This work presents results of experimental tests of surface acoustic wave vibration sensor. Measurements of the static sensitivity, resonance frequency, frequency amplitude characteristics and linearity were carried out. Measurements were carried out with the help of the acceleration of gravity and a digital oscilloscope.
In the paper feasibility analysis of the surface acoustic wave based electronic warning system was presented. As a transducer in the system the surface acoustic wave delay line was proposed. It is fabricated in standard single mask process as a pair of interdigital transducers placed on the top of piezoelectric crystal substrate. Transducer is a plate with rectangular cross-section and it converts all environmental vibration to electric signal. From electronic point of view it was considered as a two-port network. Necessary condition for proper sensor operation is that the input signal frequency from external generator should be close to central frequency of delay line. Principle of operation of the sensor is that the measured phase shift of high frequency signal has frequency equal resonant frequency of vibrating plate and its amplitude is proportional to vibration amplitude of transducer. The environmental vibrations are defined by amplitude of the output signal and the threat location is pointed by resonant frequency of excited transducer. The described above principles of sensor operation allow us designing electronic warning system consisting of many sensors with different resonant frequencies of transducers. Output signals from precisely located sensors contain all necessary information about the whole warning system. This information is easy to transmit and detect by simple electronic circuits based on phase detector and proper data acquisition system, for which necessary conditions are presented.
This paper presents the concept of a perimeter protection system with acceleration sensors with the acoustic surface wave. The system consists of subsystems. Subsystems are connected with a monitoring centre. Every subsystem consists of an identical set of acceleration sensors with the acoustic surface wave, a measurement generator and a quadrature phase demodulator and a reference generator, the frequency of which is different in every subsystem. The acoustic surface wave acceleration sensors are of a different frequency of free vibrations. The spectrum of the output signal from a subsystem is situated around the frequency which equals the difference between the measuring generator frequency and the reference generator frequency. Therefore the spectrum of every vibrating sensor is located in a different known frequency range. The analysis of the spectrum of signals from subsystems performed in the monitoring center allows monitoring the vibration status of every sensor included in a system. A system can consist of many identical acoustic surface wave acceleration sensor sets. This allows constructing a perimetrical protection system with acoustic surface wave acceleration sensors of parameters of which are comparable to parameters of presently offered perimeter protection systems. Results of the experimental research of the operation of the acoustic surface wave acceleration sensor in a subsystem are presented.
The analysis of vibrations excitation in surface acoustic wave vibrations sensors is the aim of our work. The sensors are parts of electronic warning system which is intended to be mounted at fences of guarded object. The vibration excitation with expected acceleration is needed during experiments. Elements of fences are replaced by tense strings for experimental purposes and the surface acoustic wave vibration sensors are fastened to these strings. Analysis of the assembly string-sensor takes into account not only the mass of sensor but its moment of inertia, too. Free vibrations of string-sensor assembly are considered. The standard excitation by pulling off string in chosen point causes vibrations. The normal vibrations of assembly (frequencies, orthogonal set of normal functions) are calculated and used for calculations of free vibrations. The spectrum of the standard free vibrations is calculated. The results will be used in the experimental stand. The calculations enable excitation of vibrations with expected spectrum. The stand enables tests of the whole warning system. The thresholds of detection and reaction at concurrent intruder alarm will be investigated at this laboratory stand.
The profile of the gas concentration in the sensor layer can be expressed as a polynomial function involving the diffusion coefficient (D_{K}), semiconductor film thickness (h), rate constant (k), gas concentration outside the semiconductor film (C_{S}). Before reaching a steady state of the concentration profile, its behavior depends on a few factors as the distance from the piezoelectric surface, the rate constant, the thickness of the layer and the diffusion constant and time. We are going to simulate temporary processes in the semiconductor sensor film in the surface acoustic wave gas sensor system and to describe the influence on relative changes of the surface acoustic wave velocity. The numerical results basing on the code written in Pyton, are described and analyzed.
The paper presents surface acoustic wave vibration sensor electronic system. The system cooperates with surface acoustic wave delay line. The sensor has been designed for electronic warning systems. The sensor is a four-terminal network. In the system, there is a cascade connection of sensors by means of coaxial cable. Test signal and constant supply voltage are jointly sent between sensors. Separating the signals, their summation and amplification of test signal as well as matching the line to impedance 50 Ω are performed by surface acoustic wave vibration sensor electronic system. The electronic system devices and the making of them are discussed. System development of such a sensor is presented and its design is analysed. Experimental examination results of surface acoustic wave vibration sensor are presented. Parasitic effects occurring in vibration sensor electronic system operation connected with electromagnetic coupling and ground current coupling are discussed.
