Design Of The Broadband AC Impedance Measurement System

Electrochemical impedance spectroscopy(EIS),as an important method to study the properties of materials in the field of electrochemistry,is becoming more and more widely used,and has been extended to the fields of biology,devices,new energy and so on.As the core of electrochemical impedance spectroscopy(EIS),impedance measurement has become the hottest research topic in the field of testing.Most of the current impedance measurement instrument on the domestic market has narrow band,high price and difficulties of maintenance.So this paper proposes a novel broadband impedance test system in view of the above situation,which realizes the function of the wide band measurement from 100 Hz to 20 MHz and the sweep frequency test.The paper presents the overall design scheme of the system based on the free-axis method through the study and comparison of the basic impedance measurement method.The hardware mainly includes the signal source circuit,the data acquisition circuit and the front end of the measuring circuit.The orthogonal signal source circuit is implemented by AD9854,which can provide a variable frequency orthogonal reference signal to meet the requirement of the broadband.The data acquisition circuit is based on the phase detection technology,and the vector voltage and current signals on the device under test is collected by the full wave phase detection circuit composed by the multiplier,and converted by the ADC.The software includes the embedded program and the PC program,the embedded program is mainly responsible for controlling the entire system and processing data processing in real time.The system provides the RS232 and other interfaces to facilitate the expansion of system functions.The host computer software includes the parameter setting and the frequency impedance curve drawing based on C++,which can optimize the human-computer interaction experience.The test results show that the bandwidth of the system ranges from 100 Hz to 20 MHz,the accuracy of resistance impedance measurement is 1%,and the accuracy of capacitance impedance measurement is 3%.the complete system achieves an up-to-date performance and surpasses other similar products in the width of test band.In addition,the instrument has the function of sweep frequency measurement,which can realize the automatic sweep test in the frequency band.And the maximum frequency resolution is 1 Hz.So it has great advantages when compared with the domestic instruments.The instrument also has the advantages of small size,low power consumption,good portability and extendibility.