Maximum Allowable Input Power Research Articles

A Compact-Size Multiple-Band Planar Inverted L-C Implantable Antenna Used for Biomedical Applications.

In this paper, a compact-size multiple-band planar inverted L-C implantable antenna is proposed. The compact antenna has a size of 20 mm × 12 mm × 2.2 mm and consists of planar inverted C-shaped and L-shaped radiating patches. The designed antenna is employed on the RO3010 substrate (εr = 10.2, tanδ = 0.0023, and thickness = 2 mm). An alumina layer with a thickness of 0.177 mm (εr = 9.4 and tanδ = 0.006) is used as the superstrate. The designed antenna operates at triple-frequency bands with a return loss of -46 dB at 402.5 MHz, -33.55 dB at 2.45 GHz, and -41.4 dB at 2.95 GHz, and provides a size reduction of 51% compared with the conventional dual-band planar inverted F-L implant antenna designed in our previous study. In addition, the SAR values are within the safety limits with a maximum allowable input power (8.43 mW (1 g) and 47.5 mW (10 g) at 402.5 MHz; 12.85 mW (1 g) and 47.8 mW (10 g) at 2.45 GHz; and 11 mW (1 g) and 50.5 mW (10 g) at 2.95 GHz). The proposed antenna operates at low power levels and supports an energy-efficient solution. The simulated gain values are -29.7 dB, -3.1 dB, and -7.3 dB, respectively. The suggested antenna is fabricated and the return loss is measured. Our findings are then compared with the simulated results.

Effects of the micro-post array on the maximum allowable input power for a micro pulsating heat pipe

This study is performed to experimentally investigate the effects of the micro-post array (MPA) and its arrangements on the maximum allowable input power for a micro pulsating heat pipe (MPHP). The maximum allowable input powers for MPHPs with the MPAs in three different arrangements are measured and compared to that for the conventional MPHP (without the MPA). To do this, ten-turn MPHPs with and without the MPA are fabricated using MEMS techniques. The overall dimensions of the MPHPs are 53 × 38 × 1.5 mm3, and the width and the height of the meandering rectangular channels are 1500 µm and 660 µm, respectively. The MPA in each case is placed on the bottom surfaces of the channels. The dimensions of the MPA are analytically determined in such a way to maximize the rate of the capillarity-induced flow by solving the Brinkman-extended Darcy's equation: the diameter, the pitch and the height are determined to be 33 µm, 97 µm, and 80 µm, respectively. The MPA is placed in three different arrangements: in alternating pairs of channels, in alternating channels, or in all channels. Ethanol is selected as the working fluid. The experiments are conducted in a horizontal orientation, and the flow is visualized with high-speed photography. The experimental results show that the MPA can have either a favorable or an adverse effect depending on its arrangement. If the MPA is placed in alternating channels, the maximum allowable input power is enhanced by 44%, compared to that for the conventional MPHP, and if it is placed in alternating pairs of channels, the maximum allowable input power is enhanced by 36%. On the other hand, the MPHP does not operate at all at any input power if the MPA is placed in all channels. Therefore, in case of the MPHP where a vapor plug oscillates in its own channel, the MPA should be placed in alternating pairs of channels or in alternating channels to enhance the maximum allowable input power for an MPHP.

Design Methodology of a Printed WPT System for HF-Band Mid-Range Applications Considering Human Safety Regulations

A methodology for the design of printed magnetically coupled resonant wireless power-transfer (WPT) systems is proposed. The design methodology aims at a well-matched system with a maximized power-transfer efficiency for mid-range applications. The system consists of two identical resonant coils driven by high-quality factor loops. The proposed design criteria allows obtaining maximum achievable transfer efficiency and impedance matching at any defined distance without any external matching circuits connected to the driven loops. For validation purposes, a printed WPT system at 10 MHz is fabricated targeting 1-m distance between the transmitting and receiving sides. Its performances in terms of reflection and transmission coefficients, as well as in terms of generated electric and magnetic fields, have been characterized numerically and experimentally. The impact of human body presence on the system has also been investigated observing the splitting in two frequencies of the common resonant frequency of the coils. A dosimetric study has been conducted using a detailed high-resolution anatomical human body model and considering E 99 , J 1 cm 2 , and specific absorption rate (SAR) (local and whole body averaged SAR) as exposure metrics. It has been observed that peak exposure levels appear in different tissues depending on the body location. Compliance with the international commission on nonionizing radiation protection (ICNIRP) reference level as well as basic restrictions has been studied followed by computing the maximum allowable input power. It has been found that, with the body located 1 m away from the transmitting coil, the maximum allowable input power satisfying E 99 is in the order of MW, whereas it reduces to tens of kilowatt when considering SAR and J1 cm 2 . The latter has been noticed to be the most restrictive dosimetric quantity.

