Dragan Mančić

Realization and optimization of bus bar current transducers based on Hall effect sensors

In this paper the realization and optimization of two coreless open-loop bus bar current transducers based on a Hall effect sensor are presented. Two types of bus bar are evaluated: flat rectangular and rectangular with a restrictive region in the middle. Both realized transducers are capable of measuring AC and DC currents up to 300 A and 10 kHz frequency with nonlinearity less than 0.3% in the entire range. Several methods for resolving issues with the skin effect and stray magnetic fields are presented along with the experimental test results. Some of the presented methods are novel and have never been evaluated.

New Three-dimensional Matrix Models of the Ultrasonic Sandwich Transducers

The new 3D models of the prestressed symmetrical and unsymmetrical ultrasonic sandwich transducers are described in this article. The sandwich transducers are modeled through the application of a 3D matrix model of piezoceramic rings and discs, recently proposed by the authors. Theoretical analyses prove the proposed models as simple and easy to calculate, particularly suitable for the investigation of coupled vibrations cases. Experiments show that the measured resonance and antiresonance frequencies are in good agreement with the predicted results. Compared with traditional 1D models and methods, the results obtained by the proposed models matched better with the experimental results.

Real‐time thermographic analysis of low‐density bone during implant placement: a randomized parallel‐group clinical study comparing lateral condensation with bone drilling surgical technique

OBJECTIVES To compare the effect of two surgical techniques, lateral condensation and bone drilling, on changes in temperature of the adjacent low-density bone during implant placement into posterior maxilla and to investigate the influence of the host factors - age, gender, region of implantation, bone density, and thickness of the cortical bone at the recipient sites. MATERIAL AND METHODS Local bone temperature was measured thermographically during implant placement into posterior maxilla following lateral bone condensing (test group) or bone drilling (controls). The main study outcomes were baseline bone temperature prior to implantation and maximum bone temperature recorded during implantation. Early implant success was evaluated after 6 months of healing. RESULTS A total of 40 implants were randomly allocated to test and control groups and placed into maxillary premolar and/or molar region of 18 participants of both genders and average age of 51.74 years. All recorded bone temperatures were below the threshold for thermal necrosis. Although both groups showed significant increase in bone temperature during implant placement procedure (P ≤ 0.0005), it was significantly higher for bone condensing compared with drilling (P ≤ 0.0005; 3.79 ± 1.54°C; 1.91 ± 0.70°C respectively). No host factor was singled out as a significant predictor of bone temperature changes, although trend of higher increase was observed in young patients, regardless of gender, during implant placement procedure into maxillary first premolar region with bone density type 3 and cortical layer thicker than 1 mm. Early implant success rate after 6 months follow-up was 100%. CONCLUSION Although both surgical techniques, bone condensing and bone drilling, can be considered safe regarding their thermal effect on the bone of posterior maxilla, bone drilling is associated with fewer local bone heating during implantation. Host factors do not affect the bone thermal changes significantly.

Low-cost wireless dust monitoring system

In this paper a prototype of wireless system for dust density measurement is presented. The system is developed with inexpensive commercially available components and can measure dust density up to 0.5mg/m3. The system is modular and consists of a base station connected to a PC via USB communication and an autonomous sensing node equipped with an optical dust sensor GP2Y1010AU0F. A virtual instrument made in LabVIEW is created to monitor the system operation, data acquisition and data storage.

A Matlab/Simulink 3D model of unsymmetrical ultrasonic sandwich transducers

Ultrasonic sandwich transducer is a half-wave resonant structure which oscillates in thickness direction. This paper presents a new Matlab/ Simulink model of a prestressed unsymmetrical ultrasonic sandwich transducer, which is modeled by applying three-dimensional (3D) Matlab/Simulink models of piezoceramic rings and metal endings derived from the piezoceramic ring model. With the cascade connection of the piezoceramic rings model with metal endings model, a complete model of ultrasonic transducer is obtained. Using this model one may determine any transducer transfer function, whereat is taken into the account the external medium influence, as well as the influence of the thickness and radial modes of each transducer component. The electromechanical equivalent circuit of the hammer transducer, which represents onedimensional (1D) model, is also derived and presented in this paper. The comparisons between experimental and theoretical results are quite good and validate the new analytical 3D design approach.

The system for magnetic field mapping based on the integrated 3D Hall sensor

A large number of modern devices contains permanent magnets, such as various types of magnetic sensors or motors. For the design and optimization purposes of all these devices one needs to know a very precise distribution of the magnetic field of the used magnets. These fields are often extremely inhomogeneous. For this reason it is necessary to build a magnetic field sensor that measures the magnetic flux density vector practically in a single spot. The solution to this problem is found in application of the integrated 3-axis Hall-sensor. Another problem that is described in this paper relates to the calibration of the integrated 3-axis Hall-effect sensors. For the calibration purpose there are designed the Calibration tools that reference the position of the Magnetic Field Sensitive Volume of the applied 3D Hall sensor respectively to the reference coordinate system of the Mappers, as well as the Calibration tools for the calibration and reduction of the angular errors. The Hall voltages from integrated 3-axis Hall sensor are being successively measured by placing the sensor in the Calibration Cube and rotating it. Based on these measurements it is possible to determine all 9 components of the Sensitivity matrix. A later on, during the mapping process, the measurement results can be calculated using the inverse sensitivity matrix, so that the final result corresponds to the real reference coordinate system.