Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
10.1.3 Nanorobot Synchronization
Ideally, the clocks of all nanorobots present in a patient's body will be synchronized to some universal time. This time setting may be defined by the patient, by the physician, or by reference to some external standard. As part of a chronometry-critical nanorobot installation procedure prior to infusion, an initializing signal can be transmitted throughout the infusate volume, allowing each individual nanorobot present therein to receive the signal and set its clock.
Acoustic synchronization pulses are appropriate if ~microsec precision will suffice. Sound waves passing at vsound = 1500 m/sec through an Lvial = 1.5 cm wide container of well-stirred aqueous-suspended nanorobots restricts synchronization error to Dterror ~ Lvial / vsound = 10 microsec; from Eqn. 10.7, repetition of Nobs = 100 synchronization pulses can reduce synchronization error to ~1 microsec.
For the highest pre-infusion synchronization accuracy, optical (Section 4.7.3) or rf (Section 4.7.1) pulses will be employed. Electromagnetic energy travels at c ~ 3 x 108 m/sec across the container volume until intercepted by a nanorobot optical sensor, giving Dterror ~ Lvial / c = 0.05 nsec. Allowing 100 green photons (360 zJ/photon at 550 nm) per nanorobot at a nanorobot number density of 1012 cm-3, the flash injects ~40 J/m3 of energy into the container, raising the water temperature by ~10 microkelvins after this energy is fully thermalized. A 1-nsec flash produces a peak intensity of ~4 x 1010 watts/m2, comparable to monochromatic optical tweezers which are tolerated by biological macromolecules.1630,1631 Some nanorobots inevitably will miss the signal and may later synchronize, prior to infusion, via close or direct physical contact with others who received the signal, or else multiple synchronization pulses can be used.
Onboard nanorobot clocks can also be synchronized post-infusion. For example, a pressure cuff inflated around the patient's arm can administer acoustic synchronization pulses to ~microsec precision as bloodborne nanorobots pass through the blood vessels within; after signaling for several mean blood circulation times (e.g., a few minutes), most bloodborne nanorobots should be properly synchronized. Whole-body acoustic transmissions at 0.1-1 MHz may be generated by operating tables, vibrating chairpads, wristwatch transmitters and the like (Section 6.4.1). Such methods may produce synchronization errors of ~100 microsec over 15 cm anteroposterior path lengths, reducible to ~1 microsec error using Nobs = 10,000 repetitions of the calibration signal (Eqn. 10.7). For higher precision, the physician transmits ~MHz radio wave pulses into the body; such pulses may be detected by appropriate onboard receivers (Section 6.4.2). Such waves have only ~75% attenuation over 15-cm anteroposterior path lengths (Eqn. 6.32), producing 0.5 nsec synchronization accuracy. Optical photons applied to the skin surface are subject to scattering, producing signal pulse broadening which increases synchronization error, and to absorption, which makes signal reception difficult or impossible beyond tissue depths of a few centimeters (Section 4.9.4).
Another approach is to inject a relatively small number of chronocytes -- mobile communicytes (Section 7.2.6) modified to include an onboard nanoclock of high precision (e.g., a portable frequency standard) and the ability to transmit clocking synchronization signals to calibrate neighboring nanorobots. These signals may be transmitted acoustically at close proximity to the nodes of a mobile communications network (Section 7.3.2), subsequently allowing all nanorobots within 100 microns of a calibrated node to synchronize to within <~67 nsec. Averaging algorithms can be employed to synchronize uncalibrated nodes in the system that were not recently visited by a chronocyte. Bloodborne chronocytes will normally be carried from the capillary vasculature to within ~100 microns of most tissue locations, thus allowing <~67 nsec single-pulse acoustic synchronization even in the absence of an installed communications network (Section 7.3).
Last updated on 23 February 2003