Passive Wireless Sensor Research Articles

Degradation of Sub-Micrometer Sensitive Polymer Layers of Acoustic Sensors Exposed to Chlorpyrifos Water-Solution.

The detection of organophosphates, a wide class of pesticides, in water-solution has a huge impact in environmental monitoring. Acoustic transducers are used to design passive wireless sensors for the direct detection of pesticides in water-solution by using tailored polymers as sensitive layers. We demonstrate by combining analytical chemistry tools that organophosphate molecules strongly alter polymer layers widely used in acoustic sensors in the presence of water. This chemical degradation can limit the use of these polymers in detection of organophosphates in water-solution.

Improving Water Pressure Measurement Using Temperature-Compensated Wireless Passive SAW Bidirectional RDL Pressure Sensor

Currently pressure sensors utilized for water pressure measurement need batteries for direct power supply. However, batteries are lifespan-limited and not so reliable in the buried water pipe environment. The maintenance work due to battery failures leads to high cost to utility owners. Wireless passive surface acoustic wave (WP-SAW) sensors do not need direct power supply from batteries and can work in harsh environment. They are low-cost and compatible with micro-electromechanical systems (MEMS) technologies. This study investigates a temperature-compensated WP-SAW bidirectional reflective delay line (RDL) pressure sensor and its feasibility in improving water pressure measurement. The linear temperature-compensated pressure sensing functional model between the output phase shifts and the pressure change is established theoretically and verified by experiments. An experimental framework for testing the sensor node is built. The water pressure sensing adaptor is proposed. Experimental results: the experimental data show good linearities, which fits the established functional relationship; the numerical functional relationship has been derived and expressed; the sensor node has a good performance in the range of pressure difference from 0 to 0.5 MPa, which meets the normal 28-meter water pressure sensing requirements; the accuracy of this sensor is 7.22 kPa, which can be utilized for the water pressure sensing tasks in water distribution systems.

Регенеративная система в пассивной радиосенсорной технической диагностике электронных устройств

This work is devoted to the problem of processing signal radio profiles with a duration of less than 1 ns. These radio profiles are obtained by registering the electrical component of the near field of electromagnetic radiation induced by the electronic unit of the device using the method of passive radio engineering diagnostics. The reasons for the occurrence of significant errors in the processing of signal radio profiles by modern methods of direct analog-to-digital conversion and parallel conversion of real time are shown, associated with a decrease in the number of effective bits, an increase in sampling irregularity and signal rise time. A method is proposed for reducing the arising errors by switching to the method of stroboscopic scale-to-time transformation using multiple repro duction (regeneration) of a complex signal section by means of the previously presented regenerative system. Numerical modeling of the functioning of the regeneration system together with a stroboscopic time-scale converter was carried out in the study of the area of interest in the signal radio profile in the Simulink environment of the MatLab package. Using the correlation analysis of the reconstructed and the original signal radio profile, the validity of the use of the regenerative system in the processing and recovery of signal radio profiles of subnanosecond duration is shown. An experiment was prepared and carried out using modern high-speed equipment: a real-time oscilloscope and a stroboscopic oscilloscope with a subpicosecond sampling to study the correctness of the applicability of the regeneration method when combining the scale-time transformation and real-time transformation. The result of the stroboscopic scale-to-time transformation in the equivalent time mode with the transfer of the section to the general signal reconstructed in real time is presented. It is concluded that the accuracy of processing the original signal is increased by means of regeneration followed by restoration by methods of stroboscopic scale-time transformation, which allows further analysis of the signal radio profile with the smallest errors. Also, the regeneration system together with the strobe-frame-sampler can be used as a hardware method for conducting passive radiosensor technical diagnostics.

