Passive Wireless Sensor Research Articles

Passive Wireless Hermetic Environment Monitoring System for Spray Painting Workshop.

Passive wireless sensors have the advantages of operating without a power supply and remote sensing capability. Hence, they are very suitable for some harsh environments, such as hermetic environments, rotating parts, or very high temperature environments. The spray painting workshop is such a harsh environment, containing a large amount of flammable paint mist and organic gas. Aiming at this special environment of spray painting workshop, a passive wireless hermetic environment monitoring system was designed, fabricated, and demonstrated. The proposed system is composed of a transponder and a reader, and the circuit design of each part is given in detail in this paper. The power and the data transmission between the transponder and the reader are realized by the inductive coupling mechanism. Utilizing the back scatter modulation and channel multiplexing, the frequency signals generated by three different environmental sensors—together with their interfaces in the transponder—are wirelessly read out by the reader. Because of the harsh environment of the spray painting room, the package of the monitoring system is quite important. Three different kinds of filter films for the system package were compared. The experimental results show that the composite filter film aluminum anodic oxide/polytetrafluoroethylene (AAO/PTFE) has the best performance. After fabrication, the measured temperature, humidity, and pressure sensitivities were measured and found to be 180 Hz/°C in the range of 0~60 °C, 100 Hz/%RH in the range of 15~95 %RH, and 42 Hz/hPa in the range of 600~1100 hPa, respectively. Additionally, the remote sensing distance of the monitoring system reaches 4 cm. Finally, the passive wireless hermetic environment monitoring system was installed on the glass wall of the spray painting workshop and was successfully demonstrated.

A Passive Wireless Adaptive Repeater for Enhancing the Readout of LC Passive Wireless Sensors

In this letter, a passive wireless adaptive repeater is proposed to enhance the readout of LC sensors. The frequency spectrum of the repeater can cover that of the sensor so as to realize full-spectrum-enhancing by strong magnetic coupling. The resonant frequency of the passive wireless adaptive repeater is changed via cyclic-scanning by a controlled voltage which is induced by itself through coupling from the readout coil. An LC humidity sensor, as an example, is then monitored with and without the adaptive repeater. We have demonstrated that the readout distance with the passive wireless adaptive repeater can achieve 3.18 times as long as that without a repeater, while keeping their signal intensity and sensitivity the same.

Passive Wireless Sensor for Measuring AC Electric Field in the Vicinity of High-Voltage Apparatus

A passive wireless sensor for the measurement of ac electric fields emanating from high-voltage (HV) apparatus using radio-frequency (RF) resonant cavities is presented. The sensor is composed of a coaxial transmission line resonator, where the resonant frequency is perturbed by capacitively coupled varactors. HV apparatus induces a bias voltage on the varactors through capacitively coupled electric fields. A printed circuit board on the top of the cavity provides coupling between the cavity and varactors and also between the varactors and the external electric field. The sensor is designed with a resonant frequency in the range of 2.4–2.5 GHz in the industrial, scientific, and medical band. Using capacitive coupling to an HV transmission line with 60 Hz at 1.7 kV, a resonant frequency shift of 7.2 (kHz)/12.5 (V/m) was obtained. The resonance frequency is determined remotely by sending pulses of RF signal to the sensor and recording the ring back of the resonator. RF pulses, with a frequency of 2455 MHz, are used to remotely interrogate the sensor at a repetition rate of 2.5 MHz and a pulsewidth of 100 ns. Downconverting the received signal, a ring back signal is recorded whose analysis determines the resonant frequency.

Parallel capacitive temperature micro‐sensor for passive wireless sensing applications

The parallel capacitive temperature micro-sensor is designed and fabricated based on the metal multi-user MEMS processes. The interdigitated capacitors parallelly connected with the plane capacitor are used as the temperature sensing structures. Thermal expansion of the top layer cause the out-of-plane deformation, and introduce horizontal and vertical displacements of the structure, which leads to the capacitance variation. Top metal layer is the cascaded bent beam with interdigitated end, which is used as the interdigitated capacitors. Polysilicon layer paired with metal layer to form the plane capacitor. Experimental results show that the sensor provides an average sensitivity of 32.45 fF/°C in the 0–100°C range. It is also demonstrated that the temperature sensor can be integrated with an inductor to form an LC passive wireless sensor, which provides a sensitivity of 46.61 kHz/°C in the whole temperature range.

