Modeling and Optimization Analysis for Base-Excited Magnetostrictive Vibration Harvester

Due to the low vibration frequency and weak vibration energy in natural environment, the vibration energy harvester is faced with the problem of low power and low adaptability and becoming particularly difficult in actual conditions. It is necessary to improve the harvesting capacity and efficiency by optimizing the parameters of the harvester, making full use of the energy of low and unstable atmospheric vibrations. In this paper, a mathematical model is established for the cantilever magnetostrictive vibration harvester under the base excitation, including the mechanical deformation of the composite beam, and the electromagnetic results produced thereof. The mechanical-magneticelectric energy conversion relationship is duly taken into account. The additional weight, coil parameters, external resistance and other parameters of the harvester are optimized and analyzed through numerical simulation. In addition, the theoretical results are analyzed and discussed via comparison with experiments. Finally, the effects of the above factors are assessed, which allows us to obtain the optimal winding length, number of turns of the coil, and optimal tip additional mass. The experiment result shows that the optimized magnetostrictive harvester can output 12.07[Formula: see text]mW power to the external resistor under the condition of 1[Formula: see text]g acceleration mechanical vibration, with normalized power density reaching 40.2[Formula: see text]mW/cm3/g. Moreover, the optimized magnetostrictive harvester can successfully supply power for the LED display screen of the temperature sensor and a low-power thermometer.

Microbial fuel cell power overshoot studied with microfluidics: from quantification to elimination

Power overshoot can hinder determination of maximum power densities in microbial fuel cells (MFCs). In this work, a microfluidic approach was used to study overshoot in an MFC containing a pure culture of electroactive biofilms (EAB) containing Geobacter sulfurreducens. After 1-month operation under constant flow of an ideal nutrient medium, the MFC health began to degrade, marked by voltage loss and the appearance of anomalies in the power density curves. One such anomaly was a chronic power overshoot, accompanying a loss of both measured power and current density on the high-current side of the power density curve. The degree of power overshoot was quantified while certain flow-based interventions were applied, notably the shear erosion of the EAB outer layer. Next, two approaches to acclimation were demonstrated to treat the remaining overshoot. The standard approach, which acclimates the MFC to high currents before a standard polarization test, eliminated the remaining overshoot and returned maximum power densities to initial levels, but maximum current density remained lower than the initial level. A microfluidic-assisted “long-hold polarization test” enabled efficient in situ acclimation of each external resistor during the measurement. Despite the health-compromised MFC, this method provided long-term stability during the polarization test, resulting in power and current density measurements that exceeded those made on the healthy MFC using the standard polarization test. We conclude that slower electron transfer kinetics in unhealthy MFCs can provoke overshoot by prolonging the time to reach steady state during the polarization test, but a properly designed measurement overcomes this problem.

Observation of negative capacitance in antiferroelectric PbZrO3 Films

Negative capacitance effect in ferroelectric materials provides a solution to the energy dissipation problem induced by Boltzmann distribution of electrons in conventional electronics. Here, we discover that besides ferroelectrics, the antiferroelectrics based on Landau switches also have intrinsic negative capacitance effect. We report both the static and transient negative capacitance effect in antiferroelectric PbZrO3 films and reveal its possible physical origin. The capacitance of the capacitor of the PbZrO3 and paraelectric heterostructure is demonstrated to be larger than that of the isolated paraelectric capacitor at room temperature, indicating the existence of the static negative capacitance. The opposite variation trends of the voltage and charge transients in a circuit of the PbZrO3 capacitor in series with an external resistor demonstrate the existence of transient negative capacitance effect. Strikingly, four negative capacitance effects are observed in the antiferroelectric system during one cycle scan of voltage pulses, different from the ferroelectric counterpart with two negative capacitance effects. The polarization vector mapping, electric field and free energy analysis reveal the rich local regions of negative capacitance effect with the negative dP/dE and (δ2G)⁄(δD2), producing stronger negative capacitance effect. The observation of negative capacitance effect in antiferroelectric films significantly extends the range of its potential application and reduces the power dissipation further.

Multipurpose Drivers for MEMS Devices Based on a Single ASIC Implemented in a Low-Cost HV CMOS Process without a Triple Well

This paper presents a novel topology for multipurpose drivers for MEMS sensors and actuators, suitable for integration in low-cost high-voltage (HV) CMOS processes, without a triple well. The driver output voltage, V MEMS , can be programmed over a wide, symmetrical range of positive and negative values, with the maximum output voltage being limited only by the maximum drain-source voltage that the HV transistors can handle. The driver is also able to short its output to the ground line and to leave it floating. It comprises generators for large positive and negative voltages followed by an LDO for each polarity that ensures that V MEMS has a well-controlled level and a very low ripple. The LDOs also help implement the grounded- and floating-output operating modes. Most of the required circuitry is integrated within a HV CMOS ASIC: the drivers for the large voltage generators, the error amplifiers of the LDOs, the DAC used to program the V MEMS level, and their support circuits. Thus, only the power stages of the large voltage generators, the pass transistors of the LDOs and two resistors for the LDO feedback network are discrete. A suitable configuration was devised for the latter that allows for the external resistor network to be shared by the two LDOs and prevents negative voltages from developing at the ASIC pins. Two circuit implementations of the proposed topology, designed in a low-cost 0.18 μm HV CMOS process, are presented in some detail. Simulation results demonstrate that they realize the required operating modes and provide V MEMS voltages programmable with steps of 100 mV or 200 mV, between -20 V and +20 V or between −45 V and +45 V, respectively. The output voltage ripple is relatively small, just 3.4 mVpkpk for the first implementation and 17 mVpkpk for the second. Therefore, both circuits are suitable for biasing and controlling a wide range of MEMS devices, including MEMS mirrors used in applications such as endoscopic optical coherence tomography.

