Research On Implantable MIMO Antennas For Biomedical Telemetry

The development of biomedical telemetry technology for body-centric communications which are applied in healthcare applications areas have gained great attentions from research community,due to their self-capability to obtain physiological data from inner body more conveniently and accurately than the sensors outside body.As for an implantable medical device(IMD),the implantable antenna is an essential part in exchanging data between implantable medical devices and exterior base station/gateway wirelessly.Whereas,the design of antenna needs to satisfy the demand of big data capacity and high data transmission with the increase of types of data collected from human body.Compared with single-input-single-out antenna,multiple-input-multiple-output(MIMO)technology can increase channel capacity without requiring frequency spectrum or power,especially suits for capsule endoscope systems.This dissertation was supported in part by the National Natural Science Foundation of China(61372008),in part by the Science and Technology Planning Project of Guangdong Province(2014A010103014,2015B010101006),The following work is mainly about the investigation of implantable MIMO antennas for biomedical telemetry.(1)A miniaturized four-element implantable MIMO antenna for 2.45-GHz ISM band:The antenna is investigated to supply sufficient transmission rate and fight against multipath fading.Two radiators are integrated on the same antenna,and each radiator is shared by two antenna elements,greatly reducing the overall size of the implantable MIMO system.A crossed shaped slot etched in the radiator,a branch extending on the ground,and two electromagnetic band gaps(EBG)are integrated to achieve high isolation.The proposed MIMO antenna has a dimension of 18.5×18.5×1.27 mm~3.The simulation in the three-layer phantom indicates that the impedance bandwidth is 18.64%(2.14–2.58 GHz)with a peak gain of–17.55 dBi and the mutual coupling is below–15.99 dB at the ISM band.An in-vitro test was carried out in a pork slab and the measured results are well matched with the simulated ones.Health safety considerations and link budget are discussed to validate the antenna's availability in biomedical telemetry,and the envelope correlation coefficient is illustrated the independence between antenna elements.In order to further reduce the power consumption of IMDs,and extend its life cycle,based on the above single band antenna,a dual band antenna is designed and analyzed.(2)A dual-band dual-unit implantable MIMO antenna for implantable medical devices:The base of the proposed antenna id a diamond-shaped-patch(DSP)that covers the 2.45-GHz ISM band and two narrow strips,acting as resonances paths,can be integrated with the DSP antenna to cover 915-MHz band.Some branches extending on the ground,and defected ground structure(DGS)is integrated to achieve high isolation.The proposed antenna features low profile with the dimensions of 18×14.3×1.27 mm~3.The impedance bandwidth of 17.3%(0.898–1.068 GHz)and the mutual coupling is below-20 dB for the lower band are obtained,respectively.The impedance bandwidth is 35.4%(1.87–2.675 GHz)and the mutual coupling is below-29.5 dB for the higher band.The principle of the antenna,critical parameters,radiation performance,SAR(Specific Absorption Rate),envelope correlation coefficient and link budgets are analyzed.Finally,the proposed antenna was fabricated and measured.The measured results agree well with simulated ones,validating the theoretical design.(3)A dual-band MIMO antenna for wireless capsule endoscope application:Based on the structure and principle of the dual-band dual-unit implantable MIMO antenna designed in part(2),the proposed antenna is folded to conform outer wall in a capsule by using a multi-layer stack conversion method.The multi-layer stack conversion method and the design process of capsule antenna are represented.The size of capsule is 11.8 mm×26.8 mm.Lastly,the radiation performance of the proposed antenna is analyzed and indicates the feasibility and stability of the designed capsule antenna.This works have designed implantable antennas with the characteristics of miniaturization,bandwidth enhancement,low power consumption,big data capacity and high data transmission.The design methodology of the proposed antennas would supply the reference guideline for biomedical telemetry.