CN203745542U

CN203745542U - Rapid lossless impedance spectroscopy system

Info

Publication number: CN203745542U
Application number: CN201320839666.7U
Authority: CN
Inventors: 陈晓艳; 高娜娜; 黄华芳
Original assignee: Tianjin University of Science and Technology
Current assignee: Tianjin University of Science and Technology
Priority date: 2013-12-16
Filing date: 2013-12-16
Publication date: 2014-07-30
Anticipated expiration: 2023-12-16

Abstract

The utility model relates to a rapid lossless impedance spectroscopy system, composed of a digit electrode, a one-chip microcomputer, a wireless module, and a host computer which are successively in connection. The digit electrode is composed of electrode arrays, digit switches, AD 5933 and peripheral circuits. The one-chip microcomputer employs an ATmega 16 one-chip microcomputer of Atmel company; the wireless module employs an NRF24L01 radio frequency transceiver of NordicVLSI company and works in an ISM frequency range of 2.4 GHz-2.5 GHz. Compared with prior arts, the rapid lossless impedance spectroscopy system employs integrated impedance measurement chips AD 5933 and extends circuits; the digit electrode is designed and wireless transmission is employed; the rapid lossless impedance spectroscopy system possesses the advantages of simple structure, high integrated level, good stability and wide measurement scope and is portable.

Description

A kind of quick nondestructive impedance spectrum measuring system

Technical field

The utility model belongs to biomedical engineering and commercial measurement field, and the impedance spectrum that is specifically related to the tested field domain of closed edge inside is measured, especially a kind of quick nondestructive impedance spectrum measuring system.

Background technology

Electrical impedance spectrometry technology (ElectricalImpedanceSpectroscopy, EIS) ultimate principle is to utilize the different medium of the tested field domain of closed edge inside to have different impedance (resistance or electricity are led) characteristic, by applying drive current (voltage), Measured Boundary response voltage (electric current) signal, for rebuilding the resistivity distribution of inside, thing field and the image of variation thereof.The ultimate principle of EIS is to place a circle electrode on the measurand surface of closed edge, voltage or the current signal of data collector output, first be applied in measurand by 1 electrode, then measure response voltage or current signal on other electrodes, to the impedance information that the voltage and current signal recording amplifies, AD conversion, Fourier transform etc. obtain field domain inside, finally reach host computer and realize data analysis, image reconstruction etc. again.Therefore, impedance spectrum measurement has the advantages such as non-intruding, not damaged, volume are little, with low cost, functional imaging.

But, existing impedance spectrum measuring system is made up of multiple modules conventionally, relates to signal generator (that conventional is Direct Digital Frequency Synthesizers DDS), passage change-over switch, programmable gain amplifier (PGA), low-pass filter (LPF), digital to analog converter (ADC) and signal demodulation module etc.; Between electrode and data collector, adopt cable to be connected, its stray capacitance is unstable, not only affects system signal noise ratio, and has suppressed the raising of exciting signal frequency, affects measuring speed; And the data of system output also adopt wire transmission, these make, and system architecture complexity, integrated level are low, poor anti jamming capability, be not easy to carry.

Utility model content

The purpose of this utility model is to overcome the deficiencies in the prior art part, and a kind of high integration, strong, the portable quick nondestructive impedance spectrum of antijamming capability measuring system are provided.

The purpose of this utility model is achieved in that

A kind of quick nondestructive impedance spectrum measuring system, be connected in sequence by digital electrode, single-chip microcomputer, wireless module, host computer, described digital electrode is made up of electrod-array, digital switch, AD5933 and peripheral circuit thereof, what described single-chip microcomputer adopted is the ATmega16 single-chip microcomputer of Atmel company, what wireless module was selected is the NRF24L01 radio-frequency (RF) transceiver of NordicVLSI company, works in 2.4GHz-2.5GHzISM frequency range; Described host computer can be realized data analysis, curve plotting, image reconstruction according to the data that collect; First ATmega16 single-chip microcomputer passes through I ²c bus is configured AD5933, make its pumping signal that produces required frequency, then control figure switch, makes one of them electrode as exciting electrode, other electrodes are as potential electrode, and the data that finally digital electrode measured are wirelessly transmitted to host computer by wireless module.

And the structure of the peripheral circuit of described AD5933 is: increased every straight driving circuit at the excitation end of AD5933, formed by 47nF electric capacity, two 50K Ω resistance; Increased voltage follower circuit, what select is AD8606 two-way single power supply CMOS operational amplifier; Increased I-V impact damper at measuring junction, that select is also AD8606.

Advantage of the present utility model and good effect are:

The quick nondestructive impedance spectrum measuring system of the utility model design, adopt integrated form impedance measurement chip AD5933 and it has been carried out to circuit expansion compared with system in the past, design digital electrode, adopt wireless transmission, there is the advantages such as simple in structure, integrated level is high, good stability, measurement range wide, be easy to carry.

Brief description of the drawings

Fig. 1 is the structured flowchart of the utility model AD5933;

Fig. 2 is digital impedance spectral measurement system block diagram of the present utility model;

Fig. 3 is electrode structure schematic diagram of the present utility model;

Fig. 4 is electrode operating mode circuit figure of the present utility model.

Fig. 5 is AD5933 peripheral expansion circuit of the present utility model.

Embodiment

Describe embodiment of the present utility model in detail below in conjunction with accompanying drawing; It should be noted that, the present embodiment is narrative, is not determinate, can not limit protection domain of the present utility model with this.