Signal Conditioning provided by Sensitive Elements of Electric Bioimpedance Sensors

Dry polarizable electric bioimpedance sensors for ECG (electrocardiogram) monitoring requires the use of signal conditioning electronic circuits that take over alternating ΔU voltages with a frequency of 40 kHz and peak-to-peak amplitude in the range of 10-50 mV. The sensitive elements of these sensors are made of sensitive materials like as conductive polymer polypyrrole or hybrid nanocomposite with 10 and 20% Ag incorporated in the polypyrrole polymer. The useful signal is picked up in differential mode by an instrumentation amplifier. The gain of the instrumentation amplifier is set to A = 100 by connecting a single external resistor, RG. The problem of eliminating the mass loops and obtaining a common mode signal is solved by using an amplifier with galvanic isolation, with the amplification factor A = 1, supplied with double differential voltage. To reject any parasitic signals that may accompany the useful signal, an electronic bandpass filtering module is used. Electrical measurements were performed which showed the accuracy of the signal amplified by the electronic instrumentation amplifier module used in the "differential mode" connection.

Reducing a Masked Implementation’s Effective Security Order with Setup Manipulations

Couplings are a type of physical default that can violate the independence assumption needed for the secure implementation of the masking countermeasure. Two recent works by De Cnudde et al. put forward qualitatively that couplings can cause information leakages of lower order than theoretically expected. However, the (quantitative) amplitude of these lower-order leakages (e.g., measured as the amplitude of a detection metric such as Welch’s T statistic) was usually lower than the one of the (theoretically expected) dth order leakages. So the actual security level of these implementations remained unaffected. In addition, in order to make the couplings visible, the authors sometimes needed to amplify them internally (e.g., by tweaking the placement and routing or iterating linear operations on the shares). In this paper, we first show that the amplitude of low-order leakages in masked implementations can be amplified externally, by tweaking side-channel measurement setups in a way that is under control of a power analysis adversary. Our experiments put forward that the “effective security order” of both hardware (FPGA) and software (ARM-32) implementations can be reduced, leading to concrete reductions of their security level. For this purpose, we move from the detection-based analyzes of previous works to attack-based evaluations, allowing to confirm the exploitability of the lower-order leakages that we amplify. We also provide a tentative explanation for these effects based on couplings, and describe a model that can be used to predict them in function of the measurement setup’s external resistor and implementation’s supply voltage. We posit that the effective security orders observed are mainly due to “externally-amplified couplings” that can be systematically exploited by actual adversaries.

Modeling Power Generation and Energy Efficiencies in Air-Cathode Microbial Fuel Cells Based on Freter Equations

The model proposed in this study was based on the assumption that the biomass attached to the anode served as biocatalysts for microbial fuel cell (MFC) exoelectrogenesis, and this catalytic effect was quantified by the exchange current density of anode. By modifying the Freter model and combining it with the Butler–Volmer equation, this model could adequately describe the processes of electricity generation, substrate utilization, and the suspended and attached biomass concentrations, at both batch and continuous operating modes. MFC performance is affected by the operating variables such as initial substrate concentration, external resistor, influent substrate concentration, and dilution rate, and these variables were revealed to have complex interactions by data simulation. The external power generation and energy efficiency were considered as indices for MFC performance. The simulated results explained that an intermediate initial substrate concentration (about 100 mg/L under this reactor configuration) needed to be chosen to achieve maximum overall energy efficiency from substrate in the batch mode. An external resistor with the value approximately that of the internal resistance, boosted the power generation, and a resistor with several times of that of the internal resistance achieved better overall energy efficiency. At continuous mode, dilution rate significantly impacted the steady-state substrate concentration level (thus substrate removal efficiency and rate), and attached biomass could be fully developed when the influent substrate concentration was equal to or higher than 100 mg/L at any dilution rate of the tested range. Overall, this relatively simple model provided a convenient way for evaluating and optimizing the performance of MFC reactors by regulating operating parameters.

Modeling Power Generation and Energy Efficiencies in Air-Cathode Microbial Fuel Cells Based on Freter Equations

The model proposed in this study was based on the assumption that the biomass attached to the anode served as biocatalysts for MFC exoelectrogenesis, and this catalytic effect was quantified by the exchange current density of anode. By modifying the Freter model and combining it with the Butler-Volmer equation, this model could adequately describe the processes of electricity generation, substrate utilization, and the suspended and attached biomass concentrations, at both batch and continuous operating modes. MFC performance is affected by the operating variables such as initial substrate concentration, external resistor, influent substrate concentration, and dilution rate, and these variables were revealed to have complex interactions by data simulation. The external power generation and energy efficiency were considered as indices for MFC performance. The simulated results explained that an intermediate initial substrate concentration (about 100 mg/L under this reactor configuration) needed to be chosen to achieve maximum overall energy efficiency from substrate in the batch mode. An external resistor with the value about that of the internal resistance boosted the power generation, and a resistor with several times of that of the internal resistance achieved better overall energy efficiency. At continuous mode, dilution rate significantly impacted the steady-state substrate concentration level (thus substrate removal efficiency and rate), and attached biomass could be fully developed when the influent substrate concentration was equal to or higher than 100 mg/L at any dilution rate of the tested range. Overall, this relatively simple model provided a convenient way for evaluating and optimizing the performance of MFC reactors by regulating operating parameters.