Two-dimensional directional modulation with dual-mode vortex beam for security transmission

A two-dimensional directional modulation(DM)technology with dual-mode orbital angular momentum(OAM)beam is proposed for physical-layer security of the relay unmanned aerial vehicle(UAV)tracking transmission.The elevation and azimuth of the vortex beam are modulated into the constellation.which can form the digital waveform with the encoding modulation.Since the signal is direction-dependent,the modulated waveform is purposely distorted in other directions to offer a security technology.Two concentric uniform circular arrays(UCAs)with different radii are excited to generate dual vortex beams with orthogonality for the composite signal,which can increase the demodulation difficulty.Due to the phase propagation characteristics of vortex beam,the constellation at the desired azimuth angle will change continuously within a wavelength.A desired single antenna receiver can use the propagation phase compensation and an opposite helical phase factor for the signal demodulation in the desired direction.Simulations show that the proposed OAM-DM scheme offers a security approach with direction sensitivity transmission.

Directional sensitivity of auditory ascending neuron in the bushcricket Gampsocleis gratiosa

Quantitative analyses on phonotactic behavior of the bushcricket have demonstrated that the bushcricket possesses good capability to determine direction of sound source. The morphological structure, laterality and directional sensitivity of the auditory ascending neuron in the prothoracic ganglion of the bushcricket have been studied. At its best frequency of 15 kHz, the laterality threshold difference of the neuron is great up to about 16 dB. Its directional sensitivity depends closely on stimulus frequency. The higher the stimulus frequency, the greater the directional threshold differences. Spike count and latency shift of the ascending neuron in response to each stimulus depend on the angle of incidence of sound. Therefore, the two parameters can be used as directional cues of sound source by the ascending neuron.

Highly sensitive vector magnetic fiber sensor based on hyperbolic metamaterials

Hyperbolic metamaterials(HMMs) are novel artificial materials that excite the surface plasmon resonance(SPR) because of their unique hyperbolic dispersion properties. Herein, to the best of our knowledge, we propose the first HMM-based fiber SPR(HMM-SPR) sensor for vector magnetic detection. By selecting the composite materials and structural parameters of the HMM dispersion management, HMM-SPR sensors can achieve a high refractive index sensitivity of 14.43 μm/RIU. Vector magnetic field detection was performed with the HMM-SPR sensor encapsulated with a magnetic fluid. Compared with other ferrofluidbased magnetic field fiber sensors, the proposed sensor shows pronounced advantages in intensity and direction sensitivity of 1.307 nm/Oe and 7.116 nm/°, respectively. The sensor design approach presented in this paper provides an excellent demonstration of HMM-SPR sensors in various applications.

Design and Fabrication of a Multi-electrode Metal-core Piezoelectric Fiber and Its Application as an Airflow Sensor

Crickets, similar to some other insects, have highly sensitive filiform hairs on their cerci that can detect miniscule changes in airflow. This study imitates the perception mechanism of these filiform sensory hairs of crickets by designing and fabricating a Multi-electrode Metal Core Piezoelectric Fiber （MMPF）-based airflow sensor. Four longitudinal conductive sheets were coated symmetrically on their surfaces with Metal-core Piezoceramic Fibers （MPF）. The four fan-shaped piezoelectric ceramics with surface electrode covers were polarized. After successful polarization, the cantilevered MMPF could be used as an airflow sensor. The four electrodes on the surface were symmetrically divided into two groups. Therefore, two signals can be produced by a single fiber sensor. The theoretical model of an MMPF airflow sensor has been established. The model indicates that the ratio of the two signals is equivalent to the tangent of the airflow angle. Furthermore, the sum of the squares of the two signals is not dependent on the angle, but reflects the velocity of the airflow. Therefore, a single MMPF can be used to measure both the direction and amplitude for a given airflow. The theoretical model has been confirmed via experimental measurements.