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

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

9.4.2.5.3 Volume Displacement

Locomotion may also be achieved in a high-viscosity medium by physically removing fluid from the path ahead, then occupying the void before it closes up, and filling the volume behind with the vacated fluid -- a process not unlike a tunneling mole. Forward velocity is largely determined by the speed at which blocks of fluid can be transferred from one end of the nanorobot to the other, whether along internal or external pathways.

Fluid pumping (Section 9.2.7) provides the simplest means of volume displacement. Consider a tube of radius r_tube = 100 nm and length l_tube = 1 micron installed across the diameter of a 1-micron wide spherical nanorobot (R_nano = 0.5 micron), along with a single positive displacement piston pump of single-cycle displacement volume V_cycle = 0.008 micron³ (Fig. 9.1). From the relations given in Section 9.2.7.2, operating the pump at n_pump = 1 MHz produces a time-averaged fluid flow velocity of v_flow = 26 cm/sec, a volume flow rate of 'V_pump = 8000 micron³/sec, a nanorobot velocity of v_nano = 'V_pump / p R_nano² = 1 cm/sec, and a power draw of P_flow ~ 1800 pW. From Eqn. 9.25, Dp ~ 2 atm across the nanorobot diameter, though this might be reduced to ~0.02 atm by flaring the entry and exit portals. Power usage, operating pressure, and the risks of clogging or fouling are relatively high, but this system has the virtue of simplicity, occupies less than 8% of total device internal volume, and can be expanded to three-dimensional motility by adding orthogonal entry portals. Jet propulsion is energy inefficient at small sizes and high speeds.²⁰²²

Last updated on 21 February 2003