1.Basic concepts and formulas of dielectric constant (ε)
Dielectric constant is a physical quantity that characterizes the ability of a dielectric to store charges in an electric field, also known as permittivity, and is one of the core parameters for measuring the electrical properties of insulating materials. The larger its value, the stronger the material's ability to store charges, but usually insulating materials tend to have a low dielectric constant to reduce signal loss and interference.
(1)Definition formula of dielectric constant
The dielectric constant (relative dielectric constant, εᵣ) is the ratio of a material's dielectric constant (ε) to its vacuum dielectric constant (ε₀):
εᵣ=ε/ε₀
Among them, ε₀ is the vacuum dielectric constant, which is approximately 8.854 × 10-12 F/m (Farad/m).
The relative dielectric constant (εᵣ) is a dimensionless physical quantity. The εᵣ of vacuum is 1, the εᵣ of air is approximately 1.0006, and the εᵣ of insulating materials is usually between 2-10 (such as ETFE's εᵣ of about 2.6).
(2)Formula for the relationship with capacitance
For parallel plate capacitors, the relationship between capacitance (C) and dielectric constant is:C=εᵣ⋅ε₀⋅A/d
Among them, A is the area of the electrode plate, and d is the distance between the electrode plates (insulation material thickness).
This formula indicates that under the same structure, the larger the dielectric constant and capacitance, the stronger the material's ability to store charges.
(3)Loss related: dielectric loss tangent (tan δ)
Dielectric loss is the energy loss of insulating materials due to molecular polarization hysteresis in an electric field. It is commonly represented by the dielectric loss tangent (tan δ) and is related to the dielectric constant as follows:tanδ=ε/ε′
Among them, ε' is the real part of the dielectric constant(representing energy storage capacity), and ε'' is the imaginary part(representing loss).
The smaller the tan δ, the smaller the insulation loss of the material, and the more stable the electrical performance (such as ETFE's tan δ of about 0.003, which belongs to low loss materials).
2.Key parameters and conversion relationships of insulation performance
The core parameters of insulation performance include insulation resistance, breakdown strength, dielectric constant, dielectric loss, etc. These parameters collectively reflect the insulation ability and stability of materials, and some parameters can be correlated through experiments or empirical formulas.
(1)Insulation resistance (Rins)
Insulation resistance is the ability of a material to resist current leakage, measured in ohms (Ω), and is related to the material's resistivity (ρ) as follows:Rins=ρ⋅d/A
Among them, ρ is the volume resistivity (unit: Ω·m), d is the insulation thickness, and A is the conductive surface area.
Conversion meaning: The higher the resistivity, the higher the insulation resistance, and the better the insulation performance of the material (such as ETFE, whose volume resistivity is usually greater than 10¹⁶Ω·m, belonging to high insulation materials).
(2)Breakdown strength (Eᵦ)
The breakdown strength is the critical electric field strength at which a material can withstand an electric field without being broken down, measured in kV/mm (kilovolts per millimeter), and calculated using the following formula:Eb=Ub/d
Among them, Uᵦ is the breakdown voltage(kV), and d is the insulation thickness(mm).
Conversion meaning: The higher the breakdown strength, the higher the voltage that the material can withstand at the same thickness (for example, the breakdown strength of ETFE is about 20-30 kV/mm, and only a very thin insulation layer is needed to meet the requirements at 600V voltage).
(3)The correlation between dielectric constant and signal transmission loss
In high-frequency signal transmission, signal loss (α) is related to dielectric constant (εᵣ) and dielectric loss (tan δ), and the empirical formula is:α∝f⋅√εr⋅tanδ
Among them, f is the signal frequency.
Conversion significance: Low εᵣ and low tan δ can significantly reduce high-frequency signal loss, so low dielectric materials such as ETFE are suitable for high-speed signal transmission scenarios (such as aerospace and precision electronic equipment).
3.Example of Performance Conversion in Practical Applications (Taking UL AWM 10126 Wire as an Example)
UL AWM 10126 wire adopts ETFE insulation (εᵣ≈2.6, tanδ≈0.003,breakdown strength≈25kV/mm), rated voltage of 600V, operating temperature of 150℃, the insulation performance conversion is as follows:
(1)Verification of breakdown voltage: If the insulation thickness is 0.1mm, the theoretical breakdown voltage Ub=Eb⋅d=25kV/mm×0.1mm=2.5kV,far higher than the rated 600V, with sufficient safety margin.
(2)High frequency loss estimation: At a frequency of 100MHz, its signal loss is much lower than that of high dielectric materials (such as PVC, with an εᵣ≈3.5), making it suitable for signal transmission in precision electronic devices.
(3)Insulation resistance conversion: If the surface area of the conductor is 10cm², the insulation thickness is 0.1mm, and the ETFE's ρ≈10¹⁷Ω·m,then the insulation resistance Rins=1017×0.0001/0.001=1016Ω,the leakage current can be ignored.
4.Summary
The dielectric constant is the core indicator of the energy storage capacity of insulating materials, which is directly related to capacitance and loss. Low dielectric constant (such as ETFE) is suitable for high-frequency and low loss scenarios.
The conversion of insulation performance can quantitatively evaluate the applicability of materials under different working conditions through formulas related to parameters such as resistance, breakdown strength, and loss (such as UL AWM 10126 wire, which is suitable for 600V electrical connections in compact spaces and high-temperature environments due to its low εᵣ and high breakdown strength).
The conversion of these parameters provides a scientific basis for wire selection and insulation design, ensuring cost and space optimization while meeting requirements such as voltage and temperature.
