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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...