CN115128343A - FPGA-based perturbation cavity resonant frequency acquisition method - Google Patents

Abstract

The invention relates to a method for acquiring the resonant frequency of a perturbation cavity based on an FPGA (field programmable gate array). according to the characteristic that the power of reflected signals of input signals with different frequencies by the perturbation cavity is different, a circuit structure taking the FPGA as a control center is designed, and a circuit system is realized on the basis. Compared with a method for measuring by a vector network analyzer, the circuit system constructed according to the perturbation cavity resonant frequency acquisition method provided by the invention has the characteristics of miniaturization, low cost, convenience in use and the like.

Description

FPGA-based perturbation cavity resonant frequency acquisition method

Technical Field

The invention belongs to the technical field of microwaves, and relates to a method for acquiring a resonance frequency of a perturbation cavity based on an FPGA.

Background

A microwave resonant cavity is a resonator formed by a section of waveguide short-circuited at both ends, and is often used in combination with resonance perturbation techniques to characterize the properties of a material. In the resonance perturbation technique, a sample to be measured is introduced into a resonant cavity, and the electromagnetic properties of the sample can be deduced from the change of the resonant frequency of the resonant cavity. Due to higher sensitivity and accuracy and flexibility of sample preparation, the resonance perturbation technology is widely applied to measurement of low-loss bulk samples, powder, small-sized samples and irregularly-shaped samples. In general, resonant perturbation techniques can be divided into two types, shape perturbation and material perturbation. Shape perturbations are typically applied to readjust the resonant frequency of a resonant cavity, whereas in material perturbations, where a material is introduced into the cavity of the resonant cavity, resulting in a change in the resonant frequency of the resonant cavity, the dielectric constant of the material can be determined from the change in the resonant frequency of the resonant cavity after introduction of the sample. Therefore, the change condition of the resonance frequency of the perturbation resonance cavity can be conveniently and rapidly measured, and the application value of the resonance perturbation technology can be improved. In the related application research of the perturbation technology at the present stage, a Vector Network Analyzer (VNA) is usually used, and an S parameter curve of a perturbation cavity is measured through the VNA so as to judge the change condition of the resonant frequency of the cavity. However, VNA is expensive and not portable, so it is especially necessary to research the method for obtaining the resonant frequency of the perturbation cavity. The invention provides a circuit system with a simple structure based on an FPGA control unit, and the circuit system can be used for acquiring the resonant frequency of a perturbation cavity.

Disclosure of Invention

The invention provides a method for acquiring the resonant frequency of a perturbation cavity based on an FPGA. The basic structure of the circuit system involved in the method is shown in fig. 1, and the working principle is as follows:

(1) the FPGA is used as a control unit of the whole system to realize parameter configuration of the DAC register.

(2) And the DAC circularly outputs sequentially increased voltage signals under the control of the FPGA and guides the voltage signals to the input end of the VCO.

(3) The VCO outputs a frequency sweep signal with corresponding frequency according to an input voltage signal, the signal is led into the resonant cavity, and the resonant cavity can reflect a signal with corresponding power according to different frequencies of the input signal.

(4) The detector is used for detecting the power of the resonant cavity reflected signal and outputting a corresponding voltage value, and the voltage value of the output signal is larger when the power of the input signal is larger.

(5) The oscilloscope is used for displaying a finally generated voltage signal curve, the change condition of the resonance frequency of the perturbation cavity can be represented according to the characteristics of the curve, and the resonance frequency of the perturbation cavity is obtained through the output characteristic of the VCO.

Drawings

FIG. 1 is a structural diagram of a perturbation cavity resonant frequency acquisition system based on FPGA

FIG. 2 Circuit implementation of FPGA-based perturbation cavity resonant frequency acquisition system

FIG. 3 Dual Port

Of a mode-resonant cavity

Curve of parameters

Oscilloscope display of output signals of the system of fig. 4

Detailed Description

The invention designs a perturbation cavity resonant frequency acquisition method based on an FPGA (field programmable gate array) based on a microwave perturbation principle. According to a system structure diagram based on the principle of the method shown in fig. 1, the actual construction of the circuit is carried out, as shown in fig. 2. The main working frequency of the system, namely the frequency of an output signal corresponding to the VCO, is 3.44 GHz-3.55 GHz, the power of the VCO output signal is more stable at the typical output power of 4.7 dBm in the frequency range, and the sensitivity of the VCO is about 40 MHz/V at the moment. With a 14-bit DAC voltage output and a reference voltage of 5V, the ideal frequency offset that can be resolved by the system is 12.2 kHz.

The used perturbation cavity is dual-port

A cylindrical cavity resonator, through a central tubule, for introducing a solution as a disturbance, S, under the disturbance of a pure aqueous solution ₂₁ The parametric curve is shown in fig. 3. The corresponding frequency at point M1 in the graph is the resonant frequency of the perturbation cavity at this time. In the circuit system shown in fig. 2, the DAC module is automatically controlled by the FPGA, and a pure water solution is sucked into the solution pipe by using a syringe. And setting a proper DAC output voltage range to enable the VCO to generate continuous frequency sweeping signals, wherein the output signals have different power values due to the fact that the resonant cavity has obviously-changed input reflection coefficients in the frequency band and are converted by the detector. FIG. 4 shows the output signal of the oscilloscope display in the system, and the variation trend of the output signal in a sweep interval can be seen together with the resonant cavity S shown in FIG. 3 ₂₁ The parametric curves were consistent. The topmost end of the curve corresponds to the resonant cavity S ₂₁ The maximum value of the parameter is that the resonant cavity is in a resonance state, the frequency corresponding to the signal is the resonance frequency, and in the characterization system, the power of the reflected signal at the resonance frequency is maximum, and the maximum value is detectedThe wave filter obtains the maximum stable voltage value representing the power. When the resonant cavity is in different disturbance states, the resonant frequency can shift, the position of the highest point of the curve can change accordingly, and the function of representing the change condition of the resonant frequency of the perturbation cavity can be realized by measuring the relative position of the maximum value of the output signal of the oscilloscope, so that the resonant frequency of the perturbation cavity can be obtained.

Claims (1)

1. A perturbation cavity resonant frequency obtaining method based on FPGA comprises the following steps:

(1) the FPGA is used as a control unit of the whole system structure and a signal generating end to realize the parameter configuration of the DAC related register and control the DAC to generate a specific output signal;

(2) the DAC circularly outputs sequentially increased voltage signals under the control of the FPGA, and the signals are used as input signals of the VCO;

(3) the VCO outputs a signal with corresponding frequency according to an input voltage signal, and because the input signal changes circularly, the VCO outputs a sweep frequency signal which is led into the perturbation cavity, and the perturbation cavity reflects signals with different powers according to different frequencies of the input signal;

(4) the detector is used for detecting the power of the resonant cavity reflected signal and outputting a corresponding voltage value, and the voltage value of the output signal is larger when the power of the input signal is larger;

(5) the oscilloscope is used for displaying a finally generated voltage signal curve, the change condition of the resonance frequency of the perturbation cavity can be represented according to the characteristics of the curve, and the resonance frequency of the perturbation cavity is obtained through the output characteristic of the VCO.

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