Determination of Parameters of Electronic Devices by the Method of Passive Radio-Sensor Technical Diagnostics

Introduction. Technical diagnostics (TD) as a nascent discipline is rapidly developing in the field of both software and hardware. Modern TD methods, such as vibrometry, thermal control, JTAG testing and optical control, either exhibit high inertia, consume processor time, require suspension of the electronic device, or demand a galvanic contact with the study object, which is often unacceptable. These disadvantages can be eliminated by passive radio-sensor TD. To date, little information has been published on the parameters of electronic devices provided by this method.Aim. Determination of the parameters of electronic devices, the assessment of which can be provided by passive radio-sensor TD.Materials and methods. Signal radio profiles were obtained experimentally using metrological equipment and software-numerical methods for modeling radio wave processes. The parameters of the signal radio profile were calculated by a mathematical method for solving differential equations.Results. The main principles and results of radio-sensor TD, as well as the simplest toolkit, are shown. An equation is obtained for the signal radio profile emitted by the electronic unit of the device, as well as an expression for its free components. An approach for assessing the TD correctness based on the number of free components of the received signal radio profile and the reference is described. The possibility of obtaining information about temperature, voltage drop, speed of emitting nodes, as well as the state of its components and modes of operation of p–njunctions is demonstrated. It is shown that this information is carried by the parameters of the basic equation for the signal radio profile.Conclusion. The derived basic equation allows a non-contact, remote passive radio-sensor TD to be conducted by correlation analysis of the received signal, providing a detailed examination of malfunctions in each electronic unit. The described TD method based on the presented parameters is promising for assessing the technical state of electronic devices.

Design and Characterization of a Flexible Relative Pressure Sensor With Embedded Micro Pressure Channel Fabricated by Flexible Printed Circuit Board Technology

This paper presents a relative pressure sensor fabricated by a standard industrial flexible printed circuit board (FPCB) technology. The passive wireless sensor consists of a variable sensing capacitor and a planar coil inductor. When the external pressure is applied to the sensing capacitor, it changes the air gap and shifts the LC resonance frequency which is detected by an antenna wirelessly. The sensing cavity of the variable capacitor is extended to the opening at the end of an embedded pressure channel in the FPCB strip to enable relative pressure measurement. Measurement results showed that the proposed sensor with such an open sensing cavity had much higher frequency sensitivity (up to 0.4 %/mmHg) compared with the sensor with a sealed cavity (< 0.01 %/mmHg in this work and ≤ 0.08 in literature). With the enhanced sensitivity, the measured pressure resolution could reach 0.2 mmHg. The potential application of the proposed sensor includes gauge pressure measurement with respect to local atmospheric pressure, such as intracranial pressure (ICP) monitoring, without complicated re-calibration procedures. The flat FPCB structure facilitates applications with limited space for sensor installation, such as in the subdural implantation procedures. Furthermore, the proposed technology enables future development of flexible microfluidic devices.

Enhanced Kevlar-based triboelectric nanogenerator with anti-impact and sensing performance towards wireless alarm system

An enhanced Kevlar-based triboelectric nanogenerator (EK-TENG) with excellent safeguarding and stable sensing capability in harsh loading environments was developed by integrating shear thickening materials and graphene on Kevlar fabric. EK-TENG, whose maximum peak power density reached as high as 25.8 mW/m2 under oscillator loadings of 40 N and 10 Hz, could directly power commercial LEDs, capacitors and supercapacitors. In addition, the 30-layer EK-TENG with the greatest fiber friction dissipated drop hammer impact force from 1820 N to 439 N under low-speed impact. EK-TENG with anti-ballistic property enabled to resist 126.6 m/s bullet shooting which was higher than 90.1 m/s of neat Kevlar. Besides, EK-TENG effectively absorbed and dissipated 87.4% of the explosion wave energy under blast loading which exhibited excellent safeguarding properties. Furthermore, EK-TENG could generate voltage signals under various impact loadings which could act as self-powered sensor to monitor external stimuli. Finally, a smart TENG-based wireless passive sensor alarm system with high sensitivity was designed to monitor and warn impact dangers, which opened up a new avenue for the development of next generation intelligent protective clothing.

