Sensor with feeling lends a hand

A new tactile pressure sensor could be the way forward for keyhole surgey, robot hands and prosthetic limbs

Surgeons need sure hands and a fine sense of touch in the operating theatre to distinguish between different forms of tissue and to manipulate the scalpel with precision. Keyhole surgery, however, doesn’t allow doctors to use their sense of touch to any great extent, so researchers at the Fraunhofer Institute for Biomedical Technology are working on a new type of tactile pressure sensor which is just as soft and flexible as human skin and could, if incorporated in an endoscopic instrument for example, help to restore the surgeon’s sense of touch.

The sensor consists of two superimposed films. The lower film contains the electrode components which measure pressure. The electrodes are configured like interlocking fingers, but do not contact one another, and no electricity flows between them.

The upper film consists of an insulating material to which electrically conducting silicone-rubber pyramids are attached. The tip of each pyramid is positioned exactly above the corresponding electrode component. If pressure is applied to the sensor at any point, the pyramid is pressed against the lower film and thereby widened. The conducting pyramid material brings the electrode fingers into contact with one another.

The resistance between the electrodes is reduced, and an electric current starts to flow. The greater the pressure and force exerted on the pyramid, the flatter it becomes. The contact surface between the electrodes increases in size, and a greater current flows. ‘Pressure changes the electrical resistance of the individual pressure sensor,’ explains Margit Biehl of the IBMT. ‘The spatial configuration of the sensors in the form of an array allows pressure distributions to be determined.’ The tactile sensor could have applications in a number of fields. In minimally invasive operations it could help surgeons to ‘feel’ differences between types of tissue. It could be used to give robots a sense of touch, or bring about considerable benefits in prosthetic engineering.

These applications are still visions of the future, but the team claims that within two years the sensor should be fully developed and opening up a range of possibilities for surgeons and physically disabled people alike.

Fraunhofer-Institut ENTER 50