View Latest Blog Entries
Testing & Assessment Certification Standard & Regulation Aging Wires & Systems Maintenance & Sustainment Management Conference & Report Protection & Prevention Research Miscellaneous Arcing
Popular Tags
Visual Inspection High Voltage AS50881 MIL-HDBK MIL-HDBK-525 FAR AS4373 Electromagnetic Interference (EMI) Maintenance FAR 25.1707 Wire System Arcing Damage
All Tags in Alphabetical Order
2021 25.1701 25.1703 abrasion AC 33.4-3 AC 43 Accelerated Aging accessibility ADMT Aging Systems AIR6808 AIR7502 Aircraft Power System aircraft safety Aircraft Service Life Extension Program (SLEP) altitude arc damage Arc Damage Modeling Tool Arc Fault (AF) Arc Fault Circuit Breaker (AFCB) Arc Track Resistance Arcing Arcing Damage AS22759 AS22759/87 AS23053 AS29606 AS4373 AS4373 Method 704 AS50881 AS5692 AS6019 AS6324 AS81824 AS83519 AS85049 AS85485 AS85485 Wire Standard ASTM B355 ASTM B470 ASTM D150 ASTM D2671 ASTM D8355 ASTM D876 ASTM F2639 ASTM F2696 ASTM F2799 ASTM F3230 ASTM F3309 ATSRAC Attenuation Automated Wire Testing System (AWTS) Automotive Avionics backshell batteries bend radius Bent Pin Analysis Best of Lectromec Best Practice bonding Cable Cable Bend cable testing Carbon Nanotube (CNT) Certification cfr 25.1717 Chafing Chemical Testing Circuit Breaker circuit design Circuit Protection cleaning clearance Coaxial cable cold bend collision comparative analysis Compliance Component Selection Condition Based Maintenance Conductor Conductor Testing conductors conduit Connector connector installation Connector rating connector selection connector testing connectors contacts Corona Corrosion Corrosion Preventing Compound (CPC) corrosion prevention Cracking creepage D-sub data analysis data cables degradat Degradation Delamination Derating design safety development diagnostic Dielectric breakdown dielectric constant Dimensional Life disinfectant Distributed Power System DO-160 dry arc dynamic cut through E-CFR electric aircraft Electrical Aircraft Electrical Component Electrical Power Electrical Testing Electrified Vehicles Electromagnetic Interference (EMI) Electromagnetic Vulnerability (EMV) Electrostatic Discharge EMC EMF EN2235 EN3197 EN3475 EN6059 End of Service Life End of Year Energy Storage engines Environmental Environmental Cycling environmental stress ethernet eVTOL EWIS certification EWIS Component EWIS Design EWIS Failure EWIS sustainment EWIS Thermal Management EZAP FAA FAA AC 25.27 FAA AC 25.981-1C FAA Meeting failure conditions Failure Database Failure Modes and Effects Analysis (FMEA) FAQs FAR FAR 25.1703 FAR 25.1707 FAR 25.1709 Fault fault tree Fixturing Flammability fleet reliability Flex Testing fluid exposure Fluid Immersion Forced Hydrolysis fuel system fuel tank ignition Functional Hazard Assessment functional testing Fundamental Articles Fuse Future Tech galvanic corrosion Glycol Gold Gold plating Green Taxiing Grounding hand sanitizer handbook Harness Design harness protection hazard Hazard Analysis