Gao Jinghui

Effects of 1.8GHz electromagnetic radiation on dielectric properties of SD Rat's typical tissues

With the progress of modern science and technology, the impact of electromagnetic radiation on biological health condition is increasing. The influence and the mechanism of interactions between electromagnetic radiation and biological tissues are urgently to be studied. In this paper, the variation of dielectric properties of 4 typical SD rat tissues (muscle, liver, kidney, heart) with irradiation of fixed parameters and without irradiation was investigated. For the test group, SD rats were irradiated 8 hours per day for 1–3 days, by a 200W radiation source of 1.8GHz, while the control group was under the same condition except irradiation. The experimental results show that, comparing with the control group, dielectric parameters of the test group produced certain changes, and effect of different radiation dose varies. Meanwhile, blood routine test results of SD rats for both groups were in normal physiological index. After irradiation process, the normal physiological activity of SD rats in both groups could be recovered in a short time. In a high-power radiation condition, the dielectric properties of SD rat tissues would be changed depending on the irradiation time of occurrence and its physiological characteristics like blood also had an abnormal indicator. The results of dielectric properties after irradiation can be used for further study of health effects of electromagnetic radiation on organisms, and provide theoretical analysis and experimental basis for understanding the relationship between electromagnetic environment and human health.

Relaxation polarization model of SD rat tissues at frequency range 42Hz–5MHz

With the increasing recognition of electromagnetic radiation to human health and environment, research on the dielectric phenomenon and the explanation on polarization theory of biological tissues has become an important part of biological dielectric. Our recent study about low-frequency polarization characteristics of SD (Sprague & Dawley) rat tissues found that the polarization characteristic of tissues is consistent with CS (Curie-von Schweidler) polarization theory in α and β relaxation polarization frequency band. In this paper, a designed electrode system was used to test the dielectric parameters of typical SD rat tissues (liver, etc.) by LCR impedance analyzer in-vitro at room temperature. According to related Cole-Cole plot, polarization model of SD rat liver at this range is not a single Debye polarization, but an intricate model accompanied with multiple polarization processes where Debye and CS polarization theory have different proportions at this frequency range. Meanwhile, polarizations of other typical tissues (lung, kidney) are also in line with the theory of CS polarization. With the variation of the imaginary part and the dielectric modulus, the CS polarization model of SD rat in this frequency range was obtained, and the application value of CS polarization theory in the phenomenon of biological tissue polarization was verified. Therefore, at this frequency range, CS polarization model of the biological tissues can be used for further study on the biological dielectric polarization.

Slow-freezing cryopreservation of red blood cells under the control of an AC elecric field

It is well known that amorphous ice can be used to cryopreserve biomaterials for transplantation. The main issue in this process is that liquid-solid phase transition of water. Due to the polarization of water, amorphous ice may be induced by AC electric filed. In this paper, AC electric field was applied to cryopreserve red blood cells (RBCs) to improve their viability. First, an electro-controlling apparatus for slow-freezing was established. Chicken RBCs were chosen as the sample because it is nucleated cell and it is convenient to estimate the cell viability. RBCs were cryopreserved under the control of an AC electric field at -30 °C for 24h and cell viability after thawing in a thermostatic waterbath at 37±0.5°C was determined by microscope. The result shows that the survival RBCs maintained the integrity of morphological. In the presence of AC electric field (Emax=1.63×105V/m, f=1MHz), the survival rate is 23.4±1.41%, lower than the effect of cryoprotectant (dimethyl sulfoxide, 3.3wt.%), that is, 33.2%±2.57%. the highest cell viability up to 48.4±1.54% was obtained under the above two conditions together. These results indicate that AC electric field can contribute to the success of slow-freezing cryopreservation.

Effects of AC electric fields on the cryopreservation of SD rat liver tissues

The cryopreservation, which refers to preserve the cells or tissues at the subzero temperatures, will inevitably face the problem of cryoinjury caused by the ice crystallization. The application of external field during the freezing process of specimen provides a promising approach to avoid the injury and thus promote the efficiency of the preservation. In the present work, we froze the SD rat liver tissues accompanied with the AC electric field (with field strength E=0.125kV/m~1.0kV/m, frequency f=100kHz~10MHz). The cryopreservation efficiency of the approach has been evaluated by the dielectric properties and the microstructure studies of tissues after frozen for 5h and thawed. We compared the dielectric frequency spectra and the transmission electron microscopic (TEM) images of the following three groups: a) fresh tissues; b) thawed tissues after normally freezing; c) thawed tissues after freezing with AC field. The dielectric frequency spectra results suggest that some curves in group c) to group a). Furthermore, TEM images indicate that the cellular structures in group c) are less severely injured than group b). The phenomena may result from the fact that the AC electric fields affect the formation and growth of the ice crystal during the liquid-solid phase transition, and thus inhibit the cryo-injury.

Temperature-dependence of dielectric properties for copper clad laminate used in integrated power module

As the rapid growth of integration level in the power electronic devices, the high dissipation power and low withstand voltage greatly affect the reliability of Integrated Power Module (IPM). Therefore, it is essential to study the performance of the devices or their substrates at the elevated temperatures. In the present work, we studied the temperature-dependence of dielectric properties for the copper clad laminate (CCL) substrate used in IPM at different frequencies. Two samples with different insulating coating layers (epoxy resin + alumina powder) thickness (d=70, 125μm) have been employed. Both of our two samples show that similar temperature-dependence tendency: At the elevated temperature with the frequency of 30Hz, 1) the dielectric loss angle tangent of CCL increased by about two orders of magnitude at 110°C compared with room temperature. 2) the dielectric permittivity increased over 30% at the elevated temperature ranging from 40°C to 80°C. The variation of the dielectric properties for the insulating coating also appeared obviously at other frequency band as temperature increased. Moreover, an additional relaxation polarization was generated by the elevated temperature in the high frequency band. Therefore, we can conclude that temperature for CCL is the most critical factor, which significantly affects its dielectric properties, in particular the dielectric loss. And thermal effect might greatly influence the breakdown of insulating layers, which leads to the insulation failure of CCL. The relaxation and polarization phenomena of CCL was discussed when the temperature changed. In addition, the breakdown voltage of 125μm thick insulating layer was 4.04kV and increased by 31.6% in comparison with that of CCL with 75μm one.