Throughplane

Throughplane, or through-plane, is a directional term used in science and engineering to describe processes that occur perpendicular to a reference plane, i.e., across the thickness of a material or device. It contrasts with in-plane transport, which occurs parallel to that plane. The concept is widely used to characterize anisotropic properties of layered or thin-film systems where properties differ between the through-plane and in-plane directions.

In electrochemical energy devices such as polymer electrolyte membrane fuel cells and lithium-ion batteries, through-plane transport describes movement of ions, electrons, and heat across the membrane and electrode stack. Through-plane conductivity, diffusivity, and impedance are important for performance and are often measured by through-plane impedance spectroscopy, or by through-plane diffusion experiments, and modeled with finite-element methods.

Thermal management applications likewise use through-plane thermal conductivity to describe heat transfer perpendicular to a substrate or interface, critical in layered cooling systems and electronic packaging.

Microfluidic and MEMS contexts describe through-plane flow or transport across the thickness of a device, relevant in 3D microchannels and layered microfluidics.

Other contexts include textiles and membranes, where through-plane moisture or gas transport governs barrier properties; and in imaging and tomography, through-plane projection refers to data integrated along a direction normal to a plane.

Because many materials are anisotropic, distinguishing through-plane from in-plane properties is important for design, simulation, and performance prediction.