Impedance matching circuit

Figure 1. Diagram of apparatus (M) monomer reservoir (F) flow meter (VG) vacuum gage (mercury manometer) (E) electrode (T) liquid nitrogen trap (P) mechanical pump (V,) needle valve (Vt) stop valve (Vs) pressure control valve (OSC) discharge frequency oscillator (AMP) amplifier (1MC) impedance matching circuit...

Fig. 14. A RF tank circuit (as illustrated in (b)) with Ltank= 10 nH and C parasitic - 7 pF was tested to demonstrate how an impedance matching circuit would h ansform various resistance values (as given in (a)).

Each data line requires its own impedance Less impedance matching circuit ... 

Figure 2. Details of resonator contraction. Pick-up coils are wound around the sample holder tube, tuned to frequency and connected to a selective receiver via a low-noise impedance matching circuit (after Ablart Peseta, 1980).

As described by Pescia and coworkers, pickup coils were devised to operate with sample resonators that operated at specific microwave frequencies, that is, a wire helix (0.2 GHz), a stripline (0.7 GHz), and a cavity (4, 8-12 GHz, operated in reflection mode). As a representative example, the cavity resonator that is used at X-band is illustrated in Figure 2 (detailed diagrams of the helix and stripline resonators may be foxmd in Ablart Pescia, 1980). Here the saddle-shaped pickup coil is woxmd around the sample holder tube inside the cavity. In each case the pickup coil is tuned at frequency QJItz by a variable capacitor and connected to a selective receiver via a low-noise impedance matching circuit. 

Figure 8.2.2 (a) Schematic of the four-coil probehead introduced in Reference [12]. The four individual solenoidal coils are represented by an inductance (L), series resistance (R), and inter-turn capacitance (Q. The entire circuit was impedance-matched to 50 it at a frequency of 300 MHz by using the variable capacitors Ct and Cm. (b) Photograph of the four-coil assembly. Reprinted from MacNamara, E., Hou. T., Fisher, G., Wilhams, S. and Raftery, D., Multiplex Sample NMR an approach to high-throughput NMR using a parallel coil probe , Anal. Chem. Acta, 397, 9-16, copyright (1999), with permission of Elsevier Science... 

In the use of ferrites as inductors for tuned circuits, the Q of the materials is of prime importance. Wide-band transformers are also used extensively in communications systems, for example to transform signal voltages and to provide impedance matching and d.c. isolation of one part of a circuit from another. Pulse transformers are of increasing importance because of the rapidly growing use of pulsed signals in communications technology. Since a pulse can... 

Rigid-rod polymer films made from PBO and PBZT are being developed because they provide important performance improvements over competing materials such as fiber reinforced composites and metals. Table I summarizes some of the highest payoff applications. Thin PBZT films combined with low dielectric constant resins are being developed for multilayer circuit boards and multichip modules to increase interconnection density and speed with matched circuit impedance and reduced crosstalk. 

Once the coil has been incorporated into a tank circuit, a dip meter can be used to measure the resonance frequency. For a parallel resonant circuit, the dip meter can be used in the usual way, i.e., look for a "dip" indication as a function of frequency. For a series tank circuit, it is best to use the dip meter as an rf source acting like an artificial NMR signal and maximize the receiver output when the receiving system is fully hooked up. This will work also for the parallel tank. (See section V.C.9. on impedance matching.)... 

To understand how a negative resistance oscillator works, it is easiest to consider the electrical characteristics of the waveguide cavity in which the device is housed. A waveguide cavity is in its simplest form a short piece of transmission line terminated in a short-circuit at one end and an impedance matching device coupled to the rest of the circuit at the other end (Section 2.1). 

Figure 6 (A) A series-tuned, balanced-matched, inductively coupled sample (primary) coil. This example consists of a single loop of conductor with two symmetrically positioned fixed tuning capacitors, 2Q, and a variable capacitor, Q, for fine adjustment of the resonance frequency. The series tuning capacitors lower the coil voltage and should reduce dielectric losses. A secondary (impedance-matching) coil is required for coupling the primary to the spectrometer. (B) A circuit for a balanced-matched, inductively coupled surface coil. Lg is the inductance of the sample (primary) coil, which is tuned by Q and Q. Lm is the inductance of the matching (secondary) coil. The impedance matching can be fine-adjusted using Cm. (Reproduced with permission from Cady EB (1990). Magnetic Resonance Spectroscopy. New York Plenum Plenum.)...

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