Copyright terms are indicated in the Republic of Lithuania Law on Copyright and Related Rights; Articles 4-37. In the event the above Work is not accepted and is not published in the Publication or is withdrawn by Authors(s) before acceptance by the Publication; this guarantee form becomes null and void; and the submitted Work is not returned to the Author(s).
Application of ultrasonic method for investigation of porous plates
Application of ultrasonic method for evaluating porous plates is presented in this article, The ultrasonic echolocation measurement method to evaluate porous structures is presented. The mathematical model is considered for uniform and non-uniform volume structure of the product. The pores on the surface are smaller then in the depth of a flat surface. The indirect ultrasonic measurement method is proposed for investigation of porous plates. The porosity of a product is evaluated by absorbed liquid volume versus time using this method. The volume of the absorbed liquid is calculated according to the liquid level in the cylindrical measurement vessel versus time. The level of liquid is measured by acoustical echolocation method through air. The measurement vessel construction was improved for planar objects. The obtained uncertainty in distance measurements till the liquid surface is five micrometers in the forty millimeters measurement interval. The focusing electroacoustical transducers were used for investigations. The experimentally tested technique allows to apply acoustic method for various porous plates structures investigations when others methods give results with great uncertainties. This article can be beneficial for researchers, who specialize in evaluation of porous structures.
physical-mechanical properties of porous food products
Copyright (c) 2008 Ultragarsas "Ultrasound"
The review of non-destructive testing techniques suitable for inspection of the wind turbine blades
Wind power is a promising source of environmentally safe and renewable energy with a high potential. However, in order to fully exploit energy of wind power the construction elements of the wind turbine should be inspected periodically. Wind turbine blades are complicated objects for inspection because they have an arbitrary curved surface, are multi-layered, have variable thickness and are made from anisotropic materials. The presented study covers an overview of the techniques which are used or could be used for on site condition monitoring and effective NDT of wind turbine blades. Inspection methods based on vibration analysis, thermography, X-ray imaging, acoustic emission and ultrasound are reviewed. The objective of this study is review of different NDT techniques, which are used, or could be used for non-destructive testing of wind turbine blades, taking into account the complicated structure of the wind turbine blades as well as possibility to make non-destructive testing in harsh on-site conditions.
NON-DESTRUCTIVE TESTING AND DIAGNOSTIC METHODS
Ultrasonic time-of-flight method for non-invasive physiological monitoring of the human brain
Innovative non-invasive technologies for human brain physiological monitoring which are based on the ultrasonic time-of-flight (TOF) method require zero crossing detection of ultrasound signals. A new zero crossing detection algorithm has been proposed; it evaluates the individual variability of the acoustic path properties. The algorithm is implemented in the Vittamed non-invasive intracraniospinal slow, respiratory and pulse wave monitor and in the Vittamed non-invasive cerebrovascular autoregulation real-time monitor.
non-invasive physiological monitoring of the human brain
Investigation of time-reversed ultrasonic waves focusing in multilayered media
In the paper we investigate the time-reversal approach application for non-destructive evaluation of layered structures and it is shown, that the time-reversal mirrors (TRM) can be used for detection of scattering sources in layered media and the time-reverted waves successfully pass through layer-stacking zones and refocuses to the initial source. The investigations were performed for two cases: 2-layered structure (liquid-solid) and 3-layered structure (liquid-solid-liquid). The results show that multiple reflections caused by different structure layers and boundaries were eliminated by the TRM. Wave energy does not dissipate after mode conversion at liquid-solid interfaces, but is redirected to waves which coincide in some arbitrary time instant. Numerical modeling was performed by finite element method using the commercially available software ABAQUS/Explicit.
Modelling of Lamb waves in a rectangular plate
Interpretation of the ultrasonic signals measured in guided waves applications usually are more complicated comparing to conventional ultrasonic inspection mainly due to existence of different wave modes and multiple reflections. The objectives of this work are to investigate the regularities of Lamb waves generated by transducer arrays in rectangular steel plate and to develop the model enabling to predict the waveforms of the signals in such a way simplifying the interpretation of inspection results. The directivity patterns of small shear wave transducer have been investigated in details using the finite element modelling. It was demonstrated that the directivity patterns of A0, S0 ir SH mode waves coinside with the theoretical directivity pattern of the dipole. The uncertainties of this coincidence have been evaluated. The relatively simple method have been developed for calculation of the signals reflected in the rectangular plate taking into account group and phase velocities of guided waves and losses caused by the diffraction. The model enables to predict the signals generated by a single transducer or transducer array attached at arbitrary selected point on a steel plate.
