Wireless Surface Acoustic Wave Sensors Research Articles

Angle-dependent ion-beam etching of RuAl thin films for structuring GHz-frequency electronics

The ruthenium aluminide (RuAl) alloy is a promising electrode material for wireless surface acoustic wave sensors working under harsh conditions at high temperatures. However, during the structuring of RuAl thin films using ion-beam etching, etched material can redeposit at the edges of the electrodes and form objects, so-called fences, on top of the structured features. These decrease the high-temperature stability and lead to an undesired alteration of the sensor performance. In this work, the angle-dependent ion-beam etching of RuAl thin films was investigated to inhibit the formation of such fence structures. The etch rate was determined as a function of the etching angle between ion-beam and sample surface in a range between 90° and 40°. Furthermore, finger structures with pitches below 500 nm, which are required for devices working in the intended GHz regime, were patterned to study the influence of the etching angle on the profile of the RuAl electrode fingers using transmission electron microscopy and energy-dispersive x-ray spectroscopy. The results show that an etching angle of 50° results in the highest etch rate. For etching angles of 50° and below, the width of the fences is reduced below 10 nm, so they break off during standard resist removal procedures. Such low etching angles lead to shadowed areas on the side of structured features in which unetched material remains. However, this material can be removed by using a two-step etching process combining a 50° step with a 90° step. This process is capable of structuring fence-free trapezoidal-shaped electrode finger profiles. Therefore, the developed process is well suited for the fabrication of high-temperature GHz-frequency RuAl electrodes.

Embedding a surface acoustic wave sensor and venting into a metal additively manufactured injection mould tool for targeted temperature monitoring

Injection moulding (IM) tools with embedded sensors can significantly improve the process efficiency and quality of the fabricated parts through real-time monitoring and control of key process parameters such as temperature, pressure and injection speed. However, traditional mould tool fabrication technologies do not enable the fabrication of complex internal geometries. Complex internal geometries are necessary for technical applications such as sensor embedding and conformal cooling which yield benefits for process control and improved cycle times. With traditional fabrication techniques, only simple bore-based sensor embedding or external sensor attachment is possible. Externally attached sensors may compromise the functionality of the injection mould tool, with limitations such as the acquired data not reflecting the processes inside the part. The design freedom of additive manufacturing (AM) enables the fabrication of complex internal geometries, making it an excellent candidate for fabricating injection mould tools with such internal geometries. Therefore, embedding sensors in a desired location for targeted monitoring of critical mould tool regions is easier to achieve with AM. This research paper focuses on embedding a wireless surface acoustic wave (SAW) temperature sensor into an injection mould tool that was additively manufactured from stainless steel 316L. The laser powder bed fusion (L-PBF) “stop-and-go” approach was applied to embed the wireless SAW sensor. After embedding, the sensor demonstrated full functionality by recording real-time temperature data, which can further enhance process control. In addition, the concept of novel print-in-place venting design, applying the same L-PBF stop-and-go approach, for vent embedding was successfully implemented, enabling the IM of defectless parts at faster injection rates, whereas cavities designed and tested without venting resulted in parts with burn marks.

Retracted: Construction and Simulation of Online English Reading Model in Wireless Surface Acoustic Wave Sensor Environment Optimized by Particle Swarm Optimization

Retracted: Construction and Simulation of Online English Reading Model in Wireless Surface Acoustic Wave Sensor Environment Optimized by Particle Swarm Optimization

Magnetostrictive strain monitoring in Non-Oriented Si-Fe steels using a SAW resonator sensor

The aim of this study is to introduce a new technique for characterizing the magnetostrictive behavior of non-oriented ferromagnetic steel sheets using miniaturized wireless surface acoustic wave sensors (SAW). Unlike conventional optical and electromechanical techniques, this type of sensor offers advantages such as on-board capability, high-temperature resistance (up to 400 °C), and the ability to be connected remotely. The final objective is to monitor magnetic stresses in electrical machines, aligning with the requirements of Industry 4.0 and predictive maintenance. The focus of the present study is the measurement of magnetostriction in ferromagnetic steel sheets, employing a wireless surface acoustic wave resonator operating within the 433 MHz ISM band, under various mechanical fixation configurations. To ensure the accuracy and reliability of SAW measurements, a commercial strain gauge is employed as a reference sensor. Measurements are conducted at different excitation frequencies to explore the phenomenon comprehensively.

