Research And Design On Circularly Polarized Implantable Antenna

With the increasing attention paid on human health and the convenience of medical care,the concept of biomedical devices which can be implanted into human bodies has been widely studied.To provide better service on wireless communication between implantable medical devices(IMDs)and devices outside human body,the research on implantable antennas is particularly important.In this paper,the radiation performances of circular polarization and dual-band are studied.The circular polarization performance of the antenna can prevent the polarization mismatching,suppress the multipath interference and reduce the bit error rate.The dual-band radiation performance allows the implants to switch between sleep and wake modes,extending the life time of implanted devices.The key works of the paper includes:(1)Design of a pin-loaded implantable antenna with circular polarization.The antenna operates at the 2.45-GHz Industrial,Scientific,and Medical(ISM)band and its overall size is about 99.7 mm~3.Its circularly polarized radiation performance is generated by the loading of vias and two arc-shaped open slots,where we adjust the length of the two slots to achieve better axial-ratio(AR)performance.The antenna size is miniaturized by loading two pairs of symmetrical patches at the inner edge of annular ring.In addition,we loaded a notch on the ring near the feed point to improve the matching performance and achieve a wide impedance bandwidth.Finally,a simulated impedance bandwidth of11.4%and a wide AR bandwidth of 15.9%is realized.(2)Design of dual-band implantable antenna with circular polarization.The proposed antenna operates in 1.4-GHz Wireless Medical Telemetry Service(WMTS)band and 2.45-GHz Industrial,Scientific,and Medical(ISM)band,its overall size is about 103.7 mm~3.The lower band with quarter-wavelength resonance is realized by placing two shorting pins at orthogonal positions.As a disturbance between two arc-shaped tails with open end is introduced,it can achieve circular polarization(CP)radiation property and a wide CP bandwidth of 10.7%in WMTS band.Meanwhile,the higher band with half-wavelength resonance is realized through the path connecting two asymmetric open-end tails,so as achieve linear polarization(LP)radiation property and a wide impedance bandwidth of 22%in ISM band.Finally,measurement is performed for the proposed antenna,and the results coincide well with the simulation ones.(3)Communication between the implantable antenna and the external antenna.A circularly polarized antenna operating in the 1.4GHz band is improved.It was used as an external receiving antenna to communicate with a dual-band implantable antenna with circular polarization in(2).