Experimental verification of the acoustic computer model using triangle reflector
Objective of this study was experimental verification of the acoustic computer model, which enables calculation of the signals reflected by triangles arbitrally oriented in space. Verification of the computer model was carried out comparing the C-scan images of triangle reflectors, obtained experimentally and by simulation in the case when ultrasonic beam is reflected by triangle reflectors, reflecting surfaces of which are perpendicular and inclined with respect to the symmetry axis of the directivity pattern. Comparison of the experimental and simulated results of the inclined triangle reflector revealed some discrepancies. In order to find out the reason of these discrepancies the assumption was made that during rotation of the triangle reflector, the rotation axis was not strictly perpendicular to the incident ultrasonic beam, but that it was slightly deflected. In order to check this hypothesis modelling was also performed at different transducer deflection angles from its supposed position for each triangle angle. The simulation results clearly show that this assumption was correct and correspondence between experimental and simulation results in this case (0.75° deflection) is obtained much better.
Ultrasonic transit time flow meter for diesel: initial analysis
Transport control and tracking systems allow to track the car position and other requested parameters (fuel consumption, speed, temperature etc.) over GSM networks. It is desirable to have ability to monitor the diesel fuel consumption using ultrasonic flow meter. It was suggested to use the transit time ultrasonic flow meter with beam and flow axes matched instead of conventional inclined ultrasound channel. The initial study carried out to estimate the feasibility of such device design is presented. Numerical experiments have been carried when estimation of the time of flight was accomplished using the direct correlation method combined with parabolic sub-sample interpolation. Signal energy, operation frequency and bandwidth, electronics noise, analog to digit converter (ADC) sampling speed and resolution were taken into account. System prototype has been designed for experimental investigation. System contains pulser, reception amplifiers, dual channel ADC with buffer memory and USB communication unit. Experiments with and without ultrasonic channel were carried out. It was concluded that under zero flow condition the transit time difference has 2,4 ps standard deviation and -0,29 ps average; virtual flow obtained has 0.4 .10-4 m/s standard deviation and 0.5 .10-5 m/s mean.
Propagation properties of longitudinal surface acoustic waves (creeping waves) on the cylindrical convex surface
The properties of longitudinal surface acoustic waves (LSAW) (creeping waves) when they are propagating on the cylindrical convex surface are experimentally analyzed in this research. The analysis was done with the physical seismic shock wave model from duralumin. It was experimentally observed that LSAW are the fastest propagated acoustic waves with the speed and especially strength increasing when they are propagating on the cylindrical convex surface. LSAW are the specific whispering gallery effect manifestation form in the solid.
Analysis of the digital signal processing influence on time-of-flight estimation
Application of digital filters in ultrasonic data acquisition system has been investigated. The work analyses the digital signal processing influence on a time of flight (TOF) estimation when applied on ultrasonic signals. The ToF estimation was done using the direct correlation technique of the sampled signal. The subsample estimation was done using parabolic interpolation of discrete direct correlation. The investigation covers the ADC and digital filter rounding noise influence on amplitude and TOF estimation performance. The theoretical equations for interpolation-influenced and quantization-influenced random errors assessment have been suggested. The acquisition system has been developed, including Xilinx Spartan 3E Field programmable gate array (FPGA), high speed 10 bit ADC and USB2 high speed interface. FPGA fixed point FIR filters have been developed and implemented. AccelDSP development suit was used to create the filters simulation environment in MATLAB. Numerical simulation was used to analyze the filtering performance, influence of electronics noise, rounding errors and interpolation errors on TOF. Experimental results are documented and presented in tables and figures. It has been concluded that a digital filter output has to be quantized according to the processing gain obtained; otherwise rounding noise is increased, causing the TOF estimation to degrade.