Real-Time Monitoring of Tire Condition with Fast Detection Passive and Wireless TPMS

<div class="section abstract"><div class="htmlview paragraph">Accurate tire pressure monitoring system (TPMS) is of great practical importance and the reliability and safety of its power supply module has great concern. The piezoelectric-based surface acoustic wave (SAW) sensor is considered to have great potential in this field because of its passive, wireless and small size advantages. This paper presents the application of passive and wireless SAW sensors for real-time tire condition monitoring. The pressure sensitive structure is optimized and a three-resonator structure is also designed sensing temperature and pressure. Furthermore, a fast detection system is developed to realize high-speed signal acquisition. At last, experiments are executed and the SAW temperature and pressure sensor property is measured. The results show that the designed SAW sensor can realize real-time monitoring of tire condition; the temperature measurement range can reach -40~120°C with an accuracy of ±1°C; the pressure measurement range can reach 0~2MPa with an accuracy of 0.2MPa. This paper indicates the wireless and passive SAW temperature and pressure sensor system has the potential for application in real-time monitoring of tire condition.</div></div>

A calculation method of the passive wireless surface acoustic wave sensor response phase

In this research, we propose a method to calculate the phase delay angle of the reflected wave compared to the wave emitted from the interdigital transducer (IDT) of a passive wireless surface acoustic wave (SAW) sensor by combining simulation of the finite element method (FEM) and MATLAB. Based on the result, we consider the influence of the reflector position on the phase delay of the SAW sensor consisting of an IDT and three equally spaced reflectors. The distances between the IDT and the first reflector are 870 micrometers, 939.6 micrometers, and 1009.2 micrometers, and the distances between the reflector positions are 452.4 micrometers, 522 micrometers, and 591.6 micrometers. The outputs of the FEM simulation, including delay time, amplitude loss, and the length of the reflected wave are put into the model in MATLAB to determine the phase delay of the response waves. The obtained phase delay results show that as the distance between the IDT and the reflectors increases, the phase delay angle increases to 4.49 degrees, 5.39 degrees, and 5.78 degrees, respectively.

Wireless surface acoustic wave humidity sensor with chitosan/porous cyclodextrin–TiO2 composites for monitoring air and human respiration

Wireless surface acoustic wave (SAW) technology can be used for real-time and contactless humidity measurements, as well as for monitoring human respiration and environmental humidity. In this study, we developed a wireless humidity sensor based on a 433 MHz SAW resonator covered with chitosan (CS)/heat-treated cyclodextrin(α-, β-, γ-CD)–TiO2 sensitive films. The mesoporous distribution and hydrophilicity of the CD–TiO2 composite, which affect the sensitivity of the CS/CD–TiO2/SAW sensor response to humidity, can be controlled through the CD type and TiO2 content of the composite. The frequency shift of the optimized CS/β-CD–TiO2/SAW sensor varied linearly with the relative humidity (RH) in the RH ranges of 0%76% and 76%90% with the corresponding sensitivities of − 2.96 and − 99.71 kHz%−1, respectively. The response and recovery times at 70% RH were 13.3 and 28.8 s, respectively, with an insignificant hysteresis of 0.61%. The excellent humidity response was due to the hydrophobicity of the inner cavity in the β-CD template molecule and the hydrogen bond adsorption between the surface of the CS/β-CD–TiO2 and H2O molecules. The response rates of the wireless SAW sensor system to normal air humidity and human exhaled/inhaled humidity were 3.13% and 30% RH s−1, respectively, and the wireless transmission distance was 30 m. The wireless CS/β-CD–TiO2/SAW humidity sensor has considerable application potential in forest fire early warning and firefighter tracking systems that require the remote monitoring of air humidity and human respiration.

Construction and Simulation of Online English Reading Model in Wireless Surface Acoustic Wave Sensor Environment Optimized by Particle Swarm Optimization

