Design And Research Of Implantable Intracranial Pressure Sensing System Based On PT Symmetry

Intracranial pressure is an important medical indicator.Clinically,through continuous monitoring of intracranial pressure in patients,abnormal intracranial pressure can be detected early and targeted treatment can be carried out.The traditional intracranial pressure monitoring method is mainly the external ventricular drainage method,which is widely used because of its high accuracy.However,this method may lead to serious complications such as intracranial infection and hemorrhage in the monitored person,and it will also restrict the patient’s movement,which is not conducive to recovery.Therefore,it is particularly important to develop an implantable intracranial pressure monitoring device using wireless transmission technology.Although there are many implantable intracranial pressure monitoring solutions,they still have problems such as bulky implanted devices,limited transmission distance,and insufficient measurement resolution.To overcome these defects,this thesis proposes an implantable intracranial pressure sensing system based on parity time symmetry.The main contents are as follows:（1）Based on the theory of circuit coupling model,the RLC series PT symmetrical circuit is modeled,and the influence of asymmetric perturbation on the resonance frequency and resonance point S₁₁ amplitude of the PT symmetrical system is analyzed from the perspective of capacitance and resistance.The results show that the asymmetric perturbation of the capacitor will cause a significant change in the system frequency,and at the same time the amplitude of the resonance point S₁₁ decreases gradually with the offset,and the resolution decreases;while the asymmetric perturbation of the resistor has almost no effect on the system frequency,It only leads to an decrease in the amplitude of the resonance point S₁₁.（2）An iontronic flexible pressure sensor based on PVA/H3PO4 ion gel was prepared.In order to improve the sensitivity of the sensor,a fillable surface microstructure was formed on the surface of the ion gel by sandpaper demoulding method,and the SEM characterization was carried out.Then,the ion gel and the flexible electrode were combined to test the obtained iontronic sensor.The results showed that at a frequency of 23 MHz,the capacitance value of the sensor gradually increased with the increase of the pressure,and the overall relationship was linear.（3）Combining the iontronic sensor and the PT symmetrical system,build a prototype system and test it.The results show that as the pressure increases,the resonance frequency gradually shifts to the left,and the highest pressure change of 0.01 mm Hg can be resolved.Then,on the basis of the prototype system,the sensing system is optimized,and the combination of flexible coil and multi-layer structure is adopted to greatly reduce the problem of increasing the sensor area caused by the integration of the sensing system.The final diameter of the sensor is 10 mm and the thickness is 1mm.（4）A simulation environment for intracranial pressure testing was built,and the sensing system was tested from two angles of full scale and small changes.Experimental results show that the sensing system can achieve high-precision pressure measurement between 1.5-22.5 mm Hg,and the maximum error of the full scale is 0.6 mm Hg.On the basis of the simulated environment,the biological experiment was carried out,and the influence of the rabbit’s respiratory fluctuation on the intracranial pressure was actually measured,which confirmed the feasibility of the scheme.