Performance characterisation of a new photo-microsensor based sensing head for displacement measurement

This paper presents a robust displacement sensor with nanometre-scale resolution over a micrometre range. It is composed of low cost commercially available slotted photo-microsensors (SPMs). The displacement sensor is designed with a particular arrangement of a compact array of SPMs with specially designed shutter assembly and signal processing to significantly reduce sensitivity to ambient light, input voltage variation, circuit electronics drift, etc. The sensor principle and the characterisation results are described in this paper. The proposed prototype sensor has a linear measurement range of 20 μm and resolution of 21 nm. This kind of sensor has several potential applications, including mechanical structural deformation monitoring system

Design and Characterization of Tri-axis Soft Inductive Tactile Sensors

Tactile sensors are essential for robotic systems to safely and effectively interact with the environment and humans. In particular, tri-axis tactile sensors are crucial for dexterous robotic manipulations by providing shear force, slip or contact angle information. The Soft Inductive Tactile Sensor (SITS) is a new type of tactile sensor that measures inductance variations caused by eddy-current effect. In this paper, we present a soft tri-axis tactile sensor using the configuration of four planar coils and a single conductive film with hyperelastic material in between them. The working principle is explained and design methods are outlined. A 3D finite element model was developed to characterize the tri-axis SITS and to optimize the target design through parameter study. Prototypes were fabricated, characterized and calibrated, and a force measurement resolution of 0.3 mN is achieved in each axis. Demonstrations show that the sensor can clearly measure light touch (a few mN normal force) and shear force pulses (10 to 30 mN) produced by a serrated leaf when it is moved across the sensor surface. The presented sensor is low cost, high performance, robust, durable, and easily customizable for a variety of robotic and healthcare applications

Design, Development and Performance Evaluation of Eddy Current Displacement Sensor Based Pressure Sensor with Target Temperature Compensation

In Aerospace applications, pressure measurement plays a vital role as it serves as one of the input to onboard controller to aid decision- making on initiating or terminating some of the critical events. In this paper, the design aspects of pressure sensor using linear eddy current displacement sensor (ECDS) are presented along with its performance evaluation. The static calibration is carried out to select the best position of ECDS in the proposed pressure sensor. The effect of target temperature on sensor output is presented with test results to aid compensation. A compensation algorithm is developed to minimise the error due to target temperature. The developed compensation algorithm is validated using thermal calibration. The designed pressure sensor is calibrated using Arson dynamic pressure calibrator to evaluate its bandwidth. The calibration results are analysed to aid future sensor design towards improvement of accuracy, bandwidth and miniaturisation

Effects of the target on the performance of an ultra-low power eddy current displacement sensor for industrial applications

The demand for smart, low-power, and low-cost sensors is rapidly increasing with the proliferation of industry automation. In this context, an Ultra-Low Power Eddy Current Displacement Sensor (ULP-ECDS) targeting common industrial applications and designed to be embedded in wireless Industrial Internet of Things (IIoT) devices is presented. A complete characterization of the realized ULP-ECDS operating with different metallic targets was carried out. The choice of the considered targets in terms of material and thickness was inspired by typical industrial scenarios. The experimental results show that the realized prototype works properly with extremely low supply voltages, allowing for obtaining an ultra-low power consumption, significantly lower than other state-of-the-art solutions. In particular, the proposed sensor reached the best resolution of 2 \ub5m in case of a carbon steel target when operated with a supply voltage of 200 mV and with a power consumption of 150 \ub5W. By accepting a resolution of 12 \ub5m, it is possible to further reduce the power consumption of the sensor to less than 10 \ub5W. The obtained results also demonstrate how the performances of the sensor are strongly dependent on both the target and the demodulation technique used to extract the displacement information. This allowed for defining some practical guidelines that can help the design of effective solutions considering application-specific constraints

Robust and High-Performance Soft Inductive Tactile Sensors based on the Eddy-Current Effect

