Bulk Acoustic Wave Sensor Research Articles

Alumina intercalation to enhance the performance of BAW magnetic sensors: Micromagnetic and finite element analysis

The bulk acoustic wave (BAW) magnetic sensor, which is based on a thin-film bulk acoustic wave resonator and magnetoelectric coupling, has the technological advantage of passive wireless magnetic detection and can be applied to medical diagnostics and resource exploration to achieve ultra-weak magnetic field detection. However, the enhancement of BAW magnetic sensors' performance is severely limited by the localized magnetization phenomenon and the significant eddy current loss suffered by single-layer magnetic films. In this paper, the effect and internal physical mechanism of inserting different alumina intercalation layers into a magnetic film on the performance of the magnetic film and the BAW sensor were investigated, and the optimal design of the BAW magnetic sensor was achieved. First, single-layer FeGaB films and composite FeGaB/(Al2O3 5 nm/FeGaB)n films (n = 1, 2, 4, 6, and 10) were fabricated to characterize the effect of intercalation on the static and dynamic magnetic properties of the films. When four layers of 5 nm alumina were inserted, the magnetic film was found to have the finest soft magnetic properties. Further micromagnetic simulation and microstructural characterization demonstrated that the alumina intercalation enhances the magnetic film's microstructure, resulting in a complex interlayer interaction. Second, the BAW magnetic sensor's finite element simulation model was developed using COMSOL Multiphysics. The relaxation response mechanism of the magnetic film to an external alternating magnetic field was investigated using micromagnetism, and the energy transfer and coupling between the magnetic film and the piezoelectric layer were further analyzed. The effect of the alumina intercalation on the magnetic sensor's performance, including sensitivity and linearity, was quantified. Eventually, the operating frequency of the BAW magnetic sensor was matched to 2.5 GHz by refining the design conditions of inserting four layers of 5 nm alumina into FeGaB thin films. Within the magnetic field testing range of 50000–60000 A/m, simulation results indicate that the sensitivity can reach 0.0028 Vm/A, and the linearity of the output voltage is better than 3.85%.

A Bulk Acoustic Wave Strain Sensor for Near-Field Passive Wireless Sensing.

Near-field passive wireless sensors can realize non-contact strain measurement, so these sensors have extensive applications in structural health monitoring. However, these sensors suffer from low stability and short wireless sensing distance. This paper presents a bulk acoustic wave (BAW) passive wireless strain sensor, which consists of two coils and a BAW sensor. The force-sensitive element is a quartz wafer with a high quality factor, which is embedded into the sensor housing, so the sensor can convert the strain of the measured surface into the shift of resonant frequency. A double-mass-spring-damper model is developed to analyze the interaction between the quartz and the sensor housing. A lumped parameter model is established to investigate the influence of the contact force on the sensor signal. Experiments show that a prototype BAW passive wireless sensor has a sensitivity of 4 Hz/με when the wireless sensing distance is 10 cm. The resonant frequency of the sensor is almost independent of the coupling coefficient, which indicates that the sensor can reduce the measurement error caused by misalignment or relative movement between coils. Thanks to the high stability and modest sensing distance, this sensor may be compatible with a UAV-based monitoring platform for the strain monitoring of large buildings.

A Passive Wireless Sensing Method Based on Magnetic Resonance Coupling and Bulk Acoustic Wave Device

In this article, we propose a passive wireless strain sensing system with magnetic resonance coupling and bulk acoustic wave (BAW) strain sensor to evaluate the structural safety of megastructures. The BAW sensor provides a high quality factor, and the magnetic resonance coupling enhances the transmitter’s gain at the system’s operational frequency. The experimental and analytical methods are investigated to characterize the effect of different parameters on this system. The results show that the sensing system can detect the resonant frequency of the receiver when the coupling coefficient is less than 0.01. Experimental demonstrations show that a prototype sensing system had a strain measurement range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500\,\mu \varepsilon $ </tex-math></inline-formula> and a resolution of 4 Hz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> when the separation distance between coils was 10 cm. Compared with conventional passive wireless sensing systems, the change of coupling coefficient has little effect on the resonant frequency of the receiver. We envision that this system has the potential to realize noncontact strain measurement, while the measurement device is in an unsteady movement mode. In the future, this sensing system can be integrated into an unmanned aerial vehicle (UAV) to measure the strain in megastructures.

A New Analytical Method to Quantify Ammonia in Freshwater with a Bulk Acoustic Wave Sensor.

