A simple, low-cost conductive composite material for 3D printing of electronic sensors

Abstract

3D printing technology can produce complex objects directly from computer aided digital designs. The technology has traditionally been used by large companies to produce fit and form concept prototypes ('rapid prototyping') before production. In recent years however there has been a move to adopt the technology as full-scale manufacturing solution. The advent of low-cost, desktop 3D printers such as the RepRap and Fab@Home has meant a wider user base are now able to have access to desktop manufacturing platforms enabling them to produce highly customised products for personal use and sale. This uptake in usage has been coupled with a demand for printing technology and materials able to print functional elements such as electronic sensors. Here we present formulation of a simple conductive thermoplastic composite we term 'carbomorph' and demonstrate how it can be used in an unmodified low-cost 3D printer to print electronic sensors able to sense mechanical flexing and capacitance changes. We show how this capability can be used to produce custom sensing devices and user interface devices along with printed objects with embedded sensing capability. This advance in low-cost 3D printing with offer a new paradigm in the 3D printing field with printed sensors and electronics embedded inside 3D printed objects in a single build process without requiring complex or expensive materials incorporating additives such as carbon nanotubes.

Figure 1. Characterisation of the conductive composite material produced.

a) an SEM image of a cut edge of the formulated conductive material, b) photograph showing a length of the composite being used to connect to an LED, (scale bar 5 mm) c) Large scale SEM image of the conductive material after passing through the 3D printer nozzle (inset) a reduced magnification SEM image showing the extruded material, d) photograph of 3D printed chess rook also being used to light an LED (scale bar 10 mm).

Figure 2. 3D printing of flex sensors.

ai) the CAD design of flex sensor, aii) the printed flex sensor, aiii) the printed sensor undergoing flexing, aiv) the resistance response of the sensor during flexing, bi) CAD design of the 3D printed ‘glove’, bii) the printed ‘glove’, biii) the printed ‘glove’ before flexing, biv) the printed ‘glove’ during flexing and bv) the resistance response of each finger during 5 flexings.

Figure 3. 3D printing of capacitive interface device.

a) the CAD design of the printed interface device and the simple circuit used to detect inputs, b) a photograph of the printed device, c) a macro image of the printed sensor pads (scale bar 5 mm), d) the capacitance of each printed sensor pad plotted against time e) an enlarged portion of the graph from part d showing the cross-sensitivity of each sensor pad.

Figure 4. 3D printing of capacitive ‘smart’ vessel.

a) the CAD design of the printed ‘smart’ vessel, b) the vessel during printing showing the embedded sensor strip, c) the completed vessel next to a £2 coin (coin is approximately 28 mm in diameter) and d) the capacitance response of the ‘vessel’ when water is added.