Mikrosekundinių stiprių magnetinių laukų formuotų impulsų generatorių tyrimas

Microsecond high magnetic field shaped pulse generators are investigated in the dissertation. High magnetic field technologies, circuit transition processes and the pulse shaping technique are analysed. Two prototypes of the high magnetic field generators are developed, one of them with asymmetric pulse shape with amplitude over 10 T, the rise time of 200 s and decay time of 800 s was applied for express calibration of the magnetic field sensors. Another generator generates repetitive microsecond high magnetic field square shaped pulses with amplitude up to 5 T and duration of 3–25 s. Such generator has been applied to investigate the response of the biological objects to high-pulsed magnetic fields. The dissertation consists of three parts including introduction, 3 chapters, conclusions and references. The introduction reveals the investigated problem, importance of the thesis and the object of research and describes the purpose and tasks of the paper, research methodology, scientific novelty, the practical significance of results examined in the paper and defended statements. Author’s publications on the subject of the dissertation and conference presentations are supplied. Chapter 1 revises scientific articles related to the subject of the dissertation. The analysis of the magnetic field generation technology, devices used in magnetic field generators and microinductors are presented. The behaviour of the manganite and biological materials in high-pulsed magnetic fields are described. Conclusions and the tasks of dissertation are formed. Chapter 2 describes the structure of the high magnetic field generators prototypes. High magnetic field generator, consisting from capacitor bank, crowbar circuit and SCR switch is presented. Magnetic field distribution and Joule heating in multilayer inductors are analysed. High repetitive magnetic field generator based on MOSFET switch is presented. Transient processes in generator circuits are analysed. Microinductor field distribution and Joule heating are presented. Conclusions are formed. Chapters 3 is focused on the investigation of the magnetoresistive magnetic field sensors and the biological objects behaviour in the microsecond pulsed magnetic fields. The experimental results of the express calibration using one pulse technique of the magnetoresistive sensors and biological objects response in high magnetic fields are presented. Research results related to the dissertation subject are published in 7 scientific articles; 5 articles – in Thomson Reuters Web of Science database journals with impact factor, 2 – in others international (IndexCopernicus and IEEE/IEE) database journals, 7 presentations on the subject have been done in the conferences at national and international level

High magnetic field generator of sub-microsecond duration

The article describes the possibility of generating a micro and sub-microsecond magnetic impulse reaching 1–10 T, investigates various configurations of microcoils and discusses the principal circuit of a magnetic field impulse generator of microsecond duration. The transient processes of current, temperature and magnetic field are calculated applying the finite element method. Article in Lithuanian. Mikrosekundinės trukmės magnetinių impulsų generatorius Santrauka. Nagrinėjamas mikrosekundinės ir submikrosekundinės trukmės magnetinių impulsų, siekiančių 1–10 T, generavimas. Pateikta mikrosekundės trukmės magnetinių impulsų generatoriaus, kuris susideda iš mikroritės, mažą parazitinį induktyvumą turinčio kondensatoriaus ir greitų didelės galios MOSFET raktų principinė valdymo schema. Pereinamiesiems srovės, įtampos, elektromagnetinio lauko ir termodinaminiams vyksmams gauti taikomi analizinis ir baigtinių elementų skaičiavimo metodai. Straipsnyje pateikti elektromagnetinio lauko pasiskirstymo skaičiavimo rezultatai. Reikšminiai žodžiai: submikrosekundinis, baigtinių elementų metodas, magnetinis laukas, MOSFET, IGBT, kondensatorius, mikroritė

Investigation of microcoils for high magnetic field generation

Microcoils design for high pulsed magnetic field generation is described. A possibility to generate micro and sub-microsecond magnetic field pulses in 1-10 T range is analyzed. Pulsed facilities consisting of high voltage power supply, low self-inductance capacitor bank and fast high voltage solid state switches connected in parallel and in series are able to generate high power 1 kA, 0,5-1,0 ms pulses. Three different prototypes of single, dual and multiturn microcoils are investigated. Analytical and finite element methods are used for modelling of transient electromagnetic and thermodynamic processes. Computer simulation results of current density, thermal overloads and calculations of axial magnetic flux density are presented and recommendations for further experiments are offered

