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.
The quest for out-of-plane and self-powered wind sensors
has motivated
the field of outdoor sports, exploration, space perception, and positioning.
Fine hairs of spiders act as hundreds of individual wind sensors,
allowing them to feel the nearby wind change caused by the predators
or the prey. Inspired by this natural teacher, here, we demonstrate
the fabrication of bioinspired self-powered out-of-plane wind sensors
based on flexible magnetoelectric material systems. The shape of flexible
sensors, by patterning silver nanoparticles on a thin polyethylene
terephthalate film through a screen printing technique, mimics fine
hairs of the spiders, allowing for out-of-plane tactile perceptual
monitoring caused by the wind. Owing to the employment of flexible
magnetoelectric materials, the sensors can distinguish forward/backward
winds and are totally self-powered. The working mechanism for sensors
has been explained by the Maxwell numerical simulation, allowing for
further improvement of their performance by tuning diverse factors.
Furthermore, the wind sensor can detect the wind with a velocity down
to 1.2 m/s and distinguish multidegree wind by their arrays. It is
expected that, in the near future, our design can provide new findings
for out-of-plane wind sensors with superior self-powered properties
toward new flexible electronics.
Fatigue driving can easily lead to road traffic accidents and bring great harm to individuals and families. Recently, electroencephalography- (EEG-) based physiological and brain activities for fatigue detection have been increasingly investigated. However, how to find an effective method or model to timely and efficiently detect the mental states of drivers still remains a challenge. In this paper, we combine common spatial pattern (CSP) and propose a light-weighted classifier, LightFD, which is based on gradient boosting framework for EEG mental states identification. The comparable results with traditional classifiers, such as support vector machine (SVM), convolutional neural network (CNN), gated recurrent unit (GRU), and large margin nearest neighbor (LMNN), show that the proposed model could achieve better classification performance, as well as the decision efficiency. Furthermore, we also test and validate that LightFD has better transfer learning performance in EEG classification of driver mental states. In summary, our proposed LightFD classifier has better performance in real-time EEG mental state prediction, and it is expected to have broad application prospects in practical brain-computer interaction (BCI).
Solar cells are conventionally used to harvest energy in outer space, but they are ineffective in dark locations. Here, it is shown that superconducting materials—which work best in cold environments, such as those found in outer space—provide a mechanism to harvest energy that does not require light. A superconducting magnetic levitation (maglev) magnetoelectric generator (SMMG) can convert mechanical impacts to electricity at its working temperature <90 K. The SMMG device consists of a permanent magnet, a conductive coil, and a superconducting layer (SL). Owing to the existence of the SL, the permanent magnet levitates over the SL and rapidly returns to an equilibrium height after being displaced by a mechanical impact. The impact changes the gap between the levitated magnet and the coil, resulting in a variation in magnetic flux that induces electrical current in the coil. Thus, the SMMG converts low‐frequency (<3.7 Hz) mechanical energy to electricity. The output maximum peak voltage, peak power, and peak power density of the SMMG are 4.3 V, 35 mW, and 17.8 W m−2, respectively, with a load resistance of 300 Ω. The SMMG can charge a capacitor of 10 000 µF to 3.8 V with a continuous impact, which is sufficient to power critical wireless communication. The superconductor works best in cold environments and therefore is well‐suited for providing electricity to sensors and communication devices in outer space, particularly in places where the sun may not reach.
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