CROSS-REFERENCEN TO RELATED APPLICATION

This application is a continuation of Application 466/MAS/2001 filed on 13/06/2001 (Patent No. 197946 granted on: 26/12/2005. This application is filed as patent of Addition with the said application as Parent application.

FIELD OF INVENTION

The present invention relates to accelerometer, more particularly relates to carbon nanotubes based accelerometer for detection of vibrations or accelerations in solids.

BACKGROUND OF THE INVENTION

Conventional accelerometer comprises an active element as 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. The limitations associated with convention accelerometer are that, its lower cutoff frequency (~a few Hz) and its large size (~ 5 cm length and -1.5 cm diameter). Therefore, there exists a need to develop an accelerometer which is less expensive and has response time less than the conventional accelerometers.

STATEMENT OF THE INVENTION

Accordingly, the present invention relates to an accelerometer comprising an acceleration sensor comprising at least one carbon nanotube placed between two electrodes; a solid deflectable arm connected to the acceleration sensor, wherein the solid deflectable arm and the acceleration sensor is housed in a sealed cylindrical chamber containing liquid; and electrical connections taken out from the acceleration sensor to measure electrical signals developed across the carbon nanotubes to measure acceleration.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

Figure 1: shows acceleration sensor comprising bundles of single walled carbon nanotubes packed between two metal electrodes.

Figure 2: shows accelerometer comprising carbon nanotubes to detect the vibrations of a solid according to the present invention.

Figure 3: shows graph of amplitude of induced voltage V across the carbon nanotube based accelerometer for different vibration frequencies (f) of the loud speaker.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the disclosure.

It is to be noted at this point that all of the components, whether alone or in any combination, are claimed as being essential to the invention, in particular the details depicted in the drawings and reference numerals in the drawings are as given below.

Table of referral numerals

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 present invention exploits the fact that if a moving liquid over a stationary carbon nanotube flow sensor or acceleration 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, an accelerometer is provided. The accelerometer comprises a sealed container or cylindrical chamber containing an appropriate liquid and a carbon nanotube flow sensor or acceleration sensor connected to a cantilever or a solid deflectable arm. The carbon nanotube can be either a single wall type or multi wall type carbon nanotube. The entire assembly of the accelerometer with cylindrical chamber is placed over a vibrating solid. For example, the vibrating solid can be a loudspeaker but not limited to the loudspeaker. As the solid vibrates, both the liquid and the acceleration sensor connected to the solid deflectable arm are set into forced vibration. However, due to viscous damping of the deflectable arm caused by viscous drag forces in the liquid environment, a phase lag develops between motion of the acceleration sensor and motion of the liquid (which follows exactly the motion of the solid). Thus, there exist a relative motion between the liquid and the acceleration sensor.

The 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, on which the accelerometer is mounted.
Referring to Figure 1, the acceleration sensor (11) comprises, a thin layer of bundles of single walled carbon nanotubes or multi-walled carbon nanotubes sandwiched between two metal electrodes (2, 2') (pads). The acceleration sensor (11) is fabricated on an insulating material substrate (13). Electrical contacts (3, 3') are taken out from the metal electrodes (2, 2') using enameled copper wires of thickness of 125 microns. The electrical contacts (3, 3') are connected to an ammeter and voltmeter (4, 4') (For example Keithley 61/2 digital multimeter) to measure short circuit current and open circuit voltage. A thin layer of insulating material is also coated on surface of the metal electrodes (2, 2') exposed to liquid environment to prevent electrical contact between the metal electrodes (2, 2') and the surrounding. The acceleration sensor (11) is a nanotube flow sensor to detect the vibrations in solid.

In one embodiment, Figure 2a shows accelerometer (10) comprising single walled carbon nanotube (SWNT) or multi walled nano tube to detect vibrations of a solid according to the present invention. An acceleration sensor (11) comprising the single walled nanotubes are attached to a cantilever or solid deflectable arm (12). Both the cantilever (12) and the acceleration sensor (11) are placed in a completely liquid filled cylindrical chamber (6). The liquid used in present invention is water of conductivity 50 micro-Siemens/cm. The liquid filled cylindrical chamber (6) is connected to a vibrating diaphragm of a loudspeaker (7) by a wooden stick (8) and is then made to suffer forced vibration. A function generator (9) (not shown) drives the loudspeaker (7) and the electrical connections (3, 3') are taken out from the acceleration sensor (11) as explained in Figure 1. The loudspeaker (7) is supported using a supporting element (14). An induced voltage across the acceleration sensor (11) is measured by a voltmeter (4) and waveform is shown in Figure 2b where glass slide is moved at frequency 3.2 Hz. The relative velocity between the liquid viscosity damped cantilever and surrounding liquid gives flow induced signal. Due to viscous drag forces acting on the cantilever or solid deflectable arm (12), there will be a phase difference between the motion of acceleration sensor (11) and liquid (which follows exactly the motion of solid). Due to this phase shift, there will be a relative velocity between the acceleration sensor (11) and the liquid in its immediate vicinity. Since the acceleration sensor (11) is velocity sensitive, amplitude of the output signal will depend on Here Ax is the amplitude of the cantilever. The plot is in Figure 2b shows the output voltage from the acceleration sensor (11) as a function of time. The frequency of the signal is exactly the same as the vibrational frequency of diaphragm of loudspeaker (7), thereby showing that accelerometer (10) can measure vibration of a solid surface. The acceleration of solid is given by andω0, γ are, respectively, the resonant frequency

of the cantilever (12) and damping term in forced vibration equation. The parameter p1 is related the amplitude of vibrations of the solid surface.

Figure 3 shows the amplitude of the induced voltage V across the accelerometer for different vibration frequencies (f) of the loudspeaker. The fitted equation is given by

Advantages
In one embodiment, the accelerometers can detect low as well as high frequencies. The accelerometer can detect low g acceleration of the solid.

In one embodiment, the advantage of the Single Walled Nano Tube based accelerometer will be miniature of size of the sensor that can be reduced to nano-scale dimensions.

In one embodiment, the response time of the accelerometer is better than 1 milli sec.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

We Claim:

1. An accelerometer (10) comprising:

a. an acceleration sensor (11) comprising at least one carbon nanotube (1) placed between two electrodes (2, 21);

b. a solid deflectable arm (12) connected to the acceleration sensor (10), wherein the solid deflectable arm (12) and the acceleration sensor (10) is housed in a sealed cylindrical chamber (6) containing liquid; and

c. electrical connections (3, 3') taken out from the acceleration sensor (10) to measure electrical signals developed across the carbon nanotubes (1) to measure acceleration.

2. The accelerometer (10) as claimed in claim 1, wherein the carbon nanotube (1) is selected from a group comprising a single wall type carbon nanotube and a multi wall type carbon nanotube.

3. The accelerometer (10) as claimed in claim 1, wherein response time of the accelerometer (10) is 1 milli second.

4. The accelerometer (10) as claimed in claim 1, wherein the electrodes (2, 21) is supported onto an insulating substrate (13).