What is Dielectric Constant? Influence of Dielectric Constant on Radar Level Gauge Measurement

The definition of dielectric constant The medium will generate induced charges and weaken the electric field when an electric field is applied. The ratio of the electric field reduction in the medium to the original applied electric field (in vacuum) is the relative permittivity, also known as the inductive rate, which is related to frequency. . The permittivity is the product of the relative permittivity and the absolute permittivity in vacuum. If a material with a high dielectric constant is placed in an electric field, the strength of the electric field will drop considerably within the dielectric. The relative permittivity εr can be measured using an electrostatic field in the following way: First test the capacitance C0 of the capacitor while there is a vacuum between the two plates. Then, measure the capacitance Cx with the same distance between the capacitor plates but with a dielectric added between the plates. The relative permittivity can then be calculated with the following formula εr=Cx/C0 The relative permittivity of dry air without carbon dioxide at standard atmospheric pressure εr=1.00053. Therefore, the capacitance Ca in air for this electrode configuration is replaced by When C0 is used to measure the relative permittivity εr, it also has sufficient accuracy. (refer to GB/T 1409-2006). For time-varying electromagnetic fields, the dielectric constant of a substance is frequency-dependent, commonly referred to as the permittivity. Simply put, the effect of dielectric constant on electromagnetic waves is: the medium with a large dielectric constant has a stronger ability to reflect electromagnetic waves, and a medium with a small dielectric constant has a weaker ability to reflect electromagnetic waves. ※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※※The influence of dielectric constant on radar level gauge measurement is not all radar level All gauges need to set the dielectric constant parameter. Some non-contact and guided wave radars only have a sensitivity option. Most of the radar level gauges that require a dielectric constant are the detection interface and the double-rod. The impact of the dielectric constant on the radar electromagnetic wave is reflected in two aspects. One is to affect the absorption (reflection) rate of the electromagnetic wave on the surface of the medium. The wavelength (frequency) changes when passing through the medium. On the surface, the working process of the radar level gauge transmitting→reflecting→receiving does not require a dielectric constant. By adjusting the sensitivity as needed, the desired echo can be detected from various echoes to complete the measurement.  However, in some cases, to eliminate the unnecessary echoes and detect the required echoes, it is necessary to greatly increase the calculation amount of the liquid level gauge and add a dielectric constant parameter, which makes it easier to obtain accurate liquid level values. For example: when there is foam on the liquid surface, the foam surface will be identified as the liquid surface; some liquid surface layers will precipitate some other media (such as clear water on the surface of the mud), because it is very thin, the liquid level gauge will use the underlying medium surface as the liquid level. In some media, the level gauge will use the tank bottom echo as the liquid level signal. In addition: for guided wave radars with dual rods or coaxial probes, the liquid level gauge needs to distinguish whether the interaction between the two electrodes occurs above the liquid level or in the medium.   In these cases, adding a dielectric constant can greatly reduce the computational complexity, and is sometimes necessary. Therefore, depending on the model, application, and structure, some radar level gauges require dielectric constant, while others require sensitivity settings. Radar level gauges do not measure based on the dielectric constant of the medium being measured. It should be said that the radar level gauge is based on the calculation of the time it takes for the radar wave to reach the surface of the object. The dielectric constant of the measured medium is only one of the conditions that determine the reflectivity of radar waves. Radar wave is an electromagnetic wave, and the reflectivity of electromagnetic wave is affected by the following conditions: 'The attenuation coefficient is proportional to the square root of the conductivity (σ) and magnetic permeability (μ), and inversely proportional to the square root of the dielectric constant (ε).' That is to say, the larger the dielectric constant of the target object, the smaller the attenuation rate, and the smaller the attenuation rate, the greater the reflectivity. So the dielectric constant is large - the reflectivity is strong - the signal strength is high.  On the contrary, the dielectric constant is small, the attenuation rate is large, the reflectivity is small, and the signal strength is weak, so it is beneficial to the measurement if the dielectric constant can be determined when the radar level gauge is set. Related product links: 80GHz radar level gauge 922.html
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