A new method to analyse ammonia in freshwater, based on a piezoelectric quartz crystal coated with the metalloporphyrin chloro[5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato] manganese(III) is presented. A 9 MHz quartz crystal coated on both faces with an amount of porphyrin produced a frequency decrease of 21.4 kHz, which allowed ammonia in a 10.00 mL sample to be quantified in concentrations between 5 and 70 µg L−1, with a sensitivity of 0.60 Hz L µg−1, over a period of at least eight months. The proposed method has several advantages over the officially recommended indophenol spectrophotometric method: sample volume was reduced by a factor of 2.5, toxic reagents (phenol and sodium nitroprusside) were eliminated, analysing turbid samples presented no difficulty, and there was not only a significant time saving in solution preparation, but also in sample analysis time, which was reduced from 1 h to 2 min. No statistically significant differences (α = 0.05) were found both in the mean and precision of the results obtained for ammonia in water samples collected from domestic wells, analysed by this new method and by the indophenol spectrophotometric method. Furthermore, the proposed method would allow the individual quantification, with similar sensitivity, of amines and ammonia within a single analytical run.

Potential of bulk acoustic wave (BAW) process analytical technology to monitor acid-induced skim milk coagulation

Acid-induced milk coagulation is a key processing step in the manufacture of dairy products i.e. yoghurt, and could benefit from process analytical technologies for monitoring the kinetics of milk coagulation. This study evaluates a novel, bulk acoustic wave (BAW) sensor technology to monitor acid-induced (glucono-delta-lactone (GDL)) coagulation of skim milk. The effects of GDL concentration (2.5, 3 and 3.5%) and temperature (22, 31 and 40 °C) on skim milk coagulation kinetics were evaluated using rheometry and the BAW sensor. A parameter tAVg, determined from acoustic viscosity (AV), was established to monitor the onset of gelation. Changes observed in tAVg at the onset of gelation were due to changes in particle size of samples at pH ∼5.3 and ∼5.2. A positive linear relationship (R2 = 0.97) were found between gelation point (G′ > 1 Pa) and tAVg, and was capable to monitor early stages of gel formation.

A Vapor Phase Trinitrotoluene Threshold Detector Enabled by Nonlinear Feedback

The standoff detection of energetic materials is a critical challenge in national security and defense. The detection of solid energetic materials is particularly challenging, as these materials have extremely low vapor pressures at room temperature. Accordingly, the species have very low vapor phase concentrations. This letter presents a bifurcation-based resonant mass sensor architecture, a functionalization method, and sensor testing results demonstrating a low-cost, tunable sensitivity trinitrotoluene trace vapor detector. This detector leverages TIPS-Pentacene as a selective functional layer on a bulk-acoustic wave sensor and exhibits an estimated limit of detection below 480 ppb in N $_2$ .

Assessment of a solid-state bulk acoustic wave sensor to measure viscosity of Newtonian and Non-Newtonian fluids under static and flow conditions

Monitoring and control of inline viscosity is crucial for process optimisation and for ensuring a high quality final product but currently this parameter is still under-utilised in the dairy industry. This study investigated a solid-state bulk acoustic wave sensor to measure the viscosity of Newtonian (oil standards) and Non-Newtonian fluids (reconstituted skim milk (RSM) at different concentrations) under static (off-line measurements) and flow conditions (in-line measurements). Results illustrated that an increase in total solids (TS) of RSM gave an increase in acoustic viscosity. Non-linear regression was applied to the experimental data to successfully transform the acoustic viscosity outputs into commonly-used reference viscosity values. RSM at higher TS presented a non-Newtonian behaviour and demonstrated shear-thinning properties. Under flow conditions the viscosity of the RSM decreased as a result of shearing experienced in the pipe. This study demonstrated the potential of an acoustic wave sensor to measure in-line viscosity in dairy applications.

Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review.

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine it with enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade.

Split resonances for simultaneous detection and control measurements in a single bulk acoustic wave (BAW) sensor.

A self-referenced resonator consisting of two distinct areas of the top electrode made from Mo and a thin (5-30 nm) functional Au layer is shown. The fundamental frequencies for both the shear (∼1 GHz) and longitudinal (∼2 GHz) modes are split in two, such that mass attachment on the functional layer region causes frequency shifts in only one of the resonances, allowing a new approach of using the difference between the two frequencies to be used to measure mass attachment; this reduces the importance of device-to-device variability in absolute resonant frequency as a result of device fabrication.

Influence of the oxygen content on the humidity sensing properties of functionalized graphene films based on bulk acoustic wave humidity sensors

In this work, functionalized graphene films with different oxygen contents were prepared and their humidity sensing properties, such as humidity response, humidity hysteresis, dynamic response and recovery, were studied by combining them with a bulk acoustic wave sensor. The experimental results revealed that the humidity sensing properties of the functionalized graphene films were strongly associated with their oxygen content. The humidity response of the sensor could be improved by increasing the oxygen content of the functionalized graphene films. The stability of the sensor was also investigated using an impedance analysis method. The results indicated that the stability of the sensor was also influenced by the oxygen content of the functionalized graphene films during humidity detection. An increase in the oxygen content of the functionalized graphene film reduced the sensor stability. Thus, our work suggests that the oxygen content of functionalized graphene films is a key parameter for the design of graphene-based bulk acoustic wave humidity sensors.