Tactile sensors are essential for robotic systems to interact safely and effectively with the external world, they also play a vital role in some smart healthcare systems. Despite advances in areas including materials/composites, electronics and fabrication techniques, it remains challenging to develop low cost, high performance, durable, robust, soft tactile sensors for real-world applications. This paper presents the first Soft Inductive Tactile Sensor (SITS) which exploits an inductance-transducer mechanism based on the eddy-current effect. SITSs measure the inductance variation caused by changes in AC magnetic field coupling between coils and conductive films. Design methodologies for SITSs are discussed by drawing on the underlying physics and computational models, which are used to develop a range of SITS prototypes. An exemplar prototype achieves a state-of-the-art resolution of 0.82 mN with a measurement range over 15 N. Further tests demonstrate that SITSs have low hysteresis, good repeatability, wide bandwidth, and an ability to operate in harsh environments. Moreover, they can be readily fabricated in a durable form and their design is inherently extensible as highlighted by a 4x4 SITS array prototype. These outcomes show the potential of SITS systems to further advance tactile sensing solutions for integration into demanding real-world applications

Computational Design Tools for Soft Inductive Tactile Sensors

Soft tactile sensors are a key enabling technology for next generation robotic systems and it is imperative to develop appropriate design tools to inform their design, integration and optimisation. The use of computational models can help speed this process and minimise the need for timely emperical design methods. Here we present the use of computational multi-physics modelling as a design tool for Soft Inductive Tactile Sensors (SITS) which use variation in electromagnetically-induced eddy-current effects as a transducer mechanism. We develop and experimentally validate 2D models which extend existing understanding to provide insight into the configuration of sensing elements for measurement of multi-axis forces and rejection of unwanted environmental disturbances. We analyse the limitations of this approach and discuss opportunities for future improvements to advance this burgeoning area

Controlling light-matter interactions with two-dimensional semiconductors at cryogenic temperatures

Efficient interactions between solid-state systems and photons are the basis for the emerging quantum technologies. An outstanding challenge in facilitating light-matter interactions can be solved by the introduction of an optical resonator. By trapping the photons in a small volume, the interaction time with the solid-state system is increased in such quantum optics experiments. This thesis focuses on light-matter interactions with two-dimensional semiconductor transition-metal dichalcogenides. Strongly bound electron-hole pairs (excitons) in transition-metal dichalcogenides exhibit large oscillator strength and offer a valley degree-of-freedom in the band structure that interacts with specific polarization of light, this makes them an excellent prospect for quantum optics experiments. In this work, we realize light-matter interactions with monolayer tungsten diselenide in two experiments using different optical resonators. In the first experiment, we investigated a hybrid system combining localized plasmons, on the surface of gold nanodisks, with a monolayer tungsten diselenide. The coherent interference of excitons with plasmons yield an asymmetric optical response, known as Fano line-shape, in the limit of weak light-matter coupling. This optical response of the hybrid system is corroborated with a three-level model. In addition, magnetic field-induced valley-dependent exciton energy splitting is harnessed to achieve chiral reflection. The second experiment develops a modular tunable cavity at cryogenic temperatures. A major technological challenge involving scalable cryogenic experiments is mechanical vibrations. After a thorough understanding of the functionality of a closed-cycle cryostat, a variety of vibration-reduction techniques were applied to develop an open cavity setup. In comparison to the vibrations on the standard closed-cycle cryostat, we attain 50-fold reduction to reach the root-mean-square stability of less than 100 pm over the entire period of a cooling cycle. This enables the operation of a high-finesse cavity at low temperatures. Subsequently, the versatility of the platform was demonstrated in a controlled experiment with monolayer tungsten diselenide. Exciton-polaritons were observed in the high cooperativity strong-coupling regime.Effiziente Wechselwirkungen zwischen Festkörpersystemen und Photonen bilden die Grundlage für die aufstrebenden Quantentechnologien. Die zentrale Herausforderung bei der Kontrolle von Wechselwirkungen zwischen Licht undMaterie kann durch die Verwendung eines optischen Resonators gelöst werden. Durch Einfangen der Photonen in einem kleinen Volumen wird die Wechselwirkungszeit mit dem Festkörpersystem in solchen quantenoptischen Experimenten erhöht. Diese Arbeit konzentriert sich auf Wechselwirkungen zwischen Licht und Materie in zweidimensionalen halbleitenden Übergangsmetalldichalkogeniden. Stark gebundene Elektron-Loch-Paare (Exzitonen) in Übergangsmetalldichalkogeniden weisen eine große Oszillatorstärke auf und bieten einen weiteren Pseudospin-Freiheitsgrad in der Bandstruktur, der mit spezifischer Polarisation des Lichts interagiert. In dieser Arbeit realisieren wir in zwei Experimenten Licht-Materie-Wechselwirkungenmit monolagigem Wolframdiselenid mit unterschiedlichen optischen Resonatoren. Im ersten Experiment untersuchten wir ein Hybridsystem, das lokalisierte Plasmonen auf der Oberfläche von Goldnanoscheiben mit monolagigem Wolframdiselenid kombiniert. Kohärente Interferenz von Exzitonen mit Plasmonen ergibt eine asymmetrische spektrale Antwort - als Fano-Linienformbekannt - im Grenzfall schwacher Licht-Materie-Kopplung. Diese optische Antwort des Hybridsystems wird durch ein Drei-Niveau-Modell bestätigt. Zusätzlich wird die magnetfeldinduzierte Energieaufspaltung der Exzitonen genutzt, um chirale Reflexion zu ermitteln. Das zweite Experiment entwickelt einen modular abstimmbaren optischen Resonator bei kryogenen Temperaturen. Eine große technologische Herausforderung bei skalierbaren kryogenen Experimenten sind mechanische Schwingungen. Basierend auf einem gründlichen Verständnis der Funktionalität eines Kryostaten mit geschlossenem Kreislauf wurden verschiedene Techniken zur Schwingungsreduzierung implementiert, um einen Aufbau mit offenen optischen Resonatoren zu entwickeln. Im Vergleich zu Vibrationen des Standardsystems wurde eine 50-fache Verminderung erreicht, und somit über den gesamten Zeitraum eines Kühlzyklus eine mittlere Stabilität von weniger als 100 pm gewährleistet. Dies ermöglicht den Betrieb eines optischen Resonators mit hoher Finesse bei niedrigen Temperaturen. Anschließend wurde die Vielseitigkeit des Systems in einemkontrollierten Experimentmit monolagigem Wolframdiselenid demonstriert. Exziton-Polaritonen wurden im Regime starker Kopplung mit hoher Kooperativität beobachtet

