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

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

7.2.5.4 Mechanical Cables

Information may be transferred mechanically by modulating the turning frequency of a rotating cable. In this case the mechanical load is applied by the receiver at the cable terminus as it measures frequency changes in the received signal (e.g., FM modulation). Section 6.4.3.4 discusses cable operating modes, frequencies, dimensions, and power requirements. For example, a rotating cable 2 nm in diameter and ~50 nm long (suitable for internal data transmissions) operated in AC mode can convey 6 x 10⁴ bits/sec at a power cost of 1 pW (~16,000 zJ/bit).

Power and control signals can also be transmitted through a stiff reciprocating member, operating in the manner of a bicycle brake or derailleur cable. Molecular control cables using polyyne rods encased in single-walled carbon nanotube (Section 2.3.2) sheaths is one simple example.²²⁸¹ Polyyne is a chain of carbon atoms with alternating single (0.1377 nm) and triple (0.1192 nm) bonds, hence the polyyne cable has ~7.8 carbon atoms and a mass of ~1.5 x 10^-25 kg per nanometer of length. The stretching stiffness of the single bond is ~824 N/m, the triple bond ~1560 N/m, and the length of a bond pair is 0.2569 nm, giving the compliance for a cable of length L of (7.2 x 10⁶) L (m/N), or the stiffness as k_s = (1.4 x 10^-7) / L (N/m). Thus an L = 1 micron polyyne cable stretches by ~1 nm when a tensile force of 140 pN is applied. Thermal noise produces an uncertainty in the position of the end of the polyyne cable, which varies approximately¹⁰ as Dx ~ (kT / k_s)^1/2 ~ 0.18 nm in the previous example, at 310 K.

Last updated on 19 February 2003