This paper presents a low power boost converter for thermoelectric energy harvesting that demonstrates an efficiency that is 15% higher than the state-of-the-art for voltage conversion ratios above 20. This is achieved by utilizing a technique allowing synchronous rectification in the discontinuous conduction mode. A low-power method for input voltage monitoring is presented. The low input voltage requirements allow operation from a thermoelectric generator powered by body heat. The converter, fabricated in a 0.13 μm CMOS process, operates from input voltages ranging from 20 mV to 250 mV while supplying a regulated 1 V output. The converter consumes 1.6 (1.1) μW of quiescent power, delivers up to 25 (175) μW of output power, and is 46 (75)% efficient for a 20 mV and 100 mV input, respectively.

A 20 mV Input Boost Converter With Efficient Digital Control for Thermoelectric Energy Harvesting

Mobile Radio Channels

To overcome some drawbacks of the plasma stealth technology in real-life application, a practical multilayer stealth structure composed of enclosed plasma slab and radar absorbing material (RAM) is presented in this paper. Based on a technique referred to as the transmission line analogy method, reflection coefficients of the perpendicularly polarized wave, the parallel polarized wave, and the circularly polarized wave obliquely incident upon this multilayer structure are determined, respectively. The effects of the incident angle, kinds of RAMs, and parameters of the plasma slab including electron density, collision frequency, and thickness on the stealthy effectiveness of this composite stealth structure have been studied systematically. The numerical results indicate that by a proper design, the power of reflected wave is significantly reduced over a wide frequency bandwidth, which provides some useful references to the plasma stealth technology applied to aircrafts, ships, and missiles.

Reflections of Electromagnetic Waves Obliquely Incident on a Multilayer Stealth Structure With Plasma and Radar Absorbing Material

This paper looks into the possible methods of harvesting energy for applications involving wireless sensors from renewable or sustainable sources. An overview of the fundamentals of energy harvesting models using renewable sources and the advancements in the components used for this purpose is given. It also provides an analysis of the issues that are restricting the current harvesting models and indicates possible advances in technologies that may soon solve those problems. There are two main issues that plague these harvesting models. Firstly, the technology involved in the actual harvesting of renewable energy sources is not well developed and offer poor efficiency. In addition to that, most of the models need a permanent storage device, such as a battery or capacitor in order to operate. This is a serious drawback in applications involving wireless sensors as these devices have limited capacity, lifetime, and require a large area to work efficiently. This is most often not favorable as the attractions of using wireless sensors are in its portability and form. This paper looks into the studies dedicated to solving these problems. The latter part of the paper contains a discussion regarding the technologies that are best suited for applications in wireless sensors. The two most readily available and feasible options of a sustainable energy for these applications are found out to be RF (Radio Frequency) signal and solar radiation. Therefore, the final part of the paper concentrates on reviewing a model that may potentially be able to serve as a basis for a singular model for any kind of energy harvesting from renewable sources.

Renewable energy harvesting for wireless sensors using passive RFID tag technology: A review

Energy harvesting in wireless sensor networks: A taxonomic survey

A novel and simple analytical technique referred to as transmission line analogy is developed and modified to study the transmission properties of the perpendicular polarized wave and the parallel polarized wave obliquely incident on the reentry plasma sheath. Based on the transmission coefficients, the effects of the plasma sheath on the polarization property of obliquely incident electromagnetic (EM) waves are studied. Taking the GPS navigation right hand circularly polarized wave as an example, the influences of incident angle and plasma parameters, including the electron density and the collision frequency on the EM wave’s polarization property are studied. Numerical results indicate that the larger the incident angle and the lower the collision frequency is, the worse the deterioration of the polarization property. In addition, the polarization property deteriorates most seriously when the cutoff frequency of the peak electron density is closest to the frequency of the EM waves.

Effects of Reentry Plasma Sheath on the Polarization Properties of Obliquely Incident EM Waves

An experiment on the propagation of electromagnetic (EM) signals in continuous time-varying plasma is described. The time-varying characteristics of plasma are considered to cause a parasitic modulation in both amplitude and phase, and the strength of this modulation, which carries the information of the electron density profile, is closely related to the plasma frequency and the incident wave frequency. Through theoretical analysis, we give an explanation and mechanism of the interaction between the continuous time-varying plasma and EM waves, which is verified by a comparative analysis with experiments performed under the same conditions. The effects of this modulation on the EM signals in the plasma sheath cannot be ignored.

