The EPR spectrometer is a modern analytical device that includes all the most advanced achievements of microelectronics.
The device is based on the principle of coherent superheterodyne signal detection.The essence of this principle is shown schematically in Figure 1.
The LABRADOR® EPR spectrometer contains three oscillators: two microwave generators with generation frequencies and about 9.2 and 9.3 GHz and one reference oscillator with generation frequency = 100,000 MHz.
The principle of the organization of communication sources of microwave radiation (coherence)
Signals from microwave generators (т.1 and т.2) pass through the mixer, at the output of which (V.4) the signal has a frequency and an initial phase equal to the difference between the corresponding values of the input signals. The signal from the mixer enters the phase-frequency discriminator of the PDF, which compares it with the signal from the reference generator, adjusting the operation of the microwave generator 2 so that the input signals of the PDP have the same frequency and initial phase.
The principle of double frequency conversion (superheterodyne)
The signal from the microwave generator (V.1) passing through the resonator acquires two components (V.5), the amplitude of one of which is proportional to the absorption of the medium in the resonator (G ‘is the EPR signal itself), and the other is the dispersion (G «). After the resonator signal passes through the mixer (V.6) and, due to the coherence of the microwave sources, acquires the frequency and initial phase of the reference oscillator, undergoing the first frequency conversion. Then the signal hits the synchronous detector, where the second frequency conversion occurs with the release of constant components (v .8 and v.8 ‘), one of which has absorption EPR signal.
This ensures the principle of registration of an EPR signal without using the modulation of the magnetic field characteristic of classical EPR spectrometers, which provides some advantages and opens up additional possibilities in the study of various materials.
|Type of spectrometer||Coherent X-band Superheterodyne|
|Sensitivity, spin / 0.1 mT*Hz, not more||1х10^10|
|Range of microwave power||от 1 нВт-60 мВт|
|Operating frequency, MHz||9200|
|Intermediate frequency, MHz||100|
|Range of change of a magnetic field, Tl, not less||+/- 0,03|
|Range of change of frequency of modulation of a magnetic field, Hz, not less||0-12000|
|Weight, kg, not more||20|
|Power consumption, W, not more||60|
|Overall dimensions (LxWxH), mm, not more||330х370х260|
The upper level of the system is implemented on a control computer (desktop computer, laptop, etc.) equipped with an Ethernet 10/100 Base-TX interface using TCP / IP protocol. A specially developed program is installed on the control computer, which provides a user interface for controlling the operation modes, setting variable parameters, and monitoring the status. modes of operation and the course of measurement, as well as to save the measurement result with the possibility of further processing. For interfacing the spectrometer with a control computer, there is a module for signal processing and control.
The second hierarchy level is the spectrometer control processor. This level is responsible for maintaining the Ethernet 10/100 Base-TX interface, receiving higher-level logic level directives and sending it the requested results, setting up and monitoring the status of the instrument systems.
In addition to the above, the control processor forms the command parcels to the magnetic field controller.
At the third — lowest level of the hierarchy of the control system is the processor of the magnetic field controller. He receives directives to set the required field and executes them during an iterative process involving the measurement and correction of the induction value. In addition, a directive can be sent to the controller to measure the actual value of the field without changing it.
The compact magnetic system LABRADOR® provides work with a g-factor of about 2.
Components of the magnetic system:
The LABRADOR® spectrometer can be equipped with two interchangeable types of resonators:
The LABRADOR® instrument software allows you to save data in the most common EPR survey formats. including in the format of the company Bruker.
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