|Title of Invention||
|Abstract||Disclosed herein is an accelerometer comprising of an acceleration sensor having of at least one Carbon nanotube placed between two electrodes, a solid deflectable arm (cantilever) to which the structure containing the carbon-nanotubes packed between two electrodes are attached, the entire assembly i.e., the carbon nanotubes packed between two electrodes, the solid deflectable arm is housed in a sealed liquid containing environment, electrical connections are taken out to measure the electrical signals developed across the carbon nanotubes as a means to measure the acceleration.|
|Full Text||The present invention relates to, and more particularly, Carbon nanotubes based accelerometer for detection of vibrations in solids.
PRESENT STATE OF ART:
The available accelerometer is as follows:
i) Accelerometer: The active element of accelerometer is a piezoelectric material. One side of the piezoelectric material is connected to a rigid post at the sensor base, and seismic mass is attached to the other side. When the accelerometer is subjected to vibration, the seismic mass of the accelerometer will move with an inertial response. The piezoelectric crystal acts as the spring to provide a resisting force and damping. As seismic mass moves, it places the piezoelectric crystal into compression or tension, which causes a surface charge to develop on the crystal, which is proportional to the motion.
The conventional accelerometer uses piezoelectric material and preamplifier, so these techniques are thus expensive. Limitations of the system are that its lower cutoff frequency (~a few Hz) and its large size (~ 5 cm length and -1.5 cm diameter).
Mechanical Vibrations in the solid
It has been reported that liquid flow over carbon nanotubes generates an electrical signal. The liquid flow induced signal was found to be logarithmically dependent on the liquid flow velocity. The proposed solution exploits the fact that if a moving liquid over a stationary "carbon nanotube flow sensor" generates a signal, the same must be true for the case for a "carbon nanotube flow sensor" moving with a relative velocity with respect to the liquid in its immediate vicinity. Thus, to detect any mechanical vibration of a solid a device is proposed which comprises of a sealed container containing an appropriate liquid and a "carbon nannotube flow sensor" connected to a cantilever. The carbon nanotube can be either a single wall type or multi wall type carbon nanotube. The entire
assembly is placed over the vibrating solid. As the solid vibrates, both the liquid and the "carbon nanotube flow sensor" connected to the cantilever are set into forced vibration. However, due to the viscous damping of the cantilever caused by the viscous drag forces in the liquid environment, a phase lag develops between the motion of the "carbon nanotube flow sensor" and the motion of the liquid (which follows exactly the motion of the solid). Thus, there exist a relative motion between the liquid and the "carbon nanotube flow sensor". This relative motion will then in turn generate an electrical signal whose waveform will provide the information about the details of the vibrations of the solid block, on which the device is mounted.
The following example is for the purpose of illustration only and is neither intended to be nor should be construed as a limitation on the scope of the invention:
Construction of the sensor
In order to construct the sensor, a thin layer of the single walled carbon nanotubes or multi-walled carbon nanotubes is sandwiched between two metal electrodes (pads). The whole assembly is fabricated on an insulating material base. Electrical contacts are taken out from the metal pads using enamelled copper wires of thickness of 125 microns. A thin layer of insulating material is coated on the surface of the metal pads exposed to the liquid environment to prevent electrical contact between the metal pads and the surrounding liquid. This construction is shown in Figure 1. This sensor is a nanotube flow sensor to detect the vibrations in solid.
Using the nanotube flow sensor to detect Mechanical Vibration in the solid
The "carbon nanotube based flow sensor" has been shown to detect vibrations of a solid surface, and thus can function as an accelerometer. For this purpose, the "carbon nanotube based flow sensor" is mounted at the end of a cantilever, which is immersed in
a chamber filled with a liquid. This liquid used in present demonstrations is water of conductivity 50 microsiemens/cm. The experimental setup is shown in figure 2. Due to the viscous drag forces acting on the cantilever there will be a phase difference between the motion of sensor and liquid (which follows exactly the motion of solid). Due to this phase shift, there will be a relative velocity between the "carbon nanotube based flow sensor" and the liquid in its immediate vicinity. Since the "carbon nanotube based flow sensor" is velocity sensitive, the amplitude of the output signal will depend on
Here Ax is the amplitude of the cantilever. The plot is in figure 2 shows the output voltage from the sensor as a function of time. The frequency of the signal is exactly the same as the vibrational frequency of the diaphragm of the speaker, thereby showing that our device can measure the vibration of a solid surface. The acceleration of solid is given by
where and &0, y are, respectively, the resonant frequency
of the cantilever and damping term in the forced vibration equation. The parameter p\ is related the amplitude of vibrations of the solid surface.