A lateral field excited ZnO film bulk acoustic wave sensor working in viscous environments

We present a lateral field excited ZnO film bulk acoustic resonator (FBAR) operated in pure-shear mode and analyze its performances in viscous liquids. The electrodes of the device are located on the film surface and normal to the c-axis of the ZnO film. The proposed device works near 1.44 GHz with a Q-factor up to 360 in air and 310 in water, which are higher than those of the quasi-shear thickness field excited FBAR. The resonant frequency is decreased with the increasing square root of the product of the viscosity and density with a linear dependence in the viscosity below 148.7 mPa s. The mass sensitivity of 670 Hz cm2 ng−1 was measured by monitoring the frequency change during the volatilization of saline solution loaded on the resonator. In addition, the levels of the noise and the mass resolutions were measured in various viscous environments. The proposed device yields the mass resolution of 670 Hz cm2 ng−1 and the high mass resolution of 0.06 ng cm−2. These results indicated that the lateral field excited ZnO FBAR had superior sensitivity for the bio-sensing applications in viscous biological liquids.

Lateral field excited Y-cut langasite bulk acoustic wave sensor

Previous studies have shown that lateral field excited (LFE) devices on AT-cut quartz are sensitive to liquid electrical property changes. AT-cut quartz LFE devices have low piezoelectric coupling factors. To further improve electrical sensitivities of LFE sensors, it is necessary to study LFE sensors based on other piezoelectric materials with higher coupling factors. In this paper, LFE sensors on Y-cut langasite, which has twice the higher piezoelectric coupling factor of AT-cut quartz, are investigated. Several Y-cut langasite LFE sensors are designed, fabricated, and tested. The experimental results show that the devices are over 6 times more sensitive to liquid conductivity changes and about 2.5 times more sensitive to liquid permittivity changes compared to AT-cut quartz LFE devices. It was also found that the Y-cut langasite LFE devices are about 1.3 times more sensitive to changes in liquid acoustic viscosity compared to the AT-cut quartz LFE devices.

Recent advances in lateral field excited and monolithic spiral coil acoustic transduction bulk acoustic wave sensor platforms

The quartz crystal microbalance (QCM) has been used extensively as a bulk acoustic wave (BAW) platform for applications such as chemical and biological sensors and rate monitors in thin film deposition systems. Although the QCM is capable of measuring mechanical property changes critical in many thin film deposition systems, it cannot measure electrical property changes that can occur in many sensor applications. In this paper we review the recent developments of two novel transducer configurations for BAW sensors. In the first sensor, called the lateral field excited (LFE) sensor, the transverse shear mode (TSM) in AT-cut quartz is excited by two electrodes on the reference surface, resulting in a bare sensing surface which allows both electrical and mechanical properties of target analytes to be measured. In the second sensor, called the monolithic spiral coil acoustic transduction (MSCAT) sensor, the TSM is excited by a photolithographically deposited spiral antenna on the reference surface which can excite high-order harmonics in the substrate, and potentially lead to increased sensitivity. The responses of both the LFE and MSCAT sensors to electrical and mechanical property changes of liquids have been examined and compared to the response of the standard QCM. In addition, results relating to the detection of chemical and biological target analytes using the LFE and MSCAT sensor platforms are presented.

A lateral-field-excited LiTaO3high-frequency bulk acoustic wave sensor

The most popular bulk acoustic wave (BAW) sensor is the quartz crystal microbalance (QCM), which has electrodes on both the top and bottom surfaces of an AT-cut quartz wafer. In the QCM, the exciting electric field is primarily perpendicular to the crystal surface, resulting in a thickness field excitation (TFE) of a resonant temperature compensated transverse shear mode (TSM). The TSM, however, can also be excited by lateral field excitation (LFE) in which electrodes are placed on one side of the wafer leaving a bare sensing surface exposed directly to a liquid or a chemi/bio selective layer allowing the detection of both mechanical and electrical property changes caused by a target analyte. The use of LFE sensors has motivated an investigation to identify other piezoelectric crystal orientations that can support temperature-compensated TSMs and operate efficiently at high frequencies resulting in increased sensitivity. In this work, theoretical search and experimental measurements are performed to identify the existence of high-frequency temperature-compensated TSMs in LiTaO(3). Prototype LFE LiTaO(3) sensors were fabricated and found to operate at frequencies in excess of 1 GHz and sensitively detect viscosity, conductivity, and dielectric constant changes in liquids.