Comparison of sputtering and atomic layer deposition based ultra-thin alumina protective layers for high temperature surface acoustic wave devices

Surface acoustic wave (SAW) can be used as passive wireless sensors in high temperature environments. For such applications, protective layers are crucial and important for the SAW sensors. In this paper, ultra-thin Al2O3 layers prepared by atomic layer deposition (ALD) and RF magnetron sputtering were used to protect SAW devices with platinum (Pt) electrodes and their temperature stability was studied systematically. The devices were thermally treated up to 1150 °C in air, the real-time resistance of Pt resistive tracks with a sputtering Al2O3 protective layer showed much better and improved thermal stability than those without or with an ALD Al2O3 protective layer. Microstructure characterizations showed that the superior temperature stability is attributed to its mixture of amorphous and nano-crystalline nature of the Al2O3 layer deposited by sputtering and full recrystallization at high temperatures. SAW devices with a sputtering Al2O3 protective layer after 1150 °C treatment maintained almost unchanged properties, while those with an ALD Al2O3 protective layer failed to work. Investigation also indicated there exists an optimal thickness for the sputtering Al2O3 layer to achieve best performance and thermal-stability for the SAW devices. Besides, the deposition rate of Al2O3 layer by sputtering is 10 times faster than that by ALD. All the results demonstrate that the sputtering Al2O3 protective layer is more suitable for high temperature SAW device applications owing to its lower cost, higher deposition rate and temperature stability.

Investigation of Surface Acoustic Wave Propagation Characteristics in New Multilayer Structure: SiO2/IDT/LiNbO3/Diamond/Si.

Surface acoustic wave (SAW) devices are widely used in many fields such as mobile communication, phased array radar, and wireless passive sensor systems. With the upgrade of mobile networks, the requirements for the performance of SAW devices have also increased, and high-frequency wideband SAW devices have become an important research topic in communication systems and other application fields. In this paper, a theoretical study for the realization of a layered SAW filter based on a new SiO2/IDT/128°YX-LiNbO3/diamond/silicon layered structure using the modeling software COMSOL Multiphysics is presented. The effects of lithium niobate (LiNbO3), an interdigital transducer (IDT), and SiO2 thin films on the evolution of the phase velocity, electromechanical coupling coefficient (k2), and temperature coefficient of frequency were studied by employing a finite element method simulation. Furthermore, a longitudinal coupling resonator filter was designed. To investigate the SAW characteristics of the filter, a transient analysis was conducted to calculate the electrical potential and particle displacement under the resonance condition and to analyze the frequency response. The study concluded that this new multilayer structure can be applied to design and manufacture a variety of high-frequency and wideband SAW filters with a temperature compensation function, for operation above the GHz range.

A review on advanced wireless passive temperature sensors

Now-a-days inductor-capacitor (LC) resonator based sensors are widely used in the field of measurement for the measurement of different parameters like pressure, humidity, strain, temperature, pH etc. The basic principle of the sensor is inductive coupling between two loosely coupled inductors in sensing side and reading side. It has the facility of the passive, non-contact and wireless sensing which makes it very advantageous in various field where direct contact with the measurand body is difficult like furnaces, automobile engines, rotating objects, human body etc. In the case of temperature measurement, the LC sensor really plays a crucial role as it helps to measure temperature in inaccessible areas like any harsh and sealed temperature system. A lot of research works are carried out by different researchers for many practical applications. In this paper, a review has been done for a number of recent works on the temperature measurement techniques using LC sensors, which explores the key technologies, different design considerations and methods for assisting the development of LC sensors and configurations and modifications adopted for the respective researches for different future applications.

An LC Wireless Passive Pressure Sensor Based on Single-Crystal MgO MEMS Processing Technique for High Temperature Applications.

