Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times

Capacitive-based humidity sensors were fabricated using coplanar interdigitated electrodes coated with nanostructured TiO₂ thin films produced by glancing angle deposition. In this letter, we show that increased sensitivity (nF/%RH) is obtained by decreasing the electrode periodicity or by increasing the planar area of the electrodes, or both. The devices were sensitive over a wide range of relative humidity levels (<1% to >92%) and exhibited extremely fast, subsecond response times. Typical adsorption and desorption response times were measured to be <220 and >400 ms, respectively     

Microchannel-Based Refractive Index Sensors Monolithically Integrated With Silica Waveguides: Structures and Sensitivities

Refractive index sensors using self-forming microchannels embedded in borophosphosilicate glass and monolithically integrated with silica waveguides are presented. Fabricated devices presented include solid-core and liquid-core directional couplers, liquid-core modal interferometers, Mach-Zehnder interferometers, segmented waveguides, and microchannel grating devices. Sensitivities of these devices are calculated and compared with each other and to other well-known devices. Experimental characterizations show that the performance of fabricated devices agrees well with calculations.     

RF Cavity Passive Wireless Sensors With Time-Domain Gating-Based Interrogation for SHM of Civil Structures

Many existing sensing technologies for application to the monitoring of civil structures have a serious deficiency in that they require some type of wired physical connection to the outside world. This causes significant problems in the installation and long-term use of these sensors. This paper describes a new type of passive wireless sensor that is based on resonant RF cavities, where the resonant frequency is modulated by a measurand. In the case of a strain sensor, the electrical length of the cavity directly modulates its resonant frequency. A probe inside the cavity couples RF signals from the cavity to an externally attached antenna. The sensor can then be interrogated remotely using microwave pulse-echo techniques. Such a system has the advantage of requiring no permanent physical connection between the sensor and the data acquisition system. In this type of sensor, the RF interrogation signal is transmitted to the sensor and then reradiated back to the interrogator from the sensor resulting in a signal strength that decreases with the forth power of distance. This places an upper limit on the distance over which the sensor can be interrogated. Theoretical estimates show that these sensors can be interrogated with sufficient SNR at distances exceeding 10 m for radiated powers of less than 1 mW. We present results for a strain sensor and a displacement sensor that can be interrogated at a distance of 8 m with a strain resolution of less than 10 ppm and displacement resolution of 0.01 mm, respectively.     

Automated Synthesis of Wideband Bandpass Filters Based on Slow-wave EBG Structures

This paper is focused on the automated synthesis of wideband bandpass filters operating at microwave frequencies and based on electromagnetic bandgap (EBG) structures. The classical counterpart of such filter consists of a combination of transmission line sections and shunt-connected grounded stubs placed at equidistant positions. By replacing the transmission line sections with capacitively-loaded lines (a kind of EBG-based lines) exhibiting the same phase shift at the lower cutoff frequency and the same characteristic (actually Bloch) impedance, filter size is reduced and the spurious pass bands can be efficiently suppressed. In practice, the loading capacitances are implemented by means of patches, in order to achieve a fully planar filter implementation. The presence of the patches reduces the effective phase velocity of the capacitively-loaded lines, thus providing a slow-wave effect useful for filter miniaturization. Moreover, due to periodicity, such EBG-based lines exhibit wide stop bands, which are used for spurious suppression. Even though such EBG-based filters were previously reported by some of the authors, a systematic synthesis method was not applied for filter design. In this paper, the main aim is to demonstrate the potential of aggressive space mapping (ASM) for that purpose, and it will be shown that such filters can be automatically synthesized.     

Mechanocombinatorially Screening Sensitivity of Stretchable Strain Sensors

Stretchable strain sensors have aroused great interest for their application in human activity recognition, health monitoring, and soft robotics. For various scenarios involving the application of different strain ranges, specific sensitivities need to be developed, due to a trade‐off between sensor sensitivity and stretchability. Traditional stretchable strain sensors are developed based on conductive sensing materials and still lack the function of customizable sensitivity. A novel strategy of mechanocombinatorics is proposed to screen the sensor sensitivity based on mechanically heterogeneous substrates. Strain redistribution over substrates is optimized by mechanics and structure parameters, which gives rise to customizable sensitivity. As a proof of concept, a local illumination method is used to fabricate heterogeneous substrates with customizable mechanics and structure parameters. A library of mechanocombinatorial strain sensors is created for extracting the specific sensitivity. Thus, not only is an effective strategy for screening of sensor sensitivity demonstrated, but a contribution to the mechanocombinatorial strategy for personalized stretchable electronics is also made.     

