Crafting Material Interfaces

A Study of How Conductive Materials Behaves on Leaves

I wanted to experiment with a natural material that can be found everywhere. I decided to use a leaf because it had a beautiful surface with vines that resembled electrical circuits. It is also often wasted if not used. I experimented with how various conductive materials behaved on a leaf and finally formed an electric circuit on the surface of the leaf.

Conductive Ink

Conductive ink was drawn on a piece of leaf to create an electrical circuit using a wooden stick dipped in silver ink. Brush made it difficult to control precision; pen often scratched the surface of the leaf and did not provide enough ink flow. Compared with other conductive material, the conductive ink adhered to the surface of the leaf the best, but did not connect to the microcontroller and battery very well. Silver ink painted using a stick was the most effective.

Copper-plating

Each circuit was then copper-plated separately. Time spent in copper bath directly determined the color of copper plates. For example, 3 minutes in bath yielded a dull copper color while 10 minutes in bath resulted in a bright copper color. Plating surface also determines level of adhesiveness of the copper. For example, the copper on the stem adhered well to the surface; however the copper on the leaf was fragile and broke off easily when the leaf was scrunched. The copper circuit that fell off was glued back. Electrometer also showed that silver ink was more conductive than copper. The resistance of silver ink was 0.0-0.1 Ohm and the resistivity of copper was 0.2-0.3 Ohm.

Conductive thread

Conductive string could be a substitute of ink and copper. However it broke the leaf easily. The surface of the leaf was too fragile. The metal-coated string was rougher and broke the leaf easier. This method was not pursued in the final product.

Connecting the circuits

Microcontroller and battery were connected to the circuit through soldering and conductive ink. Soldering provided a stronger bond than conductive ink and glue especially due to the slippery surface of the leaf.

The circuit will be completed when the user touches the input (the stem) while holding on to ground. Both are copper-plated for easy identification. The LEDs turn on and off when the input is touched. Video.

Challenges

Overall, fresh leaves were a difficult surface to work on due to its fragility and slippery surface. This could possibly be solved if the leaf was dry. Soldering provided better connection than ink alone.

Potential application

This could be used in an interactive installation where synthetic fabric leaves are attached to a real tree and people can touch individual leaves (inputs) and lights will turn on and off depending which input the user touches.

Download a copy of the presentation here.