OBJECTIVE: To investigate the sensing volume of open-ended coaxial probe technique for measurement of dielectric characteristics. METHODS: A measurement model combining macro- measurement device with a layer model of dielectric properties parameters was established for evaluating the sensing volume of open-ended coaxial probe technique. We defined sensing depth and sensing diameter to describe the distance that could be detected in vertical and horizontal direction. Using a variety of materials with different dielectric properties (Teflon, deionized water, ethanol, and gradient concentration sodium chloride solution), a layered model of dielectric properties differentiation was established. The total combined uncertainties (TCU) were calculated for different output power, and the output power was controlled to increase from -50 dBm to 15 dBm to calibrate the error range of the dielectric properties measurement system. The optimal output power range was determined based on the results of TCU test. In sensing volume measurement experiment, we set the control groups based on measurement parameters that potentially affect the sensing volume including output power (-10, -5, 0, 3, 6, and 9 dBm), frequency (1-500 MHz), Teflon, deionized water, and ethanol to form a dielectric constant difference between high and low contrast groups. Different concentrations of sodium chloride solution and Teflon were used to generate a conductivity difference between high and low contrast groups. These groups were tested in the sensing depth and sensing diameter measurement experiments. RESULTS: The result of TCU test indicated that accurate and stable measurement results could be obtained when the output power was greater or equal to-10 dBm (TCU < 2%). Sensing volume measurement experiment revealed a positive correlation between the sensing depth and output power ( < 0.05). As the measured power increased, the sensing depth gradually increased in deionized water and ethanol, and the difference reached 70 μm. The sensing depth was negatively correlated frequency ( < 0.05). As the concentration of sodium chloride solution increased, the corresponding sensing depth gradually decreased, with a difference reaching 270 μm. The sensing depth of high dielectric materials was greater than that pf low dielectric materials. The results of sensing diameter measurement were not obviously affected by the measurement parameters, and the sensing diameter was stable in a fixed range (1.0 to 1.8 mm) between the diameter of the inner conductor and the diameter of the insulation layer, and was less than the diameter of the probe. CONCLUSIONS The sensing volume of open-ended coaxial probe technique is affected by measurement parameters and dielectric properties of materials, which significantly affect the sensing depth.
Algorithms ; Electric Conductivity ; Electrochemistry ; instrumentation

The dielectric spectroscopy of human blood cells was measured within the frequency range of 0.01-100 MHz, and the dielectric numerical characters were determined as response to AC electric field. we measured the AC impedance of normal human blood cells with the impedance technique in the frequency domain, then the experimental data were drawn a relationship curve between the frequency of electric field and conductivity. The dielectric spectrum and the Cole-Cole plots of human blood cells were established. The characteristics of dielectric response of human blood cells were also established. The permittivity and the conductivity of human blood cells were frequency dependent, and dielectric dispersion of human blood cells had two characteristic frequencies: i.e. fc1, is 1.42 MHz, and fc2 is 3. 32 MHz.
Blood Cells ; physiology ; Electric Conductivity ; Electrochemistry ; Humans ; Spectrum Analysis ; methods

Three-electrode testing method was used to investigate the effect of temperature on electrode impedance, and the pH shifts in saline solution resulting from the electrical stimulation were also determined. Experiments in PBS (phosphate buffered solution) solution showed that the electrode impedance was almost invariable at the human body temperature range (35 degrees C-40 degrees C). And the experiments in unbuffered saline solution showed that pH shifts decreased from 0.03 to 0.005 when the frequency of biphasic charged-balanced pulses increased from 1 Hz to 100 Hz. Even stimulated by monophasic pulses (frequency is 15 Hz, amplitude is 50 microA), the stimulus-induced pH shift of electrode only varies 0.15 (anodic pulse current increased 0.15 and cathodic pulse current decreased 0.15).
Electrochemistry ; Eye, Artificial ; Materials Testing ; Microelectrodes ; Prostheses and Implants

Chromatography, High Pressure Liquid ; methods ; Electrochemistry ; Homocysteine ; blood ; Humans

OBJECTIVEThe aim of this study was to investigate the korrosionsneigung of three metal specimens for casing removable denture by means of electrochemical method.

METHODSThree kinds of test specimens were prepared, including cobalt-chromium alloy, nickel-chrome alloy with titanium and pure titanium. Then they were analyzed via linear polarization in artificial saliva simulating oral environment. From this electrochemical test the polarization curves of these kinds of specimens were recorded. Then the scanning electron microscope (SEM) and X-ray diffractometer (XRD) were applied to assess the morphology and phase changes before and after electrochemical corrosion.

RESULTSNo typical Tafel curve had been recorded for pure titanium, other than cobalt-chromium alloy and nickel-chrome alloy with titanium. Nickel-chrome alloy with titanium got more negative corrosion potential and higher corrosion current than cobalt-chromium alloy. Via SEM, the obvious changes were observed on the morphology and phase before and after corrosion on cobalt-chromium and nickel-chrome alloy with titanium specimens while pure titanium having no change. The XRD provided us little changes on these all three materials.

