Boyanka Marinova Nikolova

2D multiphysics frequency simulations of thin-film bulk acoustic wave resonator

A two dimensional (2D) finite element model of thin film bulk acoustic wave resonator (FBAR) is created in COMSOL Multiphysics to investigate the shifting of the parallel and series resonance frequencies as a function of the thickness of the electrodes. The dependence of the electromechanical coupling coefficient and quality factor from electrode thickness is also studied. A classical FBAR with aluminum nitride as piezoelectric layer and aluminum electrodes is modeled. The piezoelectric layer is chosen to resonate in the Personal Communications Service Band I (Tx: 1850.2–1909.8 MHz; Rx: 1930.2–1989.8 MHz). A methodology to build a 2D model of a FBAR in COMSOL and parameterize the electrode thickness is described.

Extraction of solar cell parameters using source measure unit

This paper presents a methodology for parameters extraction of photovoltaic cell based on real measurement. The modeling of equivalent schemes of solar cells is of great importance in order to be included in electric circuits for wireless sensor networks power supply. The parameters extraction of these devices is still a very difficult task, which requires experimental data, computing and modeling. In recent years different analytic, iterative, and evolutionary computational methods have been suggested in various references to extract the parameters of solar cell and modules. This paper presents an innovative approach to estimate model parameters by completely extracting them from real measured data.

Extraction of modified butterworth — Van Dyke model of FBAR based on FEM analysis

This paper presents a methodology for extraction of modified Butterworth-Van Dyke model (mBVD) parameters of thin-film bulk acoustic wave resonator (FBAR) using finite elements method (FEM) analysis. Simple FBAR model is developed and its frequency characteristic is obtained through FEM simulations. Then the mBVD model parameters are calculated and further optimized to fit its frequency response to those from FEM analysis with less than 1% relative error.

Cross-platform sensor networks

The development of wireless sensor networks offers new challenges for engineers and scientists from different technological areas. The involving of various hardware and software platforms in the implementation and design of sensor node increases the capabilities of sensor networks. Also, cloud services provide effective network management and access to stored data, detected and measured by sensors in the sensor network. This paper presents an approach for developing heterogeneous sensor networks and connecting it with cloud services.

System for multi-frequency capacitance-voltage characterization

Capacitance measurement at different DC voltage levels, different signal amplitudes and different frequencies, finds extensive application to qualify semiconductor and multiple-layered structures. Generally, the cost of such type instrumentation is in range of several thousand dollars and they are not very popular in the market. In present paper an approach of combining conventional measuring instruments and high-level programming environment is suggested in order to achieve system with complete functionalities for capacitance measurements.

Virtual colorimeter for water analysis

The water quality analysis is important for human health and environmental protection. There are many physical and chemical methods for such analysis, with different accuracies, complexity and time consumption. In the presented paper, a colorimetric method, based on virtual instrumentation is suggested and considered in details. At the end of the paper, the concentration of free chlorine in water is determined for example.

Cloud-managed ZigBee sensor networks

The main advantages of the open global standard ZigBee are mesh networking, low cost, low-power, low-complexity, reliability and operation on unlicensed frequency band, available worldwide. These benefits enforce ZigBee as one of the widely used standards for low-data-rate and short-range communications, used in wireless sensor networks. In recent years, with increasing interest are the management of sensor nodes beyond the borders of the personal area network and data collecting. In this paper is presented an approach to involve ZigBee based sensor networks in cloud technology in order to manage the network, collect and present the measured data.

SPICE modelling of magnetoresistive sensors

In this paper, characteristics of magnetoresistive sensors are considered and methods for their curve fitting are presented. In order to fit the sensors’ transfer characteristics, the Curve Fitting toolbox in MATLAB is used. A SPICE-based model of sensors is developed using analogue behavioural model (ABM) sources. As input data for ABM, mathematical expressions obtained from previous step of sensors’ characteristics fitting are used. The presented ABM models can be used in any SPICE-based simulation software for purposes of research design.