Dielectric loss and dielectric constant are important physical properties of various ceramics such as electrical ceramics, device ceramics, capacitors, etc. LDJD-BDielectric constant tester, dielectric loss Q tableBy measuring the dielectric loss tangent (tan δ) and dielectric constant (ε), various factors affecting dielectric loss and dielectric constant can be further understood, providing a basis for improving the performance of materials.

Test principle

According to the perspective of material electrical structure, any substance is composed of different charges, and there are atoms, molecules, and ions in dielectrics. When a solid dielectric is placed in an electric field, the intrinsic dipole and induced dipole will align along the direction of the electric field, resulting in the generation of equal and opposite numbered charges on the surface of the dielectric, that is, the entire dielectric exhibits a certain polarity. This process is called polarization. The polarization process can be divided into displacement polarization, turning polarization, space charge polarization, and thermal ion polarization. The impact of various polarization processes varies for different materials, temperatures, and frequencies.

The dielectric constant is an important performance indicator of dielectrics. In insulation technology, especially when selecting insulation materials or dielectric energy storage materials, it is necessary to examine the dielectric constant of the dielectric. In addition, since the dielectric constant depends on polarization, which in turn depends on the molecular structure of the dielectric and the form of molecular motion. Therefore, by studying the variation of dielectric constant with electric field strength, frequency, and temperature, the molecular structure of insulating materials can also be inferred.

The phenomenon of electrical energy loss caused by leakage, polarization, and other factors in ceramics and other media under the action of an electric field, which is converted into thermal energy and dissipated, is called dielectric loss. In insulation materials, the magnitude of dielectric loss is usually represented by the tangent of dielectric loss angle (tan δ).

The meaning of dielectric constant (ε) is the ratio of the capacitance C obtained by a capacitor composed of a certain dielectric under a certain voltage to the capacitance C of a capacitor with the same size of dielectric as vacuum, that is, e=C/Co. Dielectric loss is of great significance for materials and components used in high-voltage devices, high-frequency equipment, especially in high-voltage, high-frequency and other places. Excessive dielectric loss not only reduces the performance of the entire machine, but can also cause thermal breakdown of insulation materials.

The dielectric constant of the ceramic device is too high, which can lead to unnecessary stray capacitance and affect the quality of the entire machine. However, capacitor ceramics require a high dielectric constant to make the device lightweight, compact, and have a large capacitance.

The determination of dielectric loss tangent and dielectric constant is mainly carried out using the principles of bridge or resonant circuit. LDJD-B dielectric constant meter is a commonly used instrument for measuring tan δ and ε. It consists of a high-frequency oscillator, a high-frequency signal monitoring device, a testing circuit, a vacuum tube voltmeter, and a power supply.

Working principle of Q-table

Based on the principle of resonance method using Q-table, performance data such as Q value, inductance, effective capacitance, distributed inductance, dielectric loss, and dielectric constant of an inductor coil can be measured using a Q-table using series or parallel connection method (i.e. connecting the tested component to the inductor or capacitor).

LDJD series dielectric constant and dielectric loss tester

Test instrument

LDJD-BDielectric constant tester, dielectric loss Q tableThe device is shown in the above figure.

(1) Frequency range and scale error

Range: 10kHz~110MHz, accuracy 3 × 10-5 ± 1 word, 6 significant digits, sampling accuracy 11BIT;

Q-value measurement range: 1-1000 automatic/manual range; Q-value resolution of 0.1, 4 significant digits; The measurement error of Q value is less than 5%;

Inductance measurement range and error: 1nH~8.4H, resolution 0.1nH, measurement error<3%, automatic deduction function for residual inductance and test lead inductance;

Material testing thickness: 0.1mm~10mm (multi-layer bonding can be used for thin film samples)

Sample size: φ 38mm or φ 50mm

test fixture

Precautions

(1) The size of the ceramic material circular sample [φ=(38 ± 1) mm, d=(2 ± 0.5) mm] should meet the tolerance requirements, and the silver layer, tin immersion, and welding lead wires on both sides should meet the technical conditions;

(2) The severe fluctuations in voltage or frequency often prevent the bridge from achieving good balance. Therefore, when measuring, the voltage or frequency must be stable, with voltage fluctuations not exceeding 1% and frequency fluctuations not exceeding 0.5%;

(3) The contact between the electrode and the sample has a significant impact on the tan δ test results, therefore, the silver layer electrode requires good and uniform contact with an appropriate thickness;

(4) After the sample absorbs moisture, the measured tan δ value increases, which affects the measurement accuracy. Therefore, the sample should be strictly avoided from absorbing moisture.