Research On Broadband/Multi-band Implantable Antennas For MHealth Applications

As social problems such as the aging of population and the imbalance of medical resources get increasingly severe,mobile health(m Health)technology has attracted extensive attention.In the m Health system,implantable medical devices(IMDs)play an important role in sensing physiological information.Compared with the traditional methods of wired connection or coil coupling,the implantable antennas in the IMDs can wirelessly transmit the physiological information to the receiver outside the body,making the diagnosis convenient for doctors and patients.Due to the fact that the human body consists of various tissues with complex electromagnetic characteristics and varies with different tissue,and can be influenced by some factors such as electronic components in the IMDs,implantation operation errors,and manufacture errors,the impedance mismatching of implantable antennas in the desired bands may be caused.The implantable antennas with broad frequency band are robust in the harsh electromagnetic environment.In addition,multiple functions can be realized in the IMDs by employing multi-band antennas.Therefore,the research on the broadband/multi-band implantable antennas is of great application values.This dissertation was supported in part by the National Natural Science Foundation of China(61372008),and in part by the Science and Technology Planning Projects of Guangdong Province(2014A010103014,2015B010101006),the following work is carried out mainly about the investigation of broadband/multi-band implantable antennas for m Health applications:(1)A broadband implantable planar inverted-F antenna(PIFA)operating at the MICS band:Considering that the electromagnetic wave with lower frequency has less transmission loss,and the robustness of the whole system can be improved by introducing broadband antennas,a novel broadband implantable antenna operating at the Medical Implant Communication Services(MICS)band of 402–405 MHz is designed.By embedding spiral slots on the radiation patch and the ground,introducing shorting pin,and employing dielectric substrate with high dielectric constant,the miniaturization of the proposed antenna is achieved.In addition,spiral slot in the ground is embedded to improve impedance matching,thus broadening bandwidth.The proposed antenna has the dimensions ofπ×5.2~2×1.27 mm~3 with a measured impedance bandwidth of 99.2%(182–540 MHz)and a peak gain of–39.9 d Bi.The fabricated antenna was tested in the three-layer pork.Despite slight frequency shifting between the simulated and measured results takes place,the desired MICS band is still covered.The radiation performance,application scenario,and SAR distribution of the proposed antenna are given,and the link budget between the proposed antenna and an off-body dipole is analyzed.To address the issue of the battery with limited lifetime in the IMDs,alternative methods of wireless power transfer(WPT)technology or power saving are required.Considering that the single-band antenna is unable to support multiple applications simultaneously,a triple-band implantable antenna is presented,realizing the multi-functions of IMDs.(2)A triple-band implantable PIFA antenna for multifunctional applications:By embedding I-shaped slot in the radiation patch,the current path of the proposed antenna is extended,achieving miniaturization.Due to two symmetric U-shaped slots in the ground and slots in the radiation patch,the MICS and 2.45-GHz ISM bands are covered.Moreover,four meandering slots in the diagonal of the radiation patch are introduced to achieve the 915-MHz ISM band.Due to the triple bands of the antenna,multiple functions such as data transmission,WPT,and power saving,are implemented.The proposed antenna occupies the sizes of 11.6×11.6×1.27 mm~3 with measured impedance bandwidths of 18.4%(375–451 MHz),18.5%(900–1084 MHz),and 31.2%(2071–2837 MHz)and with peak gains of–41.3 d Bi,–23.5 d Bi and–28.7 d Bi,respectively.The operating mechanism of the proposed antenna is explained by analyzing evolution process,and effects of some key factors on the antenna performance are investigated.Due to the fact that a full ground enables implantable antennas to shield electromagnetic interference from electronic components in the IMDs,a multi-band implantable antenna with a full ground is studied.(3)A triple-band implantable loop PIFA with a full ground:By meandering the radiation patch,effective miniaturization is achieved,the lower and the higher bands are generated.With asymmetric structure,additional even resonance modes of the loop PIFA can be excited.Therefore,an offset shorting pin is introduced to achieve the middle band,however,with reflection coefficient more than–10 d B.A T-shaped wandering branch embedded in the radiation patch is adopted to improve impedance matching and broaden bandwidths.Hence,the MICS band,915-MHz ISM band and 1.4-GHz WMTS band are covered.The proposed triple-band antenna features low profile with the compact sizes of 11×11×1.27 mm~3.The simulated impedance bandwidths of the proposed antenna are 30.1%(367–497 MHz),15.2%(828–964MHz),and 29.2%(1110–1490 MHz)with peak gains of–44.2 d Bi,–25.6 d Bi and–28.8 d Bi,respectively.The low SAR is achieved due to the low E-field in the near-field of the proposed magnetic antenna.In addition,effects of factors such as positions of shorting pin,electrical system and implant locations on the antenna performance are discussed,and the link budget of the proposed antenna is analyzed.This work has designed implantable antennas with the advantages of compact size,wide bandwidth,low power consumption,biocompatibility and electromagnetic compatibility.The proposed broad-/multi-band antennas have the potential to the m Health applications.The methodology of the designed implantable antennas would give some guideline to the similar works.