In this paper, a comparison study on the all fiber optic non-contact vibration sensors which are designed based on the principle of reflected light intensity modulation is reported. Various structural designs were proposed to enable advancement in the sensing of the vibration. For every configuration, achieved an improvement by eliminating the dark region, exhibits single slope which enables easy alignment and the rational output method used to eliminate the effect of light source on sensing. The comparison between dual plastic optical fiber, fiber optic fused 1x2 coupler and fiber optic fused 2x2 coupler vibration sensors have been discussed in detail with respect to the vibration measurement. The results reveal that, among all the reported vibration sensors 2x2 fiber optic coupler sensor exhibits better response in all the aspects. It has high resolution of 0.03 µm and frequency range up to 3.5 kHz.
This article proposes an optical method for monitoring the growth of Escherichia coli in Luria Bertani medium and Saccharomyces cereviciae in YPD. Suitable light is selected which on interaction with the analyte under consideration, gets adsorption / scattered. Required electronic circuitry is designed to drive the laser source and to detect the intensity of light using Photo-detector. All these components are embedded and arranged in a proper way and monitored the growth of the microbs in real time. The sensors results are compared with standard techniques such as colorimeter, Nephelometer and hemocytometer. The experimental results are in good agreement with the existed techniques and well suitable for real time monitoring applications of the growth of the microbs.
A simple seismic vibration sensor is designed using fiber Bragg grating (FBG) with aid of an inverted spring-mass system. An inertial mass is attached to the spring enables to oscillate in axial direction only when it is subjected to seismic vibration (P-wave). The spring mass system facilitates free motion only in one direction that is parallel to the base. An interrogation system is developed using Single mode-Multimode- Single mode (SMS) configuration to monitor the Bragg wavelength shift of FBG into its equivalent optical intensity modulation corresponding to the seismic vibration. The experimental results show that proposed sensor is capable of measuring the vibrations of frequency over the range of 2-20Hz. Further, it is evident from the results that the sensor is highly sensitive at 7.5Hz represents the resonance frequency of the designed sensor system. The range of the frequency measurement can be optimized by changing the spring parameters or overhead weight (mass) and also the position of the FBG attached between the spring and support. Thus designed sensor head enables low-cost measurement and fast response in real time applications.
A simple geometrical fiber optic vibration sensor is designed and demonstrated using fiber optic fused 2x2 coupler that utilizes the principle of reflection intensity modulation. The rational output is used to avoid the effects of source signal power fluctuations and fiber bending losses. The calibrated 1mm linear region of the displacement characteristic curve of the sensor having high sensitivity of 2.1 mV/mm (0.36 a.u. /mm) is considered for vibration measurement. The experimental results show that the sensor is capable to measure the frequency up to 3500 Hz with ~0.03μm resolution of vibration amplitude over a dynamic range of 0-1mm. The SNR of the rational output is also improved with respect to the sensing signal. In comparison with dual-fiber and bifurcated-bundle fiber, this sensor eliminates the dark region and front slope which facilitates the easy alignment. The simplicity of design, non-contact measurement, high degree of sensitivity, economical along with advantages of fiber optic sensors are attractive attributes of the designed sensor that lend to real time monitoring and embedded applications.
A simple noncontact fiber optic vibration sensor is designed using multimode fiber optic coupler. The sensor works on
principle of reflection intensity modulation. A single fiber port of the coupler is used as sensing head. A linear change in
light intensity during its displacement from the reflecting surface within 1 mm of linear region shows a high sensitivity
of 2.45 mV/μm which is used for the vibration measurement. Experimental results show that the sensor has the
capability of measuring vibrations of frequencies up to 1300 Hz with ~1μm resolution of vibration amplitude over a
range of 0-1mm. In comparison with dual-fiber and bifurcated-bundle fiber, this sensor eliminates the dark region and
front slope which facilitates the easy alignment. The high degrees of sensitivity, economical along with advantages of
fiber optic sensors are attractive attributes of the designed sensor that lend support to real time monitoring and embedded
A single mode fiber optic vibration senor is designed and demonstrated to monitor the vibration of a simply
supported beam. A rectangular beam (length 30.8 cm, width 2.5cm and thickness 0.5mm) made of spring-steel is
arranged as simply supported beam and is made to vibrate periodically. To sense the vibrations a telecommunication
fiber is chemically etched such that its diameter reaches 50μm and is glued using an epoxy at the centre of the beam. A
broadband light (1550nm) is launched into Fiber Bragg Grating (FBG) through a circulator. The light reflected by the
FBG (1540.32nm) is coupled into the centre etched fibre through the circulator and is detected by photodiode connected
to a transimpedance amplifier. The electrical signal is logged into the computer through NI-6016 DAQ. The sensor
works on transmission power loss due to the mode volume mismatch and flexural strain (field strength) of the fiber due
to the bending in the fiber with respect to the bending of the spring-steel beam. The beam is made to vibrate and the
corresponding intensity of light is recorded. Fast Fourier transform (FFT) technique is used to measure the frequencies of
vibration. The results show that this sensor can sense vibration of low frequency accurately and repeatability is high. The
sensor has high linear response to axial displacement of about 0.8 mm with sensitivity of 32mV/10μm strain. This lowcost
sensor may find a place in industry to monitor the vibrations of the beam structures and bridges.
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.