Development Of Pulse Source And Control Module For Nitrogen-containing Material Detection System

The presence of explosives can be identified by detecting nuclear quadrupole resonance lines of 14 N nuclei in nitrogenous substances.Each of the nitrogen compounds containing explosives,has their own corresponding resonance spectrum,which is equivalent to the "fingerprint" is unique.based on this feature,this thesis combines the project to develop the signal source,power amplifier and control pulse module of the nuclear quadrupole explosive test principle prototype.The basic principle of nuclear quadrupole resonance,the excitation scheme and the overall scheme of nuclear quadrupole resonance detection system are introduced in this thesis firstly.Secondly,the RF signal source and the control circuit of the nuclear quadrupole resonant detection system are designed based on DDS technology.On the basis of introducing the basic structure,working principle,advantages and disadvantages of DDS,the hardware and software circuit design and implementation of DDS part are carried out according to the requirement of RF pulse.In order to satisfy the needs of the radix quadrupole resonant detection system for transmitting power,a circuit scheme using the Class AB power amplifier is adopted to classify the power amplifier based on the performance characteristics of various power amplifiers,and the load traction technique is used to complete the amplifier Design of Impedance Matching Network.For the reason of time shortage,this thesis does not complete the hardware amplifier implementation.Finally,the actual detection and debugging of the signal source and pulse module of the whole detection system are carried out.The test results are as follows:(1)The source can output 3.41 MHz,4.64 MHz,5.1938 MHz these three frequency signals,the output power is greater than 10 d Bm,the second harmonic suppression is more than 28 dBc.(2)FID pulse sequence 90° pulse width 50 us ~ 85 us,step 5us;excitation pulse interval period 50 ms ~ 800 ms,step 50 ms.SE pulse sequence 0° pulse width 50 us ~ 85 us,step 5us;refocus pulse width 150 us ~ 290 us,step 20 us,have been achieved through the pulse control module.The output level is greater than 3.3V.Test results show that the design of the module basically meet the expected requirements.