G. C. Poddar

Fiber Bragg grating sensor for monitoring bone decalcification

INTRODUCTION Estimation of decalcification is a vital tool to discern bone health. Different techniques are used for its quantitative measurement, e.g. DEXA, QCT & QUS. All these techniques, although noninvasive, suffer from limitations such as radiation exposure and inaccurate values. Recently, fiber optic techniques are fast emerging for medical applications owing to their various attractive features like immunity to EMI/RFI, geometric versatility, chemical inertness, etc. MATERIAL AND METHODS The effect of decalcification on strain response of a goat tibia was investigated in vitro using fiber Bragg grating (FBG) sensing technique. The bone was strained by using three-point bending technique and corresponding Bragg wavelength shifts were recorded. Two similar bone samples from the same animal were taken and one was partially decalcified. Strain response of decalcified and untreated bone was taken concurrently to monitor the effects of calcium loss and that of degradation with time. RESULTS AND CONCLUSION The strain generated for same stress increased with greater degree of decalcification and a steep increase occurred after 2g calcium loss, indicating the onset of damage. The strain response, therefore gives a direct indication of the degree of calcium present in the bone. LEVEL OF EVIDENCE Level III.

Single fiber Bragg grating sensor with two sections of different diameters for longitudinal strain and temperature discrimination with enhanced strain sensitivity

A single fiber Bragg grating (FBG) sensor with two sections of different diameters is proposed and experimentally demonstrated for discrimination and measurement of strain and temperature. A section of single FBG is etched in hydrofluoric acid solution to reduce diameter of the fiber by factor of <1/2 to increase its strain sensitivity. Different shifts of the Bragg wavelengths of chemically etched and nonetched gratings caused by different strain sensitivities are used to discriminate and measure strain and temperature. Maximum errors of +/-13 microepsilon (microstrain) and +/-1 degrees C are reported over 1700 microepsilon and 60 degrees C measurement ranges, respectively. Depending upon the diameter of the etched fiber grating, the design can also discriminate nanostrain from temperature.

Mechanically created long-period fiber gratings as sensitive bend sensors

An application of mechanically created long-period fiber grat- ings as sensitive bend sensors in structures and other areas is sug- gested. A resonance splitting of about 10 nm is observed under a maxi- mum bend curvature of 0.4 m 21 , producing a bend sensitivity of 25 nm/m 21 . The design features of the experimental setup developed for the realization of mechanically created long-period fiber gratings and measurement of their output spectrum under different bend curvatures are discussed.

Embedded dual fiber Bragg grating sensor for temperature-load (strain) discrimination

An embedded dual fiber Bragg gratings sensor for temperature and strain discrimination is proposed and demonstrated. Two nearly identical gratings are mounted opposite side of an arch-shape steel strip. The gratings in concave and convex position experiences equal blue and red shift due to bending of the strip under compressive and tensile strains respectively. The thermal response and strain response are separated by addition and subtraction of the resultant shifts from two gratings. The thermal and strain sensitivity of the sensor is improved to 30 pm/degC and 2.6 pm/muepsiv. The sensor can measure strain and temperature with a permissible error of plusmn 1 muepsiv and plusmn 1.5degC respectively.

Study of FBG sensors for cryo temperature monitoring

Experimental characterization of a fiber Bragg grating sensor probe has been carried out for cryo-temperature monitoring. The temperature sensitivity was found to be 16.7 pm/°C at room temperature and 90 pm/°C pm/°C near liquid nitrogen temperature.