Design and Fabrication of Antenna Structures for Wireless Body Area Network and Testing on A Phantom

Abstract

Wireless Body Area Network (WBAN) is an ongoing research field that enables the transmission of biological signals from human body to an off-body device for further processing and action. Compact antennas with stable on-body behaviour are achieving interest for signal transmission for WBAN applications. Advancements of flexible electronic devices and sensor nodes has demanded conformal antenna structures for the wearable devices. Moreover, human body is a non-planar structure and endures various postures and movements. Use of stiff material for making on-body antenna may cause uneasiness to the user. In addition to this, antenna performance is unavoidably exposed by the user’s movement. Thus, antenna must have stable resonance and impedance while structural deformations. Beside this, body tissue is also affected by the exposure of near field radiations which needs to follow safety regulations. The existing on-body antenna structures still grieves from number of challenges like complex and comparatively bigger structures, highly immune to body tissue, low efficiency and gain, narrow bandwidth and unstable performance. The work presented in this thesis has concentrated on the two main aspects of antenna technology: design of new structures for on-body data transfer applications and presenting the applications of antenna in medical sector. Design, realization and performance evaluations of five antenna topologies for on body and off body communication is presented. In the first design a conformal, wide band, MIMO antenna is proposed for on body and off body data transfer application. Inverted U-shaped slot is deployed at the ground plane for reducing mutual coupling between the two radiators. This antenna has the excellent diversity performance, possess wide bandwidth and it can easily withstand frequency detuning effect due to structural deformation. Antenna has compact planar dimensions of 14 mm × 25 mm and less than -30 dB mutual coupling. In the second structure, dual band resonance with high gain is achieved. Metallic reflector is used to match antenna impedance and for providing isolation between body tissue and antenna radiations. Antenna has stable frequency response along x-axis bending. With metallic back reflector antenna has good radiation characteristics for lower and upper ISM bands. It provides broadside and unidirectional radiation pattern for reliable on body to off body communication. Antenna has gain value of 6.31 dBi and 8.75 dBi. In the third structure, a defected ground patch is designed for on to off body communication. To reduce the coupling effect of body tissue on antenna performance, I-shaped AMC structure is added with the antenna. It enhances antenna radiation characteristics and reduced the specific absorption rate value. Numerical simulation is done for observing the bending effect on antenna performance. After adding of AMC structure 65% of on-body radiation efficiency is obtained with bandwidth of 600 MHz. Performance of all the antenna structures is validated through lab testing on phantom tissue. Specific absorption rate is evaluated through numerical simulation. as compared to the on-body antennas reported in literature. Flexible antennas have excellent stability of resonance frequency and impedance matching against structural deformation. Fourth and fifth antenna structures are designed for dual mode operation; on-on and on-off body data transfer. In the fourth design miniaturization and dual band performance is attained through open end slotting. Open end slotted dual mode antenna has omnidirectional and dipole like radiation characteristics at 2.45 GHz and 5.0 GHz which supports dual mode operation. Finally, in the fifth structure, square ring-shaped ground is used to excite multiple resonance mode in the truncated corner radiator. It has covered the bandwidth of ISM, LTE and WLAN bands. It makes antenna more practical for on-body and off-body communication. All the proposed structures are characterized to operate in close proximity of human body, owns smaller footprints, wider -10 dB impedance bandwidth. Further, an overview of applications of designed antennas in health care domain is presented. Main applications of antennas in close proximity of body are: (a) data transmission from implantable and on-body devices (b) diagnosis of malignant tissue cells by analysing the variation of antenna parameters and (c) treatment of various diseases though thermal ablation therapies. Antenna is the minimally invasive and cost-effective treatment method and amenable to unfavourable tumour locations. A defected ground patch antenna is designed for detection of cancerous cells in breast tissue. Antenna is covering 3.1 GHz to 10.6 GHz UWB spectrum. partial ground plane of conventional patch antenna is modified by etching two slots and adding a narrow vertical strip. A high dielectric constant substrate is added below the antenna, which shows remarkable effect on performance. Backscattered signal variation is processed through ground penetrating radar algorithm to reconstruct microwave image. Ultimate goal of this research work is to design antennas for different applications in health care system and to improve the overall system performance.