Modeling Ironless Permanent-Magnet Planar Actuator Structures

This paper describes an analytical model that includes end effects for ironless synchronous permanent-magnet planar actuators. Because of its flexibility, the model can be used to predict the performance of various permanent-magnet array and coil array topologies and commutation schemes. Moreover, since control currents have to be nonsinusoidal, it allows analysis of the motor performance without specifying a commutation scheme by directly dealing with the motor-coupling matrix that links the coil currents to the forces or accelerations acting on the translator.     

Ferroelectric Tuning of Planar and Bulk Microwave Devices

Benefits of ferroelectric component applications at microwaves is discussed. Experience recently gained in the high-temperature film-production technology has been used for obtaining high-quality ferroelectric tunable components. The disk made from bulk SrTiO₃ single crystal covered with double-sided YBa₂Cu₃Y₇ films was used as a high-quality TM₀₁₀ mode tunable resonator. Planar structures containing thin film ferroelectric layers: planar capacitor, sandwich capacitor, coplanar line, and fin line have been studied. Modeling dielectric response of low-temperature incipient ferroelectrics (SrTiO₃, KTaO₃) has been applied for simulation of tunable planar structures. The quality factor of a tunable component (QFCT) is suggested to characterize the validity of the component for practical applications. The high-quality planar capacitors are pioneered for the applications. The wide frequency band fin line phase shifter has been studied and simulated. The prospects for applications of ferroelectric planar structures at room temperature is discussed.     

用于编织结构的光纤传感器的研究

介绍了用于编织复合材料和结构的光纤传感器,分析了它们的特点,将光纤传感器粘贴或编入编织复合材料,检测复合材料的结构的应变,对有关实验结果进行了分析,并介绍了光纤传感在编织复合材料结构健康监控和成型工艺监测中的应用。     

Continuous Terrestrial Positioning Based on Microwave Displacement Sensors

Measurement Techniques - An autonomous positioning system is proposed for navigation of terrestrial transport based on microwave radar displacement sensors. An algorithm for direct and continuous...     

Spatial Sensitivity Distribution of Surface Acoustic Wave Resonator Sensors

The sensitivity distribution of surface acoustic wave (SAW) resonator sensors is investigated by theoretical and experimental means. It is shown that the sensitivity to mass loading varies strongly across the surface due to the confinement of acoustic energy toward the center of the device. A model is developed for this phenomenon based on the extraction of coupling of modes parameters from a rigorous boundary element method analysis based on a periodic Green's function. As SAW sensors for many applications include a layer covering the electrodes, a new technique is introduced to account for the mechanical interactions with buried electrodes. Using this technique, the sensitivity calculations are found to be in good agreement with measurements. It is also shown that while changes in other parameters influence sensitivity, it is velocity change that most strongly determines overall frequency change     

High Sensitivity,Wearable, Piezoresistive Pressure Sensors Based on Irregular Microhump Structures and Its Applications in Body Motion Sensing

A pressure sensor based on irregular microhump patterns has been proposed and developed. The devices show high sensitivity and broad operating pressure regime while comparing with regular micropattern devices. Finite element analysis (FEA) is utilized to confirm the sensing mechanism and predict the performance of the pressure sensor based on the microhump structures. Silicon carbide sandpaper is employed as the mold to develop polydimethylsiloxane (PDMS) microhump patterns with various sizes. The active layer of the piezoresistive pressure sensor is developed by spin coating PEDOT:PSS on top of the patterned PDMS. The devices show an averaged sensitivity as high as 851 kPa^?1, broad operating pressure range (20 kPa), low operating power (100 nW), and fast response speed (6.7 kHz). Owing to their flexible properties, the devices are applied to human body motion sensing and radial artery pulse. These flexible high sensitivity devices show great potential in the next generation of smart sensors for robotics, real‐time health monitoring, and biomedical applications.     

