Equivalent circuit of a ferrite-wound inductor in a wide frequency range (0 Hz – 500 MHz)

Based on the measured impedance of the inductors wound on various ferrite cores and with a different number of turns, an equivalent high frequency (0 Hz 500 MHz) circuit model was built. The equivalent circuit model was built taking into account the physical processes occurring in the inductor: effect of wire resistance, effect of core material, mutual effect of wire and core material. The attempt explaining why the frequency characteristics (modulus and phase) of the inductor complex impedance have such a character in a wide frequency band (up to 500 MHz) was made. It was shown that for constructing an equivalent circuit model (structure and parameters), measuring only the inductors resistance modulus is not enough. It is also necessary to measure the phase of the inductor complex resistance, which is ignored in many works on the synthesis of an e inductor equivalent circuit.

Two Wire Sensor for Measuring the Velocity of Non-Isothermal Flows

Changes in the temperature of the medium significantly affect the static characteristics of hot-wire anemometry measuring wires, which causes errors in the results of flow velocity measurements. High temperatures of the medium make it necessary to additionally heat the sensor to even higher temperatures, which may lead to its damage due to wire burnout. The article proposes a solution to the problem of measuring the flow velocity in conditions of non-stationary temperatures with the use of the method of cross-correlation of signals from two-wire resistance thermometers. The main assumptions of the method and its experimental verification were presented.

Design and Optimise a GARField MRI Resonator

The design of a Nuclear Magnetic Resonance (NMR) sensor coil for a GARField NMR system was examined. The target design has a diameter about mm and length mm tuned to frequency of MHz at 50 Ω total impedance. Nine different sets of coils were built with different numbers of turns (3, 5, and 7) and different thickness of wire to vary the wire resistance. The report was to examine based on the design parameters the best resonant circuit for a GARField MRI system. The acquired tuning characteristics from these resonant circuits were interpreted using MATLAB scripts and Excel spreadsheet to compare each coil with already existing theory of resonators. This was achieved by matching each resonant circuit using a match and tuning capacitor to the required frequency (22-23.4 MHz) and to 50 Ω total impedance at resonance. It was found that there is no easy method to estimate the inductance of the coil of wire. The result for the experimental inductance was found to be 0.5 µF and resistance of 0.4 Ω for a medium coil of wire with 5 numbers of turns, diameter of 0.45 and length of 0.7 mm. The initial attempt to fit the experimental data to that of the theory failed due to the absence of stray capacitance in the theory. However, when stray capacitor with value ranging between pF was incorporated in parallel with the tank circuit, it was found that both the experiment and theory fit as expected. Three coils were tested in the NMR laboratory using a GARField spectrometer to examine the best coil that will be suitable for NMR experiment. Coils were compared on the basis of signal to noise ratio (SNR) and P90 pulse length. It was found that medium coil of wire with 3 number of turns has the biggest SNR of 177 which is good for NMR procedures. On the other hand, coil with 5 numbers of turns has the shortest P90 pulse length of 2.0 µs which is good for spatial resolution. At all rate, this research have shown how theories are verified through experiment.

The Development of a Novel Device Based on Loss of Guidewire Resistance to Identify Epidural Space in a Porcine Model

Background. The application of additive manufacturing (3D printing) has been recently expanded to various medical fields. The new technique named loss of guide wire resistance (LOGR) was developed via 3D printing for the detection of epidural space using a guide wire instead of air or saline used in the loss of resistance (LOR) technique. Methods. The prototype model of epidural space finder consists of a polyactic acid (PLA) or a resin. It was manufactured with 3D printing. Biocompatibility test (eluate and sterility tests) was performed in both products. The advantage of the newly developed device was compared with conventional loss of resistance (LOR) technique in a porcine model. Results. Eluate and sterility tests revealed that the PLA was more biocompatible than the resin. The LOGR technique facilitated rapid access to epidural space compared with the LOR technique (41.64 ± 32.18 vs. 92.28 ± 61.46 seconds, N = 14, p=0.0102, paired sample t-test), without any differences in success rate (87.5%). Conclusion. We conclude that LOGR technique is comparable to LOR technique to access the epidural space, although the advantage of either technique in terms of complications such as dural puncture or epidural hematoma is unknown. We demonstrated the potential benefit of 3D printer for the development of a new medical device for anesthesia.

Lead-Wire-Resistance Compensation Technique Using a Single Zener Diode for Two-Wire Resistance Temperature Detectors (RTDs)

In remote measurement systems, the lead wire resistance of the resistance sensor will produce a large measurement error. In order to ensure the accuracy of remote measurement, a novel lead-wire-resistance compensation technique is proposed, which is suitable for a two-wire resistance temperature detector. By connecting a zener diode in parallel with the resistance temperature detector (RTD) and an interface circuit specially designed for it, the lead-wire-resistance value can be accurately measured by virtue of the constant voltage characteristic of the zener diode when reverse breakdown occurs, and compensation can thereby be made when calculating the resistance of RTD. Through simulation verification and practical circuit testing, when the sensor resistance is in 848–2120 Ω scope and the lead wire resistance is less than 50 Ω, the proposed technology can ensure the measuring error of the sensor resistance within ±1 Ω and the temperature measurement error within ±0.3 °C for RTDs performing 1000 Ω at 0 °C. Therefore, this method is able to accurately compensate the measurement error caused by the lead wire resistance in two-wire RTDsand is suitable for most applications.