In this paper, a dedicated study of the path loss using the three methodologies aforementioned (simulations, phantoms and in vivo measurements) and a comparison with previous researches in the literature is performed. Moreover, numerical values for a path loss model which agrees with the three methodologies and the literature are proposed. This paper aims at being the starting point for a formal path loss model in the UWB frequency band for WBANs in the GI scenarioThis work was supported in part by the European Union's H2020-MSCA-ITN Program for the "Wireless In-body Environment Communication" Project under Grant 675353, in part by the Programa de Ayudas de Investigacion y Desarrollo (PAID-01-16) from Universitat Politecnica de Valencia, and in part by the Ministerio de Economia y Competitividad, Spain under Grant TEC2014-60258-C2-1-R through the European FEDER Funds.Pérez-Simbor, S.; Andreu-Estellés, C.; Garcia-Pardo, C.; Frasson, M.; Cardona Marcet, N. (2019). UWB Path Loss Models for Ingestible Devices. IEEE Transactions on Antennas and Propagation. 67(8):5025-5034. https://doi.org/10.1109/TAP.2019.2891717S5025503467

Ultrawideband Technology for Medical In-Body Sensor Networks: An Overview of the Human Body as a Propagation Medium, Phantoms, and Approaches for Propagation Analysis

[EN] An in-body sensor network is that in which at least one of the sensors is located inside the human body. Such wireless in-body sensors are used mainly in medical applications, collecting and monitoring important parameters for health and disease treatment. IEEE Standard 802.15.6-2012 for wireless body area networks (WBANs) considers in-body communications in the Medical Implant Communications Service (MICS) band. Nevertheless, high-data-rate communications are not feasible at the MICS band because of its narrow occupied bandwidth. In this framework, ultrawideband (UWB) systems have emerged as a potential solution for in-body highdata-rate communications because of their miniaturization capabilities and low power consumption.This work was supported by the Programa de Ayudas de Investigación y Desarrollo (PAID-01-16) at the Universitat Politècnica de València, Spain; by the Ministerio de Economía y Competitividad, Spain (TEC2014-60258-C2-1-R); and by the European FEDER funds. It was also funded by the European Union’s H2020:MSCA:ITN program for the Wireless In-Body Environ-ment Communication–WiBEC project under grant 675353.Garcia-Pardo, C.; Andreu-Estellés, C.; Fornés Leal, A.; Castelló-Palacios, S.; Pérez-Simbor, S.; Barbi, M.; Vallés Lluch, A.... (2018). Ultrawideband Technology for Medical In-Body Sensor Networks: An Overview of the Human Body as a Propagation Medium, Phantoms, and Approaches for Propagation Analysis. IEEE Antennas and Propagation Magazine. 60(3):19-33. https://doi.org/10.1109/MAP.2018.2818458S193360

Experimental Assessment of Time Reversal for In-Body to In-Body UWB Communications

[EN] The standard of in-body communications is limited to the use of narrowband systems. These systems are far from the high data rate connections achieved by other wireless telecommunication services today in force. The UWB frequency band has been proposed as a possible candidate for future in-body networks. However, the attenuation of body tissues at gigahertz frequencies could be a serious drawback. Experimental measurements for channel modeling are not easy to carry out, while the use of humans is practically forbidden. Sophisticated simulation tools could provide inaccurate results since they are not able to reproduce all the in-body channel conditions. Chemical solutions known as phantoms could provide a fair approximation of body tissues¿ behavior. In this work, the Time Reversal technique is assessed to increase the channel performance of in-body communications. For this task, a large volume of experimental measurements is performed at the low part of UWB spectrum (3.1-5.1 GHz) by using a highly accurate phantom-based measurement setup. This experimental setup emulates an in-body to in-body scenario, where all the nodes are implanted inside the body. Moreover, the in-body channel characteristics such as the path loss, the correlation in transmission and reception, and the reciprocity of the channel are assessed and discussed.This work was supported by the Programa de Ayudas de Investigacion y Desarrollo (PAID-01-16) from Universitat Politecnica de Valencia and by the Ministerio de Economia y Competitividad, Spain (TEC2014-60258-C2-1-R), by the European FEDER funds.Andreu-Estellés, C.; Garcia-Pardo, C.; Castelló-Palacios, S.; Cardona Marcet, N. (2018). Experimental Assessment of Time Reversal for In-Body to In-Body UWB Communications. Wireless Communications and Mobile Computing (Online). 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Diseño de antenas UWB directivas y tamaño compacto para aplicaciones médicas operando en el entorno corporal

[ES] El objetivo de este TFM es diseñar antenas directivas y de tamaño compacto que faciliten la penetración de las ondas electromagnética en el interior del cuerpo humano para aplicaciones médicas. Se explorará la posibilidad de emplear pequeñas hélices diseñadas operando a frecuencias por encima de 3 GHz. Las hélices presentan buena directividad y buen ancho de banda, por lo que son candidatas perfectas para este tipo de aplicaciones. Con el objetivo de facilitar la penetración en el cuerpo de las ondas emitidas por la antena, la antena se sumergirá en un fluido, o se empleará algún gel de transición de alta permitividad que minimice las reflexiones que se producen en la piel. Se realizarán simulaciones de la antena y del escenario corporal empleando el software de simulación electromagnética CST, y se realizará un estudio de diferentes geles y fluidos de transición que colocados entre la antena y la piel permitan aumentar la profundidad de penetración de la ondas.[EN] The objective of this project is to design directive and compact size antennas that facilitate the penetration of electromagnetic waves inside the human body for medical applications. The possibility of using small helixes operating at frequencies above 3 GHz will be explored. The helixes have good directivity and good bandwidth, so they are perfect candidates for this type of applications. In order to facilitate the penetration into the body of the waves emitted by the antenna, the antenna will be submerged in a fluid, or a high-permittivity transitional gel will be used to minimize the reflections that occur in the skin. Simulations of the antenna and the body scenario will be performed using the CST electromagnetic simulation software, and a study will be made with different gels and transition fluids placed between the antenna and the skin, to increase the penetration depth of the waves.Palomar Cosín, N. (2019). Diseño de antenas UWB directivas y tamaño compacto para aplicaciones médicas operando en el entorno corporal. http://hdl.handle.net/10251/124628TFG

