Research On Circularly Polarized Antennas For Biomedical Telemetry

The development of biomedical telemetry technology can relieve the shortage of medical resources and provide patients with comfortable treatment services.Implantable medical devices play a critical role in biomedical telemetry,accurately collecting the physiological data within the human body to assist medical staff in disease prevention,disease monitoring and real-time treatment.Antennas can be used for wireless communications between medical devices inside and outside the body.Whereas,the design of antenna needs to consider the effects of human body movement and background environment,establishing a reliable communication link.Compared with the conventional linearly polarized antenna,circularly polarized antennas avoid the polarization mismatch caused by the change of the alignment orientation,and suppress the interference caused by the background multipath scattering.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 circularly polarized antennas for biomedical telemetry.(1)GND-slotted differentially-fed implantable circularly polarized antenna for 2.45-GHz ISM band: Substrate with high dielectric constant plus the slotting of radiating patch and ground plate are introduced to realize miniaturization.After optimization,the size of proposed antenna is 9.8 mm × 9.8 mm × 1.27 mm.The differentially-fed structure is adopted to enhance system integration and reduce the power loss.The radiation modes of TM01 and TM10 are excited on the diagonal of the square patch through the differentially-fed ports and the geometric perturbation is introduced to adjust circular polarization performance.The impedance bandwidth is 2.37 GHz to 2.49 GHz(4.9%)and the 3-dB AR bandwidth is 2.37 GHz to 2.50 GHz(5.3%),covering the 2.45-GHz ISM band.In the CST simulation,it is possible to achieve miniaturization with a peak gain of –20.7 dBi.Finally,the performance of proposed antenna is verified in a high-precision phantom and far-field gain of antenna and specific ab-sorption rate(SAR)associated with safety are analyzed.(2)Differential circularly polarized antenna for capsule endoscope system: The differentially fed structure is adopted in the design of the proposed antenna to facilitate connection to the integrated circuit within the capsule.The size of proposed antenna is 7.5 mm × 7.5 mm × 1.27 mm.Circular polarization is realized through introducing geometric perturbation.2.37–2.48 GHz(4.5%)of impedance bandwidth and 2.40–2.55 GHz(6.1%)of 3-dB AR bandwidth are obtained.The principles of miniaturization and circular polarization of the proposed antenna are analyzed,and the influence of the key parameters on the proposed antenna performance is studied.The relative permittivity and conductivity of pork used in the experiment were measured and the difference between the measured pork and the human being is analyzed,guaranteeing the accuracy of in-vitro test.Finally,the prototype was fabricated and measured.The measurement results are in good agreement with the simulation ones,verifying the theoretical design.(3)Omnidirectional circularly polarized planar receiving antenna in the exterior body: Due to the change of relative orientation between implanted medical device and off-body base station,an omnidirectional circularly polarized receiving antenna is investigated.Omnidirectional vertically linear polarization of electromagnetic waves is generated in the azimuth plane though the loaded monopole,omnidirectional horizontally linear polarization of electromagnetic waves is excited in the azimuth plane though bending L-shaped dipole,realizing omnidirectional circular polarization.The impedance bandwidth of the proposed antenna is covered from 2.395 GHz to 2.505 GHz(4.9%),the bandwidth of 3-dB AR is from 2.325 GHz to 2.570 GHz(10%),the maximum gain on the azimuth plane is 1.5 dBi,and the roundness is less than 0.6 dB.The link budget of the transceiver antenna system is analyzed to evaluate the communication performance between the implantable antenna and the proposed omnidirectional circularly polarized antenna.This works have designed implantable antennas with the characteristics of miniaturization,independence of orientation,and anti-multipath interference,and investigated exterior antenna with the advantages of wide frequency band,miniaturization,immune to interference,and omnidirectional radiation.The design methodology of the proposed antennas would supply the reference guideline for biomedical telemetry.