Temperature influence on the ultrasonic signal acquisition path
It is important to estimate the group delay time in systems where signal delay is used to extract the measured parameter. In this article the ultrasonic flow measurement system is analyzed. Measurement is carried out using ultrasonic signal, which travels along and against the measured flow. The pulsed delay time measurement technique is used. The system is synchronized by a quartz oscillator. A digital pulse former is used to excite the high voltage generator which in turn delivers the signal to ultrasonic transducer. The transducer is sending the acoustical pulse into liquid in measurement channel. This pulse is received by the transducer at the opposite channel end and converted into electrical signal. This is amplified, filtered and delivered into analog to digit converter. The goal of this investigation was to estimate the temperature influence on the group delay time of the system discussed above. Electrical models have been developed in PSPICE, simulation carried out. Theoretical analytical expressions of the delay time influence on a flow speed estimation are presented. Temperature influence of individual units was investigated experimentally. Experimental results are presented in numerical and graphical form. It has been concluded that the high voltage generator output stage has the highest temperature sensitivity on delay time among electronics units. But according to the analytical expressions, this influence can be compensated. Then the largest electronics contribution on the group delay time is due to the analog filters present in the signal path.
Investigation of the zero-crossing technique in measurement of phase velocities of the guided wave in thin CFRP composite plate
One of the main areas for application of the guided waves is inspection of composite materials. These materials usually possess anisotropy of elastic properties. In order to investigate the possibilities of the developed phase velocity measurement technique based on accurate measurements of the zero crossing points of ultrasonic signals the numerical modelling of a thin CFRP plate was carried out. The finite element model of the CFRP plate with thickness 0.2 mm, length 100 mm and width 40 mm was created and used in order to obtain the signals for analysis. The A0 mode was excited by attaching tangential force and the S0mode by attaching normal force to the one edge of the plate. The width of the excitation zone was 10 mm and it was situated in the center of the plate. The waveform of the excitation signal was 3 period, 400 kHz burst with the Gaussian envelope. In general, the investigations demonstrated the same regularities as were obtained on non-homogeneous material and enable to identify different modes in the signals and to reconstruct the segment of the phase velocity dispersion curve.
Transcranial echoscopy for diagnostic of Parkinson disease: technical constraints and possibilities
Parkinson disease (PD) is one of the most common neurodegenerative disorders. The aim of this study is to review the main problems of transcranial echoscopy (TCE) by the pilot clinical investigations and to analyze opportunities and possible technical solutions for improvement of diagnostic of Parkinson disease using ultrasound applications. TCE is subjective enough yet, and strongly dependent on experience of physician. The suggestions for standardization of TCE are presented in this paper. The influence of temporal bone should be taken into account, because defocusing effects of the skull bone drastically decrease the quality of obtained brain images and these distortions are dependent on individual features of a subject.
Development of the non-damped wide-band ultrasonic transducers
In this article low frequency non-damped wide-band ultrasonic transducers are described. The important part of the non-damped transducers is the size of the piezoelement which can operate as a broadband transducer. The two kinds of piezoelements are investigated. The first, the non-damped piezoelement with dimensions of 5×5×5 mm was used as an experimental model. Ultrasonic signals and their frequency responses are presented for a single piezoelement and for the piezoelement with matching layer. The two cases of the transmitter and the receiver, in which the piezoelement alone and with the matching layer was used, are investigated. It is shown, that the piezoelement acting as a receiver gives the shorter pulse and the wider frequency response, than piezoelement acting as a transmitter. Also, it is shown that the single non-damped transducer gives a higher amplitude (by 10 ... 12 dB) than hard damped transducers
Measurement of velocity and attenuation for ultrasonic longitudinal waves in the polyethylene samples
The plastics pipes are used widely for water and gas supplies and for different applications in industry. The non-destructive testing (NDT) of the welded joints of such pipelines is very important for the safety and long life time of them. The main technique used for it is ultrasonic NDT. The specific physical-mechanical properties of the plastics used for manufacturing of the pipes require the ultrasonic properties of them to be well known. The aim of investigations described in this article is measurement of the velocity and the attenuation of ultrasonic longitudinal waves in the material of plastic pipes. The set of polyethylene PE80 test samples of different thickness in the range from 2.5 mm up to 20.0 mm were investigated. The measurements were performed using contact through-transmission technique and ultrasonic transducers with the central frequencies 1.0 MHz, 3.0 MHz and 5.0 MHz. The measurement results demonstrate dependences of the measured ultrasonic properties on frequency. It was determined that the velocity of ultrasonic longitudinal waves varies from 2030 m/s to 2060 m/s when the frequency is changing from 1.0 MHz to 3.5 MHz. The attenuation of ultrasonic longitudinal waves in the same range of frequencies varies from 0.3 dB/mm up to 1.5 dB/mm.