The investigation of 3D magnetic field distribution in multilayer coils

The investigation of magnetic field distribution via x-y-z directions of multilayer coils has been carried out. Finite elements method was used for numerical simulation of magnetic field components. The model was verified experimentally using experimental PC controlled equipment. The control algorithm for automatic measurements was developed using LabView programming package. It allows to map a magnetic field at any point over any surface moving a 3-axis magnetic probe through a three dimensional volume while measuring the three orthogonal components of magnetic field strength at designated points and magnetic field distribution profiles can be plotted. The experimental and simulation results were compared and acceptable compliance has been achieved. The results provide a possibility to forecast parameters of multilayer coils avoiding expensive and long lasting experiments

Исследование 3D распределения магнитного поля в многослойных катушках

The investigation of magnetic field distribution via x-y-z directions of multilayer coils has been carried out. Finite elements method was used for numerical simulation of magnetic field components. The model was verified experimentally using experimental PC controlled equipment. The control algorithm for automatic measurements was developed using LabView programming package. It allows to map a magnetic field at any point over any surface moving a 3-axis magnetic probe through a three dimensional volume while measuring the three orthogonal components of magnetic field strength at designated points and magnetic field distribution profiles can be plotted. The experimental and simulation results were compared and acceptable compliance has been achieved. The results provide a possibility to forecast parameters of multilayer coils avoiding expensive and long lasting experiments.Lietuviška santrauka. Pateikta daugiasluoksnės ritės magnetinio lauko pasiskirstymo x-y-z koordinačių sistemoje analizė. Taikant baigtinių elementų metodą buvo atlikta skaitinė imitacija magnetinio lauko pasiskirstymui nustatyti. Rezultatams patvirtinti buvo sukurtas kompiuterio valdomas eksperimentinis stendas. Stendo valdymo algoritmas parašytas LabView programinio paketo aplinkoje. Matavimo stendas su erdvėje judančiu x-y-z magnetinio lauko jutikliu įgalina išmatuoti magnetinio lauko pasiskirstymą tam tikroje erdvėje. Eksperimentiniai rezultatai buvo lyginami su skaitmeniniais ir pasiektas pakankamas rezultatų tikslumas. Pasiūlyta modelį bei gautus rezultatus taikyti daugiasluoksnių ričių konstrukcijos analizei ir projektavimui

Finite element method analysis of microfluidic channel with integrated dielectrophoresis electrodes for biological cell permeabilization and manipulation

The microfluidic channel with a planar inductive microcoil for the cell membrane permeabilization and the integrated planar electrodes for cell dielectrophoretic manipulation is proposed and analyzed in the study. The analyzed setup is based on the dielectrophoretic entrapment of the biological cell followed by membrane permeabilization using high pulsed magnetic field. The finite element method analysis of the DEP force and the generated pulsed magnetic field is performed. Based on finite element method analysis the potential applications of the setup in the fields of drug delivery, biomedicine and biotechnology are discussed

Compact microsecond pulsed magnetic field generator for application in bioelectronics

High power pulsed magnetic field generator for application in the bioelectronics area has been developed. The developed magnetic field facility is capable of generating pulsed magnetic field up to 5 T with pulse width in the microsecond range. The maximum repetitive frequency of the pulses is 40 Hz. The generator has been implemented by application of three high power thyristor switches, capacitor bank, specifically designed load coil with crowbar diode and the control circuitry. The inductive coil that has an integrated cuvette with effective volume of 2.4 μ l for biological samples is presented in the study. Finite element analysis of the generated pulsed magnetic field and comparison to the acquired experimental pulse are performed. Experimental results of human lymphocyte cells treated by pulsed magnetic field and potential applications of the generator in the bioelectronics area of magnetoporation are discussed. Based on the results further development and improvement ways of the facility for better integration in the area of bioelectronics are proposed