무선 수동형 센서 망을 위한 경합형 MAC 방식의 최적 설계

별도의 RF 소스가 센서 노드에게 에너지를 공급하는 무선 수동형 센서 망은 배터리 없이 영원히 동작할 수 있는 망이다. 그러나 영원한 수명에 대한 기대와 달리 무선 수동형 센서 망은 아직 에너지의 희소성, 에너지 수신과 데이타 전송의 동시불가성, 자원 활용의 비효율성 등 많은 문제를 안고 있다. 본 논문에서는 패킷 상실에는 관대하지만 패킷의 적시 전달을 요구하는 서비스를 제공하는 무선 수동형 센서 망을 다룬다. 이러한 망에서 여러 센서 노드들이 하나의 싱크 노드에게 패킷들을 전달하도록 현실적 제약을 인식하여 framed and slotted ALOHA에 기초한 경합형 MAC 방식을 고려한다. 이어서 지리적으로 흩어져있는 센서 노드들이 전송한 패킷들이 경로 손실을 겪어 결국 capture 현상이 빚어질 때 MAC 방식이 얻을 수 있는 망전체 throughput을 조사한다. 특히 두 센서 노드만이 망에 있을 때 망 전체 throughput의 정확한 공식을 closed form으로 도출한다. 마지막으로 설계 parameter들을 조절하여 최대의 망 전체 throughput을 취하도록 경합형 MAC 방식을 최적화한다.

An <italic>LC</italic> Passive Wireless Multifunctional Sensor Using a Relay Switch

This paper presents an LC passive wireless sensor for monitoring both humidity and pressure by using a relay switch. The LC sensor system consists of an inductor, two capacitors, and a relay switch. The two capacitors are successively connected to the inductor controlled by the relay switch, forming two different LC resonant circuits. The relay switch is actuated by induced voltage, which is coupled from the readout coil. The theoretical model is proposed and analyzed, and operation equations are derived. To demonstrate the proposed scheme, a print circuit board inductor, two capacitive sensors to monitoring humidity and pressure, and a relay switch are constructed. Ambient humidity and pressure are tested by utilizing the sensor system. The capacitance derived from the detected resonant frequencies indicates that the sensitivity of the humidity sensor is 277.1-fF/% RH, and the sensitivity of the pressure sensor is 38.3 fF/kPa.

A batteryless temperature sensor based on high temperature sensitive material

The major challenge in wireless sensor networks is the reduction of energy consumption. Passive wireless sensor network is an attractive solution for measuring physical parameters in harsh environment for large range of applications requiring sensing devices with low cost of fabrication, small size and long term measurement stability. Batteryless temperature sensing techniques are an active research field. The approach developed in our work holds a promising future for temperature sensor applications in order to successfully reduce the energy consumption. The temperature sensor presented in this paper is based on the electromagnetic transduction principle using the integration of the high temperature sensitive material into a passive structure. Variation in temperature makes the dielectric constant of this material changing, and such modification induces variation in the resonant frequencies of high-Q whispering-gallery modes (WGM) in the millimeter-wave frequency range. Following the results achieved, the proposed device shows a linear response to the increasing temperature and these variations can be remotely detected from a radar interrogation.

Passive Wireless Torque Sensor Based on Surface Transverse Wave

This paper presents a passive wireless torque sensor based on a surface transverse wave (STW). An analysis was conducted on the sensitivity mechanism of STW, and a numerical analysis on the torque sensitivity and temperature coefficient using different cut types was performed. Torque sensitivities with different normalized wavelengths were also analyzed. Numerical calculation results showed that the Y+36° cut quartz was selected to prepare the substrate of the STW torque sensors. Resonators with center frequencies of 435.81 and 438.79 MHz were also prepared and constituted a differential structure as the torque sensing element, with the insertion losses of −11.2 and −9.5 dB and Q of approximately 10 283 and 12 915, respectively. Experimental results indicated that the torque sensitivity of this STW torque sensor was 4.14 kHz/Nm, with a nonlinearity of 0.64%.

