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Single Wall NanoTube Acoustic Velocity Sensor

IP.com Disclosure Number: IPCOM000018621D
Publication Date: 2003-Jul-28
Document File: 4 page(s) / 850K

Publishing Venue

The IP.com Prior Art Database

Abstract

An acoustic velocity sensor is disclosed that employs a newly reported effect. The effect is the generation of a voltage when a dielectric fluid flows along the axis of a bundle of single walled nano tubes. Reported response times suggest that the sensor should easily respond to frequencies of 1,000 hertz or above and that it will have a noise floor at or below 40 decibels relative to a micro Pascal in sea water. The sensor will have a logarithmic response to acoustic intensity over nearly eight decades of sound pressure level. This can be either an advantage or a disadvantage depending on the application. Modern electronics can easily transform the response to be linear.

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Single Wall NanoTube Acoustic Velocity Sensor

                  

                   © 2003 Lockheed Martin Corporation.  All Rights Reserved.

A sensor is disclosed that measures the acoustic velocity, employing a newly reported effect: the ability of a flowing, ionic fluid to induce a voltage in a single walled nanotube (SWNT) ([1]).  The investigators suggested that this discovery can be used for flow sensors and possibly for producing electrical power.  They expressed the opinion that the flow sensors would be useful in microfluidics. 

The  characteristics of the SWNT bundles can be found in reference (1).  For water the voltage dependence appears to go as V = 0.5e-5*log(1.0e8*u(m/s)+1) volts. Figure  illustrates a theoretical response curve as a function sound pressure level in water.  This curve is based on characteristics published in reference (1). Salt water would be expected to be in some where in the middle of that range.  No results were reported below 1e-7 meters per second.  The theory of this phenomena is still under investigation, but the mechanisms discussed suggest that the results may extrapolate to flow rates on the order of 1e-8 meters per second.

The basic geometry of the sensor is shown in Figure .  The sensor consists of a SWNT bundle with electrodes attached to the ends of the bundle.  The bundle itself must be aligned along the direction of sound propagation.  This will give the sensor an intrinsic directivity, even for wavelengths that are very long compared to the sensor dimensions.  SWNT have been produced with lengths of several centimeters.  The longer SWNT will produce a proportionally higher voltage.

The response time for the phenomena is reported to be less than 1 millisecond.  Refe...