Análisis experimental de la propagación en redes de área corporal para la banda de Ultra Wideband

[SPA] La posibilidad de monitorizar la actividad del cuerpo humano, ya sea desde la perspectiva médica, del deporte o del entretenimiento, utilizando dispositivos de diversa índole desplegados en el interior o sobre el cuerpo es en la actualidad un tema que está despertando un enorme interés tanto en el ámbito científico como social. Desde implantes inteligentes a elementos capaces de registrar nuestras constantes vitales o cuantificar nuestra actividad física, multitud de dispositivos son susceptibles de organizarse formando una red de elementos interconectados de manera inalámbrica con el objetivo de transmitir la información que sus respectivos sensores han recogido. A esta estructura de red centrada en el cuerpo se le denomina de manera genérica red de área corporal inalámbrica (WBAN, Wireless Body Area Network). La interacción con el cuerpo hace que la propagación de señales entre dispositivos de una WBAN presente características diferenciadoras respecto a las encontradas en otros canales radio tradicionales. Además, debido a que los tejidos biológicos presentan características dieléctricas (permitividad relativa y conductividad) dependientes de la frecuencia, el diseño de sistemas que operen de manera eficiente en este entorno requiere el desarrollo de modelos que describan, según la frecuencia de operación, los fenómenos que afectan a la propagación en los distintos canales radio entre dispositivos ubicados en el interior, la superficie o en la proximidad del cuerpo. Entre las diferentes bandas de frecuencias propuestas para redes WBAN, la banda de Ultra Wideband (UWB) de 3.1 GHz a 10.6 GHz ha captado un gran interés en los últimos años debido a que, características tales como el alto ancho de banda, baja potencia de emisión, alto nivel de seguridad, reducidas dimensiones de los dispositivos y alta resolución temporal, la hacen especialmente adecuada en su aplicación a este tipo de redes. Con el objetivo de caracterizar la propagación entre dispositivos de una WBAN operando a frecuencias dentro de la banda de UWB, la presente tesis recoge los resultados de los estudios realizados, destinados por un lado a la caracterización del canal de propagación off-body entre un dispositivo colocado sobre la superficie del cuerpo y un punto de acceso externo considerando el canal estacionario en el tiempo (o estático) y condiciones de visión directa, y por otro lado la caracterización de los efectos sobre el canal radio derivados del movimiento relativo entre dos dispositivos en una WBAN debido a la respiración, considerando al menos uno de ellos ubicado en el interior del cuerpo. En el primer caso el canal off-body estático se ha modelado a partir de las medidas sobre sujetos reales considerando diferentes posiciones de colocación de una antena receptora sobre el cuerpo y dos posturas: de pie y tumbado. En el segundo caso, el canal de propagación in-body se ha modelado empleando un phantom líquido para emular las condiciones de propagación en el interior del cuerpo en la banda de UWB y se han analizado los escenarios de propagación correspondientes a considerar un dispositivo en el interior del cuerpo y otro ubicado sobre la superficie del mismo (canal in-body a on-body), fuera de este a una cierta distancia (canal inbody a off-body) y, también en el interior conjuntamente con el primer dispositivo (canal inbody a in-body). [ENG] Monitoring the body activity from the health, sport or entertainment point of view, by means of smart devices deployed in, on or around the human body is one of the most appealing topics from the last years in the scientific research and social areas. From smart implants to electronic devices designed to register our vital signs or to quantify our every day activity, a plethora of devices with sensing capabilities can be able to arrange into an interconnected wireless network topology in order to transmit the collected data. This kind of network where the human (or even animal) body is the main interaction element is called wireless body area network (WBAN). The electromagnetic interaction among the devices and the body makes the signal propagation phenomenon in a WBAN exhibits unique characteristics compared to the ones shown in traditional radio channels. Due to the frequency dependence of the dielectrical properties (relative permittivity and conductivity) of biological tissues, there is a need of new models describing the propagation among network nodes placed inside the human body, on the surface or in an external (around the body) position at several frequencies. From the group of proposed frequency bands to establish wireless connections among nodes in a WBAN, the Ultra Wideband (UWB) band from 3.1 GHz to 10.6 GHz is getting great attention during the last years because special characteristics like the high available bandwidth, low transmission power, high security level, low profile devices and high temporal and spatial resolution, just to name a few, make this band particularly appropriate to this kind of networks. With the aim of fulfilling the lack of models describing the UWB radio channel in WBAN, this thesis presents the results of the experimental channel characterization research activity performed on the one hand, from the time invariant (or static) off-body channel point of view between a node placed on the body surface and an external access point considering line of sight conditions, and from the other hand, from the dynamic point of view considering the effects of the relative movement between two WBAN nodes due to breathing on the radio channel, considering at least one of them placed inside the human body. The off-body radio channel has been modeled from the measurements performed on real subjects considering different attachment positions of a receiver antenna on the body and two body postures: standing and lying down. The dynamic channel has been modeled using a liquid phantom to emulate the propagation inside the body at UWB frequencies and the propagation channel has been studied considering one device inside the body and another placed on the body surface (in-body to on-body channel), off the body at some separation distances (in-body to off-body channel) and both devices inside the body (in-body to in-body channel).Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Tecnologías de la Información y las Comunicacione