The paper presents an analysis of surface acoustic wave delay line. The line consists of two simple interdigital transducers placed on a ST-cut quartz plate. Mid-band operation frequency of the line is 74 MHz. The line will be applied for surface acoustic wave vibration sensor. At the immovable end of the plate there are electric signal feeds to both transducers. This is the cause of increase in signal value going directly between the transducers and the cause of line losses. By means of equivalent electric model of interdigital transducer a loss analysis of the line has been made at 50 Ω load. The analysis allows to minimize line losses by matching the transducers to 50 Ω impedance. This has been practically achieved by a design of transducer geometry and configuration matching 50 Ω impedance, by means of inductance. An analysis of repeated operation characteristics of two interdigital transducers has been made. A signal going directly through capacitance between transducers and signals reflected from the edge of piezoelectric substrate have been presented. Results of theoretical analysis have been compared with experimental examinations.
The topic of the paper is analysis of feasibility of surface acoustic wave vibration sensors for linear electronic warning systems. In linear warning systems localisation of the object is realised by pointing out the sensors which detect vibrations caused by the object. The information sent out by the detector enables identification of the sensor and its state. The sensor contains surface acoustic wave delay line in four-terminal network. The delay line is formed at the surface of piezoelectric plate. The vibrations of the plate are caused by vibrations of the medium surrounding the sensor. The frequency of the input signal is equal to the working frequency of delay line. The phase of the output signal is shifted in comparison with the input signal. The frequency of the phase shift would be equal to the resonance frequency of the sensor plate. The change of the output signal amplitude would be proportional to the amplitude of plate vibrations. The measured amplitude and frequency of the output signal would be registered by simple electronic devices. The measurements give us knowledge which sensor vibrates and the intensity of these vibrations. Such sensors enable construction of the electronic warning system.
The paper presents the numerical results of investigations of the layered gas surface acoustic waves sensor. The base electric load of the piezoelectric acoustic line is predicted by the effect of surface acoustic waves velocity changes vs. surface conductivity, which depends on the profile concentration by gas diffused molecules into the porous film. Inside the sensor layer Knudsen's model of gas diffusion was used.
In the paper a new theoretical model for analyzing a surface acoustic wave gas sensor is presented. Basing on the electric load of the piezoelectric acoustic line the effect of surface acoustic wave velocity changes vs. surface conductivity is predicted which depends on the profile concentration of gas molecules diffused into the porous film. Inside the sensor layer Knudsen's model of gas diffusion was used.
A Rayleigh acoustic wave travelling on the surface of a semi-infinite piezoelectric medium may be changed by interaction with carriers and diffused gas in an adjacent semiconductor. The configuration, which uses a thin semiconductor film supported by a catalytic layer (Pd), is described in detail and the theoretical results of gas-sensor layer interaction are presented.
We have investigated the acousto-optic diffraction by shear horizontal surface acoustic waves in 36° rotated Y-cut X-propagation lithium tantalate (LiTaO_{{3}}) crystals. The measurements were performed at the optical wavelength 633 nm of He-Ne laser and acoustic wavelengths of 50-60 μ m. The anisotropic diffraction with the light polarization rotation in the transmission mode was observed. The measured and calculated values of the light incidence angle corresponding to the strongest diffraction differed significantly. A narrow strip of a thin metal film deposited on the crystal surface drastically affected the light diffraction. We attribute these effects to the conversion processes between the shear horizontal leaky surface acoustic wave and shear horizontal surface skimming bulk wave.
In the paper a new sensor structure for surface acoustic wave gas system is presented. A bilayer structure WO_3-Pd thin films may be useful for hydrogen detection in low concentration in air. A bilayer sensor structure of tungsten oxide WO_3 with a very thin catalytic film of palladium on the top has been studied for gas-sensing application at room temperature (about 25°C) in surface acoustic wave system. The bilayer structure of WO_3 layers with a thickness of about 50 nm, 100 nm and 150 nm was made onto a LiNbO_3 Y-cut Z-propagating substrate by means of the vacuum sublimation method using a special aluminum mask. The vapor source consisted of commercially available WO_3 powder (Fluka 99.9%) and molybdenum heater. The thin palladium (Pd) layer (about 10 nm) was made separately on each WO_3 layer by means of vapor deposition in high vacuum. There have been investigated three structures: 50 nm WO_3 + 10 nm Pd, 100 nm WO_3 + 10 nm Pd and 150 nm WO_3 + 10 nm Pd in three canal surface acoustic wave system with reference oscillator. Numerical results obtained by analysis of the surface acoustic wave gas sensor model have been compared with experimental results.
