Resrach Of Apple Impedance Monitoring System Under Low Frequncy Current-Source

In recent years, people have an increasing demand for fruits quality with theimprovement of living standard as varieties and output of fruits greatly increase in themeantime. The mainly evaluation indices of fruit quality usually include many kinds ofphysical and chemical targets such as maturity, freshness, rigidity, saccharinity, acidity andso on through which a variety of macroscopic electricity characteristic parameters(impedance Z, conductance Y, permittivity) can be reflected. Therefore, considerableresearches on the fruit quality detection have been carried out worldwide.Bioelectrical impedance is a kind of physical characteristic reflecting biology tissue,apparatus, cell or even the electrical characteristic of organism. Bioelectric ImpedanceMeasuring Technology is a non-invasive detecting technique which extracts biomedicalinformation related to organism's physiological and pathology status, through the change ofelectrical characters(impedance, conductance, permittivity) in biological tissue and organ.This technology has many advantages, such as non-invasive, low-cost, safety, nontoxic,hurtless, easy to operate and abundance in information. Consequently, it has extensiveapplication perspective.Biological tissue's impedance frequency spectrum characteristic, mainly refers to thebiological tissue electricity impedance, the complex impedance of bio-tissue varies with thefrequency of driven current change. This article rests on the characteristic, to carry on theapple research about the impedance frequency spectrum, exploration relations of fruit'sfreshness and its impedance.This paper introduces the principle of operation, hardware and software designs of thebiology's impedance measuring system in which the apple is taken as the object. There aretwo parts of this work:One is to complete the experimental hardware system design. This system mainly dealswith the acquisition of apple impedance signal, the pre-amplification, the middle filter, thedisplay of the signals on the digital storage oscilloscope, analysis and processing, andfinally electrical signals are transmit into the computer through the USB connection lineand stored. The concrete design content includes: to design and fulfil the exciting sourceand the measuring circuit which includes the filter circuit, to design pre-amplification which possesses very high input resistance, common-mode rejection and voltage gain andto design the electrode and the power circuit.The other is to research into the impedance value of apples according to the biologicalimpedance principle, i.e. the biological tissue R-C three parameter models, the Cole-Coletheory and the frequency dispersion theory. The result proves the biological tissue electricalimpedance information differs under different frequency stimulation and impedance valuegradually reduces along with the frequency increase.We also take red Fuji and the quartz apples as example for further research. After theyare separately lain aside for 2 days, 10 day and 1 month, then their impedance values aredetected. The result indicates that the impedance value increases as time goes by. Thus thiscan reflect the relation between fruit freshness and its impedance. This conclusion providesreference value and the theory basis for on-line examination of fruit's quality to somedegree. Moreover, this article also makes the beneficial attempt on the anti-disturbancetechnology.Finally some suggestions on further improvement of the system is presented.