English reading is an important way to consolidate and expand English language knowledge, and it is also an important way to obtain information and understand British and American culture. Therefore, reading teaching has always been an important part of English education and teaching at all levels and types of schools, and college English teaching is no exception. College English teachers have been carrying out teaching reflections in their reading teaching practice and constantly exploring teaching modes and teaching directions that improve students’ reading engagement and reading comprehension ability. However, the current daily teaching of English reading still generally maintains the traditional teaching mode. The entire reading learning process is monotonous, boring, and stylized, and the ability to acquire and process information cannot be combined with language knowledge and language skills. This kind of teaching mode severely inhibited the college students’ involvement in English learning model. Based on the electromagnetic-polarization response expression in a uniformly polarized half-space, this paper transforms the problem of polarization parameter extraction into a minimum optimization problem and constructs a fitness function. A set of polarization parameters is selected to calculate the electromagnetic-polarization response under trapezoidal waves in a uniform half-space, and the basic particle swarm algorithm is used to extract single and multiple parameters, respectively. In this paper, by adding a window to the test data in the time domain, the multiplicative and additive interference in the test signal is suppressed, and the signal-to-noise ratio of the test result is improved. We use the platform built in this article to wirelessly test the temperature characteristics of the surface acoustic wave sensor. The research results identified eight cognitive attributes of English reading and successfully generated diagnostic information at the group and individual levels and finally formed graphics and textual diagnostic feedback. There is a certain correlation between students’ vocabulary mastery and English reading performance, which shows that the vocabulary teaching method can help students better understand the reading materials and improve their reading performance. Combining two student interviews and learning logs, it can be seen that students’ understanding and frequency of use of vocabulary knowledge have increased significantly after the action research. It is generally recognized that vocabulary has a positive effect on improving reading level and can be based on the recognition and understanding of vocabulary. The mastery of vocabulary can promote the improvement of college students’ English reading level to a certain extent. Learners should strengthen vocabulary learning and face up to the importance of vocabulary knowledge in English reading.

Wireless passive surface acoustic wave (SAW) technology in gas sensing

PurposeThis paper aims to give an overview about the state of wireless passive surface acoustic wave (SAW) gas sensor used in the detection of chemical vapor. It also discusses a variety of different architectures including delay line and array sensor for gas detection, and it is considered that this technology has a good application prospect.Design/methodology/approachThe authors state the most of the wireless passive SAW methods used in gas sensing, such as CO2, CO, CH4, C2H4, NH3, NO2, et al., the sensor principles, design procedures and technological issues are discussed in detail; their advantages and disadvantages are also summarized. In conclusion, it gives a prospect of wireless passive SAW sensor applications and proposes the future research field might lie in the studying of many kinds of harmful gases.FindingsIn this paper, the authors will try to cover most of the important methods used in gas sensing and their recent developments. Although wireless passive SAW sensors have been used successfully in harsh environments for the monitoring of temperature or pressure, the using in chemical gases are seldom reported. This review paper gives a survey of the present state of wireless passive SAW sensor in gas detection and suggests new and exciting perspectives of wireless passive SAW gas sensor technology.Research limitations/implicationsThe authors will review most of the methods used in wireless passive SAW sensor and discuss the current research status and development trend; the potential application in future is also forecasted.Originality/valueThe authors will review most of the methods used in wireless passive SAW sensor and discuss the current research status and development trend; the potential application in future is also forecasted.

GHz AlN-based multiple mode SAW temperature sensor fabricated on PEN substrate

Polymeric based surface acoustic wave (SAW) devices represent one of the most interesting platform for the development of wireless passive sensors for IoT and smart packaging applications. An important feature to be addressed in order to develop a compact and conformable wireless SAW sensor is the increase of the working frequency which allows an easy antenna integration and miniaturization.In this work, we present a disposable polymeric SAW temperature sensor device working in the GHz range, based on aluminum nitride (AlN) and built on a 125 μm thick film of polyethylene naphthalate. The flexible device has been compared to the same SAW device fabricated onto silicon substrates. The polymeric based SAW device shows three operating wave modes corresponding to the Rayleigh, Love, and Lamb, highlighting that the Lamb mode exhibits a resonance frequency as high as 1.325 GHz, corresponding to a phase wave velocity of 10,600 m/s, an electromechanical coupling of 2.91 % and Q factor of 109. Temperature coefficient of frequency (TCF) values of 149, 109, 53 ppm/°C have been calculated for the Rayleigh, Love and Lamb waves, respectively.The different behavior of the three SAW modes let us envision the development of a multiple sensing platforms based on different modes in the same device (e.g. temperature, microbiological contamination, light exposure).

A passive wireless surface acoustic wave sensor for pillar load measurement

This paper presents a passive wireless pillar load measurement method based on surface acoustic wave (SAW) technology. A strain transfer mechanical structure was designed, and the strain distribution of an elastic substrate was analyzed using elastic thin plate bending theory. In addition, the relationship between the strain and frequency shift of the SAW resonator (SAWR) was analyzed, and a strain sensitivity numerical analysis using different bonding directions was performed. Results corroborated that the differential structure of resonators, one of which is placed at the edge along the direction of a diameter and the other is placed at the center with an angle of 45° to the diameter, is a suitable form of the SAW load sensors. Moreover, the SAWR parameters were optimized to obtain a high-performance resonator. Furthermore, The SAWRs and strain transfer mechanical structures were manufactured, the pillar load measurement system was set, and the proposed SAW load measurement method was evaluated. Experimental results affirmed that the load sensitivity is 8.64 kHz/kN. The SAW pillar load method is feasible for practical application.