NASA Tech Briefs Index, 1977, volume 2, numbers 1-4

Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977

Investigation of Tx-Rx mutual inductance eddy current system for high lift-off inspection

PhD ThesisEddy current (EC) testing is a popular inspection technique due to its harsh environment tolerance and cost-effectiveness. Despite the immense research in EC inspection, defect detection at high lift-off still poses a challenge. The weakening mutual coupling of EC probe and sample due to the increase in lift-off degrades signal strength and thus reduces the detection sensitivity. Although signal processing can be used to mitigate lift-off influence, it is laborious and time consuming. Therefore, in this study, a Tx-Rx probe system is proposed to deal with high lift-off inspection. The parts of the study of the Tx-Rx EC system includes optimisation of probe configuration, improvement of signal conditioning circuit and comparative study of excitation modes. In optimisation of probe configuration, lift-off and coil gap are optimized to mitigate the offset caused by the direct coupling of Tx-Rx coils. The optimum coil gaps of Tx-Rx probe for different lift-offs are found by observing the highest signal strength. The optimisation of coil gap against lift-off extends the detection sensitivity of the EC system to a lift-off of about 30 mm which is by far higher than 5 mm lift-off limit of a single-coil EC probe. In signal conditioning aspect, a modified Maxwell bridge circuit is designed to remove the offset due to self- impedance of the Rx coil. The proposed circuit mitigates the influence of the self-impedance of Rx coil and improves signal-to- noise ratio SNR. In the excitation mode, pulse and sweep frequency signals are compared to study detection sensitivity, SNR and crack quantification capability. The result of the comparative study reveals that pulse excitation is good for crack sizing while sweep frequency excitation is better for crack detection. Simulations and experimental studies are carried out to show the efficacy of the Tx-Rx EC system in high lift-off crack detection