CONCLUSIONThe results confirm that the korrosionsneigung of the studied cobalt-chromium alloy in artificial saliva is lower than that nickel-chrome alloy with titanium. Pure titanium is the most stable one of the three materials and is extreme hard to be etched.

OBJECTIVETo study the effect on the corrosion resistance of Cr alloy in the artificial saliva with different pH value in vitro.

METHODSCompared to Ti alloy, electrochemical technique was used to measure the electric potential of corrosion (E(corr)), current density of corrosion (I(corr)) Cr alloy in the artificial saliva with different pH value. The corrosion and corrosion resistance mechanism on Cr alloy in the artificial saliva with different pH value had been investigated by the EIS curves.

RESULTSThe corrosion resistance of Co-Cr alloy was better than Ti alloy. The value of I(corr) was lower and the value of R(p) was larger than Ti alloy. The corrosion resistance of Ni-Cr alloy was worse than Ti alloy. The value of I(corr) was larger and the value of R(p) was lower than Ti alloy. The pH value in the artificial saliva was decreased, the I(corr) value of three types of alloy increased, the R(p) value of three types of alloy decreased. But the changes of Co-Cr alloy was smaller than that of Ti alloy or Ni-Cr alloy.

CONCLUSIONThe corrosion resistance of Co-Cr alloy was superior to that of Ni-Cr alloy and Ti alloy. In the acid artificial saliva, the corrosion resistance of three types of alloy descended evidently.

OBJECTIVETo investigate the variation of the corrosion resistance of micro-arc oxidation film on titanium by electrochemical methods in simulated body fluid.

METHODSMicro-arc oxidation film was formed on the titanium surface using micro-arc oxidation. The morphology was observed with scanning electron microscopy (SEM) and the phase composition was analyzed using X-ray diffraction (XRD). Polarization curves and electrochemical impedance spectroscopy (EIS) in simulated body fluid were examined with electrochemical methods.

RESULTSOn the titanium surface with micro-arc oxidation, the film consisted of many volcanic micropores. The film formed was a titanium dioxide (TiO(2)) with peaks for both anatase and rutile phases. In addition, hydroxylapatite was also observed. The self-corrosion potential and self-corrosion current density of titanium with micro-arc oxidation film were -0.255 V and 0.80 microA/cm(2) respectively, while those of untreated titanium were -0.358 V and 0.55 microA/cm(2). Electrochemical impedance spectroscopy confirmed the model of equivalent circuits reasonable.

CONCLUSIONSThe results of electrochemical examinations indicate that micro-arc oxidation film increases the corrosion resistance of titanium.

In this study, based on the correlation between the blood and saliva glucose, we proposed and developed a new conceptual method of using mobile phone to measure wirelessly the glucose concentration in saliva. According to the experiments on simulated saliva, the new system could draw, display, store and carry out calculation on the correlation curves between saliva glucose and electrical parameters. This demonstrates the feasibility and bright future of the new technique.
Cell Phone ; Electrochemistry ; methods ; Glucose ; analysis ; Humans ; Saliva ; chemistry ; Wireless Technology

Sodium dodecyl benzenesulfonate (SDBS) self-assembled monolayers in situ modified electrode (SDBS/CPE) was prepared. The electrochemical behaviors of dopamine (DA) on SDBS/CPE were studied. Electrochemical behaviors and kinetic parameters of DA were investigated at SDBS/CPE by cyclic voltammetry (CV), chronoamperometry (CA) and chronocoulometry (CC). The changes of the oxidation peak currents with concentration of DA were examined by square wave voltametry (SWV). The difference of peak potential at CPB/CPE was less than 149 mV comparing with that at CPE. The charge transfer coefficient alpha, diffusion coefficient D and the apparent reaction rate constant k(f) are 0.61, 3.6 x 10(-5) cm2 x s(-1) and 4.2 x 10(-3) cm x s(-1), respectively. The oxidation peak currents of DA versus its concentration have a good linear relationship in the concentration range of 2.0 x 10(-6)-1.0 x 10(-3) mol x L(-1) with the correlation coefficient of 0.9979 and the detection limit of 9.0 x 10(-7) mol x L(-1) by square wave voltammetry (SWV) response. The modified electrode showed an excellent electrocatalytic activity for the DA electrochemical oxidation. The method can be applied in the determination of DA in injection samples with the satisfactory results.
Benzenesulfonates ; chemistry ; Catalysis ; Dopamine ; analysis ; chemistry ; Electrochemistry ; methods ; Electrodes ; Oxidation-Reduction

Chromatography, High Pressure Liquid ; methods ; Drug Residues ; analysis ; Electrochemistry ; Ethidium ; analysis ; Luminescent Measurements ; methods ; Sensitivity and Specificity