Development of a Wireless Surface Acoustic Wave Methane Sensor Using a Metal-Organic Framework As a Sensing Layer for Natural Gas Pipelines

Methane emission from the processing and transportation of fossil fuels can create serious environmental and safety issues as well as a financial burden. The need to monitor the energy infrastructure creates an opportunity for developing low-cost and robust sensors with wireless options. Wireless surface acoustic wave (SAW) devices, which are highly sensitive, cost-efficient, and passive, are a potential candidate for these applications. Nanoporous metal-organic frameworks (MOFs), which can selectively adsorb large amounts of gases in engineered pores at ambient conditions, are potential sensing layers. Here, we present on the development of a wireless and passive SAW sensor using the MOF zeolitic imidazolate framework-8 (ZIF-8) as the sensing layer for methane detection at ambient conditions. The SAW delay lines (nominal operating frequency = 436 MHz) were custom fabricated on Y-Z LiNbO3 piezoelectric substrates and coated with a 500 nm thick ZIF-8 layer using a dip coating method. The devices were excited by 428 MHz RF pulses to test for various concentrations of CO2 and CH4 in N2 background at a constant gas flow rate. Wireless measurements were performed via dipole antennas of nominal resonant frequency 433 MHz. When the sensor was exposed to the gases, surface acoustic wave phase shifted in a negative direction relative to the N2 baseline. This shift was attributed to the decrease in SAW velocity due to the increased mass of the MOF film upon gas adsorption. The CO2 and CH4 sensitivities extracted as the slopes of the respective calibration curves were 1.26 deg/vol-% and 0.03 deg/vol-%, respectively. It is important to note that currently tested minimum concentrations of CO2 and CH4 were 1% and 20%, respectively. Also, the wireless measurements were highly affected by the housing and metal reflectors around it. The demonstration on wireless methane sensing is of great importance for remote monitoring of methane emission sites and transmission pipelines. Our current investigations are focused in advancing the detection limit for leak detection and addressing the electromagnetic interferences in wireless measurement caused by the housing.

Analysis and test of a wireless impedance‐loaded SAW sensor

Instead of a conventional wireless transceiver system that requires batteries and complex circuits, the surface acoustic wave (SAW) sensor enables wireless passive measurement. A sensor consisting of an SAW device and external impedance sensing element is analysed. Since the reflection coefficient of the reflective grating on the SAW device depends on the load impedance, the echo characteristics are influenced by the change in the impedance of external sensing element. A resistance sensor or a capacitive sensor is selected as the external sensing element. The two different types of sensors are simulated using coupling-of-mode (COM) modelling, and the relationships between amplitude and phase with load impedance are analysed. On the basis of COM theory, a wireless impedance-loaded SAW sensor is fabricated by the lift-off process and tested by a network analyser to verify the simulation results. It is observed that the test results agree well with the simulation results. The phase change is more sensitive than the amplitude based on the results obtained. The sensitivity is 0.274°/Ω for the sensor with resistance and the sensitivity of the sensor with capacitance is 1.096°/pF. These results can guide the design of the high sensitivity impedance-loaded SAW sensors in the future.

Fast and Accurate Finite Transducer Analysis Method for Wireless Passive Impedance-Loaded SAW Sensors.

An accurate and fast simulation tool plays an important role in the design of wireless passive impedance-loaded surface acoustic wave (SAW) sensors which have received much attention recently. This paper presents a finite transducer analysis method for wireless passive impedance-loaded SAW sensors. The finite transducer analysis method uses a numerically combined finite element method-boundary element method (FEM/BEM) model to analyze non-periodic transducers. In non-periodic transducers, FEM/BEM was the most accurate analysis method until now, however this method consumes central processing unit (CPU) time. This paper presents a faster algorithm to calculate the bulk wave part of the equation coefficient which usually requires a long time. A complete non-periodic FEM/BEM model of the impedance sensors was constructed. Modifications were made to the final equations in the FEM/BEM model to adjust for the impedance variation of the sensors. Compared with the conventional method, the proposed method reduces the computation time efficiently while maintaining the same high degree of accuracy. Simulations and their comparisons with experimental results for test devices are shown to prove the effectiveness of the analysis method.

