This paper simulates Ca 2+ transmembrane transport through voltage-gated Ca 2+ channels in response to terahertz electromagnetic irradiation. The active transport of Ca 2+ ions is taken into considerations in the Ca 2+ transport. Temperature variations due to terahertz electromagnetic loss in physiological medium are simulated. The electromagnetic interaction between terahertz fields and physiological mobile ions at the cellular level is deduced from relativistic electrodynamics. It shows that effects of 0.1 ∼ 3 THz electromagnetic fields on cell mobile ions are primarily due to effects of electric fields, and effects of magnetic fields at the cellular level are insignificant. In addition, numerical simulation reveals that terahertz irradiation causes vibration of membrane potential, which is able to activate voltage-gated Ca 2+ channels. Besides, bioeffects of terahertz frequency, irradiation duration and electric intensity on the increment of intracellular Ca 2+ concentration due to activation of voltage-gated Ca 2+ channels are revealed. Meanwhile, numerical results show that temperature rises are inconsequential in the case of different irradiation parameters, indicating the non-thermal bioeffects of voltage-gated Ca 2+ transmembrane transport due to terahertz irradiation. Furthermore, the results also reveal that thermal bioeffect can be significant if the irradiation duration is raised long enough for high-dose terahertz irradiation. The numerical simulations lay the basis for understanding the bioeffects of terahertz irradiation on Ca 2+ transmembrane transport and pave the way for further exploration in modulation of intracellular Ca 2+ concentration with terahertz electromagnetic wave. INDEX TERMS Biological effects of electromagnetic radiation, modeling and simulations, calcium ions, voltage-gated calcium channel, active transport.

In this paper, a nested dual-arm spiral antenna (NDASA) is proposed to generate multiple orbital angular momentum (OAM) modes at the same operating frequency. The NDASA consists of the feeding network and three nested dual-arm spiral structures with different sizes. Meanwhile, a metal reflector is located between the spiral structures and the feeding network to enhance the radiation directivity, which can also reduce the impact of the radio frequency (RF) coaxial cables. Both the experimental and simulated results show OAM waves with topological charges of l = 1, l = 3 and l = 5 can be independently generated at f = 3 GHz, and their maximum gains are 6.94dBi, 6.76dBi and 5.49dBi, respectively. In addition, the OAM modes multiplexing and demultiplexing technology are investigated in simulations and experiments. The isolations between the OAM modes of l = 1, l = 3 and l = 5 and the other different OAM modes are greater than 13.8dB, 13.2dB and 25.1dB, respectively, which proves the potential ability of the proposed NDASA for multiplexing and demultiplexing multiple OAM modes. INDEX TERMSOrbital angular momentum (OAM), spiral antenna, OAM multiplexing, OAM demultiplexing.

In this paper, we focus on the generation of broadband underwater vortex waves carrying multiple OAMs. Based on a wideband underwater antenna, a water-immersed horn antenna array is designed and tested. The experimental results, which are in agreement with the simulation ones, validate that the proposed antenna array can readily generate high-quality vortex waves. To further validate the performance of the proposed underwater antenna array, experimental verifications of 2-D underwater imaging for the targets of two corner reflectors have been carried out, and the result shows that the targets can be distinguished efficiently. Meanwhile, two generation methods and one detection method of the multiplexed OAMs are also presented, from which the multiplexed OAMs can be generated and detected efficiently. And the performances of two generation methods have also been compared and discussed, from which we can know that the first generation method with a smaller structure costs lower and is more efficient.INDEX TERMS Broadband, orbital angular momentum (OAM), antenna array, underwater, multiplexing and demultiplexing.

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In order to extend the applications of vortex waves, we propose a water-immersed rectangular horn antenna array for generating underwater vortex waves carrying the orbital angular momentum (OAM). Firstly, a single dielectric-loaded rectangular horn antenna with the central frequency of 2.6 GHz was designed for generating underwater electromagnetic (EM) waves. Due to the supplementing dielectric-loaded waveguide in this single antenna, the problems with difficult sealing and fixation of the feed probe could be solved effectively. The simulation results show that it has a good impedance characteristics (S11 < −10 dB) and reasonable losses (less than 3.5 dB total for two antennas and a coaxial line) from 2.5 GHz to 2.7 GHz. Experiments on the single antenna were also carried out, which agree well with the simulations. Based on the designed single antenna, the water-immersed rectangular horn antenna array was proposed, and the phase gradient from 0~2π was fed to the horn antennas for generating underwater OAM waves. The simulation results demonstrate high fidelity of the generated OAM waves from the intensity and phase distributions. The purity of the generated OAM modes was also investigated and further verifies the high fidelity of the generated OAM waves. The generated high-quality OAM waves meet the requirements for underwater applications of OAM, such as underwater communication and underwater imaging.