Single Channel Based Interference-Free and Self-Powered Human-Machine Interactive Interface Using Eigenfrequency-Dominant Mechanism.

The recent development of wearable devices is revolutionizing the way of human-machine interaction (HMI). Nowadays, an interactive interface that carries more embedded information is desired to fulfill the increasing demand in era of Internet of Things. However, present approach normally relies on sensor arrays for memory expansion, which inevitably brings the concern of wiring complexity, signal differentiation, power consumption, and miniaturization. Herein, a one-channel based self-powered HMI interface, which uses the eigenfrequency of magnetized micropillar (MMP) as identification mechanism, is reported. When manually vibrated, the inherent recovery of the MMP causes a damped oscillation that generates current signals because of Faraday's Law of induction. The time-to-frequency conversion explores the MMP-related eigenfrequency, which provides a specific solution to allocate diverse commands in an interference-free behavior even with one electric channel. A cylindrical cantilever model is built to regulate the MMP eigenfrequencies via precisely designing the dimensional parameters and material properties. It is shown that using one device and two electrodes, high-capacity HMI interface can be realized when the magnetic micropillars (MMPs) with different eigenfrequencies have been integrated. This study provides the reference value to design the future HMI system especially for situations that require a more intuitive and intelligent communication experience with high-memory demand.

Miniature Fiber Optic Acoustic Pressure Sensors With Air-Backed Graphene Diaphragms.

Graphene has been known to possess exceptional mechanical properties, including its extremely high Young's modulus and atomic layer thickness. Although there are several reported fiber optic pressure sensors using graphene film, a key question that is not well understood is how the suspended graphene film interacts with the backing air cavity and affects the sensor performance. Based on our previous analytical model, we will show that the sensor performance suffers due to the significantly reduced mechanical sensitivity by the backing cavity. To remedy this limitation, we will, through experimental and numerical methods, investigate two approaches to enhance the sensitivity of fiber optic acoustic pressure sensors using graphene film. First, a graphene-silver composite diaphragm is used to enhance the optical sensitivity by increasing the reflectivity. Compared with a sensor with pure graphene diaphragm, graphene-silver composite can enhance the sensitivity by threefold, while the mechanical sensitivity is largely unchanged. Second, a fiber optic sensor is developed with enlarged backing air volume through the gap between an optical fiber and a silica capillary tube. Experimental results show that the mechanical sensitivity is increased by 10× from the case where the gap side space is filled. For both approaches, signal-to-noise ratio (SNR) is improved due to the enhanced sensitivity, and COMSOL Thermoviscous acoustics simulation compares well with the experimental results. This study is expected to not only enhance the understanding of fluid-structural interaction in sensor design but also benefit various applications requiring high-performance miniature acoustic sensors.

Planar photonic crystal based multifunctional sensors: erratum.

Here, we acknowledge related papers that should have been cited in our recent work [Appl. Opt.56, 1775 (2017)APOPAI0003-693510.1364/AO.56.001775].

Planar photonic crystal based multifunctional sensors: publisher's note.

This note points out a missed correction to the math on p. 1779 of Appl. Opt.56, 1775 (2017)10.1364/AO.56.001775.

Planar photonic crystal based multifunctional sensors.

A planar photonic crystal (PPC) structure capable of simultaneous detection of multiple parameters is presented in this paper. We analytically and numerically demonstrate that the reflection spectrum of the PPC structure exhibits multiple high-Q resonant modes that could respond distinctively to different external perturbations, rendering the PPC sensor superior capabilities for multiparameter sensing. We further demonstrate simultaneous pressure and temperature sensing with a PPC sensor. Other advantages of this device include efficient free-space-to-multimode coupling, high sensitivity, on-chip integration, and wafer-scale fabrications.

Low cost, high performance white-light fiber-optic hydrophone system with a trackable working point.

A working-point trackable fiber-optic hydrophone with high acoustic resolution is proposed and experimentally demonstrated. The sensor is based on a polydimethylsiloxane (PDMS) cavity molded at the end of a single-mode fiber, acting as a low-finesse Fabry-Perot (FP) interferometer. The working point tracking is achieved by using a low cost white-light interferometric system with a simple tunable FP filter. By real-time adjusting the optical path difference of the FP filter, the sensor working point can be kept at its highest sensitivity point. This helps address the sensor working point drift due to hydrostatic pressure, water absorption, and/or temperature changes. It is demonstrated that the sensor system has a high resolution with a minimum detectable acoustic pressure of 148 Pa and superior stability compared to a system using a tunable laser.

On-fiber plasmonic interferometer for multi-parameter sensing.

We demonstrate a novel miniature multi-parameter sensing device based on a plasmonic interferometer fabricated on a fiber facet in the optical communication wavelength range. This device enables the coupling between surface plasmon resonance and plasmonic interference in the structure, which are the two essential mechanisms for multi-parameter sensing. We experimentally show that these two mechanisms have distinctive responses to temperature and refractive index, rendering the device the capability of simultaneous temperature and refractive index measurement on an ultra-miniature form factor. A high refractive index sensitivity of 220 nm per refractive index unit (RIU) and a high temperature sensitivity of -60 pm/ °C is achieved with our device.

Enhanced acoustic sensing through wave compression and pressure amplification in anisotropic metamaterials.

Acoustic sensors play an important role in many areas, such as homeland security, navigation, communication, health care and industry. However, the fundamental pressure detection limit hinders the performance of current acoustic sensing technologies. Here, through analytical, numerical and experimental studies, we show that anisotropic acoustic metamaterials can be designed to have strong wave compression effect that renders direct amplification of pressure fields in metamaterials. This enables a sensing mechanism that can help overcome the detection limit of conventional acoustic sensing systems. We further demonstrate a metamaterial-enhanced acoustic sensing system that achieves more than 20 dB signal-to-noise enhancement (over an order of magnitude enhancement in detection limit). With this system, weak acoustic pulse signals overwhelmed by the noise are successfully recovered. This work opens up new vistas for the development of metamaterial-based acoustic sensors with improved performance and functionalities that are highly desirable for many applications.

Trapping and releasing light by mechanical implementation in metamaterial waveguides.

We show that light trapping and releasing can be switched by a mechanic tuning effect in metamaterial waveguides. The transition mechanism between the trapping and releasing states relies on the synergetic effect of the local Bragg reflection and cavity resonance in the waveguides. As a proof-of-concept demonstration, a heterostructured metamaterial waveguide comprised of dielectric claddings and a tapered metamaterial core formed by arrays of metal slats is analytically and numerically investigated. The spatial separation of the trapped light with various frequencies and the transition between the trapping and releasing states can be predicted by a "rainbow equation." The proposed light trapping and releasing scheme based on the mechanical implementation of waveguide geometrical parameters can be exploited to develop opto-mechanical devices for slow light technology.

Effective surface plasmon polaritons on the metal wire with arrays of subwavelength grooves.

In this paper we explore the existence of electromagnetic surface bound modes on a perfect metal wire milled with arrays of subwavelength grooves. The surface modes are axially symmetric transverse magnetic (TM) waves and have the same polarization state with the dominant propagating surface plasmon polaritons on the real metal wires. The dispersion of the fundamental surface mode has close resemblance with the dispersion of the surface plasmon polaritons. Moreover, we note that for TM polarization this metallic structure can be equivalent to a dielectric coated metal wire with defined geometrical parameters and effective refractive index of the dielectric coating. This metallic structure is expected to have some potential applications in the optical research in microwave or THz region.