Pavel Kulha

Thermal simulation and validation of 8W LED Lamp

This work deals with thermal simulation and characterization of solid state lightening (SSL) LED Lamp in order to get precise 3D thermal models for further lamp thermal optimization. Simulations are performed with ANSYS-CFX and CoventorWare software tools. The simulated thermal distribution has been validated with thermal measurement on a commercial 8W LED lamp. Materials parametric study has been carried out to discover problematic parts for heat transfer from power LEDs to ambient. The objectives are to predict the thermal management by simulation of LED lamp and environment and to get more insight in the effect of lamp shape and materials used in order to design more effective LED lamps.

Gas sensing properties of nanocrystalline diamond at room temperature.

Summary This study describes an integrated NH3 sensor based on a hydrogenated nanocrystalline diamond (NCD)-sensitive layer coated on an interdigitated electrode structure. The gas sensing properties of the sensor structure were examined using a reducing gas (NH3) at room temperature and were found to be dependent on the electrode arrangement. A pronounced response of the sensor, which was comprised of dense electrode arrays (of 50 µm separation distance), was observed. The sensor functionality was explained by the surface transfer doping effect. Moreover, the three-dimensional model of the current density distribution of the hydrogenated NCD describes the transient flow of electrons between interdigitated electrodes and the hydrogenated NCD surface, that is, the formation of a closed current loop.

Simple wireless A/D converter for isolated systems

Motivation for this paper is to present possible solution for measuring analog values in isolated systems without batteries. It can be suitable for biomedical probes, enclosed systems such as tubes, extreme temperature environments etc. The system is considering no batteries because of their finite lifetime, toxicity or an extreme temperatures environment that is improper for the batteries. System thus must be powered wirelessly and also the information must be transmitted without any wires. It is not necessary a long distance for this powering. Usually it is enough to transfer up to 20 cm. The paper presents basic theory needed for a design of the powering, communication and also the analog to digital converter. The converter is presented consisting of discrete devices and also it is presented scheme for chip realization using the 500 nm CMOS technology.

Fabrication of Diamond Based Quartz Crystal Microbalance Gas Sensor

Synthetic diamond has remarkable properties comparable with natural diamond and hence is a very promising material for many various applications (sensors, heat sink, optical mirrors, cold cathode, tissue engineering, etc.). Nowadays, deposition of diamond films is normally employed in chemical vapor deposition (CVD) usually at high temperatures (800900 °C), what limit its application to high melting substrates. Gravimetric (mass) sensors belong to the major categories of chemical sensors and the most common type of mass sensor is the bulk acoustic quartz crystal microbalance (QCM). This contribution deals with a nanocrystalline diamond (NCD) growth from the H2/CH4/CO2 gas mixture at low temperature (400 °C) by pulsed linear antenna microwave plasma system on 10 MHz circular AT-cut quartz resonators substrate. Gas sensor based on the NCD-coated QCM was developed for detection of ammonia (NH3) at room temperature. Measurements not only confirmed the functionality of this first published NCD-coated QCM sensor, but in addition its sensitivity was twofold to a virgin QCM sensor with a gold active layer.

Design and characterization of NCD piezoresistive strain sensor

Nanocrystalline Diamond (NCD) is a very promising material for fabrication of high-temperature devices because of its unique mechanical and electrical properties. The prospective of using diamond is not only in sensors (MEMS) but in RF and power electronic as well. The strain gauges based on nanocrystalline diamond layers have been successfully designed and fabricated using mainly domestic technological background. The CoventorWare FEM calculations of the mechanical stress and geometrical deformations of a 3-D structure are used for a proper localization of the piezoresistor on the carrying substrate. The boron-doped piezoresistive sensing element was realized using a directed patterned growth of NCD film on SiO2/Si by microwave plasma enhanced chemical vapor deposition (CVD). Cantilever beam configuration was used for sensor characterization. The sheet resistance of tensometric layers as well as contact edge resistivity were measured by Transmission Line Method (TLM). The gauge factor of boron-doped NCD films was investigated in the range from room temperature up to 250 °C and from 0 to 1 N of applied force.

Optimization of position of piezoresistive elements on substrate using FEM simulations

This paper presents an example of optimization of piezoresistive element placement on substrates for different types of deformation transducers (single side fixed cantilever beam and membrane). Modelling of structures was performed by simulator utilizing finite element method (FEM). Modelling and simulation of stress and strain distribution and deformations is practically essential for any design of MEMS structures. The modern simulation tools make the design easier and enable optimization of many different parameters before fabrication of new structure. Designed piezoresistive structures were consequently fabricated and tested.

Screen printed and laminated electrodes for low-cost capacitive level measurement systems

Abstract The fabrication procedure and characterization of low-cost electrodes for capacitive level sensors realized on a flexible substrate are presented in this paper. The aim was to prepare conductive electrodes by printing of silver and PEDOT:PSS pastes on coated PET foil. Individual interdigital capacitors and a system with embedded microcontroller readout were designed for a comparative study. Individual capacitors in the form of interdigital electrodes (IDT) were designed with different finger width/spacing dimensions from 300/300 μm to 800/800 μm, a finger length 10 mm and 15 mm and an overall length of 100 mm. A demonstrator device featuring an integrated microcontroller, sensing and reference capacitive sensors and a resistive temperature sensor was realized to proof a practical utilization. The microcontroller is used to calculate capacitances of IDT electrodes in terms of charging time proportional to the fluid level. The design with reference capacitor can be directly applied to different fluids with a wide range of conductivities and dielectric constants without recalibration. The printed structures were thermally laminated with covering PET foil. The sensitivity of the fabricated devices was characterized in liquids with different relative permittivity and conductivity (water and oil). The highest measured sensitivity was 0.7 pF/mm and 0.08 pF/mm for water and oil respectively, with resolution down to 0.1 mm.

Quartz Crystal Micro–Balance Gas Sensor with Ink–Jet Printed Nano–Diamond Sensitive Layer

Abstract the paper presents fabrication and characterization of a Quartz Crystal Microbalance based gas sensor with a diamond powder sensitive layer deposited using the ink-jet printing technique. The sensor was exposed to a low concentration of ammonia, acetone vapors and different levels of humidity. Impedance characteristics close to the natural resonant frequency of 10 MHz were examined. The sensor exhibits significant shifts in serial resonant frequency under different gas environments.

Quality water analyzer

The core of the article deals with the principles of analysis of pollutants in water by molecular absorption spectrometry. The spectrometer is used for analysis. Design and implementation of software for the evaluation of water analysis is part of the work. The software is designed with ease of use and retrieval of data. Analysis of water is mainly focused on nitrates. The detection is focused on determining levels of particular components, suitable algorithm recognizes the substance. The method with the exchange of energy between radiation and the material under investigation (the spectrometric method) is used in the work. The energy exchange is the absorption or emission of radiation.

FEM Simulation of Quartz Thickness Shear Mode Resonator for Gas Sensing Applications

The objective of this paper is to present simulation results of the Thickness Shear Mode (TSM) resonator based on quartz using finite element simulation method. 3D model of quartz resonator and simulations were completed using finite element method in CoventorWare software suite for design and simulation of MEMS devices. Different techniques for simulation of adsorption effect on selective layer were studied: influence of change in mass of the sensitive layer and influence of change in density of the sensitive layer. Analyses of resonant modes were performed for both cases and displacement profiles in selected modes were determined for the resonator under study. Impedance and phase characteristics were calculated and measured for clean sample and sample with selective layer coated. The adsorption model calculates the frequency shift in basic resonant frequency with adsorbed amount of sensed gas. The simulation results were used in design of gas sensors for dangerous substances detection.