Ultra-sensitive current sensor based upon a thermal-sensitive FPI and conductive material combination

This paper introduces an ultra-high sensitivity current sensor based upon a thermal-sensitive Fabry-Perot interferometer (FPI) and a conductive material. First, <i>F</i><i>P</i><i>I</i>₁ and <i>F</i><i>P</i><i>I</i>₂ with different cavity lengths were prepared by canning the heat-sensitive material, polydimethylsiloxane (PDMS), into a capillary tube. Experiments have shown that both <i>F</i><i>P</i><i>I</i>₁ and <i>F</i><i>P</i><i>I</i>₂ are very sensitive to temperature, with temperature sensitivities of 2.30 and 1.75 nm/°C, respectively. Then, <i>F</i><i>P</i><i>I</i>₁ and <i>F</i><i>P</i><i>I</i>₂ are respectively attached to thin copper rods, conducting current through the copper rods to generate abundant heat, which is converted into temperature changes on <i>F</i><i>P</i><i>I</i>₁/<i>F</i><i>P</i><i>I</i>₂ to measure the current. The experiment exhibited that the current square sensitivity of <i>F</i><i>P</i><i>I</i>₁ and <i>F</i><i>P</i><i>I</i>₂ reached 4.56 and 2.43<i>n</i><i>m</i>/<i>A</i>². To further improve the current square sensitivity of <i>F</i><i>P</i><i>I</i>₂, a current-insensitive reference interferometer, <i>F</i><i>P</i><i>I</i>₃, was linked in parallel with <i>F</i><i>P</i><i>I</i>₂ to construct the sensor <i>S</i>₁. Experiments had shown that <i>S</i>₁ had a vernier effect (VE) spectrum, which enhanced the current square sensitivity to 28.97<i>n</i><i>m</i>/<i>A</i>². Comparison showed that it improves the current square sensitivity of <i>F</i><i>P</i><i>I</i>₂ by nearly 12 times. The experiment also showed that <i>S</i>₁ has good measurement repeatability and static stability. In addition, <i>S</i>₁ offers low cost, easy manufacturing, and repeatable manufacturing, providing an innovative design method and a structural solution for manufacturing high-sensitivity current sensors.