Page 90 - Handbook of Biomechatronics

Sensors and Transducers 85

After a month or two of the IMES, Jacob’s control is improving, but now
he is having trouble with sensing what is happening at the prosthetic foot.
An avid rock climber preaccident, he is trying to get back into the sport, but
lacks the foot feedback he desires. After consultation with his medical team
and with you, he decides to undergo an invasive surgery to install a nerve
cuff electrode as part of a Food and Drug Administration (FDA) field trial.
After the surgery and necessary recovery time, you determine which
nerve areas are stimulated by which embedded nerve cuff electrode. You
install two FSR sensors on his prosthetic foot, one on the toe and one on
the heel. You connect and program the system such that when one of
the FSR sensors is touched, the processor sends a signal to an appropriate,
or close to appropriate, nerve area so that Jacob now can “feel” his toe
and heel.

5.5 Brain Array

Perhaps, the most invasive method of collecting muscle and sensory signals is
to use a brain implant. This device generally consists of 4mm 4mm plate
with an array of 100 needle electrodes (Fig. 29). The array is surgically
implanted into the brain, generally in the motor cortex, needles interacting
with the gray matter. The electrode array is then calibrated by having the
patient think about performing a variety of motor tasks. Using pattern

Fig. 29 Brain electrode array.