Which material becomes conductive when squeezed and is used in membrane switches and pressure sensors?

• A. Quantum tunnelling composite (QTC)
• B. Nanotechnology
• C. Carbon fibre
• D. Shape memory plastics

Answer: (A)

This question tests how a material can switch from insulating to conductive with applied pressure. Quantum Tunnelling Composite (QTC) is a conductive filler dispersed in an insulating elastomer. When nothing is pressed, the filler particles are spaced apart, so electrons can’t easily move between them and the material behaves as an insulator. Apply pressure and the particles are pushed closer together; electrons can tunnel between nearby particles, and sometimes direct contact forms an electrical path. As more particles come within tunneling distance, a conductive network forms, causing a sharp drop in resistance. This pressure-activated change in conductivity makes QTC ideal for membrane switches and pressure sensors, as a simple touch or squeeze can reliably complete a circuit or produce a measurable change in signal on flexible substrates.

The other options don’t fit this behavior. A field like nanotechnology isn’t a specific material with this pressure-activated conductivity, carbon fibre is conductive but not inherently a squeeze-activated switch material, and shape memory plastics respond primarily to temperature or deformation for shape recovery rather than creating a conductive path with pressure.