MATHEMATICAL SIMULATION OF A DEVICE WITH FREQUENCY OUTPUT FOR MEASUREMENT OF HUMIDITY

The device for measuring humidity with a moisture-sensitive resistive element HR202 has been developed. The self-generating transducer is designed as a hybrid integrated circuit based on a bipolar transistor VT1 and a field-effect two-gate transistor VT2. The negative differential resistance, which is formed by the parallel connection of the impedance with a capacitive component at the collector electrodes of the bipolar transistor VT1, the drain of the field-effect transistor VT2 and inductance L1, leads to the occurrence of electrical oscillations in the circuit. When exposed to moisture on the sensitive resistive element RW, the capacitive component of the impedance at the electrodes of the transistor structure changes, which causes an effective change in the frequency of the oscillatory circuit. On the basis of mathematical modeling of electrical characteristics, analytical expressions for the transformation function and the sensitivity equation are obtained. It has been experimentally established that an increase in the ambient temperature in the range of relative humidity W = 30 ÷ 85% leads to an expansion of the generation range of the autogenerating humidity transducer, as well as to an increase in the sensitivity of the device to the measured value. The generation range of the autogenerating humidity transducer at a temperature of T = 20 °C acquires a value of 823 kHz (the average value of the sensitivity is 16.18 kHz /%), and at a temperature of T = 50 °C – 1323 kHz (the average value of the sensitivity is 29.10 kHz / %). To confirm the theoretical results of circuit solutions developed device in the computer modeling of LTSpice modeling environment. The studies were carried out at different temperatures (20°C, 30°C, 40°C, 50°C) in the range of change in the resistance of the moisture-sensitive resistive element from 1750 kOhm to 2.1 kOhm, which corresponds to an increase in the value of the relative air humidity from 30 % to 90 %. The results of theoretical and experimental studies have shown that at the output there are periodic oscillations device for measuring the humidity rate which increases with increasing values ​​of relative humidity. The obtained theoretical and experimental studies are in good agreement, the relative error does not exceed 2.5%.

MATHEMATICAL SIMULATION OF A DEVICE WITH FREQUENCY OUTPUT FOR MEASUREMENT OF HUMIDITY

The device for measuring humidity with a moisture-sensitive resistive element HR202 has been developed. The self-generating transducer is designed as a hybrid integrated circuit based on a bipolar transistor VT1 and a field-effect two-gate transistor VT2. The negative differential resistance, which is formed by the parallel connection of the impedance with a capacitive component at the collector electrodes of the bipolar transistor VT1, the drain of the field-effect transistor VT2 and inductance L1, leads to the occurrence of electrical oscillations in the circuit. When exposed to moisture on the sensitive resistive element RW, the capacitive component of the impedance at the electrodes of the transistor structure changes, which causes an effective change in the frequency of the oscillatory circuit. On the basis of mathematical modeling of electrical characteristics, analytical expressions for the transformation function and the sensitivity equation are obtained. It has been experimentally established that an increase in the ambient temperature in the range of relative humidity W = 30 ÷ 85% leads to an expansion of the generation range of the autogenerating humidity transducer, as well as to an increase in the sensitivity of the device to the measured value. The generation range of the autogenerating humidity transducer at a temperature of T = 20 °C acquires a value of 823 kHz (the average value of the sensitivity is 16.18 kHz /%), and at a temperature of T = 50 °C – 1323 kHz (the average value of the sensitivity is 29.10 kHz / %). To confirm the theoretical results of circuit solutions developed device in the computer modeling of LTSpice modeling environment. The studies were carried out at different temperatures (20°C, 30°C, 40°C, 50°C) in the range of change in the resistance of the moisture-sensitive resistive element from 1750 kOhm to 2.1 kOhm, which corresponds to an increase in the value of the relative air humidity from 30 % to 90 %. The results of theoretical and experimental studies have shown that at the output there are periodic oscillations device for measuring the humidity rate which increases with increasing values ​​of relative humidity. The obtained theoretical and experimental studies are in good agreement, the relative error does not exceed 2.5%.

Curing of Glass Fiber/Epoxy Resin Composites Using Multiwalled Carbon Nanotubes Buckypaper as a Resistive Element

Glass fiber/epoxy resin composites (GF/EP) were prepared using one and three multiwalled carbon nanotube buckypapers (BPs) as a resistive element. Compared to the conventional hot compression molding process that demanded 4200 W to fabricate the GF/EP laminate, the proposed curing process consumed only 63 W, representing a saving power of 98.5%. The thermal distribution of the BP and their composites were recorded using an infrared thermometer. Differential scanning calorimetry (DSC) curves have not shown a residual cure, suggesting the curing process using the BP as a resistive element was effective. The cross section views of the laminates were analyzed by scanning electron microscopy (SEM), and the mechanical characterizations were performed by impulse excitation technique (IET), compression shear test (CST), and interlaminar shear strength (ILSS). The results demonstrated that the BP composites showed a good consolidation between the prepregs layers, and presented no significant variations in the mechanical tests compared to the traditional hot compression molding process. Nevertheless, dynamic mechanical analyses (DMA) showed a slight decrease in the BP composites’ storage moduli compared to GF/EP laminate.

Design and construction of a compact rotary substrate heater for deposition systems

We have designed and constructed a compact rotary substrate heater for the temperature range of 25 °C to 700 °C. The heater can be implemented in any deposition system where crystalline samples are needed. Its main function is to provide heat treatment in situ during film growth. The temperature is monitored and controlled by a temperature controller coupled to a type-K thermocouple. A heater case was designed to host a resistive element and at the same time allow the substrate holder to freely rotate. Rotation is crucial not only for film homogeneity during deposition but also for the elimination of temperature gradients on the substrate holder. To tolerate oxidizing and corrosive environments, the instrument was made of stainless steel, which also works as a “coolant”, taking advantage of heat dissipation. The instrument performs well for long periods of time with stable temperatures. We hope that this project is useful for laboratories wishing to have a compact rotary heater that meets the requirements for crystal growth and film homogeneity.