© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

7.2.5.1 Electrical Cables

Uninsulated wires risk electrical leakage and unnecessary heat transfer; unshielded wires produce stray fields that may attract unwanted attention from mobile elements of the immune system, e.g., electrosensitive leukotaxis (Section 4.9.3.1). Thus coaxial cable or "coax" is the proper transmission line for in vivo electrical cable communications. Unlike waveguides, coaxial cable is not a resonant device, hence the traveling wave frequencies it carries may be varied continuously down to DC. The electric fields within a coax line have axial symmetry. However, serious design complications may arise if the transmitted wavelength (l) is less than the circumference of the annular dielectric space between the conductors, because a second (nonaxial) mode of rf propagation with diametral symmetry can then be excited simultaneously. To avoid this complication, a 1-micron diameter coax should be held to a practical upper frequency limit of c / p d_coax < 1 x 10¹⁴ Hz for cable lengths >> l.

Intracoaxial scattering and absorption are negligible, so for single-channel bandwidth the maximum coaxial bit rate 'I_max consistent with a nanorobot onboard communication power budget P_comm using rf or microwave photons (hn_coax / kT ln(2) << 1) occurs at the full-power transmission frequency

{Eqn. 7.16}

Thus the maximum coaxial transmission frequency is 0.1 GHz (10⁸ bits/sec) for P_comm = 0.3 pW, 1 GHz at 3 pW, and 100 GHz (10¹¹ bits/sec) for P_comm = 300 pW (>3 zJ/bit).

Last updated on 19 February 2003