An Analytical Energy Harvester Model for Interdigitated Ring Electrode on Circular Elastic Membrane

Energy harvesters are devices that accumulate ambient vibrational energy from the environment, and for the time being, variable capacitance is the most widely used mechanism. Various designs were proposed to increase the power of such devices, and in particular, the interdigitated electrode (IDE) pattern is the mainstream. Nevertheless, most IDE designs focus merely on the parallel-type vibrations of electrodes. In this study, the performance of a novel harvester, which combined circular membrane and interdigitated ring electrodes (IRE), was investigated. This design allows the device to collect energy from the rotational structure motions of electrodes through the vibrating membrane. Besides, the circular structure provides a dense capacitive arrangement that is higher than that of the arrangement obtained using regular rectangular chips. The IRE diagram is composed of many capacitive rings, each of which harvests vibrated energy simultaneously. Three gaps (1, 10, and 100 μm) of the ring are investigated for the first four vibrational modes of the membrane to understand the effect of energy output. It is found that the energy outputs are approximately the same for the three gaps; however, rings with a wider gap are easier to manufacture in MEMS.

A Disturbance Suppression Micro-Newton Force Sensor Based on Shadow Method

<div>The precision of micro-force measurement is determined by the sensitivity of force sensors and the magnitude of environmental disturbances. Damping, a process that converts vibrational energy into heat, is one of the most effective methods of suppressing disturbances. Inspired by the shadow formed at a pond when water striders walked on the water, a bionic viscoelastic-polymer micro-force (VPMF) sensor with a high damping ratio based on the shadow method was developed. In the VPMF sensor, the surface of the polymer was deformed by the contact of a cylindrical flat punch when the sensor was subjected to a normal force. A shadow with a bright edge was formed due to the refraction that parallel light went through the deformed surface. The force was in proportion to the change of the shadow diameter. The sensor optimal sensitivity was 2.15 μN/pixel and the measurement range was 0.981 mN. The damping ratio of the VPMF sensor was 0.22 on account of viscoelasticity, which could suppress disturbances effectively. The VPMF sensor could reduce the influence of disturbances by about 96.23% compared to the cantilever. The present study suggests that the VPMF sensor is hopefully applied to the reliable measurement of micro force under complex environments.</div>

A Disturbance Suppression Micro-Newton Force Sensor Based on Shadow Method

<div>The precision of micro-force measurement is determined by the sensitivity of force sensors and the magnitude of environmental disturbances. Damping, a process that converts vibrational energy into heat, is one of the most effective methods of suppressing disturbances. Inspired by the shadow formed at a pond when water striders walked on the water, a bionic viscoelastic-polymer micro-force (VPMF) sensor with a high damping ratio based on the shadow method was developed. In the VPMF sensor, the surface of the polymer was deformed by the contact of a cylindrical flat punch when the sensor was subjected to a normal force. A shadow with a bright edge was formed due to the refraction that parallel light went through the deformed surface. The force was in proportion to the change of the shadow diameter. The sensor optimal sensitivity was 2.15 μN/pixel and the measurement range was 0.981 mN. The damping ratio of the VPMF sensor was 0.22 on account of viscoelasticity, which could suppress disturbances effectively. The VPMF sensor could reduce the influence of disturbances by about 96.23% compared to the cantilever. The present study suggests that the VPMF sensor is hopefully applied to the reliable measurement of micro force under complex environments.</div>

Concurrent vibration attenuation and low-power electricity generation in a locally resonant metastructure

We investigate piezoelectric energy harvesting on a locally resonant metamaterial beam for concurrent power generation and bandgap formation. The mechanical resonators (small beam attachments on the main beam structure) have piezoelectric elements which are connected to electrical loads to quantify their electrical output in the locally resonant bandgap neighborhood. Electromechanical model simulations are followed by detailed experiments on a beam setup with nine resonators. The main beam is excited by an electrodynamic shaker from its base over the frequency range of0–150 Hz and the motion at the tip is measured using a laser Doppler vibrometer to extract its transmissibility frequency response. The formation of a locally resonant bandgap is confirmed and a resistor sweep is performed for the energy harvesters to capture the optimal power conditions. Individual power outputs of the harvester resonators are compared in terms of their percentage contribution to the total power output. Numerical and experimental analysis shows that, inside the locally resonant bandgap, most of the vibrational energy (and hence harvested energy) is localized near the excited base of the beam, and the majority of the total harvested power is extracted by the first few resonators.

