Metamaterial absorber integrated microfluidic terahertz sensors

Spatial overlap between the electromagnetic fields and the analytes is a key factor for strong light-matter interaction leading to high sensitivity for label-free refractive index sensing. Usually, the overlap and therefore the sensitivity are limited by either the localized near field of plasmonic antennas or the decayed resonant mode outside the cavity applied to monitor the refractive index variation. In this paper, by constructing a metal microstructure array-dielectric-metal (MDM) structure, a novel metamaterial absorber integrated microfluidic (MAIM) sensor is proposed and demonstrated in terahertz (THz) range, where the dielectric layer of the MDM structure is hollow and acts as the microfluidic channel. Tuning the electromagnetic parameters of metamaterial absorber, greatly confined electromagnetic fields can be obtained in the channel resulting in significantly enhanced interaction between the analytes and the THz wave. A high sensitivity of 3.5 THz/RIU is predicted. The experimental results of devices working around 1 THz agree with the simulation ones well. The proposed idea to integrate metamaterial and microfluid with a large light-matter interaction can be extended to other frequency regions and has promising applications in matter detection and biosensing

Terahertz Metamaterial and its Sensing Application

Spatial overlap between the electromagnetic fields and the analytes is a key factor for strong light-matter interaction leading to high sensitivity for label-free optical biosensors. Usually, the exponential fields of cavity modes or surface plasmon resonances are applied to monitor the refractive index variation from bio-reactions. The sensitivity is therefore limited by the influence of local index variation to the weak exponential field. In this paper, by constructing a metallic microstructure array-dielectric-metal (MDM) structure, a novel metamaterial integrated microfluidic (MIM) sensor is demonstrated in terahertz (THz) range, where the dielectric layer of the MDM metamaterial is hollow and acts as the microfluidic channel. Tuning the electromagnetic parameters of metamaterial, greatly confined electromagnetic fields can be obtained in the channel resulting in significantly enhanced interaction between the analytes and the THz wave. A record high sensitivity of 3.5 THz/RIU is predicted by numerical simulation. Normalized the sensitivity to the working frequency, the calculated and measured normalized sensitivity is 0.55/RIU and 0.31/RIU, respectively. The proposed idea to integrate metamaterial and microfluid with a large light-matter interaction can be extended to other frequency regions and has promising applications in biosensing and matter detection

Gbps Terahertz External Modulator Based on a Composite Metamaterial with a Double-Channel Heterostructure

The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nanoscale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this Letter, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultrafast, and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1 GHz modulation speed and 85% modulation depth during real-time dynamic tests. Moreover, a 1.19 rad phase shift was realized. A wireless free-space-modulation THz communication system based on this external THz modulator was tested using 0.2 Gbps eye patterns. Therefore, this active composite metamaterial modulator provides a basis for the development of effective and ultrafast dynamic devices for THz wireless communication and imaging systems

Enteral nutrition feeding in Chinese intensive care units: a cross-sectional study involving 116 hospitals

Abstract Background There is a lack of large-scale epidemiological data on the clinical practice of enteral nutrition (EN) feeding in China. This study aimed to provide such data on Chinese hospitals and to investigate factors associated with EN delivery. Methods This cross-sectional study was launched in 118 intensive care units (ICUs) of 116 mainland hospitals and conducted on April 26, 2017. At 00:00 on April 26, all patients in these ICUs were included. Demographic and clinical variables of patients on April 25 were obtained. The dates of hospitalization, ICU admission and nutrition initiation were reviewed. The outcome status 28 days after the day of investigation was obtained. Results A total of 1953 patients were included for analysis, including 1483 survivors and 312 nonsurvivors. The median study day was day 7 (IQR 2–19 days) after ICU entry. The proportions of subjects starting EN within 24, 48 and 72 h after ICU entry was 24.8% (84/352), 32.7% (150/459) and 40.0% (200/541), respectively. The proportion of subjects receiving > 80% estimated energy target within 24, 48, 72 h and 7 days after ICU entry was 10.5% (37/352), 10.9% (50/459), 11.8% (64/541) and 17.8% (162/910), respectively. Using acute gastrointestinal injury (AGI) 1 as the reference in a Cox model, patients with AGI 2–3 were associated with reduced likelihood of EN initiation (HR 0.46, 95% CI 0.353–0.599; p < 0.001). AGI 4 was significantly associated with lower hazard of EN administration (HR 0.056; 95% CI 0.008–0.398; p = 0.004). In a linear regression model, greater Sequential Organ Failure Assessment scores (coefficient – 0.002, 95% CI – 0.008 to − 0.001; p = 0.024) and male gender (coefficient – 0.144, 95% CI – 0.203 to − 0.085; p < 0.001) were found to be associated with lower EN proportion. As compared with AGI 1, AGI 2–3 was associated with lower EN proportion (coefficient – 0.206, 95% CI – 0.273 to − 0.139; p < 0.001). Conclusions The study showed that EN delivery was suboptimal in Chinese ICUs. More attention should be paid to EN use in the early days after ICU admission