Ultra-thin wideband cross-polarization converter with integrated high-sensitivity terahertz biosensing

The combination of broadband polarization conversion and sensitive biosensing within a single terahertz platform has seen minimal exploration. Most reported designs focus on a single function and depend on expensive materials such as noble metals or complex 2D structures, resulting in high fabrication costs and limited scalability. Additionally, these designs usually suffer from narrow bandwidths and low-sensitivity biosensing, restricting their practical utility. This work presents an ultra-thin terahertz metasurface design capable of achieving both ultra-broadband polarization conversion and high-sensitivity biosensing. Constructed from low-cost aluminum and polyimide, the design provides a polarization conversion ratio (PCR) exceeding 90% across a 4.428 THz bandwidth and maintains PCR above 96% over a 4.226 THz range. Additionally, it determines refractive index sensing with a peak sensitivity of 1.30 THz/RIU in distinguishing healthy and cancerous biological tissues. This study presents a significant enhancement over existing metasurface designs by integrating an ultra-wideband frequency range, excellent average polarization conversion, and highly sensitive biosensing capabilities into a single, cost-effective device.