What are the precautions for using induction coil? Below, follow Getwell induction coil manufacturer to understand.
During the oscillation time, the output signal of the coil is composed of oscillation energy and nuclear magnetic signal energy.Both frequencies are the same, and the oscillating energy is much greater than the NMR signal energy, and much greater than the input power the post-stage receiver can withstand.So the signals that are in this time period need to be filtered out, and the nuclear magnetic signals that are useful in this time period need to be filtered out.
The time of death affects the application range of the system, especially for the sample with short relaxation time, such as solid fat, the time of death of the magnetic resonance system is shorter, otherwise the NMR signal generated by the sample has been completely relaxed at the time of system death, and the system cannot receive the death signal of the sample.
Air coil inductors
The traditional method of using RF induction coils
In this way, the passive diode is connected to a large resistor to shorten the time of death. The principle is that during the oscillation time, the larger oscillating energy can conduct the passive diode, forming a discharge path with the large resistor through the resistance.The limitations of this approach are:
(1) When the radio frequency is transmitted, the passive diode also needs to be switched on, and a considerable part of the useful radio frequency energy also needs to be consumed on the resistance, resulting in the reduction of coil efficiency;
(2) when the oscillation energy is consumed, useful RF power signals are also consumed;
(3) When the amplitude of the oscillation voltage is less than the diode opening voltage (generally considered to be 0.7V), the structure is no longer effective, but the amplitude of the oscillation signal is still much larger than that of the NMR signal;
(4) The temperature of the resistor is often so high that the resistor burns out or the solder at both ends melts.The results show that this method can not achieve good results from theoretical analysis to practical application.
Crossover air coil
The current method of using RF induction coil
Using high-frequency induction coils, dual-channel coils also solve the dead-time problem by separating the transmitting and receiving coils in order to shorten the coil oscillation time.However, there is a serious coupling problem in the two-channel coil. The oscillation of the transmitting coil will be coupled to the receiving coil, and the oscillation time is basically the same as that of the receiving and receiving integrated coil. Moreover, the debugging of the two-channel coil will lead to double the workload.
Therefore, how to overcome the problem that the passive coil generated by the large series resistance of the diode consumes both the oscillating energy and the useful RF energy at the same time, while avoiding the consumption of the oscillating energy less than the diode opening voltage, has become a difficulty in this regard.
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Post time: Apr-21-2021