The generation of a second harmonic wave (SHW) is a process of electromagnetic radiation at a specific frequency, often occurring in polarized ferroelectric crystals (FCs). In this article, a multitask graphene electromagnetic detection device (GEDD) based on second harmonic generation (SHG) is proposed. Through the periodic arrangement of different dielectric materials, the SHW conversion efficiency steadily increases within the structure, enabling multiscale detection of graphene thickness, angle, and hemoglobin concentration. By utilizing the shift $f_{1}$ in the SHW peak (SHWP), the number of graphene layers (ranging from one to ten layers) can be accurately identified through thickness detection. The sensitivity ( S ) is 62.1 GHz/nm. Leveraging the high- S of 147 GHz/ $^{\circ}$ , the shift $f_{2}$ in the SHWP within the graphene structure can be employed for precise small-angle detection within a range of 4 $^{\circ}$ –6 $^{\circ}$ . Furthermore, by altering the filling medium of the test cavity, positioning the change value of SHWP can promote high-precision identification of hemoglobin concentrations of different blood types within the refractive index (RI) range of 1.6–1.7. The design of high- S multitask GEDD holds significant importance for expediting graphene material research. Moreover, it offers a novel approach for the precise application of SHW in the field of electromagnetic detection.

Second harmonic wave (SHW) generation is a nonlinear optical phenomenon wherein electromagnetic radiation undergoes a process of doubling its frequency. A multi-task Janus metastructure (MJMS) based on liquid crystal (LC) tunable defects is introduced in this paper, enabling temperature detection and biosensing. Due to the asymmetric arrangement of dielectrics, MJMS exhibits Janus characteristics in both forward and backward directions. Significant enhancement in the output efficiency of SHW can be achieved through the adjustment of LC defects and structural design. When the cavity under test is filled with air, high-precision temperature sensing can be achieved by detecting the shift of the SHW’s peak (SHWP), with a detection range of 15 °C ~ 40 °C. The highest sensitivity (S) can reach 0.00164 THz/°C. When the cavity under test is filled with analytes, different types of waterborne bacteria can be identified on the forward scale by the amplitude shift of SHWP, with a measurement range of 1.365 ~ 1.425, S = 0.9826 /RIU. On the backward scale, MJMS can detect glucose solution with concentrations ranging from 0 g/L ~ 400 g/L with a detection range of 1.33 ~ 1.38, S = 3.402 /RIU. This MJMS has the potential to drive breakthroughs in electromagnetic detector design, opening up new avenues for exploring SHW applications and LC research.

Identifying brain-tissue types holds significant research value in the biomedical field of non-contact brain-tissue measurement applications. In this paper, a layered metastructure is proposed, and the second harmonic generation (SHG) in a multilayer metastructure is derived using the transfer matrix method. With the SHG conversion efficiency (CE) as the measurement signal, the refractive index ranges that can be distinguished are 1.23~1.31 refractive index unit (RIU) and 1.38~1.44 RIU, with sensitivities of 0.8597 RIU⁻¹ and 1.2967 RIU⁻¹, respectively. It can distinguish various brain tissues, including gray matter, white matter, and low-grade glioma, achieving the function of a second harmonic mode sensor (SHMS). Furthermore, temperature has a significant impact on the SHG CE, which can be used to define the switch signal indicating whether the SHMS is functioning properly. When the temperature range is 291.4~307.9 Kelvin (K), the temperature switch is in the “open” state, and the optimal SHG CE is higher than 0.298%, indicating that the SHMS is in the working state. For other temperature ranges, the SHG CE will decrease significantly, indicating that the temperature switch is in the “off” state, and the SHMS is not working. By stimulating temperature and using the response of SHG CE, the temperature-switch function is achieved, providing a new approach for temperature-controlled second harmonic detection.

A metalayer (ML) composed of indium antimonide, ferroelectric crystals and porous silicon with high transmission, sensing properties, wide detecting range, and multiple physical measurements is proposed which optimized by the improved ant colony algorithm (IACO). Due to the quasi-phase matching principle and nonlinear optical properties, the second harmonic waves with high conversion efficiency are successfully generated in the micron operating band, and forms a high and narrow transmission peak for sensing detection. Through analysis using the transfer matrix method which is driven by IACO to accelerate the optimization of structures, the sensing performance sensitivity ( S ), quality factor ( Q ), figure of merit ( FOM ), and detection limit ( DL ) are calculated. The proposed ML demonstrates the capability to measure thickness ( S =18.75, Q =11885, FOM =332 μm ^-1 ), external temperature ( S =4.6 nm/K, Q =7046, FOM =0.049 K ^-1 ), and magnetic field intensity ( S =1332 nm/T, Q =8146, FOM =16.3 T ^-1 ). Additionally, it exhibits an ultra-wide refractive index sensing range from 1 to 5, and excels in detecting hydrobacteria, and viruses with good sensing performance ( S =44000 nm/RIU and 43460 nm/RIU), high Q values (5585 and 6103), and low DL (1.38×10 ^-4 RIU and 1.3×10 ^-4 RIU). This versatile and promising ML design offers possibilities for comprehensive multi-physical and chemical parameter measurements in diverse fields.