Heisenberg's uncertainty principle explains single slit diffraction1 where maximum is always at the centre. The same
experiment has been conducted but with transparent walls i.e. the material present on either side of the slit, instead of
opaque material. The observed result is a minimum at the centre in between two maximum. It is intuitive that atleast
some photons passed through the slit must end up at the centre of the diffraction pattern but the result is different. The
diffraction pattern occurs as the photons interact with the material around the slit. While uncertainty principle cannot
give quantitative explanation as the photons confined in gap between slits still occupy the same space whether it is
passing through a slit or not. This paper discusses various experiments and results by examining the interactions between
photons and the material of the wall which makes the slit for better understanding of properties of light.
Tunable LASER source is a device which emits a particular light wavelength based on the tuning done. The tuning depends on certain characteristic of the LASER source which makes it customised within a gamut of wavelengths. Most Conventional LASER sources in the market are bulky and complex. The Tunable LASER source designed is established on the simple idea that Optical Amplifier can act as a broadband source, and temperature and strain sensitive Fiber Bragg Grating can be used to filter the required wavelength. This makes the design very light and elementary.
Pressure and temperature are fundamental properties of the oceanic water. They have varying effects on the processes that take place in oceans be they biological, physical or chemical while pressure always increases with respect to surface when you go down, temperature has a more complex variation with respect to the depth. Various tools and techniques are available to measure these properties. A combination sensor with high accuracy and response time would enable better measurements of these two parameters. This paper presents a novel structure based on simultaneous measurement of temperature and pressure sensing using Fiber Bragg grating (FBG) sensors. For this, proposed sensor heads for both temperature and pressure. Temperature measurement, two different types of sensor heads has been designed for this implementation. The first sensor head consists of a FBG which is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of the FBG which is fixed between two bimetallic strips. For pressure, in first type the FBG is fixed between silicon rubber foil and sensor head wall. In second method the FBG is fixed between two silicone rubber foils. The pressure on walls of silicon rubber foils elongates FBG, which results in shift of wavelength. Theoretical studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor and pressure sensitivity of about eight times greater than that of bare FBG. Further, the proposed sensors have shown good linearity and stability.
This is the study of relation between thermal and magnetic properties of permanent magnets. The concept of adiabatic demagnetization gives the basic idea on variation in temperature of paramagnetic substances due to the application of magnetic field. With the understanding of adiabatic demagnetization the variations in temperature of ferromagnetic materials can be explained. In both cases, adiabatic demagnetization tells us about conservation of energy. The study on thermal properties of ferromagnetic materials at cryogenic temperatures gives the amount of thermal energy being transferred from or to the surroundings and hence gives the variations in magnetic fields due to temperature changes. As samarium cobalt rare earth permanent magnet do quite well at cryogenic temperatures, this study is much useful in future applications of permanent magnets in space for a renewable energy source. This will enable us to look into the design and working of a device that can convert thermal energy to mechanical energy which leads to thinking of energy conversion without causing harm to our environment. Numerous research works report the successful use of samarium cobalt to temperatures as low as 2 K.
This study focused on the development of high sensitivity pressure sensor based on reduced clad FBG encapsulated
in a stainless steel cylinder, partially filled with silicon rubber. The sensor works by means of transferring radial or
lateral pressure into an axially stretched- strain along the length of the FBG. The experiment is carried out using two
different FBG's have core/clad diameters of 9/125μm (FBG1) and 4/80μm (FBG2). FBG2 is chemically etched to reduce
the cladding diameter which significantly enhances the pressure sensitivity. The shift of the Bragg wavelength in
response to applied pressure is monitored with an optical spectrum analyser (OSA). The measured pressure sensitivity of
FBG2 and FBG1 are found to be 5.85 x 10-2 MPa-1 and 2.07 x 10-2 MPa-1, which are approximately 18870 and 6677
times respectively higher than that can be sensed with a bare FBG. A very good linearity is observed between Bragg
wavelength shift and pressure. This compact, low cost and robust design of the sensor can find applications in the areas
of low and medium pressure measurement.
A small and simple hydrostatic pressure sensor using fiber Bragg grating sensor for liquid level sensing is reported. The working principle of the sensor head design is based on transferring hydrostatic radial pressure to axial strain to the FBG. An FBG written in a fiber of diameter 50μm has been used for the measurement. The experimental result shows that sensitivity of the sensor can reach 23pm/cm of liquid column. The sensor can be useful in applications that involved with less hydrostatic pressure, like a tank with inflammable liquid in a fuel gas station.
A simple technique to discriminate the Strain and Temperature with a single Fiber Bragg Grating (FBG) at cryogenic
regime is presented in this paper. An uniform FBG is divided into two parts, one half is without coating (FBG1) and
other half is coated with Cyno-Acrylic Adhesive (FBG2). The measured temperature and strain sensitivities of the FBG1
are 4.05x10-6/K and 2.13x10-6/με and FBG2 are 1.39x10-5/K and 1.72x10-6/με respectively.
Fiber Bragg Gratings have been shown to have a much improved thermal sensitivity when coated by Polymethyle methacrylate (PMMA) at cryogenic regime has been proposed. The PMMA has large thermal expansion coefficients and acts as driving elements. It is coated on the FBG at room temperature and the FBG is under compression at lower temperatures. This allows a much wider tuning of Bragg grating as fiber can stand at more compression than tension. An overall sensitivity of 0.039nm/K in the 1550nm wavelength regime has been achieved and the Bragg wavelength has been tuned upto 8.97nm in the temperature range 77K to 303K.
A fiber optic vibration sensor is demonstrated using bifurcated bundle fiber based on the principle of extrinsic
displacement sensor. An IR source is used along with glass fibers to avoid the effect of stray light in sensing. The
encapsulation of the sensor enables easy alignment, flexible handling and usage in harsh environments. The sensor is
capable of measuring the frequencies up to 650Hz with vibration amplitude resolution of 10μm, enough to monitor the
vibrations generated in heavy machines. The sensor is tested in the field to monitor the health condition of the diesel engine.
A temperature compensated liquid level sensor using FBGs and a bourdon tube that works on hydrostatic pressure is
presented. An FBG (FBG1) is fixed between free end and a fixed end of the bourdon tube. When hydrostatic pressure
applied to the bourdon tube FBG1 experience an axial strain due to the movement of free end. Experimental result
shows, a good linearity in shift in Bragg wavelength with the applied pressure. The performance of this arrangement
is tested for 21metre water column pressure. Another FBG (FBG2) is included for temperature compensation. The
design of the sensor head is simple and easy mountable external to any tank for liquid level measurements.
A simple and effective method of encapsulation of a fiber Bragg grating (FBG) sensor for use at elevated temperatures and harsh and corrosive environments using a rigid probe technique is presented in this paper. A thorough characterization has been carried out on the encapsulated, as well as bare, FBGs. The experimental studies reveal that encapsulated FBGs are superior in their responsivity, linearity, sensitivity, and repeatability when compared with unencapsulated ones.
An encapsulated fiber optic sensor head for the detection of level of fuel in a tank is presented. The design is
based on a concentric cam used along with a float and extrinsic intensity modulation of light. The sensor has been tested
for its performance to measure a fuel level range of 35cm and a sensitivity of 0.2316 volts/cm was observed during rise
in fuel level. The sensitivity and range of level sensing can be varied by varying the length of the connecting rod.