Experimental Peak Efficiency Research Articles

Ultra-Low-Power Low-Input-Voltage Charge Pump for Micro-Energy Harvesting Applications

A subthreshold input voltage charge pump based on the well-known cross-coupled voltage doubler and using boosted gate voltages for the transfer switches is presented. A level shifter and some inverters, including a novel inverter architecture proposed in this work and referred to as negative low-state voltage inverter, are used to generate the clock signals for the switching transistors with the purpose of significantly improving their drive capability. A complete analysis of the proposed charge pump is provided to highlight the advantages of the implemented structure, revealing the power efficiency improvement when the input voltage is below the threshold voltage of the transistors. An extensive experimental characterization of silicon prototypes in 180 nm CMOS technology was carried out, showing that the proposed scheme is able to pump charge from an input voltage as low as 110 mV. The experimental peak efficiency remains above 70% for input voltages between 180 mV and 400 mV and input power levels from 45 nW to 25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> , which are appropriate for different miniaturized transducers implementable on chip.

Unveiling the dopant segregation effect at hematite interfaces

Understanding the effects of atomic structure modification in hematite photoanodes is essential for the rational design of high-efficiency functionalizations. Recently, it was found that interface modification with Sn/Sb segregates considerably increases hematite photocatalytic efficiency. However, the understanding of the different electronic effects of these modifications at the atomic level is still lacking. This Letter describes the segregation effects of two different dopants–Sn and Sb–on both the solid–solid (grain boundaries) and solid–liquid interfaces (surfaces) of hematite. Within an ab initio approach, we quantitatively extract the potential barrier reduction on polycrystalline interfaces due to the dopant, which causes an increase in the inter-grain electron transport. Concomitantly, the dopants' segregation on hematite surfaces results in a decrease in the oxygen vacancy formation energy. Such vacancies lead to the experimentally observed rise of the flatband potential. The comprehension of the electronic effects of dopants on both types of interfaces explains the experimental peak efficiency of interface-modified hematite with dopant segregates, also enabling the control and design of interfaces for different higher-efficiency applications.

Verification of physical parameters of insity p-type HPGe detector by scan method using collimated low energy photon beam and MCNP simulation

In this work, the physical dimensions and the actual position of germanium crystal within a detector housing, the homogeneity of the crystal surface and outer dead layer thickness for a p-type HPGe detector were confirmed by the scan method using the collimated low energy photon beams combined with Monte Carlo simulation. The length and the diameter of the crystal were found to match with the values supplied by the manufacturer in discrepancy of about 3%. Only one mounting strap (Typical) for holding the crystal inside the mounting cup instead of two which is indicated in the detector drawing supplied by manufacturer was revealed by scanning along the lateral face of detector. Scanning on the front surface and around the lateral face of detector by the collimated 59.5 keV photon beam verified the outer dead layer thicknesses at the front surface and lateral face of the crystal averagely increases about 6.5% and 12% respectively. Adjusting the detector parameters for MCNP simulation by these verified values, the simulated peak efficiencies for different photon energies become being in accordance with the experimental peak efficiencies.

On-chip unidirectional dual-band fiber-chip grating coupler in silicon nitride

We report, for the first time, a single state polarization (TE) dual-band grating fiber-chip coupler on a 700 nm thick silicon nitride platform that couples to both O and C band channels. Dual-band coupling with a single grating coupler is achieved using cross mode k-space equalization. By phase matching the first-order vertical TE01 mode and the fundamental TE00 mode in two distinct bands, we observe simultaneous co-directional dual-band coupling to a single waveguide. Experimental peak efficiency per coupler is measured to be −7.3 dB in the O-band and −8.2 dB in the C-band and the combined 1 dB bandwidth is observed to be 82 nm.

Efficiency calibration and measurement of self-absorption correction for environmental gamma-spectroscopy of soil samples using Marinelli beaker

A nonlinear function was applied in combination with the method of mixing activity calibration for fitting the experimental peak efficiency of HPGe spectrometers in the 50-2614 keV energy range. The preparation of Marinelli beaker standards of mixed gamma- and RG-Set at secular equilibrium with its daughter radionucliedes was studied. Self-absorption was measured for the activity calculation of the gamma-ray lines for daughters of 238 U series, 232 Th series, as well as 137 Cs and 40 K in soil samples. Self-absorption in the sample depends on a number of factors including sample composition, density, sample size and gamma-ray energy. Seven Marinelli beaker standards were prepared in different degrees of compaction with bulk density (p) of 1.000 to 1.600 g·cm -3 . The detection efficiency versus density was obtained and the equation of self-absorption correction factors was calculated for soil samples.

Combination of nonlinear function and mixing method for fitting HPGe efficiency curve in the 59–2754 kev energy range

A nonlinear function in combination with the method of mixing activity-calibrated and uncalibrated gamma-ray sources is applied for fitting the experimental peak efficiency of HPGe spectrometers in the 59–2754 keV energy range. In addition, a step function was developed for fitting the gamma-ray background under the peak. Calibrated 241Am, 133Ba, 137Cs, 152Eu, 60Co and 88Y sources, as well as one 24Na source (treated as uncalibrated) were used for obtaining the experimental peak efficiency curve. The results were compared to the conventional linear polynomial fitting. From the fitted parameters, the 24Na activity was determined and compared with the result obtained from absolute measurements in a 4 πβ– γ coincidence system.