Research On Medical Accelerometer Based On Ionic Liquid

Accelerometer is a kind of sensor that can measure acceleration,composes with inertia proof mass,damper,elastic component,sensitive element,and processing circuit.During the acceleration motion,according to the Newton's second law,the acceleration value can be got by measure the inertial force pushed onto the inertial proof mass.In biomedical,accelerometer can be used for surgical navigation system,cardiopulmonary resuscitation(CPR)equipment and limb rehabilitation,etc.Inspired by the detection mechanism for linear acceleration of utricle/ balloon in the human ear vestibular system,a novel accelerometer based on an ionic liquid was put forward in this work and its performances meet the requirements of body motion detection.This article is devoted to introduce the structure design,material selection,detection mechanism,and characterization mainly.The more superior room temperature ionic liquid(ILs)compared with traditional solution was used as the liquid inertial mass.Using the active carbon paper with high specific surface area and electrochemical properties of stability as detection electrodes,polymethyl methacrylate(PMMA)as substrate and packing materials,an accelerometer with the size of 2×2×5 mm3 was fabricated.The theory of interface electrical double layer(EDL)between solid and liquid well explain the detection mechanism of the ILs accelerometer.In the theory model,the electrical and mechanical models of the liquid-state inertial mass accelerometer were established.The detection principle of ILs accelerometer was verified by numerical analysis of finite element.The models of micro-liquid motion in three dimensional(3D)and EDL in one dimensional(1D)were established to analyze the volume of liquid,viscosity and the contact angle between solid wall and liquid how effect the accelerometer work and the structure of EDL on the solid-liquid interface,respectively.Then a joint two models analysis explained the electrical charge change on the interface of EDL during the liquid motion.Two accelerometer structures were fabricated,single inertial structure and multi-inertial structure receptively.Under the frequency of 6.89 Hz,the motion displacement is 40 mm,the sensitivity of accelerometer with single inertial mass was 0.689 m V/g,without any signal processing circuit.In the frequency range from 2.5 Hz to 11.75 Hz,when the motion displacement of the ILs accelerometer is fixed at 40 mm,the resonant frequency fres is 7.13 Hz and the output signal Vp-p is 10.2 m V.However in the testing,the 3 d B bandwidth is ~2.5 Hz,the narrow bandwidth limits its application.In the same motion conditions,the sensitivity of the multi-inertial accelerometer was 1 m V/g,has 45% increases.Compared with the commercial accelerometer ADXL335,the motion information was expressed by ILs accelerometer as distinct as commercial sensor,under the same motion condition,however the signal to noise ratio(SNR)of output signal is low,compared with ADXL335.In addition,when the multi-inertial ILs accelerometer was installed on hand,it can identify the motion state of arm,under frequency of 3.6 Hz and 6.2 Hz.The result shows that the ILs accelerometer has a promising prospect in the low frequency motion sensing,such as living body motion in medical.