A NEW TECHNIQUE FOR TRANSMISSION OF SIGNALS FROM IMPLANTABLE TRANSDUCERS

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.