Research Of Near-field Focusing Impulse Radiation Antenna In Bioelectric Applications

Picosecond pulsed electric field has precise time resolution and millimeter spatial resolution,and the waveform is not easily distorted during propagation.At the same time,when the psPEF used in the lesion reaches a certain threshold,the cells can be induced to produce corresponding bioelectric effects.Based on the theory,psPEF matching IRA can be applied in biomedical field to achieve non-invasive localization and focusing,and to achieve tumour detumescence,neurological disease treatment and so on.As for biological tissues,they can be roughly divided into homogeneous tissues and highly heterogeneous tissues.In order to enhance the field strength at the target as much as possible and achieve the possible effect,this paper designs a dielectric-loaded antenna for brain and an ultra-wideband antenna array for breast tissue from the perspective of ultra-wideband pulse antenna,focusing on two types of biological tissues.Firstly,for a human brain model with complex dielectric structure,the radiation characteristics of V-conical antenna in it are analyzed under three kinds of plate spacing transformation modes: linear,exponential and quadratic function modes,and the effect of dielectric loading on antenna performance is discussed.Finally,an improved V-conical dielectric loading antenna with plate spacing changing to quadratic function and dielectric relative permittivity of 20 is designed,which is used in CST Microwave Studio.When usesing a Gaussian pulse with an amplitude of 1V and a rising edge of 120 ps as the excitation source,the focal field intensity is 13.6V/m at the depth of 2cm in the brain and the impedance bandwidth is 2.51GHz-5GHz.The feasibility of the design is verified by processing and hardware testing,and comparing with the simulation results.Secondly,in order to reduce the phase difference of electromagnetic wave propagating to the antenna aperture and the reflection loss,two optimization methods of antenna structure are designed to improve the near-field radiation performance of the antenna based on the idea of loading materials with larger dielectric constant at the shorter part of the electromagnetic wave path to increase the wave path.At the same time,it is found that the tissues with complex dielectric properties are selective to the rising edge of the stimulus pulse,and the higher the conductivity of the tissues,the more difficult the electromagnetic wave is to penetrate.Finally,aiming at the breast tissue with simple dielectric structure and combining with the properties of ellipsoid reflector antenna,the idea of superimposing antenna reflector and feed structure into array at the same time is put forward.On the basis of satisfying the time and space consistency of electromagnetic wave at the target,the electric field intensity at the target is greatly increased by vector superposition,and the size of focal spot is reduced,and its positioning is enhanced.When the amplitude of the stimulating pulse is 1V and the rising edge is 120 ps,the focal field intensity of the single antenna element at the target is 24.05V/m,and the focal spot size is 12mm×8mm×8mm.The focal field intensity of the eight-element antenna array at the target is 68.56V/m,and the focal spot size is 5mm×8mm×8mm.