In this study, a sensor based on the located defect mode resonance is proposed, which can be used to simultaneously measure changes in magnetic induction intensity, plasma density, refractive index, and incident light angle. Plasma is introduced as the defect into a one-dimensional periodic structure, exciting the located defect mode resonance. The sensitivity, linear range, and figure of merit of the sensor are investigated using the transfer matrix method. The increase in the number of cycles can be used to improve the quality factor and FOM. We also consider the influence of the loss tangent on the sensor to a certain extent. The one-dimensional layered structure is utilized, which has the merits of small volume and simple manufacture. In addition, compared with the traditional sensors design, which focuses on the improvement of performance parameters, our proposed sensor concentrates on the study of multiple physical quantities. Therefore, we hope that our work can have some application potential in the field of measurement.

The design of tunable and multifunctional metastructures (MSs) is currently a trend in the terahertz (THz) field. Based on the characteristic that thermal excitation can cause the phase transition of vanadium dioxide (VO₂), a MS that concentrates both cross-polarization conversion and absorption functions is proposed in this paper, and switching two functions can be achieved by controlling the temperature. At high temperatures (68°C), the proposed MS exhibits a narrow-band absorption function in the range of 0.67 THz-0.95 THz. When the temperature drops below 68°C, VO₂ is in the insulated state, and the structure can be considered as a polarization converter. Simulation results indicate that the broadband cross-polarization conversion can be realized in 0.69 THz-1.38 THz with a polarization conversion ratio above 90% and a relative bandwidth of 66.7%. This paper analyzes the amplitude, phase, and surface current distributions under the polarization conversion function, as well as the impedance, power loss distributions, and equivalent circuits under the absorption function. In addition, the angular stability and the influences of the structural parameters on performance are also discussed. The proposed MS is suitable for complex applications due to its tunability and dual functionality.

We present a multitasking tailored device (MTD) based on phase change material vanadium dioxide (VO₂) and photoconductive semiconductor (PS) in the terahertz (THz) regime, thereby manipulating the interaction between electromagnetic waves and matter. By altering the control multitasking device, its room temperature, or pump illumination, we switch the function of absorption or polarization conversion (PC) on and off, and realize the tuning of absorptivity and polarization conversion rate (PCR). Meanwhile, the construction of cylindrical air columns (CACs) in the dielectric provides an effective channel to broaden the absorption bandwidth. For the MTD to behave as a polarization converter with VO₂ pattern in the insulating phase (IP), exciting the PS integrated to the proposed device via an optical pump beam, the PCR at 0.82-1.6 THz can be modulated continuously from over 90% to perfectly near zero. When the PS conductivity is fixed at 3×10⁴ S/m and VO₂ is in the metal phase (MP) simultaneously, the MTD switched to an absorber exhibits ultra-broadband absorption with the absorptivity over 90% at 0.68-1.6 THz. By varying the optical pump power and thermally controlling the conductivity of VO₂, at 0.68-1.6 THz, the absorbance of such a MTD can be successively tuned from higher than 90% to near null. Additionally, the influences of the polarization angle and incident angle on the proposed MTD are discussed. The designed MTD can effectively promote the electromagnetic reconfigurable functionalities of the present multitasking devices, which may find attractive applications for THz modulators, stealth technology, communication system, and so on.

Small displacement detection has been studied for extracting heart rate signal from the respiratory variation component of the human body with the FMCW radar method. And a new signal processing method of vital signal has been proposed for suppression of unrequired variation components called projection matrix method. We have presented experimental results of small displacement detection to confirm the validity of the method.

Metastructure analogs of electromagnetically induced transparency (EIT) provide a new approach for engineering realizations of nonlinear optical manipulations regardless of harsh conditions; further can be employed in polarization conversions for its low-loss transmission and phase modulation. In this work, dual-band EIT in a dielectric-metal hybrid metasurface achieved via providing different coupling channels is theoretically investigated with a maximum group delay of 404 ps. The linear-to-circular polarization conversion (LCPC) behaviors are observed respectively holding the transmittance of 0.58 at 0.68 THz, 0.73 at 0.76 THz, 0.61 at 0.90 THz, 0.53 at 0.99 THz, owning to the asymmetric EIT responses in the transverse magnetic (TM) and transverse electric (TE) modes incidence. On the other hand, phase-transition VO₂ is doped to perturb the dark mode resonances. With its conductivity σ = 10⁵ S/m, dual transparency peaks transform into unimodal broadband transmission windows with relative bandwidths of 17.1% and 9.1% under the TE and TM excitations apart. Induced LCPC possesses a bandwidth of 10.4% centered at 0.76 THz attributed to the drastic dispersion. The as-proposed design exploits pattern asymmetry of EIT responses to realize LCPC, promising the wide prospect of reconfigurable multiplexings.

We report on a highly sensitive optical temperature sensing material based on two thermally coupled energy levels (⁴I_15/2 and ⁴F_9/2) of Dy³⁺.