Brief Description of the Drawings:
Figure 1 shows the realization of Example 1 where bundles of single walled carbon nanotubes (1) are packed between two metal electrodes (2,27). The whole structure was supported on an insulating substrate (5). Electrical leads (3,37) taken out from the metal electrodes were connected to an ammeter/voltmeter (4) (Keithley 6 Vi digital multimeter) to measure short circuit current /open circuit voltage.
Figure 2 shows the experimental setup for Example 2 where the Single Walled Carbon Nanotube (SWNT) is used to detect the vibrations of a solid. The "carbon nanotube based accelerometer" (14) is attached to a cantilever (15). Both the cantilever (15) and the "carbon nanotube based accelerometer" (14) are maintained in a completely liquid (16) filled cylindrical chamber (17). The liquid filled chamber (17) is connected to the vibrating diaphragm of a loud speaker (18) by a wooden stick (19) and is then made to suffer forced vibration. A function generator (20) drives the loud speaker (18) and the electrical connections (3,3') are taken out from the "carbon nanotube based accelerometer" (14) as explained in Example 1. The induced voltage across the "carbon nanotube based accelerometer" (14) is measured by the Voltmeter (21) and the waveform is shown in Fig. 2 where the glass slide is moved at frequency 3.2 Hz. The relative velocity between the liquid viscosity damped cantilever and the surrounding liquid gives the flow induced signal.
Figure 3 shows the amplitude of the induced voltage V across the "carbon nanotube based accelerometer" for different vibration frequencies (J) of the "loud speaker". The fitted
equation is given by which is discussed in Example 3.
Advantages of the Invention
1. The accelerometers can detect low as well as high frequencies. The device as explained in this patent application can detect low g acceleration of the solid.
2. The main advantage of the SWNT based accelerometer will be the miniature of size of the sensor that can be reduced to nano-scale dimensions.
3. The device does not require any external power source and on the contrary is capable of generating its own electrical signals.
4. The device as described herein above wherein the response time of the device is better then lmilli sec.
1. An accelerometer comprising of an acceleration sensor having at least one Carbon
nanotube placed between two electrodes,
-a solid deflectable arm (cantilever) to which the structure containing the carbon-nanotubes packed between two electrodes are attached,
-the entire assembly i.e., the carbon nanotubes packed between two electrodes, the solid deflectable arm is housed in a sealed liquid containing environment, -electrical connections are taken out to measure the electrical signals developed across the carbon nanotubes as a means to measure the acceleration.
2. The device as claimed in claim 1, wherein the carbon nanotube is a single wall type carbon nanotube
3. The device as clamimed in claim 1, wherein the carbon nanotube is a multi wall type carbon nanotube.
4. The device as claimed in claim 1, 2, or 3, wherein the electricity measurement device comprises an ammeter to measure the short-circuit current or a voltmeter to measure the open circuit voltage.
5. The device as claimed in any one of claims 1 to 4, wherein the response time of the device is better then lmilli sec.
DATED 29th THIS DAY OF MAY 2006.
(MRS. A. V. NATHAN) AGENT FOR THE APPLICANT
|Indian Patent Application Number||663/CHE/2005|
|PG Journal Number||25/2013|
|Date of Filing||01-Jun-2005|
|Name of Patentee||INDIAN INSTITUTE OF SCIENCE|
|Applicant Address||BANGALORE-560 012 KARNATAKA INDIA|
|PCT International Classification Number||F02D41/00|
|PCT International Application Number||N/A|
|PCT International Filing date|