In this paper, a Janus metastructure sensor (JMS) based on the photonic spin Hall effect (PSHE), which can detect multiple physical quantities, is proposed. The Janus property is derived from the fact that the asymmetric arrangement of different dielectrics breaks the structure parity. Hence, the metastructure is endowed with different detection performances for physical quantities on multiple scales, broadening the range and improving the accuracy of the detection. When electromagnetic waves (EWs) are incident from the forward scale of the JMS, the refractive index, thickness, and incidence angle can be detected by locking the angle corresponding to the PSHE displacement peak that is enhanced by the graphene. The relevant detection ranges are 2~2.4, 2~2.35 μm, and 27°~47°, with sensitivities (S) of 81.35°/RIU, 64.84°/μm, and 0.02238 THz/°, respectively. Under the condition that EWs incident into the JMS from the backward direction, the JMS can also detect the same physical quantities with different sensing properties, such as S of 99.3°/RIU, 70.07°/μm, and 0.02348 THz/° in corresponding detection ranges of 2~2.09, 1.85~2.02 μm, and 20°~40°. This novel multifunctional JMS is a supplement to the traditional single-function sensor and has a certain prospect in the field of multiscenario applications.

In this paper, a multitasking layered nonlinear metastructure (NM) with polarization conversion (PC) and multi-physical quantities detection (MQPD) is investigated, comprising two common media, nonlinear Kerr medium and indium antimonide (InSb). The incident electromagnetic waves (EWs) are considered linear waves. Considering the temperature-tunable property of InSb, the transmission phase difference and polarization form can be tuned by the temperature. When the temperatures are adjusted to 286 K or 300 K, the transmitted EWs can be converted to circular polarization waves (CPWs), classified as left-handed CPWs and right-handed CPWs, whose polarization energy transmission rates (PER) are 0.9147 and 0.9128. With the introduction of the nonlinear Kerr medium, the NM will have the feature of tunability for the electromagnetic intensity, which can be employed to encrypt the polarization information and adjust the PER peak related to the performance of MQPD. Moreover, With EWs being incident, the detection of the refractive index, incident angle, and temperature can be realized by confirming the frequency of the special EWs PER peak. The relevant detection ranges are 1.45~2.20, 246~296 K, and 72°~82°. This multifunctional layered NM integrating PC and MQPD can not only be applied to the antenna fields but also has certain application scenarios in industrial production and detection.

A parity-time (PT) symmetric photonic sensing metastructure (PSM) is proposed which realizes biological detection, pressure measuring, and biomedical blood glucose sensing, and coherent perfect absorption (CPA) is excited in the PSM with magnetized plasma films. The proposed PSM is capable of multiscale sensing, implementing non-CPA and CPA schemes at different frequencies. Because of the fragility of CPA, the PSM can precisely distinguish cancerous cells from normal cells via refractive index detection by CPA schemes. Furthermore, utilizing non-CPA schemes, one can achieve the detection of glucose solution concentration and the detection of external pressure using the photo-elastic effect by observation of resonance frequency. More importantly, the designed PSM has great advantages in the detection performance such as the linear range, sensitivity, quality (Q), figure of merit (FOM), and detection limit (DL), which will be precisely described by the calculation of the transfer matrix method. For cancerous cell detection, the relevant Q, FOM, and DL are high at 2943, 2100 RIU^-1, and -46.23 dB. When using non-CPA schemes, the Q, FOM, and DL of the pressure detection reach 55155, 150.78 GPa^-1, and -34.8 dB. Also, related to the detection of glucose concentration, the Q, FOM, and DL are 55315, 17667.3 RIU^-1, and -55.48 dB. Therefore, the proposed PSM provides a multi-physical, accurate biochemistry and medical detection solution.

Recently, more and more attention has been paid to human health with the rapid development of society. A designed virtual polarizer (VP) can realize multiscale and multi-biomass sensing, including temperature, cancerous cells, and COVID-19. Based on coherent perfect polarization conversion, a certain polarization conversion can be fulfilled within 1.72~2.14 THz. Then, through observing the displacement of a perfect matching point (PMP), variations in temperature can be accurately determined, covering from 299 K to 315 K, with a sensitivity (S) of 0.0198 THz/K. Moreover, a sharp coherent perfect absorption (CPA) peak generated from the VP can be employed for the detection of cancerous cells and COVID-19. The refractive index (RI) detection range of cancerous cells is from 1.36 RIU to 1.41 RIU with the sensitivity being −4.45881 THz/RIU. The average quality factor (Q), figure of merit (FOM), and detection limit (DL) are 825.36, 241.11 RIU⁻¹, and −36.83 dB. For the COVID-19 solution concentration (SC) from 0 mM to 525 mM, by mapping SC to RI, the RI sensing range is 1.344 RIU–1.355 RIU with the S being −5.03467 THz/RIU. The relevant Q, FOM, and DL are 760.85, 244.94 RIU⁻¹, and −36.89 dB. Based on two strategies of PMP and CPA, the proposed VP is capable of multiscale and multi-biomass sensing with excellent detection performance, providing a new detection method for biosensing.

Based on the interference of electromagnetic (EM) waves, an electromagnetic logic metastructure (ELM) with the graphene layers (GLs) is proposed to emulate the functionality of a conventional JK flip-flop. When two coherent EM waves are simultaneously incident on the ELM from opposite directions, a coherent near-perfect absorption (CNPA) peak can be generated within the frequency range of 12~13.8 terahertz (THz), where the phase difference between the coherent waves is denoted as ΔΦ. If the value of the CNPA peak exceeds 0.55, the output level F of the ELM is defined as ‘1’; otherwise, it is defined as ‘0’. With the assistance of the ΔΦ, the chemical potential (μC) of the GLs and the incident angle (θ) are utilized as the input signals corresponding to the J and K inputs of the JK flip-flop, which can effectively simulate JK flip-flop functions: set function, clear function, toggle, and no-change. Therefore, by appropriately configuring the logical parameters ΔΦ, μC, and θ, the proposed ELM can effectively emulate the part functions of a JK flip-flop, offering a promising approach for enhancing the capabilities of EM logic devices.

Encoding and encryption are essential parts of information transmission based on electromagnetic (EM) waves, where the traditional methods related to encoding and encryption often need complex structures like special-shaped channels and unit arrays. To reduce the limitation of mass manufacture of encoding and encryption devices, a layered metastructure (LM), based on the interference of EM waves, is designed for the function of encoding and encryption, which is composed of indium arsenide (InAs) and E7 liquid crystal (LC). Assuming the phase difference between EM waves, elected as linear polarization waves, incident from the front and back terms of the LM as ΔΦ, the magnetic field B (0.8 or 3.30 T) and ΔΦ (180° of 9°) can serve as the first and second input logic levels to control the certain polarization conversion in the range of 15.733–16.095 Terahertz (THz), where the InAs has the tunability of the B. By the combinations of the logic levels, an information relationship is established between the external parameters and output polarization forms. When the supersaturation bias voltage (190 V) is applied, the long axis in E7 LC will be rotated, meaning that the correspondence relationship between logic levels and polarization output is destroyed to obtain the effect of encryption in the coverage of 15.733–16.095 THz. Therefore, the proposed LM can realize the function of encoding and encryption with excellent application possibility and value, benefiting the mass production of encoding and encryption devices of EM waves.