A Linear and High Sensitive Interfacing Scheme for Wireless Passive LC Sensors

This paper presents a simple and efficient interfacing scheme for passive LC sensors, connected to the measurement unit through a magnetically coupled readout and sensor coils. The proposed scheme always measures at or near the parallel resonant frequency $f_{p}$ of the system. The scheme first converts the capacitance of the sensor into a phase angle ( $\phi $ ) between the excitation voltage ( $V_{\textrm {in}}$ ) and the current $I_{1}$ through the readout coil. The final output is given by tan( $\phi $ ), but easily realized using a phase sensitive detector (PSD). The inputs to the PSD are $V_{\textrm {in}}$ and a signal proportional to the $I_{1}$ . This new approach gives the following advantages: 1) it realizes a simple, hardware optimized measurement system, which draws the minimum current from $V_{\textrm {in}}$ as the measurement is at $f_{p}$ ; 2) the time taken for the measurement is much less, compared with the frequency sweep approach; 3) the output is linear; and 4) the output is insensitive to the variations in the coupling coefficient ( $k$ ), for a wide range of $k$ . In addition, a new, but simple method is employed to calibrate the system from the readout coil side. This enables the output to be less sensitive to the variation in the quality factor, coupling coefficient, and resistance of the coil. A prototype of the proposed readout system has been developed and tested for a range of ±5 pF. The output of the interfacing scheme showed a high sensitivity of 5.5°/pF. The worst case linearity noted was 0.52% and the worst case error observed in the test was less than 0.67%.

Inkjet Printed Single use Humidity Threshold Monitoring Sensor Solution Employing a Mixed Nanoparticle and Salt Region

A continuous monitoring of critical environmental parameters to detect threshold or dosage violations is of strong interest throughout the life cycle of goods. The task is challenging, when there is no continuous supply of electric energy available and lowest cost sensor solutions are required - two common application constraints in wireless passive sensor applications, i.e., sensor enhanced RFID tags. Presented is an inkjet printed humidity threshold violation sensor, providing a permanent and pronounced electric resistance change due to a humidity exposure above a critical threshold. Exploited natural phenomena are the deliquescence of salts as humidity threshold detection mechanism, as well as chemical sintering of silver metal nano particles, in order to realize an irreversible state change. In difference to existing solutions based on spatially separated nanoparticle and salt reservoirs, it is possible to use an intermixed salt and nanoparticle region, in which a partially developed conductive percolation network exists after manufacturing.

High Q Ba(Zn1/3Ta2/3)O3 microwave resonator in a closed cavity for sensor applications

Microwave dielectric resonator having a high Q-factor results in high sensitivity and it can be used as a sensing element in wireless passive sensor systems. In the present work, we demonstrated high Q resonator enclosed in a metallic cavity which is highly sensitive to resonance frequency and quality factor change arising from small test samples kept on the surface of the resonator. The measurements are made at the resonance frequency of TE10δ mode. The Ba(Zn1/3Ta2/3)O3 resonators prepared by solid state reaction method exhibits high Q value of >12,500. The experimental studies have been conducted on different type of rice grains cut to uniform size and shape to explore the response of resonance frequency and Quality factor. The change in effective dielectric constant and loss tangent of resonator with test samples were measured. Our work should provide a general guidance in development of high Q dielectric resonators for sensor applications.

Wireless Passive RFID Crack Width Sensor for Structural Health Monitoring

All mechanical structures are subjected to deformation and cracks, due to fatigue, stress, and/or environmental factors. It is, therefore, of uttermost importance to monitor the mechanical condition of critical structures, in order to prevent catastrophic failures, but also to minimize maintenance costs, i.e., avoid unnecessary inspections. A number of technologies and systems can be used for this purpose: among them, the ones proposing the use of wireless passive crackmeters have a strong impact potential, in terms of simplicity of installation and measurement and low cost. This paper, hence, shows a crack width wireless radio-frequency identification sensor, developed for applications on various materials (such as concrete and metal) and able to detect submillimeter deformations occurring on the object, on which it is placed. A design method based on high-sensitivity phase detection is shown.

