The effects of low-calorie sweeteners on energy intake and body weight: a systematic review and meta-analyses of sustained intervention studies.

Previous meta-analyses of intervention studies have come to different conclusions about effects of consumption of low-calorie sweeteners (LCS) on body weight. The present review included 60 articles reporting 88 parallel-groups and cross-over studies ≥1 week in duration that reported either body weight (BW), BMI and/or energy intake (EI) outcomes. Studies were analysed according to whether they compared (1) LCS with sugar, (2) LCS with water or nothing, or (3) LCS capsules with placebo capsules. Results showed an effect in favour of LCS vs sugar for BW (29 parallel-groups studies, 2267 participants: BW change, -1.06 kg, 95% CI -1.50 to -0.62, I2 = 51%), BMI and EI. Effect on BW change increased with 'dose' of sugar replaced by LCS, whereas there were no differences in study outcome as a function of duration of the intervention or participant blinding. Overall, results showed no difference in effects of LCS vs water/nothing for BW (11 parallel-groups studies, 1068 participants: BW change, 0.10 kg, 95% CI -0.87 to 1.07, I2 = 82%), BMI and EI; and inconsistent effects for LCS consumed in capsules (BW change: -0.28 kg, 95% CI -0.80 to 0.25, I2 = 0%; BMI change: 0.20 kg/m2, 95% CI 0.04 to 0.36, I2 = 0%). Occurrence of adverse events was not affected by the consumption of LCS. The studies available did not permit robust analysis of effects by LCS type. In summary, outcomes were not clearly affected when the treatments differed in sweetness, nor when LCS were consumed in capsules without tasting; however, when treatments differed in energy value (LCS vs sugar), there were consistent effects in favour of LCS. The evidence from human intervention studies supports the use of LCS in weight management, constrained primarily by the amount of added sugar that LCS can displace in the diet

Nonscattering waveguides based on tensor impedance surfaces

A tensor impedance surface waveguide is built using anisotropic unit cells. The waveguide can propagate a confined waveguide mode along its axis while waves incident to the guide at an orthogonal direction pass through as if the waveguides were not present. Both straight and curved implementations are demonstrated. Surface waves incident at an angle to the waveguide show reflection and refraction at the impedance interface. A theoretical model for tensor impedance surface waveguides is generalized to include dispersive unit cells and bending loss around curves. Dispersion results for modes propagating in the waveguide show agreement between the theory, simulation, and experimental measurements. A curved waveguide is also constructed which guides surface waves around a curve and is transparent to surface waves incident at an orthogonal angle

Stable multiple non-Foster circuits loaded waveguide for broadband non-dispersive fast-wave propagation

Periodically loading non-Foster circuits (NFCs) in a conventional waveguide has been proved to be possible for achieving broadband non-dispersive fast-wave (FW) propagation. However, the unconditional stability of such structures has been argued due to the multiple NFC loadings. Despite the potential instability, it is demonstrated that the NFC-loaded waveguide can still be stable for specific terminations, in particular, with the 50 Ω load that is commonly used in radio frequency/microwave applications. For purpose of demonstration, a NFC-loaded waveguide that contains substantially more unit cells than in prior work has been designed and measured, showing a stable and causal FW propagation with a 1.2 c phase velocity over the bandwidth of 80-120 MHz

A compact broadband dual-polarized patch antenna for satellite communication/navigation applications

In this letter, a compact and robust dual circularly polarized patch antenna for combined Globalstar/GPS application has been presented. The designed patch antenna is accomplished with size of 40×40×6mm3 over the frequency bandwidth of 1570-1650 MHz, which is 0.21λ0× 0.21λ0× 0.03λ0 (λ0 is the free-space wavelength at the lowest frequency of the operating bandwidth). Instead of air substrate, high-permittivity substrate is adopted for the size reduction. The bandwidth reduction due to the inclusion of the high-permittivity substrate is compensated by introducing a parasitic patch. In addition, a 90° hybrid is utilized for achieving dual circular polarization. The designed antenna is validated by the measurement, presenting a 5% fractional bandwidth (1570-1650 MHz) for both VSWR < 2, axial ratio less than 3 dB, and port isolation less than -6dB

A compact broadband dual-polarized patch antenna for satellite communication/navigation applications

In this letter, a compact and robust dual circularly polarized patch antenna for combined Globalstar/GPS application has been presented. The designed patch antenna is accomplished with size of 40×40×6mm3 over the frequency bandwidth of 1570-1650 MHz, which is 0.21λ0× 0.21λ0× 0.03λ0 (λ0 is the free-space wavelength at the lowest frequency of the operating bandwidth). Instead of air substrate, high-permittivity substrate is adopted for the size reduction. The bandwidth reduction due to the inclusion of the high-permittivity substrate is compensated by introducing a parasitic patch. In addition, a 90° hybrid is utilized for achieving dual circular polarization. The designed antenna is validated by the measurement, presenting a 5% fractional bandwidth (1570-1650 MHz) for both VSWR < 2, axial ratio less than 3 dB, and port isolation less than -6dB

Theoretical limitations for tm surface wave attenuation by lossy coatings on conducting surfaces

