Making inexpensive strain sensors

Two methods of making inexpensive strain sensors:

Flexible Graphite-on-Paper Piezoresistive Sensors

A paper in the journal Sensors demonstrates novel graphite-on-paper piezoresistive devices. The graphite was used as the sensing component. The fabrication process can be finished in a short time with simple tools (e.g., a scissor and a pencil).

A small array of six paper-based piezoresistive devices is made. The whole device is flexible. The test results showed that the change of resistance was proportional to the applied force. A paper-based weighing balance was also made as an example of applications. This novel array of paper-based piezoresistive devices will open wide applications in force and acceleration sensing areas – Paper.

Tactile sensors based on soft polymers

Piezoresistive carbon black/polydimethysiloxane (CB/PDMS) is a widely used material in the field of artificial skin development because of its high gauge factor to all forms of stress, including tension, compression and shear. While its durability, inexpensive-ness and customizability make CB/PDMS makes it the quintessential active material for pressure-sensing skin, the material itself has not been well-characterized electrically or mechanically.

A series of mechanical tests on 0.625″ cubes of CB/PDMS revealed that the material’s resistance increases monotonically with strain and that CB/PDMS have similar sensitivities to tension and compression across different CB concentrations. Shear sensitivity, however, was relatively poor and inconsistent between samples.

To overcome this lack of sensitivity to shear forces, a hair-inspired “pillar” sensor was designed to detect shear forces. The pillar sensor contains two 2 mm x 2 mm x 28 mm CB/PDMS strain gauges embedded in a 3 mm thick PDMS base, and a silicone pillar that has a 5 mm diameter and 6 mm height – Abstract and Paper (PDF).

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