An Acoustic Waveguide with Tight Field Confinement for High Temperature Sensing

A fused quartz acoustic waveguide structure was reported as the suspended core waveguide. The waveguide featured good acoustic wave confinement within the core and a relatively small diameter. Consistent high-temperature sensing was also demonstrated with the waveguide after a temperature sensor was fabricated inside. The waveguide was fabricated by suspending its core rod in the middle of the hollow cladding tube by discrete thin supporting disks. It was found that the characteristics of acoustic propagation in the waveguide was similar to that in a bare core rod and that the waveguide was largely insensitive to lossy surface perturbations. The diameter of the waveguide was relatively small, little more than the bulk longitudinal acoustic wavelength. For sensing, the periodic structure, the acoustic fiber Bragg grating, was fabricated on the core of the suspended core waveguide. A temperature test up to 1000 °C was performed. The central frequency of the reflected acoustic wave was found to change unidirectionally and consistently with changes in temperature. With its good field confinement and consistent sensing capabilities, the suspended core waveguide could find vast potential in many applications.