Metamaterial perfect absorbers (MPAs) are artificial materials composed of an array of subwavelength structures that manipulate electromagnetic waves to achieve extraordinary light absorption properties. Driven by the advent of the Internet of Things, MPAs are employed in microelectromechanical systems for the development of efficient and miniaturized IR detectors, imagers, and spectrometers, thanks to their lithographically tunable peak absorption, spectral selectivity, and ultrathin thickness. MPAs characterized by high absorptance in narrow spectral bands are particularly desirable for the implementation of high‐resolution IR spectroscopic sensors. Yet, no accurate analytical model is currently available to guide the design of an MPA with ultra‐narrow absorption bandwidth, while meeting all the stringent requirements for spectroscopic sensors. Here, a circuit model capable of accurately predicting spectral responses of metal–insulator–metal (MIM) IR absorbers is reported. The model is experimentally validated in the mid‐wavelength IR spectral range and exploited for the first demonstration of an MIM IR absorber that exhibits performance approaching the predicted physical limits: full‐width at half‐maximum ≈3% and near‐unity absorption (η > 99.7%) at 5.83 µm wavelength, while independent of incident angle and polarization of the impinging IR radiation. These unprecedented absorption properties are key enablers for the development of miniaturized, low‐cost, and high‐resolution spectrometers.

In this paper, for the first time we demonstrate zero-power volatile-organic-chemical (VOC) detectors based on micromechanical switches suitable for plant health monitoring. Differently from state-of-the-art active chemical sensors, the device presented here exploits a completely passive, chemically-sensitive switch based on a bimaterial microcantilever and a passive switch-based readout mechanism to detect VOCs exceeding a predetermined concentration released by unhealthy plants. When exposed to target VOCs, the polymer/metal bimaterial beam bends downward and trigger the switch due to the stress induced from the absorption of chemicals in the polymer layer. Here we show experimental demonstrations of detecting toluene, hexenol (cis-3-Hexen-1-ol, a chemical released from plants under attack by pests) and ethanol, respectively, with our fabricated prototypes. The demonstrated high sensitivity to ethanol (∼ 8 nm/ppm) and hexenol (∼ 3.3 nm/ppm) was achieved by the optimization of device geometries showing a great promise of the proposed technology to ultimately achieve 10s ppm detection limit (with a sub-micron contact gap and voltage bias) which is required for the device operation in close proximity to a plant in an open environment.

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Nano- and micro-electromechanical systems (N/MEMSs) are traditionally based on electrostatic or piezoelectric coupling, which couples electrical and mechanical energy through acoustic resonator structures. Most recently, N/MEMS devices based on magnetoelectrics are gaining much attention. Unlike electrostatic or piezoelectric N/MEMS that rely on an AC electric field or voltage excitation, magnetoelecric N/MEMS rely on the electromechanical resonance of a magnetostrictive/piezoelectric bilayer heterostructure exhibiting a strong strain-mediated magnetoelectric coupling under the excitation of a magnetic field and/or electric field. As a consequence, magnetoelectric N/MEMS enable unprecedented new applications, ranging from magnetoelectric sensors, ultra-compact magnetoelectric antennas, etc. This Tutorial will first outline the fundamental principles of piezoelectric materials, resonator design, specifically different acoustic modes, and piezoelectric-based N/MEMS applications, i.e., radio frequency front end filters and infrared radiation sensors. We will then provide an overview of magnetoelectric materials and N/MEMS focusing on the governing physics of the magnetoelectric effect, magnetic material properties for achieving high magnetoelectric coupling, state-of-the-art magnetoelectric N/MEMS devices, and their respective applications.