health monitoring heat shrink heat shrink tubing high current high Frequency high speed data cable High Voltage High Voltage Degradation HIRF History Hot Stamping Humidity Variation HV connector HV system ICAs IEC 60851 IEC60172 IEEE immersion insertion loss Inspection installation installation safety Instructions for Continued Airworthiness insulating material insulating tape Insulation insulation breakdown insulation resistance insulation testing interchangeability IPC-D-620 ISO 17025 Certified Lab ISO 9000 J1673 Kapton Laser Marking life limit life limited parts Life prediction life projection Lightning lightning protection liquid nitrogen lithium battery lunar Magnet wire maintainability Maintenance Maintenance costs Mandrel mean free path measurement mechanical stress Mechanical Testing MECSIP MIL-C-38999 MIL-C-85485 MIL-DTL-17 MIL-DTL-23053E MIL-DTL-3885G MIL-DTL-38999 MIL-E-25499 MIL-HDBK MIL-HDBK-1646 MIL-HDBK-217 MIL-HDBK-454 MIL-HDBK-516 MIL-HDBK-522 MIL-HDBK-525 MIL-HDBK-683 MIL-STD-1353 MIL-STD-1560 MIL-STD-1798 MIL-STD-464 MIL-T-7928 MIL-T-7928/5 MIL-T-81490 MIL-W-22759/87 MIL-W-5088 MIL–STD–5088 Military 5088 modeling moon MS3320 NASA NEMA27500 Nickel nickel plating No Fault Found OEM off gassing Outgassing Over current Overheating of Wire Harness Parallel Arcing part selection Partial Discharge partial discharge at altitude Performance physical hazard assessment Physical Testing polyamide polyimdie Polyimide-PTFE Power over Ethernet power system Power systems predictive maintenance Presentation Preventative Maintenance Program Probability of Failure Product Quality PTFE pull through Radiation Red Plague Corrosion Reduction of Hazardous Substances (RoHS) regulations relays Reliability Research Resistance Revision C Rewiring Project Risk Assessment S&T Meeting SAE SAE Committee Sanitizing Fluids Secondary Harness Protection separation separation distance Separation Requirements Series Arcing Service Life Extension Severe Wind and Moisture-Prone (SWAMP) Severity of Failure shelf life Shield Shielding Shrinkage signal signal cable Silver silver plated wire silver-plating skin depth skin effect Small aircraft smoke Solid State Circuit Breaker Space Certified Wires Splice standards Storage stored energy superconductor supportability Sustainment System Voltage Temperature Rating Temperature Variation Test methods Test Pricing Testing testing standard Thermal Circuit Breaker Thermal Endurance Thermal Index Thermal Runaway Thermal Shock Thermal Testing tin Tin plated conductors tin plating tin solder tin whiskering tin whiskers top 5 Transient Troubleshooting TWA800 UAVs UL94 USAF validation verification video Visual Inspection voltage voltage differential Voltage Tolerance volume resistivity vw-1 wet arc white paper whitelisting Winding wire Wire Ampacity Wire Bend Wire Certification Wire Comparison wire damage wire failure wire performance wire properties Wire System wire testing Wire Verification wiring components work unit code

