Dp. Lindsey et al., A NEW TECHNIQUE FOR TRANSMISSION OF SIGNALS FROM IMPLANTABLE TRANSDUCERS, IEEE transactions on biomedical engineering, 45(5), 1998, pp. 614-619
To reduce space requirements for implant electronics in in vivo teleme
try applications, the purpose of this project was to develop and test
a new data transmission method that utilizes the ionic properties of b
odily fluids as the transmission medium. Motivated by an interest in u
sing the new method to transmit information from a sensor which measur
es tension in anterior cruciate ligament (ACL) grafts, a sine wave was
injected into a cadaver leg using platinum electrodes implanted into
the lateral femoral epicondyle, The signal was detected by electromyog
ram (EMG) surface electrodes. The effect of transmission frequency, th
e current injected, interelectrode separation, distance of the electro
des from the joint line, and the surface of electrode placement on the
signal attenuation was studied. The logarithmic relation between atte
nuation and frequency was constant from 2 kHz until 10 kHz. For freque
ncies above 10 kHz, the attenuation increased linearly at the rate of
1 dB/octave. Attenuation,vas inversely sensitive to both current and i
nterelectrode separation with larger separations and currents giving l
ess attenuation. Attenuation was significantly less for the lateral th
igh surface than for the anterior surface and increased with increasin
g distance from the joint line for both surfaces. For the application
of interest here, suitable values of transmission variables to avoid t
he possible negative consequences of injecting current into living tis
sue are a current of 3 mA injected at a frequency of 37 kHz, The value
s of reception variables for minimum attenuation are wide interelectro
de separation (5 cm) with the electrodes placed 5 cm proximal of the j
oint line on the lateral surface of the thigh. With the exception of t
he surface which is application dependent, these values of the recepti
on variables should also he appropriate for other applications.