Application Cases

Experimental Name: Radio Frequency Signal Sensing Characteristics Testing System Design

Testing Equipment: High-voltage amplifier, arbitrary function generator, oscilloscope, RF signal sensor, laser, photodetector, etc.

Experimental Procedure:

Figure 1: Radio Frequency Signal Sensing Characteristics Testing System

A radio frequency signal sensing characteristics testing system was constructed as shown in Figure 1. A laser generates a light beam that passes through the RF electric field sensor, undergoing electro-optic modulation and polarization interference. The modulated optical signal is converted into an electrical signal at the photodetector and transmitted to the oscilloscope to express the output of the RF signal sensor. A signal generator produces arbitrary small signals (e.g., sine waves, square waves, triangular waves) to be measured. These signals are then amplified by a high-voltage amplifier to produce high-voltage outputs. The high-voltage output is applied to the parallel plate electrodes at both ends of the RF signal sensor via high-voltage leads to generate a uniform electric field for testing and calibrating the characteristics of the RF signal sensor. Another output is connected to the oscilloscope for signal monitoring and comparison with the actual output of the RF signal sensor.

Experimental Results:

In the experiment to test the input-output characteristics of the RF signal sensor, the RF signal sensing characteristics testing system was used to evaluate its actual performance. A 633 nm laser generated light transmitted to the RF signal sensor, where the RF electric field to be measured modulated the light. The modulated light was transmitted to the photodetector, which converted it into an electrical signal. The output signal was transmitted to the oscilloscope to display the results, while one output of the high-voltage amplifier was also connected to the same oscilloscope for monitoring and comparison with consistent time coordinates. A signal generator produced a power-frequency sine wave signal, which was applied to the parallel plate electrodes via the high-voltage amplifier. The positive and negative electrodes of the parallel plate were placed on the upper and lower surfaces of the sensing crystal, respectively.

Figure 2: Response of RF Signal Sensor Under Power-Frequency Electric Field

As shown in Figure 2, the response of the RF signal sensor under a power-frequency electric field indicates that the output of the sensor exhibits a positive correlation with the electric field strength.

Keeping the input voltage frequency constant at 50 Hz, the amplitude was gradually increased from 10 V. A power-frequency sine wave voltage was applied to the RF signal sensor, and the corresponding sensor output voltage for each input voltage was recorded. The test results are shown in Figure 4(a). It can be observed that within a certain range, the input-output relationship of the RF signal sensor is linear. If the frequency of the applied voltage is increased, the same linear relationship can still be obtained.

Figure 3: Linear Fitting Analysis Results

The measurement results were subjected to linear fitting, and the parameters of the linear fitting equation are shown in Figure 3. The closer the linear fitting degree is to 1, the more closely the data points are distributed around the regression line, indicating a better fit. From the experimental data and numerical analysis, the output voltage of the RF signal sensor designed in this work shows a strong linear relationship with the applied electric field.

To test the frequency response of the RF signal sensor, the amplitude of the applied signal was kept constant at 50 V, and the signal frequency was gradually increased from 50 Hz to 2 kHz. The frequency response curve of the RF signal sensor is shown in Figure 4(b). It can be seen that as the frequency increases, the output voltage of the RF signal sensor exhibits a non-linear decline, mainly due to the frequency response limitations of the parallel plate electrodes themselves. For the measurement of high-frequency, low-vibration RF signals, a waveguide structure design for the electro-optic crystal is required.

Figure 4: RF Signal Sensor Characteristics. (a) Input-Output Characteristics of RF Signal Sensor. (b) Frequency Response Curve of RF Signal Sensor

Recommended High-Voltage Amplifier: ATA-7010

Figure: ATA-7010 High-Voltage Amplifier Specifications

The experimental materials in this article were compiled and published by Xi’an Aigtek Electronics.