Electric-Field-Controlled Adsorption of Microcapsules under Fabrication of Planar Structures

It is found that an electric field applied parallel to a substrate surface influences the adsorption of positively charged core–shell microcapsules on glass substrates. As a result, the amount of microcapsules adsorbed near negative contact is up to 2 times larger than the one absorbed near positive contact. It is also found that small concentration (less than 0.2 M) of salt in microcapsule suspension decreases this effect, while an increase in the concentration to 0.45 M results in enhancement of the effect.     

An ASIC Front End for Planar High-Frequency Contactless Inductive Position Sensors

We describe an application-specific integrated circuit (ASIC) front end for readout and control of planar high-frequency contactless inductive position sensors that contain transmitter and receiver coils on a fixed printed circuit board and a moving passive resonant target. Such an inductive position sensor suffers from transmitter-to-receiver signal coupling, which can result in a phase-sensitive offset; hence, an error in the position measurement occurs. For the receiver front end, we consider two analog synchronous mixer demodulators, which we call mixer-1 and mixer-2, and analyze their ability to reject phase-sensitive offsets due to transmitter signal breakthrough. The mathematical analysis is validated with measured results from the fabricated ASIC in a 0.35-$muhbox{m}$ CMOS process technology. The ASIC front end contains the transmitter driver, the two receiver mixer variants, a frequency divider/shifter, and an amplifier low-pass filter. Measurements from five ASIC samples connected to the sensor show that, with a system gain of 320, the average output offset variation with phase difference from $-$ 99 to $+117^{circ}$ is more than 237 mV with mixer-1 compared to less than 7 mV with mixer-2.      

Ferroelectric-HTSC Microwave Structures: Fundamental Limitations

Frequency-tunable microwave devices utilizing ferroelectric/HTSC multilayer structures, in which the dielectric constant of the nonlinear dielectric is varied by application of an electric field, have been demonstrated. Significant problems related to losses in the dielectrics have been shown to lead to not insignificant insertion losses in many cases, and fundamental limitations related to these losses are discussed in this paper. Intrinsic and extrinsic losses are described in detail, and some suggestions for reducing these losses are given.     

Auxetic Mechanical Metamaterials to Enhance Sensitivity of Stretchable Strain Sensors

Stretchable strain sensors play a pivotal role in wearable devices, soft robotics, and Internet‐of‐Things, yet these viable applications, which require subtle strain detection under various strain, are often limited by low sensitivity. This inadequate sensitivity stems from the Poisson effect in conventional strain sensors, where stretched elastomer substrates expand in the longitudinal direction but compress transversely. In stretchable strain sensors, expansion separates the active materials and contributes to the sensitivity, while Poisson compression squeezes active materials together, and thus intrinsically limits the sensitivity. Alternatively, auxetic mechanical metamaterials undergo 2D expansion in both directions, due to their negative structural Poisson's ratio. Herein, it is demonstrated that such auxetic metamaterials can be incorporated into stretchable strain sensors to significantly enhance the sensitivity. Compared to conventional sensors, the sensitivity is greatly elevated with a 24‐fold improvement. This sensitivity enhancement is due to the synergistic effect of reduced structural Poisson's ratio and strain concentration. Furthermore, microcracks are elongated as an underlying mechanism, verified by both experiments and numerical simulations. This strategy of employing auxetic metamaterials can be further applied to other stretchable strain sensors with different constituent materials. Moreover, it paves the way for utilizing mechanical metamaterials into a broader library of stretchable electronics.     

Nano Chemical Sensors With Polymer-Coated Carbon Nanotubes

A simple sensor platform consisting of an interdigitated electrode (IDE) pattern has been fabricated for sensing gas and organic vapors. Purified single-walled carbon nanotubes (SWNTs) in the form of a network laid on the IDE by solution casting serve as the sensor material. The electrical conductivity of the SWNT network changes reproducibly upon exposure to various gases and vapors. Selectivity to specific gases, for example, chlorine and hydrochloric acid vapor, is demonstrated by coating the SWNTs with polymers such as chlorosulfonated polyethylene and hydroxypropyl cellulose.     

Submillimeter Crack Detection With Brillouin-Based Fiber-Optic Sensors

Submillimeter crack is detected with a dedicated fiber-optic strain cable, a 1-m-spatial-resolution (w) distributed Brillouin sensor and an advanced signal processing technique. The signal processing approach consists in spectrum shape analysis and multiple peaks detection.