Orbital ultrasonography for diagnosis and evaluation of retrobulbar vascular disorders
Diagnostic and differential diagnostic of orbital diseases are considered to be one of the most difficult problems in ophthalmology because most orbital pathologies display the same signs and symptoms. Condition of orbital tissues can be evaluated using three different radiology imaging techniques: A/B-scan ultrasonography, computed tomography, and magnetic resonance imaging. A/B-scan ultrasonography is highly informative, non-invasive and poses no risk on the patient, therefore may be repeatedly performed in order to evaluate treatment effectiveness or disease progression. Ultrasonography has become an extremely useful tool in assesment of orbital vascular disorders. Orbital vascular disorders are divided into two main groups: neoplasms and malformations. Vascular malformations are: cavernous sinus fistula, carotid-cavernous sinus fistula, dural-cavernous sinus fistula, superior ophthalmic vein thrombosis, orbital varix, arteriovenous malformation and orbital aneurysm. In this article, we present the case of a difficult superior ophthalmic vein thrombosis in which orbital ultrasonography imaging was used in confirming the diagnosis and evaluating treatment effectiveness.
Investigation of the characteristics of the low frequency broadband contact transducers
In this paper experimental investigation of the characteristics of low frequency ultrasonic broadband contact type transducers is presented. The low frequency transducers are widely used for non-destructive testing and material characterisation, ultrasonic testing and in acoustic emission applications. One of the most important requirements to the low frequency transducers is that their characteristics during long-term contact scanning should not change. In order to measure the beam pattern of the low frequency transducers the special experimental set-up was created. The experimental set-up enables to carry out the measurements of the beam pattern of the contact type transducers which is impossible to perform by other (air-coupled, immersion) methods. The characteristics of the beam pattern of investigated different diameter transducers are presented. In the case of using contact type transducers possessing diameter of the contact surface 0.1 mm, the angle of the beam pattern divergence is about 116°. It shows possibility to excite the shear and the Lamb waves in the layered structures. It was determined experimentally, that the most noticeable differences between the beam patterns of the different diameter transducers are at small angles.
Testing of the middle zone of the rail weld
There are several millions aluminothermic welds on the European rail network. The welds are a critical safety component of the rail infrastructure. The consequences of a single failure could result in the derailment. The objective of this investigation was to test using CIVA software the proposed configuration of the ultrasonic phased array for testing of the middle zone of the weld, where shrinkage of the body is usually present. The propagation of the ultrasonic wave in the rail with shrinkage type defects has been modelled using CIVA software. The presented results demonstrate that it should be possible to locate shrinkage type defects in the rail weld using 2MHz ultrasonic phased array.
Comparison of modelling and experimental results of the phase velocity measurement of Lamb wave in aluminium plate
The analysis of the phase velocity measurement using zero-crossing technique presented in previous our articles revealed some regularities which can be exploited for mode identification in the complicated signals of guided waves. However the investigations were carried out using the signals obtained by a finite element method. The objective of the work presented is to carry out similar investigation using experimental signals and to determine is it possible to measure a needed parameter with accuracy sufficient for mode identification. The experiments were carried out on the 2mm thickness aluminium plate with dimensions 1100 mm x 620 mm. The guided waves were excited and recorded using the contact type wide band transducers. The waveform of the excited waves is the 300 kHz burst with Gaussian envelop. The receiver was scanned on the plate in the distance ranges 60-260 mm from the excitation point with the step 0.1 mm. The analysis has shown that scattering of results is almost three times bigger then in the case of the simulated signals. Comparison of the modelling and the experimental results also revealed some differences which partially can be explained by different excitation condition, however the experimental investigation proved main regularities obtained using simulated signals. So, in general the experimental investigation demonstrated the possibility of mode identification based of the phase velocity measurement using the zero-crossing technique.