Excited States Computation of Models of Phenylalanine Protein Chains: TD-DFT and Composite CC2/TD-DFT Protocols

The present benchmark calculations testify to the validity of time-dependent density functional theory (TD-DFT) when exploring the low-lying excited states potential energy surfaces of models of phenylalanine protein chains. Among three functionals suitable for systems exhibiting charge-transfer excited states, LC-ωPBE, CAM-B3LYP, and ωB97X-D, which were tested on a reference peptide system, we selected the ωB97X-D functional, which gave the best results compared to the approximate coupled-cluster singles and doubles (CC2) method. A quantitative agreement for both the geometrical parameters and the vibrational frequencies was obtained for the lowest singlet excited state (a ππ* state) of the series of capped peptides. In contrast, only a qualitative agreement was met for the corresponding adiabatic zero-point vibrational energy (ZPVE)-corrected excitation energies. Two composite protocols combining CC2 and DFT/TD-DFT methods were then developed to improve these calculations. Both protocols substantially reduced the error compared to CC2 and experiment, and the best of both even led to results of CC2 quality at a lower cost, thus providing a reliable alternative to this method for very large systems.

Understanding Proton Transfer in Non-aqueous Biopolymers based on Helical Peptides: A Quantum Mechanical Study

Histidine (an imidazole-based amino acid) is a promising building block for short aromatic peptides containing a proton donor/acceptor moiety. Previous studies have shown that polyalanine helical peptides substituted at regular intervals with histidine residues exhibit both structural stability as well as high proton affinity and high conductivity. Here, we present first-principle calculations of non-aqueous histidine-containing 310-,  and -helices and show that they are able to form hydrogen-bonded networks mimicking proton wires that have the ability to shuttle protons via the Grotthuss shuttling mechanism. The formation of these wires enhances the stability of the helices, and our structural characterizations confirm that the secondary structures are conserved despite distortions of the backbones. In all cases, the helices exhibit high proton affinity and proton transfer barriers on the order of 1~4 kcal/mol. Zero-point energy calculations suggest that for these systems, ground state vibrational energy can provide enough energy to cross the proton transport energy barrier. Additionally, ab initio molecular dynamics results suggests that the protons are transported unidirectionally through the wire at a rate of approximately 2 Å every 20 fs. These results demonstrate that efficient deprotonation-controlled proton wires can be formed using non-aqueous histidine-containing helical peptides.

Vibration Energy Harvester Based on Torsionally Oscillating Magnet

Most of the miniaturized electromagnetic vibrational energy harvesters (EVEHs) are based on oscillating proof mass suspended by several springs or a cantilever structure. Such structural feature limits the miniaturization of the device’s footprint. This paper presents an EVEH device based on a torsional vibrating magnet over a stack of flexible planar coils. The torsional movement of the magnet is enabled by microfabricated silicon torsional springs, which effectively reduce the footprint of the device. With a size of 1 cm × 1 cm × 1.08 cm, the proposed EVEH is capable of generating an open-circuit peak-to-peak voltage of 169 mV and a power of 6.9 μW, under a sinusoidal excitation of ±0.5 g (g = 9.8 m/s2) and frequency of 96 Hz. At elevated acceleration levels, the maximum peak-to-peak output voltage is 222 mV under the acceleration of 7 g (±3.5 g).

Refraction of Flexural Waves by Ultra-broadband Achromatic Meta-slab with Wavelength-dependent Phase Shifts

Great progress has been made in modulating flexural waves by elastic metasurfaces. Most of the proposed elastic metasurfaces suffer from chromatic aberration, limited in a narrow bandwidth around the designed frequency. In this paper, overcoming the chromatic aberration, an ultra-broadband achromatic meta-slab (UAM) with subunits of gradient thickness is proposed to realize the refraction angle unchanged with the incident frequency. Based on the phase compensation principle, wavelength-dependent phase shifts for the UAM that realize achromaticity are obtained. In order to verify the effectiveness of the theoretical design, the transmitted wavefields are solved according to the phased array theory, and the results correspond with those obtained by the finite element (FE) simulations and experiments, which show that the refraction angle is unchanged for incident frequencies from 2 kHz to 8 kHz. Besides, the UAM is extended into a periodic meta-slab, and multifrequency achromaticity is realized. Our designed meta-slabs overcome the chromatic aberration by simple configurations, which have significance in the applications of vibration control, vibrational energy harvesting, and health monitoring.