An LC wireless passive pressure sensor based on a single-crystalline magnesium oxide (MgO) MEMS processing technique is proposed and experimentally demonstrated for applications in environmental conditions of 900 °C. Compared to other high-temperature resistant materials, MgO was selected as the sensor substrate material for the first time in the field of wireless passive sensing because of its ultra-high melting point (2800 °C) and excellent mechanical properties at elevated temperatures. The sensor mainly consists of inductance coils and an embedded sealed cavity. The cavity length decreases with the applied pressure, leading to a monotonic variation in the resonant frequency of the sensor, which can be retrieved wirelessly via a readout antenna. The capacitor cavity was fabricated using a MgO MEMS technique. This MEMS processing technique, including the wet chemical etching and direct bonding process, can improve the operating temperature of the sensor. The experimental results indicate that the proposed sensor can stably operate at an ambient environment of 22–900 °C and 0–700 kPa, and the pressure sensitivity of this sensor at room temperature is 14.52 kHz/kPa. In addition, the sensor with a simple fabrication process shows high potential for practical engineering applications in harsh environments.

Microwave gas sensor for detection of ammonia at room-temperature

The innovative application of microwave transduction technology in the field of gas sensors make it possible to develop wireless passive room-temperature gas sensor integrated on wearable device. Herein, the ultra-narrowband microwave filter was designed as microwave transducer device, and the microwave sensing measurements were extended to reflected coefficient. Meanwhile, the SnO2/bionic porous (BP) carbon composites based thick film were deposited on the coupled line spacing blank surface via blade coating method. According to the SnO2 nanoparticles were well distributed on BP carbon with abundant micro pores, the gas adsorption and desorption can be enhanced, and the sensor response signal base on microwave transduction was finally improved. Without the influence of temperature and humility, the proposed SnO2/BP carbon microwave gas sensor exhibited excellent NH3 sensing behavior at room temperature including wide concentration range (10–200 ppm), relatively fast response and recovery rate, superior selectivity, as well as good reversibility and stability. More importantly, the dielectric constant of microwave sensor has been proved strongly correlation with injected ammonia concentration. This work further proves the feasibility and frontier of microwave transduction technology in gas sensor application.

An Innovative LC-C Resonant Pressure Sensor Based on Capacitive Feedthroughs

LC resonant wireless passive pressure sensor has been receiving increased attention nowadays. In this paper, an innovative LC-C resonant wireless passive pressure sensor based on dual capacitors was designed and manufactured to replace the traditional LC device. In addition to the inductor and capacitor structure required by the traditional LC device, this paper innovatively designs the fixed capacitor as the inter-layer interconnection structure. The key structural dimensions of the sensor were determined through the numerical analysis of the planar inductor theory and the electromechanical coupling simulation of the dual capacitors model in the previous stage, and the processing of the sensor was carried out through MEMS technology. The final test results showed that within the pressure range of 5kPa to 100kPa, the sensor’s average sensitivity was greater than 69.0 kHz/kPa, while the maximum linear fitting error was smaller than 4.18%. The temperature drift in atmospheric environment was 2.7kHz/°C, and the sensitivity temperature drift was 0.0062kHz/(kPa·°C).

Asymptotic Normality of and Normal Approximation to Interference Power in Wireless Passive Sensor Networks