Analysis of the zero-crossing technique in relation to measurements of phase velocities of the S0 mode of Lamb waves
It was demonstrated by previous works that the regularities obtained in phased velocity measurement of A0 mode of Lamb waves using zero-crossing technique creates possibilities for identification of the modes. The objective of the work presented was to investigate the similar approach on the So mode of Lamb waves and to determines if difference of regularities is sufficient or strong enough to be used for mode identification. The signals obtained by finite element modelling of S0 mode in 2mm thickness aluminium plate were analysed. The excitation signal was 300 kHz burst with the Gaussian envelop It was demonstrated that the distribution of lower and higher frequency components in the signals are different for A0 and S0 modes, what can be exploited as criteria for mode identification
Feasibility study of application of ultrasonic method for precise measurement of the long distances in air
The ultrasonic devices for distance measurement in air are simple in exploitation and their price in most cases is one of the smallest. However, high-precision measurements are affected by deviation of parameters of the surrounding medium, like temperature, relative humidity, CO2 concentration and other parameters. Changes in air temperature by ±1°C cause deviation of ultrasound velocity by ±0.59 m/s. Such deviation gives the source of the distance measurement uncertainty of 0.17%, in the case of measurement of relatively long distance (4 m). The change of relative humidity by 5% gives the source of distance measurement uncertainty of 0.02%. In the case of carbon dioxide CO2 concentration increases by 1%, ultrasound velocity decreases and it gives source of distance measurement uncertainty of 0.3%. In order to eliminate such factors, the additional calibration channel should be used. Also, the appropriate signal processing technique should be used in order to increase the resolution of time of flight (TOF) measurement. The uncertainty of TOF measurement was ±0.5 ns, which corresponds to the uncertainty of distance measurement ±0.18 mm (with a confidence probability 68%) and ± 0.36 mm (with a confidence probability 95%).
The application of the ultrasonic method for evaluating the porosity of bread
For evaluation by using acoustic methods bread is complex structure due to its geometric shape, density and porosity. This article reviews the use of direct and indirect acoustic measurement methods for evaluating the porosity of bread. The basic principle along with advantages and shortcomings of such methods is explained. Physical-mechanical properties of bread are described, along with mathematical equations, which are necessary for their theoretical calculation. The ability to determine physical-mechanical properties of bread (like porosity) is necessary, because they are directly linked to the quality of the product from the consumer’s point of view. Basic ingredients of bread are also briefly described. Ultrasonic waves are very suitable for the evaluation of porous food products due to their physical properties and wide range of operating frequencies. Correct preparation of the measurement sample is required for accurate results therefore guidelines are presented. This article can be of benefit to researchers, specializing in the evaluation of porous structures like bread.
Investigations of the inspection possibilities of the inner surface of the nozzle using ultrasonic phased array
The objective of this work was to investigate the inspection possibilities of the inner surface of the nozzle using ultrasonic linear phased array. The task was to determine ranges of angles and positions, which would enable to cover completely the areas necessary to inspect. The propagation of the ultrasonic wave in the nozzle has been modelled using CIVA software. The modelled ultrasonic field at different positions on the nozzle and at different steering angles of ultrasonic phased array are presented. The presented results demonstrate possible positions of ultrasonic phased array for the inspection of the inner curved surface of the nozzle.
Investigation of diffusion bonding quality by ultrasonic technique
For high-temperature ultrasonic transducers piezoelement-to-metal thermosonic bonding technology was developed based on gold-to-gold diffusion. Bond quality strongly depends on bonding parameters – pressure, temperature, ultrasonic power and time. The first step for achieving good bonds was ultrasonic monitoring of the process. In ultrasonic transducers good diffusion bond means good acoustic coupling of piezoelement to the protector and this coupling must withstand high temperatures. Bond quality tests comprise piezoelement electrodes adhesion issues as well. Bismuth titanate and PZT piezoelements were bonded to thick stainless steel protectors and membranes. For bond quality determination normal-incidence immersion scanning method from metal side was chosen. It is based on measurement of reflection/transmission signals in the bond interface and determination of their ratio which defines acoustic coupling. The whole piezoelement bonding interface was scanned automatically in x and y directions with respect to 10 MHz wideband ultrasonic transducer, having lateral beam width 1.4 mm at – 6 dB level. With optimal bonding parameters good bond quality was found. Weak or non-bonded areas are absent. Finally thus bonded transducers were used in successful temperature experiments – pulse response measurements up to 400 °C and tests in a liquid Pb/Bi at 290 °C.
Contact ultrasonic transducers for mechanical scanning systems
In this article the low frequency contact transducers for mechanical scanning systems are considered. The important part of the contact scanning transducer is protector which can be replaceable if it is wearing away. The two kinds of the replaceable protectors are investigated. The first, the planar protector the thickness of which may be from 0.25 mm up to 3.0 mm and the second, the convex protector having the surface of acoustic contact, diameter of which may be from 0 up to 7 mm were made. Ultrasonic signals and their frequency responses are presented for the planar and the convex protectors. The amplitude of ultrasonic signals depends on the thickness of the protector. For the planar protector the amplitude of the ultrasonic signals decreases when the thickness of the protector increases. For the convex protector the amplitude of the ultrasonic signals increases when the planar part of the protector increases.
