Research On Implantable Antenna Based On Multimode Resonance

Since implantable antennas are located inside the human body,their working environment is very complicated compared with the traditional antennas.Therefore,the design requirements of implantable antennas for biomedical applications are very strict,including broadband,miniaturization,dual-band,and circular polarization.In order to meet these requirements,three novel implantable antennas are proposed based on multi-mode theory in this thesis,obtaining attractive properties like dual-band,circular polarization and broadband,separately.The main work of this thesis is organized as follows:(1)The design of dual-band implantable antenna with shorting pins.Base on the halfwavelength resonance of a traditional patch antenna,a new quarter-wavelength resonance is newly introduced by loading two shorting pins on the diagonal of radiation patch.Thus,miniaturization and dual-band performance can be realized of the implantable antenna.Furthermore,by introducing four straight slots on the antenna radiation patch and three L-shaped slots on the ground,the two frequencies can be adjusted to the required bands with good impedance matching.As a result,the proposed antenna with a size of 12.6×12.6×1.27 mm3 achieves a simulated impedance bandwidth of8.5% and 12% in ISM(915MHz)and WMTS(1.4 GHz)frequency bands,respectively.(2)The design of right-handed circular polarization(RHCP)implantable antenna with enhanced gain.By loading two shorting pins on the two corners(at the same side)of a rectangular patch antenna,two non-degenerate orthogonal resonant modes are formed with large resonant frequency separation.Subsequently,by introducing two open slots on the patch,these two orthogonal resonant frequencies can be merged together with a 90° phase difference generated.Therefore,a broadband RHCP performance is obtained of the proposed antenna in human muscle tissue.On the other hand,by loading via walls around this CP patch antenna,the energy absorbed by the surrounding human tissue can be weakened,thereby increasing the gain of the antenna by 1.5 d Bi.This final proposed antenna works in the ISM(2.45 GHz)band,and its simulated CP bandwidth is 12.8%,which is consistent with the measured ones.(3)The design of miniaturized three-dimensional conformal capsule antenna with broadband performance.Firstly,by loading shorting pins at the center of a sector patch antenna,preliminary miniaturization can be achieved.Furthermore,a pair of symmetrical metal stubs is connected to this sector patch,serving as disturbance,thereby greatly expanding the impedance bandwidth by introducing new resonant frequencies.Besides,these two stubs are attached on the inner wall of the capsule,so that the inner space of the capsule is saved.Finally,this capsule antenna can achieve an impedance bandwidth of 9.1% in the ISM(2.45 GHz)frequency band.