Smart Electrodes

Type: Diploma thesis
Students: Oliver Peitz, Stéphane Peter
Advisor:
Project:

Introduction
Functional electrical stimulation (FES) is a method to contract paralyzed muscles of spinal cord injured and stroke subjects with the aim to generate or improve lost motor function, e.g. for walking or hand grasp. Stimulation is normally applied between two electrodes (active and indifferent) of large area (e.g. 5cm x 5cm), the placement of which is critical in achieving maximal response.
The 'Smart Electrode' project is investigating ways to improve muscle selectivity by dynamically changing the electrode position through the use of an array of elements.

Hardware
The hardware unit is a programmable multiplexer that detects and distributes stimulation pulses to the different electrode pads. It consists of a current-detector, a 16 channel PhotoMOS switching unit, a level-shifting input for force measurements and a RS232 interface. Different switching architectures were evaluated, whereby high voltage resistance of the device and patient safety were important points.

Software
The software gives easy access to the functions implemented on the microprocessor. The electrode settings can be changed easily by mouse clicks and the received data is immediately displayed on the screen before saving it to a file.

Results
This project has shown that by selecting a subset of elements (1cm x 1cm) from a 4 x 4 array, it is possible to achieve 3 distinct contractions of the little, ring and index finger. Similar results could be shown when using an array constructed from standard electrodes, or from conductive fibers stitched into fabric. Although limited in scope, the project clearly indicates that array based stimulation has the potential to significantly improve the quality of life for the physically disabled.

Future
In a next step the number of electrodes will be increased. The existing finger forces measurement kit will be improved in order to make it reliable and easy to use.