The response of a bistable energy harvester to different excitations: the harvesting efficiency and links with stochastic and vibrational resonances

Energy harvesting of ambient vibrations using a combination of a mechanical structure (oscillator) and an electrical transducer has become a valuable technique for powering small wireless sensors. Bistable mechanical oscillators have recently attracted the attention of researchers as they can be used to harvest energy within a wider band of frequencies. In this study, the response of a bistable harvester to different forms of ambient vibration is analysed. In particular, harmonic noise, which has a narrow spectrum, similarly to harmonic signals, yet is stochastic, like broad-spectrum white noise, is considered. Links between bistable harvester responses and stochastic and vibrational resonance are explored. This article is part of the theme issue ‘Vibrational and stochastic resonance in driven nonlinear systems (part 2)’.

Vibrational resonances in driven oscillators with position-dependent mass

The vibrational resonance (VR) phenomenon has received a great deal of research attention over the two decades since its introduction. The wide range of theoretical and experimental results obtained has, however, been confined to VR in systems with constant mass. We now extend the VR formalism to encompass systems with position-dependent mass (PDM). We consider a generalized classical counterpart of the quantum mechanical nonlinear oscillator with PDM. By developing a theoretical framework for determining the response amplitude of PDM systems, we examine and analyse their VR phenomenona, obtain conditions for the occurrence of resonances, show that the role played by PDM can be both inductive and contributory, and suggest that PDM effects could usefully be explored to maximize the efficiency of devices being operated in VR modes. Our analysis suggests new directions for the investigation of VR in a general class of PDM systems. This article is part of the theme issue ‘Vibrational and stochastic resonance in driven nonlinear systems (part 1)’.

Multiple Fermi Resonances in Liquid Benzene

A number of coupled Fermi vibrational resonances (FRs) in liquid benzene from a multitude of them are systematically studied. The spectral structure of the vibrational bands in the IR absorption and Raman scattering spectra are determined by their numerical decomposition into individual components. The complication of vibrational resonances with an increase in their order is due to the overlapping of FRs and the appearance of additional resonant vibrational modes. To clarify the identification of the vibrations of the benzene FR v1+v6, v8 and the correction of the frequencies of a number of inactive vibrations, including v13(E1u), the experimental results are compared to the data obtained by quantum-chemical calculations. With regard for the collective-wave properties of vibrational modes in the benzene liquid state, we propose a new content of the analysis of FRs. It should include the study of 1) the intensity changes for various spectral components in the IR absorption and Raman scattering for FR vibrational bands of various orders, 2) half-widths δv of the bands, and 3) anharmonic shifts ΔvA for various components in the vibrational bands of FRs.

Detection of Estrogenic Hormones Using Plasmonic Nanostructures

<div> <div> <div> <p>By optimising the geometry of asymmetric split-H (ASH) resonators fabricated on zinc selenide, we have produced a total of four distinct plasmonic resonances that could be matched with six molecular vibration wavelengths (for O-H, C-H, C=O, C=C, CºC-H and C-C bonds) which are relevant to the detection of four estrogenic hormones: estrone (E1), 17β-estradiol (E2), estriol (E3) and synthetic estrogen; 17α-ethinyl estradiol (EE2). Specifically, sensitivities of 363 nm/RIU and 636 nm/RIU were achieved from the deposition of E2 on ASH1 (2 μm and 4 μm) and ASH2 (5 μm and 8 μm) respectively. A Fourier transform infrared (FTIR) spectrometer was used to measure the transmittance resonances of the fabricated ASH arrays. The amplitudes of the molecular vibrational resonances were also around 500 times greater when matched with the plasmonic resonances of the ASHs as compared with deposit on on bulk ZnSe substrates. Finally, when mixtures of two hormones were deposited on the nanoantennas, the molar ratio for each of the hormones could also be calculated by using the peak intensities for the different molecular vibration wavelengths. By engineering the spectral response of ASH resonators to match specific estrogenic fingerprints, the work paves the way for the development of metamaterial sensors with better specificity and enhanced functionalities.</p> </div> </div> </div>

Detection of Estrogenic Hormones Using Plasmonic Nanostructures

<div> <div> <div> <p>By optimising the geometry of asymmetric split-H (ASH) resonators fabricated on zinc selenide, we have produced a total of four distinct plasmonic resonances that could be matched with six molecular vibration wavelengths (for O-H, C-H, C=O, C=C, CºC-H and C-C bonds) which are relevant to the detection of four estrogenic hormones: estrone (E1), 17β-estradiol (E2), estriol (E3) and synthetic estrogen; 17α-ethinyl estradiol (EE2). Specifically, sensitivities of 363 nm/RIU and 636 nm/RIU were achieved from the deposition of E2 on ASH1 (2 μm and 4 μm) and ASH2 (5 μm and 8 μm) respectively. A Fourier transform infrared (FTIR) spectrometer was used to measure the transmittance resonances of the fabricated ASH arrays. The amplitudes of the molecular vibrational resonances were also around 500 times greater when matched with the plasmonic resonances of the ASHs as compared with deposit on on bulk ZnSe substrates. Finally, when mixtures of two hormones were deposited on the nanoantennas, the molar ratio for each of the hormones could also be calculated by using the peak intensities for the different molecular vibration wavelengths. By engineering the spectral response of ASH resonators to match specific estrogenic fingerprints, the work paves the way for the development of metamaterial sensors with better specificity and enhanced functionalities.</p> </div> </div> </div>