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.

ANALISIS RANGKAIAN OSCILATOR COLPITTS 20 KHZ UNTUK PENERAPAN MODULASI AMPLITUDO (AM)

Rangkaian Osilator Colpitts adalah suatu osilator yang cukup efektif digunakan sebagai pembangkit gelombang sinus. sehingga dapat dimanfaatkan sebagai gelombang pembawa (carrier). Pada osilator colpitts menggunakan dua buah kapasitor dan sebuah induktor yang disebut rangkaian tank (tank circuit). Fungsi dari kedua kapasitor ini adalah sebagai pembagi tegangan keluaran dan masukan ke penguat. Komponen induktor dan dua kapasitor ini yang akan menentukan frekuensi resonansi pada oscilator colpitts. Pada artikel ini akan membahas analisis oscilator colpitts yang diterapkan pada modulator AM. Hasil pengujian rangkaian osilator colpitts dengan mengubah-ubah harga kapasitor C1 dan C2 yakni antara : 10 nF dan 100 nF, sedang induktor dibuat tetap L=10 mH, diperoleh amplitudo osilator sekitar Vo = 5,5 - 12,6 V dan besar frekuensi sekitar : 5,4 – 7,6 Khz. Sedang untuk hasil pengujian osilator colpitts yang diterapkan pada modulasi amplitudo (AM), dengan tegangan input : 7,5 -12,6 Volt, diperoleh bentuk gelombang AM masih kurang bagus atau sempurna. Hal ini disebabkan amplitudo tegangan input lebih kecil dibanding amplitudo gelombang pembawa (osilator). Sedangkan untuk besar tegangan input antara : 15-22,4 Volt, ternyata menghasilkan gelombang termodulasi AM sangat bagus, hal ini disebabkan amplitudo input besarnya hampir sama dengan amplitudo gelombang pembawa (carrier) yakni sekitar 22 Volt.

Isolated Soft Switching Current Fed Series LC Resonant DC-DC Convertor for Electrical Vehicle Application

The current fed series resonant converter for electrical vehicle application is offered in this paper. The converter is able to achieve ZVS for primary side semiconductor switches. In the overlap time of voltage and current at zero crossing series resonant tank circuit is gives short interval of resonant pulse. This resonant pulse provide natural voltage decrease for semiconductor switches and voltage pulse is zero earlier compare to current across switches and ZVS achieve for semiconductor switches. All devices turn off softly so dependency on snubber is decreased to clamp the voltage across the switches. Presented converter reduce the circulating current so switching losses is decreased and converter efficiency will improvise. The proposed converter is simulated in MATLAB Simulink environment to investigate and analyses the proposed converter.

Design and Fabrication of Magnetic Loop Antenna for 5MHz

In the short-wave range, size of the antenna become large and therefore is a major constraint. Magnetic Loop Antenna provides an advantage over other antennas in terms of a smaller size, higher quality factor and better signal to noise ratio. It works on the principle of resonance with the inductor provided by loop and external tuning capacitor operating like a tank circuit. The tunable magnetic loop antenna is designed to work in the high frequency range. The antenna consists of a circular hollow copper pipe, an inductive loop feed and a variable tuning capacitor. The antenna is tuned using variable 9-140pF capacitor paralleled with 150pF capacitor. The designed antenna is simulated using 4NEC2 software. The simulated antenna has high efficiency and quality factor of more than 1000. The real time testing show great result at 5.45MHz with bandwidth of 8KHz.

An improved zero-voltage zero-current transition boost converter employing L-C-S resonant network

An improved zero-voltage zero-current transition boost converter (IZVZCTBC) is introduced. This converter is basically a fourth-order DC-DC converter wherein a L-C-S (Inductor–Capacitor–Switch) resonant circuit is embedded for soft-switching. L-C-S tank network is the modified version of conventional ZVZCT switch cell. The main feature of L-C-S tank circuit is to enhance the performance of zero-voltage zero-current transition boost converter in terms of eliminating the high current stress, decreasing the switching losses and increasing the efficiency of converter. This converter exhibits both zero-voltage turn on and zero-current turn off switching characteristics based on the gating signals applied to switches. The principle of operation and time domain expressions of IZVZCT boost converter with L-C-S cell are presented. For the closed loop operation, digital controller is designed and the performance of the controller has been validated through simulation for different line and load variations. The mathematical and theoretical analysis is verified accurately by a 12-24 V, 30 W converter through PSIM simulation software and the results ensures that overall efficiency of the converter has improved to 97% along with elimination of current stress.