The work proposes a synthesis method of capacitive fractional-order impedance element which is composed of homogenous distributed resistive-capacitive (RC) structures (lines). The method employs genetic algorithm and searches for optimal connection schemes and parameters of the partial RC structures. The synthesis algorithm is described in detail including the coding of the properties of the structures for the purpose of the genetic algorithm. The user interface of the design tool is introduced and the input and output parameters of the synthesis are explained. The algorithm was verified by computer simulations and particularly by measurements of element samples fabricated in thick-film technology. The results correspond to the required impedance characteristics, which confirm the validity of the synthesis method.

• Klíčová slova
• Circuit synthesis, Distributed resistive-capacitive structure, Fractional-order element, Fractional-order impedance,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

The article presents a synthesis method to design electrical circuit elements with fractional-order impedance, referred to as a Fractional-Order Element (FOE) or Fractor, that can be implemented by Metal-Oxide-Semiconductor (MOS) transistors. This provides an approach to realize this class of device using current integrated circuit manufacturing technologies. For this synthesis MOS transistors are treated as uniform distributed resistive-capacitive layer structures. The synthesis approach adopts a genetic algorithm to generate the MOS structures interconnections and dimensions to realize an FOE with user-defined constant input admittance phase, allowed ripple deviations, and target frequency range. A graphical user interface for the synthesis process is presented to support its wider adoption. We synthetized and present FOEs with admittance phase from 5 to 85 degrees. The design approach is validated using Cadence post-layout simulations of an FOE design with admittance phase of 74 ± 1 degrees realized using native n-channel MOS devices in TSMC 65 nm technology. Overall, the post-layout simulations demonstrate magnitude and phase errors less than 0.5% and 0.1 degrees, respectively, compared to the synthesis expected values in the frequency band from 1 kHz to 10 MHz. This supports that the design approach is appropriate for the future fabrication and validation of FOEs using this process technology.

• Klíčová slova
• Distributed element, Fractional-order element, Fractor, Genetic algorithm, MOS transistor,
• Publikační typ
• časopisecké články MeSH

Electrical characteristics of living cells have been proven to reveal important details about their internal structure, charge distribution and composition changes in the cell membrane, as well as the extracellular context. An impedance flow cytometry is a common approach to determine the electrical properties of a cell, having the advantage of label-free and high throughput. However, the current techniques are complex and costly for the fabrication process. For that reason, we introduce an integrated dual microneedle-microchannel for single-cell detection and electrical properties extraction. The dual microneedles utilized a commercially available tungsten needle coated with parylene. When a single cell flows through the parallel-facing electrode configuration of the dual microneedle, the electrical impedance at multiple frequencies is measured. The impedance measurement demonstrated the differential of normal red blood cells (RBCs) with three different sizes of microbeads at low and high frequencies, 100 kHz and 2 MHz, respectively. An electrical equivalent circuit model (ECM) was used to determine the unique membrane capacitance of individual cells. The proposed technique demonstrated that the specific membrane capacitance of an RBC is 9.42 mF/m-2, with the regression coefficients, ρ at 0.9895. As a result, this device may potentially be used in developing countries for low-cost single-cell screening and detection.

• Klíčová slova
• Single-cell analysis, impedance analysis, impedance flow cytometry, microfluidic,
• MeSH
• analýza jednotlivých buněk MeSH
• buněčná membrána fyziologie   MeSH
• elektrická impedance * MeSH
• elektrická kapacitance MeSH
• erytrocyty * fyziologie   MeSH
• lidé MeSH
• průtoková cytometrie * přístrojové vybavení   metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe2-xGdxO4; x=0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd3+ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe2-xGdxO4 nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd3+ substitution in CoFe2O4 nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd3+ doped cobalt ferrite (CoFe2-xGdxO4; x=0.20) exhibit enhanced dielectric constant (277 at 100Hz) and ac conductivity (20.2×10-9S/cm at 100Hz). The modulus spectroscopy demonstrated the impact of Gd3+ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd3+ substitution from 234.32Oe (x=0.00) to 12.60Oe (x=0.05) and further increases from 12.60Oe (x=0.05) to 68.62Oe (x=0.20). Moreover, saturation magnetization decreases with Gd3+ substitution from 40.19emu/g (x=0.00) to 21.58emu/g (x=0.20). This work demonstrates that the grain size and cation distribution in Gd3+ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications.

• Klíčová slova
• Cavitation, Dielectric property, Impedance and modulus spectroscopy, Magnetic property, Nanoparticles, Sonochemical synthesis,
• Publikační typ
• časopisecké články MeSH