Vortex Express Method for Parameter Determination Thermoelectric Materials

The method is based on the possibility of determining the heat loss of electric power during the flow of Foucault eddy currents in the volume of a thermoelectric sample, placing in the field of action of the ferrite core an inductor through which electric currents that are symmetrical and asymmetric in nature flow sequentially in time. Mathematical expressions are obtained for the coefficients of electrical conductivity σ, thermal conductivity ϰ, thermo-emf α and thermoelectric figure of merit Z. Minimization of the error of the proposed method, carried out by computer simulation of the physical processes occurring in the sample using appropriate programs, showed that the operating frequency of the device measuring sensors should be located in the range of 36 ÷ 250 kHz, and the electric current flowing through it — taking into account the inequality qф/П/ qф/ qϰ > 10. The magnetic field induction ratio in terms of components is selected from the condition В0/В > 8.6, which corresponds to the conditions of minimal impact on the parameters of the sample by galvanic thermomagnetic phenomena. The block diagram of a device for non-contact measurement of symmetric σс and asymmetric σа components of the electrical conductivity of thermoelectric materials consists of: 1 — SV switch block; 2 — electronic switch; 3 — auto generator; 4 — AC amplifier; 5 — synchronous detector; 6 — DC amplifier; 7 — pulse generator; 8 — signal processing unit; 9 — indicator device; 10 — DC indicator; 11 — correction unit; FR1, FR2. Measurement of the parameters of the thermoelectric sample based on Bi-Te-Se-Sb crystals showed that the real error of the proposed method is 2 %. This indicates that the eddy current method can be successfully used to determine the main parameters of thermoelectric materials. The use of this method allows solving the relevant problem of avtomazation of the process of monitoring and sorting out thermoelectric ingots, billets and parts.

A High-Performance Optoelectronic Sensor Device for Nitrate Nitrogen in Recirculating Aquaculture Systems

The determination of nitrate nitrogen (NO3-N) in recirculating aquaculture systems is of great significance for the health assessment of the living environment of aquatic animals. Unfortunately, the commonly used spectrophotometric methods often yield unstable results, especially when the ambient temperature varies greatly in the field measurement. Here, we have developed a novel handheld absorbance measurement sensor based on the thymol-NO3-N chromogenic rearrangement reaction. In terms of hardware, the sensor adopts a dual channel/dual wavelength colorimeter structure that features a modulated light source transmitter and a synchronous detector receiver. The circuit measures the ratio of light absorbed by the sample and reference containers at two LEDs with peak wavelengths at 420 nm and 450 nm. Using the modulated source and synchronous detector rather than a constant (DC) source eliminates measurement errors due to ambient light and low frequency noise and provides higher accuracy. In terms of software, we design a new quantitative analysis algorithm for absorbance by studying colloid absorbing behavior. The application of a buffer operator embedded in the algorithm makes the sensor get the environmental correction function. The results have shown that the sensitivity, repeatability, precision and environmental stability are higher than that by ordinary spectrophotometry. Lastly, we have a brief overview of future work.

METHODS OF SMALL CAPACITANCE MEASUREMENT IN ELECTRICAL CAPACITANCE TOMOGRAPHY

The paper presents the main methods of small capacitance measurement used in electrical capacitance tomography: the AC method with a sine wave excitation and the charge-discharge method with square wave excitation. Construction of synchronous detector for both circuits was discussed. A modified "charge-discharge" method was presented.

Investigations on the Equivalent Magnetic Noise of Magneto(Elasto)Electric Sensors by Using Modulation Techniques

The equivalent magnetic noise of the magnetoelectric (ME) layered composite sensors has been investigated for various modulation techniques. The ME thin film response to an electric modulation or a magnetic modulation can be sensed by using either a charge amplifier or a coil wound around the sample and then demodulated by a synchronous detector. The equivalent magnetic noise for these excitations methods has been compared. As expected, the low-frequency fluctuations can be lowered when the magnetoelectric sensor is operated in a modulation mode. Results show that these methods can give the same level of equivalent magnetic noise for a certain strain-excitation. In theory, mechanical noise appears as the only dominant noise source after the demodulation process in the case of a certain strong amplitude excitation carrier signal. By using these modulation techniques, an equivalent magnetic noise level of 10-100 pT/Hz at 1 Hz was achieved with DC capability.