Unwanted Energy Storage in Cables – Dielectric Constant

Testing & Assessment

Key Takeaways
  • A wire’s dielectric constant is related to the energy stored in the insulation.
  • Lower insulation dielectric constants are preferred for high-speed data applications
  • This parameter must be tightly controlled for impedance controlled systems.

A good wire insulation is more than just preventing electrical energy from leaving the conductor; there are dozens of properties that are important to its performance and usability. One of these that is easy to overlook is the wire’s dielectric constant.

From a conceptual viewpoint, a wire’s dielectric constant is usually thought of as a capacitor. Similar to a capacitor, the wire insulation can store energy. This energy storage capacity can be increased by choosing an insulating material with a higher dielectric constant.

But how does the dielectric constant play into electrical wire interconnection systems (EWIS)? The answer is that, in modern systems, it matters in several interesting ways.

What is Dielectric Constant

Dielectric constant (a.k.a relative permeability) is most easily understood in the context of a parallel plate capacitor. The formula for capacitance of parallel plate capacitor is the following: \(C = \epsilon D\frac{A}{d}\)

Harness and Wire Cross Section
A wiring harness cross section [Left] and eight (8) wire cable [Right].

Where ‘ε’ is the permeability of free space (empty), ‘D’ is the dielectric constant, ‘A’ is the plate area and ‘d’ is the plate separation. This means a capacitor of given dimensions that has a capacitance ‘C0’ when there is a hard vacuum between the capacitor plates will have a capacitance of D * C0  when the insulating material (dielectric constant ‘D’) is inserted between the plates.

Air has a dielectric constant very close to that of a vacuum (empty space). Since material dielectric constants are greater than 1, inserting an insulating material increases the system’s capacitance.

Impedance of Capacitive Systems

When a sinusoidal signal is input into a system, the system’s impedance begins to have an impact on performance. Impedance of a purely capacitive system is given by the formula \(X=\frac{1}{2\pi fc}\) . This means that sinusoidal signals can be transmitted between system/components when there is capacitance between the components. The amount of transferred energy relates directly to the impedance between the components at the frequency of the signal source (it also relates to the power of the signal source). Low impedances will transfer more of the signal energy. Note that the impedance of the capacitive system decreases with increasing frequency and decreases with increasing capacitance.

As higher frequencies signals are used, the capacitive effects will increase due to the lower impedances at those frequencies. This also suggests that one way to limit this increase is by decreasing the capacitance between components. Decreasing capacitance can be done in several ways including:

  1. Decreasing the dielectric constant
  2. Increasing separation distances
  3. Decreasing the area of an electrode

Indeed, these are some of the strategies employed when considering Electromagnetic Interference (EMI) mitigation strategies and they specifically limit capacitive coupling as described above.

Relation to Noise and EMI Within Harnesses

Consider a typical wiring harness shown in first figure. Some of the wires may be power carrying wires, some of them may be low power signal wires. Some of the power from the power wire will transfer to the signal wire because of the capacitive impedance mentioned above. Since the power levels of the power carrying lines are much greater than on signal wire, and that hardware using signal wire will generally rely on low line level voltages, there is a real potential for noise (interference) on the signal circuits from the power lines.

One way to decrease the power transfer between wires would be to pick insulation and filler materials with low dielectric constants. This would decrease capacitance and increase the impedance between components. This is far from the only way to decrease power transfer, but it is one design choice that could lead to weight savings and a general decrease in power transfer between circuits.

The same thinking can be applied to capacitances within cables, however, in high frequency cable design, the characteristic impedance is another separate design consideration that is affected by changing the dielectric constant of cable materials. Changing the dielectric constant may be employed to, for example, decrease cross-talk within cables without increasing the volume or weight of the cable. Contact Lectromec if you would like cross-talk measurements made on your cable designs.

Relation to Cable Characteristic Impedance

The characteristic impedance of a cable will change depending on the dielectric constant of the materials used in cable construction. A model for an ideal transmission line is shown in the accompanying figure. Note that the capacitances in the model will be changed by such things as separation distance from inner conductor and shield (coax) or separation distance between the conductors of balanced twisted pairs. The capacitance will also be dependent on the dielectric constant of the insulating/filler materials used in cable construction. This will affect the characteristic impedance of the cable.

Harness and Wire Cross Section
Ideal transmission line (coaxial cable).

Cables manufactured to specific characteristic impedances use materials with well-known dielectric constants. In high frequency circuits, impedance matching and controlled characteristic cable impedance is necessary to limit signal reflections. A fuller description of characteristic impedance and the need to control it is beyond the scope of this article and will be covered in future Lectromec articles.

Bringing it Together

The dielectric constant of a cable to is not just an interesting fact, but an important parameter than has an impact on the transmission of data. The dielectric constant factors into signal attenuation primarily limiting the performance at high frequencies.

Most wire/cable standards related to data/signal transmission test this parameter. It can be expected to see a progressive decrease in the dielectric constant as wire/cables continue to evolve for those critical, high-speed applications.

Tristan Epp Schmidt

Tristan Epp Schmidt

Engineer, Lectromec

Since starting at Lectromec in early 2015, Tristan has been key in many of test and assessment wire systems assessment projects wire systems assessment. His attention to detail has lead to several key insights in Lectromec’s research initiatives.