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
Average source power for conversational speech in air is ~10 microwatts at the vocal cords (60 dB), up to ~1000 microwatts for shouting (90 dB) and as little as 0.1 microwatts (30 dB) for whispering.3511 Vocal cord surface area ~1 cm2, giving an acoustic intensity I ~ 0.001-10 watts/m2. (Using the decibel notation, dB = 10 log10 (I/I0), where I0 ~ 5 x 10-13 watts/m2 in air, I0 ~ 1 x 10-16 watts/m2 in water.) In a planar traveling wave, pressure amplitude Ap (N/m2) is related to power intensity I by
For water at 310 K, r = 993.4 kg/m3 and vsound = 1500 m/sec, therefore Ap = 0.0005-0.05 atm for speech, detectable by nanodevices throughout the body due to minimal attenuation at audible frequencies (Section 220.127.116.11). Other easily detectable vocalizations include whistling, humming, coughing, sneezing, rales, wheezing, expectorating, eructations, flatus, vomiting, hawking and noseblowing.
In the case of spherical waves diverging from an omnidirectional transmitter of radius r at a distance X from the transmitter, average intensity declines inversely as the square of the distance and so I in Eqn. 4.53 must be replaced by (I r2 / X2).
Last updated on 17 February 2003