A kind of quick nondestructive impedance spectrum measuring system, this system is made up of digital electrode, single-chip microcomputer, wireless module, host computer, part in Fig. 2 in square frame is digital electrode block diagram, its structural drawing as shown in Figure 3, comprise that electrod-array, digital switch, AD5933 and peripheral circuit thereof form, the present embodiment by electrode and AD5933 and peripheral circuit integrated one, by digital switch, to select electrode be with AD5933 excitation end (VIN end) or measuring junction (VOUT end) is connected, thereby determine that this electrode is as exciting electrode or potential electrode.Fig. 4 is that the mode of operation of electrode is selected circuit diagram, what digital switch was selected is the ADG711 chip of ADI company, when K1 closure, when K2, K3 disconnect, electrode is as exciting electrode, when K1 disconnects, when K2, K3 are closed, this electrode is as potential electrode, and excitation power supply is introduced the earth by K2, get rid of the interference of the right circuit to metrical information, in native system, adopted eight groups of these digital electrodes.

What controller adopted is the ATmega16 single-chip microcomputer of Atmel company, first ATmega16 single-chip microcomputer is configured eight AD5933 by I2C bus, make it produce the pumping signal of required frequency, then control figure change-over switch, make No. 1 electrode of electrod-array as exciting electrode, 2-8 electrode is as potential electrode, and the data that finally 2-8 digital electrode measured, by wireless module, are wirelessly transmitted to computing machine.What wireless module was selected is the NRF24L01 radio-frequency (RF) transceiver of NordicVLSI company, works in 2.4GHz-2.5GHzISM frequency range.Computing machine can be realized the functions such as data analysis, curve plotting, image reconstruction according to the data that collect.

Native system has carried out circuit expansion to AD5933, as shown in Figure 5.Excitation end (VOUT end) at AD5933 has increased every straight driving circuit, formed by 47nF electric capacity, two 50K Ω resistance in Fig. 5, eliminate the potential difference (PD) of AD5933 excitation end with measuring junction existence, thereby avoided tested impedance to produce the measuring error that polarization causes; In addition, also increase voltage follower circuit, as the A1 in Fig. 5, what A1 selected is AD8606 two-way single power supply CMOS operational amplifier, this circuit can be eliminated the impact of AD5933 output impedance on tested impedance, thereby expand the measurement range of AD5933 to 100 Ω-10M Ω from 1K Ω-10M Ω, increased driving force simultaneously.Increase I-V impact damper at measuring junction (VIN end), as A2 circuit in Fig. 5, that A2 selects is also AD8606, and this circuit can be eliminated bias current, offset voltage and the CMRR impact that the inner I-V amplifier of AD5933 brings, and improves the conversion accuracy of current-voltage amplifier.

It should be noted that, although AD5933 communicates by I2C bus, but due to No. ID of AD5933 all the same, therefore 8 AD5933 can not serial carry, use same I2C bus, but with ATmega16 parallel join, and for 8 AD5933 can synchronization onwards be surveyed, in native system, 8 AD5933 use same active crystal oscillator, as shown in Figure 2.

Principle of work of the present utility model is:

The integrated form impedance measurement chip AD5933 that this measuring system has adopted AnalogDevices company to release, it integrates the unit such as DDS, ADC, DSP micro-processor kernel, can directly export the information such as real part and imaginary part of impedance to be measured, thereby reduce the complexity of system, improved the integrated level of system; The DDS of AD5933 inside can produce specific frequency and encourage non-essential resistance, the response signal obtaining on resistance is sampled by ADC, and carry out discrete Fourier transform (DFT) by the DSP on sheet, after conversion, return to the value of real part and the imaginary values that under this output frequency, obtain, calculate easily required resistance value according to initial calibration data, and AD5933 is by I2C bus (SCL, SDA interface) and PERCOM peripheral communication.

This measuring system has adopted eight AD5933, measure, and system in the past can only be processed a-road-through road simultaneously, thereby improve measuring speed when can realizing simultaneously 7 passages (7 groups of electrodes); And native system has designed digital electrode, be integrated on electrode by AD5933, electrode is directly connected with signal measurement apparatus (AD5933 and peripheral circuit), shorten the transmission range that exchanges weak signal, eliminate external interference, avoided wave reflection phenomenon, improved the antijamming capability of system.

The digital signal of native system output adopts radio communication, be wirelessly transmitted to computing machine, for next step image reconstruction, wireless transmission has been avoided the constraint of wire cable, be easy to carry, have that integrated level is high, accuracy is high, high interference ability is strong, low in energy consumption, cost is low, wireless transmission, the advantage such as be easy to carry, have a extensive future.

Claims

1. a quick nondestructive impedance spectrum measuring system, it is characterized in that: be connected in sequence by digital electrode, single-chip microcomputer, wireless module, host computer, described digital electrode is made up of electrod-array, digital switch, AD5933 and peripheral circuit thereof, what described single-chip microcomputer adopted is the ATmega16 single-chip microcomputer of Atmel company, what wireless module was selected is the NRF24L01 radio-frequency (RF) transceiver of NordicVLSI company, works in 2.4GHz-2.5GHzISM frequency range; Described host computer can be realized data analysis, curve plotting, image reconstruction according to the data that collect; First ATmega16 single-chip microcomputer passes through I ²c bus is configured AD5933, make its pumping signal that produces required frequency, then control figure switch, makes one of them electrode as exciting electrode, other electrodes are as potential electrode, and the data that finally digital electrode measured are wirelessly transmitted to host computer by wireless module;

The structure of the peripheral circuit of described AD5933 is: increased every straight driving circuit at the excitation end of AD5933, be made up of 47nF electric capacity, two 50K Ω resistance; Increased voltage follower circuit, what select is AD8606 two-way single power supply CMOS operational amplifier; Increased I-V impact damper at measuring junction, that select is also AD8606.