A Distance Compensated Approach Used in Wireless Passive Pressure Sensor Readout System for High Temperature Application

This paper proposed a distance compensated measurement system for a wireless passive sensor based on the high temperature cofired ceramics (HTCC) applied to high temperature environment. The sensor model is provided and fabricated. Also, a telemetric measurement system consists of a readout instrumentation and a heat insulation unit is described due to the thickness of heat insulation material between the sensor and readout unit’s inductance coils in high temperature testing environment. Consideration of the leakage inductance and parasitic parameters which depend on the coupling distance is equivalent to the thickness of heat insulation material, and a distance compensated method is presented. The compensation is based on the mathematical feature of the testing results from readout unit which show us information about the relation between the extracted resonant frequencies. This method can be used simply and reliably in the other telemetric mutual inductance coupling readout system as a viable solution to compensate the coupling distance related error when inductive coupling is varied. It has been experimentally tested, and the results are in good agreement with those measured by a reference impedance analysis instrument. Theoretical explanations, experimental results, and discussion are reported.

Erratum: 3D-printed microelectronics for integrated circuitry and passive wireless sensors

Erratum: 3D-printed microelectronics for integrated circuitry and passive wireless sensors

Antenna-resonator integrated wireless passive temperature sensor based on low-temperature co-fired ceramic for harsh environment

This paper proposes a resonator-antenna integrated microstrip antenna temperature sensor based on a low-temperature co-fired ceramic (LTCC), whose permittivity varies monotonously with the temperature. The dimensional design process was first analyzed in detail, and by combining the standard LTCC technology, the sensor was fabricated using 15 layers of a green tape. To interrogate the sensor, a coplanar waveguide (CPW)-fed microstrip antenna, possessing a relatively large bandwidth, was designed and optimized using high frequency structure simulator software, and then fabricated on alumina ceramic through a screen-printing process. The sensor was then tested on a developed high-temperature measurement system. Because the original detected sweep signal was difficult to distinguish, a time-domain (T-D) gating method for filtering a background signal was introduced. The extracted peak frequency was found to decrease linearly with an increase in temperature to within 400°C at a 30-mm reading distance, with a measurement sensitivity of 0.24MHz/°C. Simultaneously, the antenna polarity was found to have a significant influence on the readout signal. Finally, for the introduced T-D gating method, this study analyzes that the sensor can be sensed at a long distance when using a high-gain interrogation antenna. It is expected that the proposed sensor can be used in monitoring the temperature in a harsh environment.

Sensitivity Modeling of an RFID-Based Strain-Sensing Antenna With Dielectric Constant Change

An radiofrequency identification (RFID)-based folded patch antenna has been developed as a novel passive wireless sensor to measure surface strain and crack, for the structural health monitoring of metallic structures. Up to 2.5 m of read range is achieved by a proof-of-concept prototype patch antenna sensor with a strain sensitivity around −760 Hz/ $\mu \varepsilon $ , which is equivalent to a normalized strain sensitivity of −0.74 ppm/ $\mu \varepsilon $ . In this paper, we propose to consider the change of the substrate dielectric constant due to strain when modeling the antenna sensor. An enhanced strain sensitivity model is introduced for more accurately estimating the strain sensing performance of the hereby introduced smart skin antenna sensor. Laboratory experiments are carried out to quantify the dielectric constant change under strain. The measurement results are incorporated into a mechanics–electromagnetics coupled simulation model. Accuracy of the multi-physics coupled simulation is improved by integrating dielectric constant change in the model.

A Phase Readout Method for Wireless Passive Sensor Used in Pressure Measurement System

A phase difference detection method usedfor reading the resonant frequency through mutual coupling is designed to meet the pressure measurement inharsh environments, and a testing device of integratedmodular by developing the hardware circuits is proposed.Description and discussion of the novel theoretical modelin the phase readout system is presented, and a pressuretest platform based on the phase difference detection isalso established, which is to measure the frequency of a LCresonant sensor on the basis of 96% alumina ceramic substrate. The experimental results show that the proposedphase difference readout system presents sweep-frequencydetection in the range of 1–100MHz bandwidth, and a highfrequency resolution of 0.006MHz. Sensitivity of the sensoris approximately 0.225 MHz/bar from 1 bar to 2 bar. Theaccuracy and functionality of the phase readout systemhave emphasized a wider engineering application range, sothat we can make it possible that the wireless passive LCresonant sensor revolves well in practical engineering occasions outside the laboratory environment.

