Milan Radovanovic

Monitoring of Water Content in Building Materials Using a Wireless Passive Sensor

This paper describes an innovative design of a wireless, passive LC sensor and its application for monitoring of water content in building materials. The sensor was embedded in test material samples so that the internal water content of the samples could be measured with an antenna by tracking the changes in the sensor’s resonant frequency. Since the dielectric constant of water was much higher compared with that of the test samples, the presence of water in the samples increased the capacitance of the LC circuit, thus decreasing the sensor’s resonant frequency. The sensor is made up of a printed circuit board in one metal layer and water content has been determined for clay brick and autoclaved aerated concrete block, both widely used construction materials. Measurements were conducted at room temperature using a HP-4194A Impedance/Gain-Phase Analyzer instrument.

Design, Modeling, and Analysis of a Compact Planar Transformer

This paper presents a new design of a planar transformer. Over the surface of a flat core, meander-type design was engraved, so that symmetrically adjusted primary and secondary coils, of the same meander-type, can fit into the engraved design. Primary and secondary coils were covered with another flat core consequently forming a compact planar transformer. Windings of primary and secondary coils are printed on both sides of PCB. Conductive stripes of a winding from upper and bottom layer are connected by vias. The transformer was analyzed when the primary and secondary coils were without a core and with a core. High frequency parameters of the transformer were obtained by finite element modeling software and Impedance Analyzer HP4194A in the frequency range from 50 kHz to 1 MHz. The transformer is intended to be used in DC-DC converters (for switching frequency up to several hundred kHz).

A New Fractal-Based Design of Stacked Integrated Transformers

Silicon-based radio-frequency integrated circuits are becoming more and more competitive in wide-band frequency range. An essential component of these ICs is on-chip (integrated) transformer. It is widely used in mobile communications, microwave integrated circuits, low-noise amplifiers, active mixers, and baluns. This paper deals with the design, simulation, and analysis of novel fractal configurations of the primary and secondary coils of the integrated transformers. Integrated stacked transformers, which use fractal curves (Hilbert, Peano, and von Koch) to form the primary and secondary windings, are presented. In this way, the occupied area on the chip is lower and a number of lithographic processes are decreased. The performances of the proposed integrated transformers are investigated with electromagnetic simulations up to 20 GHz. The influence of the order of fractal curves and the width of conductive lines on the inductance and quality factor is also described.

A Wireless LC Sensor Coated with Ba0.9Bi0.066TiO3 for Measuring Temperature

This paper presents a passive LC wireless sensor for measuring temperature. The sensor is designed as a parallel connection of a spiral inductor and an interdigitated capacitor and it was fabricated in a conductive layer using LTCC (Low Temperature Co-fired Ceramic) technology. The inderdigitated capacitor electrodes were coated with a thin film of bismuth doped barium titanate (Ba0.9Bi0.066TiO3), whose permittivity changes with temperature, which directly induces changes in the capacitance of the interdigitated capacitor and consequently changes the resonant frequency of the sensor. The measurements of S-parameter of the sensor were performed using a Vector Network Analyzer (E5071B, Agilent Technologies, Santa Clara, CA, USA), whose port was connected to the antenna coil that was placed around the sensor in order to be able to wirelessly detect temperature, in the temperature range from 25 °C to 165 °C.

Computer as a tool for controlling measurement of water content in building materials

This paper describes the application of wireless LC sensor for measuring the concentration of water (or moisture) in the building materials. The sensor has manufactured on a double layered PCB (Printed Circuit Board) and placed in a test sample of a building material that is immersed in water. The change of water concentration in the sample can be measured wirelessly (antenna coil) by monitoring variations in sensors resonant frequency. Clay brick and aerated autoclaved concrete block are used for examination and testing as the often used building materials. Dielectric constant of water is much higher compared to the dielectric constant of test samples, and the higher concentration of water (or moisture) content of samples dictated a reduction in the sensor resonant frequency. Measurements were done at room temperature, using a PC with in-house developed software and an Impedance Analyzer HP-4194A. The program has been developed in LabVIEW software package allowing remote control and acquisition of measured data.

Determination of electrical parameters of dried blood spot samples with different concentration of methotrexate

The dried blood spot (DBS), a sample of filter paper bearing dried blood, has been applied in the field of clinical chemistry and pharmaceutical industry, for detection of different diseases and for drug development. This paper presents electrical characterization of DBS samples with different concentrations of a chemotherapy agent — drug methotrexate (MTX). Experimental characterization was conducted using a Hall-effect measurement system, profilometer, and impedance analyzer. Obtained results revealed that mobility decreases and resistivity increases with an increase of MTX concentration in DBS samples.