Advancementsin the integrated circuit technology, resulting in miniaturization of theelectronics and use of the ultra-low power wireless technology, have enabled manycompact wireless devices or sensors which are wearable or implantable.
Smartwatches, hearing aids, body temperature sensors, and more recently announcedGoogle Glass are such compact ultra-low power wearable devices. Pacemakers,retinal prosthesis, and cochlear implants are examples of the implantabledevices. As these examples suggest, the users of these devices are bothpatients as well as healthy people. These devices have made the life ofpatients comfortable by increasing their mobility. Moreover, as the worldpopulation is aging as presented in the UN report, there is a growing need forconstant monitoring of the health of elderly people. Hence, these devices andsensors are increasingly being used for such purpose. Additionally, sportsmenand athletes monitor their vital health parameters like blood pressure,temperature etc.
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using wearable devices. Two or more such devices close to thebody or implanted may communicate with each other, or with a central controlunit, forming together a network called a wireless body area network (WBAN).Some other terms which are commonly used for the WBAN are body sensor network(BSN) or body-centric wireless communication.
The focus of the research fielddiscussed in the thesis is antennas, wave propagation and localization for thedevices in various applications of the WBAN. In many applications of bodycentric communication such as in a pacemaker, the battery should last thedevice life time, making the ultra-low power consumption a necessity. As thesedevices are either close to the human body or implanted inside the body, theoverall size of the device including the size of the antenna should be small.Moreover, the power of the electromagnetic (EM) waves radiated by these devicesshould be within a safe level. Further, the communication between these devicestakes place through the body or over the body and hence the propagation channelneeds to be investigated and the signal loss has to be estimated. The lossy andheterogeneous tissues of the human body also makes the localization of animplanted RF-source a challenging task.
Localization of an implanted RF-sourceis needed in applications like wireless capsule endoscopy. Therefore, antennas,wave propagation, and localization plays a critical role for the devices in theWBANs. 1.2 Wireless Body Area NetworksAWireless Body Area Network (WBAN) consists of several wireless nodes or sensorslocated on the body and/or implanted which may communicate with each otherand/or with an external base-station. The WBAN evolved from the WirelessPersonal Area Network (WPAN) with the need for the communication between thedevices located on the body or within its immediate proximity.
Though thetypical communication range of the devices in the WBAN is within a meter, an internetor a cellular network connection can be used as a gateway to connect variousnetworks with the WBAN . For example, sensors for recording vital signs of aheart patient can alert the hospital or a doctor through internet or a cellularnetwork by measuring the changes in the vital sign about a possible heartattack. Fig. 1.1 shows some of the typical devices/sensors in a WBAN system. Asmentioned earlier, the WBAN technology can be used for both medical as well asnon-medical applications. Some of the non-medical applications of the WBANinclude video sharing, data file transfer, sports, monitoring and tracking, andentertainment applications as in gaming and social networking.1.
2.1 Scenarios WBAN applications can be divided intodifferent scenarios depending on the communication needs and requirements.These can be classified as: (1) on-body to off-body (2) on-body to on-body (3)in-body to on-body and/or off-body (4) body to body.
Each of these scenariosuses a different channel and have a different set of requirements for theantenna, the transmitted power and other communication parameters of the device.For example, for the on-body to on-body case, the devices communicating witheach other are located on the body and hence uses an on-body channel which havehigher attenuation than on-body to off-body scenarios where the propagationchannel is mainly in free space. These scenarios are described in the followingsections. Figure 1.
1:Typical devices in Wireless Body Area Network. A rectangle represent anon-body/wearable device and a circle represent an implantable device. On-Body to Off-Body Thesescenarios consist of the wearable sensors communicating to external devices andvice-versa as shown in Fig. 1.2. These are similar to a cellular phone networkwhere the mobile stations located in the immediate proximity of the humanscommunicate with the base station. A typical WBAN use-case would be a scenariowhere a patient is lying on a hospital bed monitored by the wearable sensors.
These sensors send the data to an external computer placed in the same roomthrough a wireless link. The data could be then analyzed in a real time orlater by a specialist. An antenna for on-body to off-body WBAN