Study of Molecularly Imprinted Post‐Microspheres as Dipyridamole Sensors

Dipyridamole molecularly imprinted post‐microspheres were synthesized and studied using a bulk acoustic wave (BAW) sensor technique. Compared with other molecularly imprinted polymerized particles, this kind of post‐microsphere exhibits higher selectivity and sensitivity to dipyridamole. The linear response range of such post‐microsphere based sensor was from 4 × 10−8 to 1 × 10−4 M, with a detection limit of 4 × 10−9 M. TEM study indicates that there is a cavity existing in each post‐microsphere with an average diameter of 150 nm. It is suggested that this kind of post‐microsphere will find its application in many aspects.

Microspheres Sensor Based on Molecularly Imprinted Polymer Synthesized by Precipitation Polymerization

AbstractA new biomimetic bulk acoustic wave sensor based on molecularly imprinted microspheres (MIM) technique was described. The sensing materials were synthesized by precipitation polymerization. By using the Scatchard analysis, the equilibrium dissociation constant KD and the apparent maximum number Qmax of the binding sites were calculated to be 3.70 mmol·L−1 and 9.11 μmol·g−1, respectively. The sensor exhibited a sensitive response to the template compound (dipyridamole) in liquid phase with a detection limit of 2 × 10–9 mol· L−1. The recoveries of the sensor were 95.1%‐105.4%. Studies presented in this paper show that the stability of this sensor is excellent. The sensor has been applied successfully to the determination of dipyridamole in human urine.

A study of a bio-mimetic recognition material for the BAW sensor by molecular imprinting and its application for the determination of paracetamol in the human serum and urine

A new bio-mimetic bulk acoustic wave (BAW) sensor for paracetamol, with a high selectivity and sensitivity, was fabricated by using the molecularly imprinted polymer (MIP) as the sensing material. Non-covalent molecular imprinting polymers were synthesized simultaneously using two different functional monomers, namely the weakly basic 4-vinylpyridine (4-VP) and the acidic and hydrogen binding methacrylic acid (MAA). Such imprinted polymers improved recognition capability as compared with the polymers that were synthesized using only one of the functional monomers. Dynamic quartz crystal impedance analysis was employed to study the effect of the viscoelasticity of the polymer coating on the measurement. There was no variation in the viscoelasticity during the detection. The sensor was stable and exhibited good reproducibility. Satisfactory results were obtained in the determination of paracetamol in real samples.

Simultaneous determination of nitrate and nitrite in saliva and foodstuffs by non-suppressed ion chromatography with bulk acoustic wave detector.

In the present paper, nitrate and nitrite in foodstuffs and saliva were simultaneously determined using a non-suppressed ion chromatography (IC) method with a bulk acoustic wave sensor (BAW) as detector, and 1.5 mmol/L potassium hydrogenphthalate (KHP) as mobile phase. The IC-BAW method is simple, rapid and accurate. The determination limits for nitrite and nitrate are 0.20 and 0.30 mg/L, respectively. The IC-BAW is comparable and agrees with the conventional spectrophotometric method for nitrite and nitrate determination.

A new assay system for phenacetin using biomimic bulk acoustic wave sensor with a molecularly imprinted polymer coating

A new biomimic bulk acoustic wave (BAW) sensor with a molecularly imprinted polymer (MIP) coating has been designed and applied to the determination of phenacetin in human serum and urine. The MIP was prepared using phenacetin as the imprinted molecule and methacrylic acid as the functional monomer. The sensor showed high selectivity and sensitivity in aqueous system. A linear calibration response curve between 5.0×10 −8 M and 5.0×10 −4 M was obtained and the detection limit was 5.0×10 −9 M. The coating of the sensor was stable and can be reused for many times. In the determination of real samples, satisfactory results were achieved.

Construction and application of phenytoin anion-selective electrode based on bulk acoustic wave (BAW) sensing technique.

This paper describes the construction of an anion-selective bulk acoustic wave (BAW) sensor for the direct determination of phenytoin sodium for the first time. Based on the sensitive mass response of a piezoelectric quartz crystal (PQC) and selective adsorption-desorption across the modified film, the BAW sensor was fabricated by coating a polyvinylchloride (PVC) film containing activator on one side of a PQC. The method was found to be sensitive, rapid and easy to handle without pretreatment of the sample. The logarithm of the frequency shift of the PQC shows a linear relationship to the logarithm of the concentration of phenytoin over the range 6.7 x 10(-8)-8.0 x 10(-4) M with a detection limit of 1.0 x 10(-8) M at pH 10.0. Recoveries were in the range 98.5-102.0%. Influencing factors were examined and optimized. Also discussed is the preliminary application of the phenytoin BAW sensor in serum and injection. The results for real samples obtained by the proposed method agreed with those obtained by conventional methods.