A context-aware frequency estimation method for wireless passive resonant SAW sensors

PurposeThis paper aims to present an context evaluation and frequency measurement method for surface acoustic wave (SAW) resonant sensor.Design/methodology/approachThis method is based on a signal subspace construction, which, along with assembling optional value set, provides the results.FindingsThe method can assess the application context and improve the resolution and accuracy of the passive wireless SAW resonator sensor system.Originality/valuePassive wireless SAW resonators have been used as sensor elements for different physical parameters such as temperature, pressure and force in a number of industrial and medical applications. Various wireless channel environments introduce different application contexts.

Noise Radar Approach for Interrogating SAW Sensors Using Software Defined Radio

Passive, wireless surface acoustic wave (SAW) sensor systems can be approached from a radar perspective, where the SAW device is thought of as a cooperative target. This paper investigates the use of a commercial-off-the-shelf software defined radio to interrogate wireless SAW sensors with a randomly generated interrogation pulse. The USRP B200mini is utilized as the transceiver platform with custom field-programmable gate array (FPGA) modifications to generate the random interrogation waveform and provide synchronization and buffering to the received signal. Each transmit sample bit in the FPGA is fed by an independent linear-feedback shift register, which generates pseudo-random I and Q samples for the interrogation pulse. An RF daughterboard has also been developed and integrated with the B200mini to increase the transmit power, provide filtering of the RF signals, and switch a signal antenna between the transmit and receive channels. Radio control and matched filter correlator post-processing are accomplished using Python. Design and implementation details for the FPGA modifications, RF daughterboard, and post-processing are discussed. The system is demonstrated by wirelessly interrogating SAW temperature sensors at 915 MHz.

Matrix Method for Multiple Wireless Orthogonal Frequency-Coded SAW Sensor Tags Identification

Reflected signals from multiple wireless surface acoustic wave (SAW) sensors are generally asynchronous, which causes difficulty in simultaneous identification of multiple SAW sensor tags. This paper proposes a matrix method for multiple SAW sensor tags identification based on orthogonal frequency code (OFC). The characteristics of ideal overlapped signals from multiple OFC SAW tags are analyzed. According to the analysis, the amplitudes and the phases of the overlapped signals with the same center frequency from the identical reflector positions of different tags can be measured. A matrix equation for the relationship between the measurable values and the amplitudes delay of signals from each tag is presented. Tag identification is accomplished by solving this matrix equation. According to the characteristics of this matrix equation, the maximum number of simultaneous identifiable tags is roughly equal to the square of the number of selectable matching frequencies of reflectors. A set of simultaneous identifiable tags are selected. All tags randomly chosen from this tag set can be identified correctly by the simulation test. This result verifies that the matrix method for multiple OFC SAW sensor tags identification is feasible in theory.

Wireless surface acoustic wave sensors for displacement and crack monitoring in concrete structures

In this work, we demonstrate that wireless surface acoustic wave devices can be used to monitor millimetre displacements in crack opening during the cyclic and static loading of reinforced concrete structures. Sensors were packaged to extend their gauge length and to protect them against brittle fracture, before being surface-mounted onto the tensioned surface of a concrete beam. The accuracy of measurements was verified using computational methods and optical-fibre strain sensors. After packaging, the displacement and temperature resolutions of the surface acoustic wave sensors were 10 and 2 °C respectively. With some further work, these devices could be retrofitted to existing concrete structures to facilitate wireless structural health monitoring.

Concrete temperature monitoring using passive wireless surface acoustic wave sensor system

In this paper, a novel nondestructive method for detecting temperature variations of concrete using a passive wireless surface acoustic wave (SAW) sensor system is described. Performance of the SAW orthogonal frequency coded (OFC) temperature sensors was evaluated in air, liquid, and concrete. To verify the response of the SAW sensor, temperature was also measured using commercially available thermocouples and compared with the extracted temperature in all environmental conditions. Analysis of the measured data showed that the SAW temperature sensor system was successful in detecting temperature over a wide range in all tested conditions with a high degree of accuracy and short interrogation time. When the sensors were embedded within a 2-in. thick concrete cover, the maximum read distance was approximately 4m.

Water Pressure Sensingbased on Wireless Passive SAW Technology

The conventional water pressure measurement method requiresbatteries as power sources for pressure sensors. This methodis unreliable because the risk of damaging batteries is high especially in harsh environment. This paper provides a novel method that wireless passive surface acoustic wave (SAW) pressure sensoris introduced for water pressure measurement. Wireless passive SAW sensors do not need direct power supply. Therefore, batteries are not requiredby using this new technology. The main types of wireless passive SAW sensors are reviewed. The performance of wireless passive SAW sensor is tested. The water pressure sensing framework is proposed.