Abstract-A broadside radiating, linearly polarized, electrically small Huygens source antenna system that has a large impedance bandwidth is reported. The bandwidth performance is facilitated by embedding non-Foster components into the near-field resonant parasitic (NFRP) elements of this metamaterial-inspired antenna. High quality and stable radiation performance characteristics are achieved over the entire operational bandwidth. When the ideal non-Foster components are introduced, the simulated impedance bandwidth witnesses approximately a 17-fold enhancement over the passive case. Within this -10dB bandwidth, its maximum realized gain, radiation efficiency, and front-to-back ratio (FTBR) are, respectively, 4.00 dB, 88%, and 26.95 dB. When the anticipated actual negative impedance convertor (NIC) circuits are incorporated, the impedance bandwidth still sustains more than a 10-fold enhancement. The peak realized gain, radiation efficiency, and FTBR values are, respectively, 3.74 dB, 80%, and 28.01 dB, which are very comparable to the ideal values.Index Terms-Directivity, electrically small antennas, front-to-back ratio, Huygens source antenna, impedance bandwidth, non-Foster elements.

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The development of flexible sensors with low cost, facile preparation and good reproducibility is of profound significance for wearable electronics and intelligent systems.

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Two 28 GHz, planar, electrically small Huygens source antennas are presented that are broadside radiating and are based on multi-layer PCB technology. The designs seamlessly integrate electric Egyptian axe dipole (EAD) and magnetic capacitively loaded loop (CLL) near-field resonant parasitic (NFRP) elements with a coax-fed dipole radiator. Both linearly polarized (LP) and circularly polarized (CP) systems are demonstrated. The simulations of the LP system indicate that it is electrically small: ka = 0.961; has peak realized gains and front-to-back ratios (FTBRs) in the range from, respectively, 3.77 to 4.54 dBi and 7.16 to 33.92 dB; and radiation efficiencies higher than 81.14% over its entire 2.14%, -10-dB fractional impedance bandwidth (FBW -10dB ). A prototype was fabricated and tested; the measured and simulated results are in good agreement. The CP system exhibits similar properties: ka = 0.942; 1.41% FBW -10dB with a 0.47% 3-dB axial ratio (AR) fractional bandwidth; and peak realized gain, FTBR, and radiation efficiency values equal to 2.03 dBi, 26.72 dB, and 73.4%, respectively. To confirm their efficacy for on-body applications, the specific absorption rate (SAR) values of both the LP and CP Huygens source antennas were evaluated and found to be very low. Index Terms-Broadside radiation, directivity, electrically small antennas, Huygens source antenna, near-field resonant parasitic element, planar antennasManuscript

An electrical capacitance method is described for the measurement of multi-interface levels of gas/liquid/solid, including the foam layer. It uses a novel multi-electrode capacitance sensing element. A capacitance transducer based on the charge/discharge principle is used, which is stray immune and capable of operating at high frequencies to reduce t h e effects of the liquid conductivity on the measurement. The presence of foam is detected by processing the fluctuating component of the capacitance signal, which reflects the inherently unstable feature of the foam, whereas t h e multi-interface levels are reconstructed by processing the steady-state component of the measured capacitances

A dual-linearly-polarized, electrically small, low-profile, broadside radiating Huygens dipole antenna is presented that is an advanced combination of electric and magnetic near-field resonant parasitic (NFRP) elements. Its prototype was fabricated and tested. The measured results are in good agreement with their simulated values. At 1.515 GHz the prototype is electrically small (ka = 0.904) and low profile (0.0483λ 0). It exhibits high port isolation and a large front-to-back ratio (FTBR). The isolation between its two ports is demonstrated to be over 25.8 dB within its-10-dB fractional impedance bandwidth (FBW), 0.46%. When port 1 (port 2) is excited, the peak realized gain is 2.03 dBi (2.15 dBi) strictly along the broadside direction with a 12.4 dB (12.1 dB) FTBR.

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