This paper explores the data collection method for the ultrasonic array which can drastically decrease the scanning time, because the minimum excitation-reception sequences were used for reconstruction of the coordinates of the defects. The described data collection and processing method do not use classical phased array possibilities such as beam steering and focusing, but can reconstruct the object under the test for all physically possible deeps and angles. Mentioned approach was modeled with the ultrasonic arrays which are used in non-destructive testing, but basic principles of it can be employed by other applications or industries where array are used.
Increasing the accuracy of measurement for the small-shift, two-channel ultrasonic echolocation-based distance meter
Non-contact film thickness meters are most useful to measure physical-mechanical properties of thin polymer-based films. When polymerizing PVC resin at high temperature, the environment becomes very turbulent and is a source for measurement errors. This article explores the measurement errors, which arise when using an echolocation-based distance meter in such environments. Sources of measurement errors are identified and solutions for elimination of these errors are presented. This article provides the solution to avoid the effects of the turbulent environment on measurement accuracy. Additionally, design guidelines for acoustic distance measurement equipment are presented, along with schematic block diagrams. The equipment is designed for maximum measurement accuracy. When acoustic measurements have to be done in a turbulent environment, a version of the electro-acoustic part of the distance meter is presented. It eliminates the negative effects of the turbulent environment on measurement results, therefore very accurate acoustic measurements of small distances become possible.
The prototype of ultrasonic imaging system–attachment for diagnosis of human eye tumours
The most important problem in ophthalmology is early-stage diagnosis of malignant tumours of the eye in order to prevent metastasis of cancer and to save the human life. This problem required the development of prototype of ultrasonic imaging system-attachment for conventional non-invasive ultrasonic diagnostic equipment. The performed experimental study shows that the developed data acquisition system is suitable to acquire, synchronise and digitize with a higher sample rate and amplitude resolution (not less than 200 MHz and 12 bits), also to store the ultrasonic diagnostic signals, which are received from conventional ophthalmological scanners. These stored raw ultrasonic signals can be further processed using advanced digital signal processing algorithms, independently from the basic features installed into a conventional medical diagnostic equipment. The experimental research has revealed the tasks of improvement of the developed system, like reduction of the own noise level of the preamplifier, optimization of the time varying gain law, selection of cut-off frequencies of the band-pass filters and necessity to acquire the signals reflected from the internal structure of eye.
Analysis of the zero-crossing technique in relation to measurements of phase velocities of the Lamb waves
The delay time estimation using zero-crossing technique is widely used in ultrasonic measurements. The measurements of the phase velocity of guided waves are more complicated due to the dispersion. Application of zero-crossing technique for the measurements of the phase velocities is more complicated due to changes of the waveform of the signals and limited ranges of the measurements base. The objective of the work presented was to investigate in more details the influence of different parameters of the zero – crossing technique on measurement of the phase velocity of A0 mode of the Lamb waves. Using the signals obtained from the finite element modelling of Lamb waves in a 2 mm thickness aluminium plate it was demonstrated that an insufficient sampling frequency can lead to the errors in the phase velocity and corresponding frequency estimations. On the other hand it was shown also, that in order to obtain a higher equivalent sampling frequency it is reasonable to exploit interpolation. The optimal parameters of the zero-crossing technique and necessary steps for phase velocity measurement are presented also.
Progress towards noninvasive intraocular tumor diagnostics
Differential diagnosis of human eye tumors is one of the most important problems in ophthalmology in dealing with cancer prevention and diagnostics. Noninvasive diagnostics methods are of a high importance managing eye tumors. The main directions are: ultrasound and optical methods. State of the art of these methods shows trends for a further development.
Design and modeling of surface acoustic wave sensor with staggered ID – tag
A design methodology of wireless surface acoustic wave (SAW) sensor with staggered ID – tag is presented. For longer reading distances and technology improvement unidirectional transducers, working on the main frequency harmonics, are proposed. To reduce the number of strips and the size of devices is offered to increase the reflection coefficient and use open circuit reflectors. Unique technological realizations of SAW reflecting elements and unidirectional transducers, that enable to increase reflection coefficient and unidirectionality are proposed. A model of wireless sensor based on transfer matrixes of equivalent circuits of the device elements is created. The model discloses interaction among separate elements, assessed charge distribution in electrode's type, secondary effects, losses, wave's speed change constituents and allows to analyze characteristics and parameters of SAW sensors that have various structures. Simulation results are presented.