Insulation Properties of Medical Plastics

Plastics are generally considered insulators, but can transmit some electrical energy at higher frequencies. The effectiveness of a material as an insulator is usually measured by dielectric constant and dissipation factor properties.

Dielectric constant measures how well an insulator stores electrical energy so as to isolate electrical elements from each other and the ground. This is important in designing medical devices that include connectors and electronic circuits.  The more conductive a material, the greater its dielectric constant. Vacuum and dry air have very low dielectric constants approaching 1.0. Water has a very high dielectric constant.  Many plastics have moderate to low dielectric constant values.

Material with low dielectric constants also tend to have a low dissipation factors. That is, they do not let the charge they hold dissipate easily. Dissipation factor represents the inefficiency of dielectric materials. It is the ratio of the loss factor (a measure of all losses in a dielectric) to the dielectric constant of that material.

As electronic medical devices become more compact, the need for low dielectric constant becomes more important.  Variations in dielectric constant as small as 0.1 in a structure can make a difference in how a device performs.

Dielectric Constant Comparison:

Water 7.8
Neoprene 9.8
PVDF 6.0
Polyimide 3.0
PEEK 2.8
Polystyrene 2.7
Polyethylene 2.5
PTFE 2.1
Air 1.0