Modelling the cell transmembrane potential dependence on the structure of the pulsed magnetic field coils

During high power pulsed magnetic field treatment of biological samples the cells are subjected to both the high magnetic and induced electric fields. The extent of the influence of each treatment component is poorly studied. The work presents the finite element method analysis of pulsed inductive coils that are used for generation of pulsed magnetic and induced electric fields. The simulated coils, electrical parameters and the output characteristics are evaluated in respect to the induced cell transmembrane potential. The model of the Jurkat T lymphocyte cells is introduced in the analysis. The study includes finite element method analysis of four solenoid coils with different structure and inductance in the range of 2.8 μ H to 62 μ H. Pulsed magnetic field amplitudes up to 5 T are investigated in this work

High frequency electroporation efficiency is under control of membrane capacitive charging and voltage potential relaxation

The study presents the proof of concept for a possibility to achieve a better electroporation in theMHz pulse repetition frequency (PRF) region compared to the conventional low frequency protocols. The 200 ns × 10 pulses bursts of 10–14 kV/cm have been used to permeabilize Chinese hamster ovary (CHO) cells in a wide range (1 Hz–1 MHz) of PRF. The permeabilization efficiency was evaluated using fluorescent dye assay (propidium iodide) and flow cytometry. It was determined that a threshold PRF exists when the relaxation of the cell transmembrane potential is longer than the delay between the consequent pulses, which results in accumulation of the charge on the membrane. For the CHO cells and 0.1 S/melectroporationmedium, this phenomenon is detectable in the 0.5–1MHz range. Itwas shown that the PRF is an important parameter that could be used for flexible control of electroporation efficiency in the high frequency rangeAplinkos tyrimų centrasBiologijos katedraVilniaus Gedimino technikos universitetasVilnius Gediminas Technical University, LithuaniaVytauto Didžiojo universiteta

Membrane permeabilization of mammalian cells using bursts of high magnetic field pulses

Background Cell membrane permeabilization by pulsed electromagnetic fields (PEMF) is a novel contactless method which results in effects similar to conventional electroporation. The non-invasiveness of the methodology, independence from the biological object homogeneity and electrical conductance introduce high flexibility and potential applicability of the PEMF in biomedicine, food processing, and biotechnology. The inferior effectiveness of the PEMF permeabilization compared to standard electroporation and the lack of clear description of the induced transmembrane transport are currently of major concern. Methods The PEMF permeabilization experiments have been performed using a 5.5 T, 1.2 J pulse generator with a multilayer inductor as an applicator. We investigated the feasibility to increase membrane permeability of Chinese Hamster Ovary (CHO) cells using short microsecond (15 µs) pulse bursts (100 or 200 pulses) at low frequency (1 Hz) and high dB/dt (>106 T/s). The effectiveness of the treatment was evaluated by fluorescence microscopy and flow cytometry using two different fluorescent dyes: propidium iodide (PI) and YO-PRO®-1 (YP). The results were compared to conventional electroporation (single pulse, 1.2 kV/cm, 100 µs), i.e., positive control. Results The proposed PEMF protocols (both for 100 and 200 pulses) resulted in increased number of permeable cells (70 ± 11% for PI and 67 ± 9% for YP). Both cell permeabilization assays also showed a significant (8 ± 2% for PI and 35 ± 14% for YP) increase in fluorescence intensity indicating membrane permeabilization. The survival was not affected. Discussion The obtained results demonstrate the potential of PEMF as a contactless treatment for achieving reversible permeabilization of biological cells. Similar to electroporation, the PEMF permeabilization efficacy is influenced by pulse parameters in a dose-dependent manner