고출력 LED 패키지에서 칩 배열에 따른 정션온도 변화

It is extremely important that the junction temperature of a high-power, multi-chip LED package be managed so as not to exceed the allowable temperature range (‒40-100 °C) due to the large heat dissipated from the package. In this study, chip configuration was modified in a 4-chip LED package, and the number of chips was changed to 12-chip and 16-chip packages to investigate their effects on the thermal characteristics of the packages. Thermal resistance was estimated using thermal transient analysis, and the ambient temperature of the package was measured by thermo-couple. Ultimately, the junction temperatures of the packages were obtained using these data. The results showed that the maximum allowable input power of the 4-chip package was 3.4 W, which was enlarged up to 5.5 W using 12-chip and 16-chip LED packages. †(Received July 10, 2012)

Delta-sigma-based transmitters: Advantages and disadvantages

Power efficiency is one of the most important parameters in designing communication systems, especially battery operated mobile terminals. In a typical transceiver, most of the power is dissipated in the power amplifier (PA) and consequently, it is very important to obtain the maximum efficiency from the PA. A PA operating in Class AB or B is at its maximum efficiency when it is driven by its maximum allowable input power [1]. In practice, the input signal of the PA usually has a varying envelope, and to avoid distortion the PA should not be driven to more than its maximum input saturating power. Unfortunately, this peak power of the input signal happens at very short periods, and most of the time the signal power is around its average power, which is much smaller than its peak power, meaning that, often, the PA works at much lower efficiencies than its maximum efficiency. The power difference is defined as the peak to average power ratio (PAPR) of the signal. For example, for a signal with 12 dB PAPR, a Class B PA would be driven with 12 dB power back-off from its peak input power, and at this power back-off, the efficiency of the PA will degrade from 78.5% to around 20% [1]. Unfortunately, by moving to high throughput modulation schemes, for example, quadrature amplitude modulations (QAMs) such as 16-QAM and 64-QAM mean that more envelope variation is needed to encode the information, and, consequently, lower efficiency is achieved.

Highly linear transmission and EVM improvement of vector modulation signals for radio-over-f iber applications

The principle of error vector magnitude (EVM) against modulator nonlinearity for vector modulation signal (VMS) transmission in radio-over-fiber (RoF) systems is theoretically and experimentally investigated. A highly linear modulation scheme is proposed and demonstrated using a single-drive dual parallel Mach–Zehnder modulator (MZM). This method improves EVM performance and enlarges the linear input dynamic range of the VMS transmission. An index of maximum allowable input power difference (MAIPD) that reflects the difference of upper input power limits between these two schemes is measured. An EVM limitation of 5% MAIPD has 5 dB. Both 16- and 64-QAM results indicate that the proposed scheme supports VMS transmission better than the MZM one.

Hybrid narrow-band tunable bandpass filter based on varactor loaded electromagnetic-bandgap coplanar waveguides

A varactor-loaded resonator inserted between two Bragg reflectors has been implemented to design high-selectivity tunable bandpass filters. First, a mechanical tuning method is demonstrated. A varactor tunable bandpass filter is then implemented at 9 GHz, yielding good agreement between computational and experimental results. The tuning range reaches 3.5% with a loaded quality factor Q/sub L/=40, a maximum insertion loss of 4.75 dB, and a return loss exceeding 20 dB. The theory is carefully explained, showing the importance of the parameters of the Bragg reflectors and of the resonator, in particular, the effect of diode-case parasitics and varactor position with respect to the resonator. A large-signal experimental analysis is done, showing a maximum allowable input power of a few dBm. Finally, possible filter improvements are discussed, and simulations with a microelectromechanical systems varactor are shown.

New techniques for the suppression of the four-wave mixing-induced distortion in nonzero dispersion fiber WDM systems

The performance of a wavelength-division multiplexing (WDM) optical network can be severely degraded due to fiber nonlinear effects. In the case where nonzero dispersion (NZD) fibers are employed, the four-wave mixing (FWM) effect sets an upper limit on the input power, especially in the case of narrow channel spacing. In order to reduce FWM-induced distortion two new techniques, the hybrid amplitude-/frequency-shift keying (ASK/FSK) modulation and the use of prechirped pulses are investigated. It is shown that both techniques can greatly improve the Q-factor in a 10 Gb/s WDM system. This happens even for very high input powers (/spl sim/10 dBm), where the degradation of the conventional WDM system is prohibitively high. The proposed methods are also applied and tested in higher bit rates (40 Gb/s). It is deduced that although the hybrid ASK/FSK modulation technique marginally improves the system performance, the optical prechirp technique can still be used to greatly increase the maximum allowable input power of the system.