In this work, we theoretically analyze the limitations for TM surface wave attenuation on lossy coated conducting surfaces containing electric and/or magnetic loss. We use both an analytical approach as well as numerical simulations, and find excellent agreement between them. We also find that the loss can be described by a simple approximate expression for a wide range of material properties. Furthermore, we analyze lossy slabs with simple equivalent circuit boundaries on top, such as may be provided by frequency selective surfaces or other patterned structures. We find that such composite lossy coating can exceed the attenuation of a simple lossy slab, but with limited bandwidth. We also find that only by increasing permeability, and not permittivity, can the peak absorption frequency be lowered for a given thickness without reducing the relative absorption bandwidth. © 2013 IEEE

Non-foster loaded parasitic array for broadband steerable patterns

Parasitic arrays can generate steerable patterns using tunable reactive loads at the parasitic elements to provide the required phase for the scattered radiation. However, the radiation that is coupled to the parasitic elements and reflected by the attached loads has a frequency dependent phase delay, leading to a beam/null squint effect and a limited instantaneous squint-free bandwidth. In this paper, we introduce a technique for eliminating this frequency dependence using non-Foster parasitic loads, whose reflection phase has a positive phase dispersion slope that can cancel the negative phase dispersion slope associated with propagation delays. Further, by tuning the non-Foster load, we can tune the total scattered phase to achieve steerable patterns. Tunable non-Foster impedances can be designed using transistor-based negative impedance convertor (NIC) circuits. A two element parasitic array was designed for the frequencies of operation of discrete device NICs. Non-Foster impedances required for obtaining broadband or squint-free nulls at different azimuth angles were calculated using array theory and simulations. An NIC that generated the non-Foster impedance for a broadside broadband null was fabricated and attached to the parasitic antenna. Simulation and measurement results showed broadband uniform nulls from 180-350 MHz, providing about twice the null bandwidth of a passive parasitic load. Null steering across some angles of the azimuth was restricted by the stability constraints of the NIC while being tuned. With a judicious design of the parasitic antenna and the NIC, we can achieve broader bandwidths and steerable patterns with non-Foster parasitic arrays

An Epsilon-Near-Zero Total-Internal-Reflection Metamaterial Antenna

The total-internal-reflection (TIR) principle and the concept of an epsilon-near-zero (ENZ) material are combined to form an antenna exhibiting sum and difference patterns with good impedance properties. The ENZ material has been realized using a uniaxial wire medium (WM) metamaterial, and the departure from the behavior of an ideal ENZ material is discussed. The radiation pattern of the fabricated antennas has been measured and compared with simulation results

Broadband fast-wave propagation in a non-foster circuit loaded waveguide

Frequency independent fast-wave (FW) propagation with phase velocity greater than the speed of light can be ideally realized in a dielectric medium whose relative permittivity is positive, but less than 1. Conventionally, FW propagation is implemented by non-TEM waveguides or antiresonance-based metamaterials, which suffers from the narrow bandwidth due to the dispersion. In contrast, non-Foster circuits provide a brand new method for reducing the dispersion so as to broaden the bandwidth. This paper demonstrates broadband FW propagation in a microstrip line that is periodically loaded with non-Foster circuits. Discrete transistor-based non-Foster circuits functioning as negative capacitors are successfully designed with the novel modified negative impedance converter circuits. A-10-pF negative capacitor over a bandwidth of 10-150 MHz has been implemented. The fabricated circuits have been integrated into a microstrip line to form a FW waveguide. The retrieved phase velocity of the effective medium from the measured S-parameters characterizes a stable and causal FW medium with constant phase velocity of 1.2c from 60 to 120 MHz, and this has been further verified by Kramers-Kronig relations and the near-field measurements along the waveguide. In conclusion, a stable, causal, and broadband FW waveguide has been achieved by means of transistor-based non-Foster circuits. The implemented broadband FW propagation can potentially be applied in broadband leaky-wave antennas and cloaking techniques. © 1963-2012 IEEE

Broadband fast-wave propagation in a non-foster circuit loaded waveguide

Frequency independent fast-wave (FW) propagation with phase velocity greater than the speed of light can be ideally realized in a dielectric medium whose relative permittivity is positive, but less than 1. Conventionally, FW propagation is implemented by non-TEM waveguides or antiresonance-based metamaterials, which suffers from the narrow bandwidth due to the dispersion. In contrast, non-Foster circuits provide a brand new method for reducing the dispersion so as to broaden the bandwidth. This paper demonstrates broadband FW propagation in a microstrip line that is periodically loaded with non-Foster circuits. Discrete transistor-based non-Foster circuits functioning as negative capacitors are successfully designed with the novel modified negative impedance converter circuits. A-10-pF negative capacitor over a bandwidth of 10-150 MHz has been implemented. The fabricated circuits have been integrated into a microstrip line to form a FW waveguide. The retrieved phase velocity of the effective medium from the measured S-parameters characterizes a stable and causal FW medium with constant phase velocity of 1.2c from 60 to 120 MHz, and this has been further verified by Kramers-Kronig relations and the near-field measurements along the waveguide. In conclusion, a stable, causal, and broadband FW waveguide has been achieved by means of transistor-based non-Foster circuits. The implemented broadband FW propagation can potentially be applied in broadband leaky-wave antennas and cloaking techniques. © 1963-2012 IEEE