Embedded Flexible Hybrid Electronics for the Internet of Things

The Internet of Things (IoT) “things” are often times described as active or smart devices and objects augmented with sensing, processing, and network capabilities. These smart objects are in the heart of the IoT concept but they alone cannot realize the full potential of IoT. The most ubiquitous objects in the IoT ecosystem, those that reside at the lowest system level and interact with the higher-level smart object, are based on the passive RFID technology. In the form of wireless passive sensors these objects are found in smart packaging, they form the backbone of the structural health monitoring systems, they provide non-invasive and continuous monitoring of physiological parameters, etc. RFID capability is already added to everyday items in the physical form of adhesive “smart” labels, enabling them to become “citizens” of the IoT ecosystem, but this “add-on“ approach increases the implementation cost and oftentimes impacts negatively the host item's form factor and appearance. It also does very little in terms of security and counterfeit prevention. On the other hand, the key economic factor that drives the deployment of the IoT is the cost at the end points. Therefore, the future of the IoT depends on developing an ultra-low-cost technology solution that can mass-produce low cost, RFID-enabled IoT objects on flexible substrates, ready for integration into everyday items. In some cases, such as in intelligent packaging, these objects will be non-obstructive and seamlessly integrated in their hosts. This integration will minimize the cost of implementation and will provide an insurmountable barrier to counterfeiters as they will need access to sophisticated and capital-intensive technologies in order to be able to alter or replicate the product's embedded configuration. Presented are two disruptive processes for packaging of ultrathin flexible hybrid electronic systems with ICs as thin as 15–20 μm and as small as 250 μm per side. The first generation technology is a modification of the conventional pick-and-place technique and has been already demonstrated on a commercial-grade roll-to-roll assembly line with packaging rates exceeding 10,000 cph. The second generation technology uses a laser beam to scan and transfer ultrathin, ultra-small ICs for high-precision assembly onto various flexible and rigid substrates. It provides packaging rates significantly exceeding those of the conventional pick-and-place equipment. Reported are also results from integrating the resulting ultrathin flexible hybrid electronic devices into thin materials such as paper and plastics.

High-Temperature Dielectric Properties of Aluminum Nitride Ceramic for Wireless Passive Sensing Applications.

The accurate characterization of the temperature-dependent permittivity of aluminum nitride (AlN) ceramic is quite critical to the application of wireless passive sensors for harsh environments. Since the change of the temperature-dependent permittivity will vary the ceramic-based capacitance, which can be converted into the change of the resonant frequency, an LC resonator, based on AlN ceramic, is prepared by the thick film technology. The dielectric properties of AlN ceramic are measured by the wireless coupling method, and discussed within the temperature range of 12 °C (room temperature) to 600 °C. The results show that the extracted relative permittivity of ceramic at room temperature is 2.3% higher than the nominal value of 9, and increases from 9.21 to 10.79, and the quality factor Q is decreased from 29.77 at room temperature to 3.61 at 600 °C within the temperature range.

Archimedean Spiral Pairs with no Electrical Connections as a Passive Wireless Implantable Sensor

We have developed, modeled, fabricated, and tested a passive wireless sensor system that exhibits a linear frequency-displacement relationship. The displacement sensor is comprised of two anti-aligned Archimedean coils separated by an insulating dielectric layer. There are no electrical connections between the two coils and there are no onboard electronics. The two coils are inductively and capacitively coupled due to their close proximity. The sensor system is interrogated wirelessly by monitoring the return loss parameter from a vector network analyzer. The resonant frequency of the sensor is dependent on the displacement between the two coils. Due to changes in the inductive and capacitive coupling between the coils at different distances, the resonant frequency is modulated by coil separation. In a specified range, the frequency shift can be linearized with respect to coil separation. Batch fabrication techniques were used to fabricate copper coils for experimental testing with air as the dielectric. Through testing, we validated the performance of sensors as predicted within acceptable errors. Because of its simplicity, this displacement sensor has potential applications for in vivo sensing.