Parasitic modulation of electromagnetic signals caused by time-varying plasma

Radio blackout during the re-entry has puzzled the aerospace industry for decades and has not yet been completely resolved. To achieve a continuous data link in the spacecraft's re-entry period, a simple and practicable communication method is proposed on the basis that (1) the electromagnetic-wave backscatter of the plasma sheath affects the voltage standing wave ratio (VSWR) of the antenna, and the backscatter is negatively correlated to transmission components, and (2) the transmission attenuation caused by the plasma sheath reduces the channel capacity. We detect the voltage standing wave ratio changes of the antenna and then adjust the information rate to accommodate the varying channel capacity, thus guaranteeing continuous transmission (for fewer critical data). The experiment was carried out in a plasma generator with an 18-cm-thick and 30-cm-diameter hollow propagation path, and the adaptive communication was implemented using spread spectrum frequency, shift key modulation with a variable spreading factor. The experimental results indicate that, when the over-threshold of VSWR was detected, the bit rate reduced to 250 bps from 4 Mbps automatically and the tolerated plasma density increased by an order of magnitude, which validates the proposed scheme. The proposed method has little additional cost, and the adaptive control does not require a feedback channel. The method is therefore applicable to data transmission in a single direction, such as that of a one-way telemetry system.

Re-entry communication through a plasma sheath using standing wave detection and adaptive data rate control

A high-speed vehicle flying through the atmosphere between 100 and 20 km may suffer from a “communication blackout.” In this paper, a low frequency system with an on-board loop antenna to receive signals is presented as a potential blackout mitigation method. Because the plasma sheath is in the near-field region of the loop antenna, the traditional scattering matrix method that is developed for the far-field region may overestimate the electromagnetic (EM) wave's attenuation. To estimate the EM wave's attenuation in the near-field region, EM interference (EMI) shielding theory is introduced. Experiments are conducted, and the results verify the EMI shielding theory's effectiveness. Simulations are also conducted with different plasma parameters, and the results obtained show that the EM wave's attenuation in the near-field region is far below than that in the far-field region. The EM wave's attenuation increases with the increase in electron density and decreases with the increase in collision frequency. The higher the frequency, the larger is the EM wave's attenuation. During the entire re-entry phase of a RAM-C module, the EM wave's attenuations are below 10 dB for EM waves with a frequency of 1 MHz and below 1 dB for EM waves with a frequency of 100 kHz. Therefore, the low frequency systems (e.g., Loran-C) may provide a way to transmit some key information to high-speed vehicles even during the communication “blackout” period.

The propagation characteristics of electromagnetic waves through plasma in the near-field region of low-frequency loop antenna

A hypersonic flight or a reentry vehicle is surrounded by a plasma layer that prevents electromagnetic wave transmission, which results in radio blackout. The magnetic-window method is considered a promising means to mitigate reentry communication blackout. However, the real application of this method is limited because of the need for strong magnetic fields. To reduce the required magnetic field strength, a novel method that applies a traveling magnetic field (TMF) is proposed in this study. A mathematical model based on magneto-hydrodynamic theory is adopted to analyze the effect of TMF on plasma. The mitigating effects of the TMF on the blackout of typical frequency bands, including L-, S-, and C-bands, are demonstrated. Results indicate that a significant reduction of plasma density occurs in the magnetic-window region by applying a TMF, and the reduction ratio is positively correlated with the velocity of the TMF. The required traveling velocities for eliminating the blackout of the Global Positionin...

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Kai Xie

Papers

Effects of Reentry Plasma Sheath on the Polarization Properties of Obliquely Incident EM Waves

Parasitic modulation of electromagnetic signals caused by time-varying plasma

Re-entry communication through a plasma sheath using standing wave detection and adaptive data rate control

The propagation characteristics of electromagnetic waves through plasma in the near-field region of low-frequency loop antenna

Mitigating reentry radio blackout by using a traveling magnetic field