A wireless passive sensor network is distinguished from ordinary wireless sensor networks by radio frequency (RF) sources that radiate RF waves and supply energy to sensor nodes. Against theoretical expectations, such a network suffers from a scarcity of energy, which compels to employ a contending-type medium access control (MAC) scheme. Consequently, a collision may take place among the packets sent by some sensor nodes. Also, the interference power brought by the colliding packets may hinder a sink node from identifying any packet. Apparently, the interference power highly influences the performance of a wireless passive sensor network. Thus, it is essential to appropriately describe the interference power to evaluate the performance. In this paper, we characterize the interference power, occurring in a wireless passive sensor network, as a sum of random variables governed by log-normal distributions, which are mutually independent but are not necessarily identical. Then, we prove the asymptotic normality of the interference power and, in pursuit of tractability rather than accuracy, we propose a normal approximation to the interference power brought by a finite number of sensor nodes. To investigate the accuracy of the proposed normal approximation, we take the Kolmogorov-Smirnov distance and present an exact expression of the Berry-Esséen bound associated with the interference power. Also, to explore the acceptability of the normal approximation, we employ three well-known statistical tests for normality. Comparative studies of Berry-Esséen bounds reveal that the normal approximation to the interference power is moderately accurate. Furthermore, hypothesis testing for normality shows that the normal approximation is acceptable even in the case that the interference power is incurred by a relatively small number of packets (or, equivalently, sensor nodes) in a wireless passive sensor network.

Flexible Wireless Passive LC Pressure Sensor with Design Methodology and Cost-Effective Preparation.

Continuous monitoring of physical motion, which can be successfully achieved via a wireless flexible wearable electronic device, is essential for people to ensure the appropriate level of exercise. Currently, most of the flexible LC pressure sensors have low sensitivity because of the high Young’s modulus of the dielectric properties (such as PDMS) and the inflexible polymer films (as the substrate of the sensors), which don’t have excellent stretchability to conform to arbitrarily curved and moving surfaces such as joints. In the LC sensing system, the metal rings, as the traditional readout device, are difficult to meet the needs of the portable readout device for the integrated and planar readout antenna. In order to improve the pressure sensitivity of the sensor, the Ecoflex microcolumn used as the dielectric of the capacitive pressure sensor was prepared by using a metal mold copying method. The Ecoflex elastomer substrates enhanced the levels of conformability, which offered improved capabilities to establish intimate contact with the curved and moving surfaces of the skin. The pressure was applied to the sensor by weights, and the resonance frequency curves of the sensor under different pressures were obtained by the readout device connected to the vector network analyzer. The experimental results show that resonant frequency decreases linearly with the increase of applied pressure in a range of 0–23,760 Pa with a high sensitivity of −2.2 MHz/KPa. We designed a coplanar waveguide-fed monopole antenna used to read the information of the LC sensor, which has the potential to be integrated with RF signal processing circuits as a portable readout device and a higher vertical readout distance (up to 4 cm) than the copper ring. The flexible LC pressure sensor can be attached to the skin conformally and is sensitive to limb bending and facial muscle movements. Therefore, it has the potential to be integrated as a body sensor network that can be used to monitor physical motion.

Voltage standing wave ratio reading circuit design for inductance capacitance wireless passive ammonia sensors.

It is not easy to conduct wired tests on sensors in harsh environments, and network analyzers are large, heavy, and inconvenient to carry. At the same time, the price of network analyzers is usually very high, which greatly limits their application. In this study, a voltage standing wave ratio reading circuit is designed to test inductively coupled (LC) wireless passive sensors. By introducing the theory of the standing wave ratio, the design concept and function of each module are analyzed from each specific module. The resonant frequency reading circuit of the sensor is designed and fabricated, and its sweep frequency range covers the frequency range of the commonly used LC wireless sensor, which widens the bandwidth measurement range. The main control chip adopts STM32 series, which makes the circuit and sensor module simple in structure and low in cost. This circuit can accurately obtain the resonant frequency of the sensor through the standing wave ratio and can measure the dynamic change in the sensor standing wave ratio. The output frequency range and output precision of the linear sweep source of the signal reading circuit were tested, and the dynamic testing ability of the circuit to the changing frequency was verified and improved the measurement accuracy.

