Construction Of ESR System Based On Microstrip Resonator

The traditional ESR system uses a resonant cavity as a fixture.This system can only measure liquid and powder samples,but can not measure film samples without breaking it into pieces.In this work,we designed two systems.Both systems use direct loading samples resonant cavity and microstrip resonator as fixtures.In this way,we can measure the ESR signal of the film without damaging the sample.The first system uses the lock-in amplifier as the signal terminal.The second system uses the vector network analyzer as a signal terminal.The first system uses a microwave source and a power amplifier to generate a high-power microwave signal.When resonance occurs,the sample absorbs this signal.And the circulator transmits the change of the signal to the lock-in amplifier.In the second system,the vector network analyzer is the signal transmitting and receiving port at the same time.We define the ESR signal by measuring S11 parameters.In this work,firstly we designed two resonators through HFSS software.The first is a TE₀₁₁cylindrical resonator with a resonance frequency in the X-band.The second is a microstrip resonator with a resonant frequency in the C-band.In order to improve the conductivity and prevent oxidation,the surfaces of these two types of resonators have been gold-plated.The theoretical resonance frequency of the resonant cavity is 9Ghz.The actual measure is 8.83-8.85Ghz,and the Q value is 12000.Finally,we designed two tuning methods to improve its resonance capability.The microstrip resonator has a large bandwidth and a stable resonance point.Because the shape of the sample has little interference to the microstrip resonator,it can measure film samples.Then we use DPPH to evaluate the performance,sensitivity,and SNR of the system.For the first system,we optimized the microwave power,the time constant of the lock-in amplifier,and the magnitude of the modulated magnetic field.For the second system,we optimized different parameters such as the number of scanning points,taking the average of points,and power.Finally,we compared the performance of the two systems.The second system has higher sensitivity,while the first system has more room for improvement.We optimized the measure points of the system by measuring DPPH.Measure the film sample at this test point.The tan? of the film sample at the test frequency is 5.17×10^-2.We can measure the ESR signal of the PTAA thin film by using the microstrip resonator in this medium's condition.Finally,we calculated g=2.0047 of the sample PTAA.In short,we designed two resonant devices and built two systems.Experiments show that PTAA film and DPPH film on high-loss substrates can be characterized.Our system provides a reliable method for detecting the ESR signal of thin film samples on high-loss substrates.