Research on Monitoring System of Cable Joints of Ring Network Cabinet Based on Wireless Temperature Sensor

In this paper, a state monitoring system for the cable joints of the ring main unit is constructed based on the passive wireless temperature sensor. Considering the sensor packaging structure and housing material, a temperature sensor that can meet the monitoring requirements of the T-shaped insulating sheath of the cable joint is designed. Based on the thermal circuit method, the real temperature value of the internal cable joint is calculated by using the outer surface temperature of the T-shaped insulating sheath to provide more accurate data for monitoring and early warning. The background monitoring software of the monitoring system is designed to realize the temperature of the T-shaped cable joint in the ring network cabinet. Online monitoring and abnormal early warning facilitate the operation and maintenance personnel to take timely measures, which can effectively improve the operation and maintenance efficiency of the ring cabinet of the distribution network and ensure the reliability of power supply.

Optimization and design of bending‐insensitive paper‐based LC wireless passive sensors

AbstractHow to monitor the freshness of packaged food, the safety of sealed medicine, or the other substances in sealed space wirelessly and environment‐friendly has become an urgent problem in recent years. After summarizing the theory of the LC sensor, a design of a paper‐based resonator (30 mm × 30 mm × 0.15 mm) consisting of a finger capacitor is proposed in this paper. The sensor is embedded inside the package by adhering it to the package's inner wall. Its response is remotely detected through a readout coil. This paper establishes a circuit simulation model and an electromagnetic simulation model to verify the feasibility of the design. Compared with the real object and the theoretical simulation model, the difference between the results only within 1 MHz, which verifies the correctness of the theory. Additionally, the measured results indicate that the resonant frequency of the resonator shifted from 102.441 MHz to 88.195 MHz, after dropping water on the sensor. Besides, the simple fabrication technology and inexpensive sensor material ensure a low cost, thus making this technology economically viable.

Passive wireless respiratory sensor

Passive wireless respiratory sensor

Ultra-sensitive passive wireless sensor exploiting high-order exceptional point for weakly coupling detection

Since the quantum concept of parity-time (PT) symmetry has been introduced into the conventional inductor–capacitor resonance, strategies based on exceptional points (EP) based strategies redefine our understanding of sensitivity limitation. This considerable enhancement of sensitivity originated in exploration of the non-Hermitian physics in photonics, acoustics and electronics, which exhibits a substantial application to the miniaturization of implanted electronic sensors in medicine field. By continuously accessing the EP, the spectral response of reader ∆ω follows a dependency of Δω ∼ κ 2/3 to a weakly coupling rate (|κ| ≈ 0), which may approach the theoretical limit of sensitivity in a second-order EP system. In this paper, we experimentally demonstrate a high-order (higher than second-order) PT symmetric system for weak coupling detection, in which a third-order EP can be employed to fulfill the sensitivity of Δω ∼ κ 1/2. Particularly, we introduce the incoming wave as an effective gain to balance the loss and obtain a pair of purely real eigenfrequencies. There are absence of imaginary parts despite corresponding real parts shifts dramatically by using a neutral resonator, without a broadening of the reflection spectrum so that maintaining a high resolution on the sensitivity. This work may reveal the physical mechanics of a small perturbation at a high-order EP and promote applications in implanted medicine devices.

Novel Multilayer SAW Temperature Sensor for Ultra-High Temperature Environments

Performing high-temperature measurements on the rotating parts of aero-engine systems requires wireless passive sensors. Surface acoustic wave (SAW) sensors can measure high temperatures wirelessly, making them ideal for extreme situations where wired sensors are not applicable. This study reports a new SAW temperature sensor based on a langasite (LGS) substrate that can perform measurements in environments with temperatures as high as 1300 °C. The Pt electrode and LGS substrate were protected by an AlN passivation layer deposited via a pulsed laser, thereby improving the crystallization quality of the Pt film, with the function and stability of the SAW device guaranteed at 1100 °C. The linear relationship between the resonant frequency and temperature is verified by various high-temperature radio-frequency (RF) tests. Changes in sample microstructure before and after high-temperature exposure are analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The analysis confirms that the proposed AlN/Pt/Cr thin-film electrode has great application potential in high-temperature SAW sensors.