Over the last few years we have developed a new method to control single-electrons by isolating and moving them through a submicron width channel formed in a GaAs/AlGaAs heterostructure using a surface acoustic wave. The acoustic wave acts to push electrons through the depleted submicron channel in packets each containing an integer number of electrons. Our primary motivation for studying this system has been to develop a new standard of dc current for metrological purposes, but our recent focus has widened to investigate the possibility of single-photon emission. Here we show new experimental results which demonstrate acoustoelectric current flow in adjacent 1D wires. These results have relevance both to the use of the system in a single-photon emission scheme, as well as in the creation of a proposed acoustoelectric quantum computer.
This paper presents the results of the analysis of surface acoustic waves sensor equivalent model. They were the sensor response of the surface acoustic waves sensor in the steady state gas: H_2, CO_2, NO_2, NH_3, C_nH_m, CO. Thin layer of WO_3 has been used as a sensor layer. Impedance replacement of sensor layer, taking into account the profile of the concentration of gas molecules in the layer, has been implemented into the equation of Ingebrigtsen, which enabled us to obtain analytical expressions for the relative changes in surface wave velocity in the steady state. The results of the analysis show that there is an optimum thickness of layer sensor for which an acoustoelectric effect (change in the acoustic wave velocity) is the highest.
The analytical expression for mutual capacitance of periodic strips is presented in this paper. This expression utilizing the spectral theory is obtained. It is studied how the metallization ratio affects a mutual capacitance of periodic strips. The mutual capacitance of periodic strips as a function of metallization ratio, for split electrodes, was shown in the paper. This approach should be applicable to modeling of the surface acoustic waves interdigital transducers.
The paper presents the acoustic method for determining some parameters of fast surface states in semiconductors. This method uses the interactions of the phonon-electron type for determining both the effective carrier lifetime τ influenced by the fast surface energetic states and the velocity g of the carrier trapped by the surface states. Some experimental results of the parameters τ and g in near-surface region of real Si(111) samples for their various surface treatments, obtained by the offered method, are presented.
The application of diamond in surface acoustic wave sensors is considered. The new method of the complete analyses of diamond-based gas chemical sensors is presented. It is based on the electromechanical equivalent circuit of the surface acoustic wave sensor. The method is very efficient and can be used for the optimal design of gas sensors. Since the diamond can be easily merged into solid state and biological systems, the development of smart biological sensors is possible. The advantages over silicon based sensors are also shown.
A bilayer sensor structure of nickel oxide NiO_x ( ≈ 60 nm) with a very thin film of palladium (Pd ≈ 18 nm) on the top, has been studied for gas-sensing application at relatively low temperatures of about 30°C and 60°C. The bilayer structure was obtained by rf sputtering and by vacuum deposition (first the NiO_{x} and then the Pd film) onto a LiNbO_{3} Y-cut Z-propagating substrate, making use of the surface acoustic wave method, and additionally (in the same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of the planar resistance of the layered structure. Such a bilayer structure was investigated in a low concentration range (from 50 ppm to 400 ppm in air) of nitrogen dioxide (NO_{2}), carbon monoxide (CO) and ammonia (NH_{3}) in a dry and wet air atmosphere and in a medium hydrogen concentration (1-2.5%) in dry air. The NiO_{x} and Pd bilayer structure interact rather weakly with NO_{2} molecules but with CO and NH_{3} this interaction is much greater, especially at higher temperature ( ≈ 60°C). The hydrogen sensitivity is on the medium level, not exceeding 600 Hz (relative change in the differential frequency of ≈ 2.3%) at interaction temperature of 35°C.
The paper presents results of theoretical analysis as well as practical measurements of efficiency in ultrasonic welding system with main focus on ultrasonic generator. Through analysis and tests were performed using 3 kW 20 kHz Sonic Blaster ultrasonic generator manufactured by ITR. Special equipment was used to perform accurate measurements of input and output power of such generator since an output signal of the ultrasonic generator has high voltage amplitude up to 3 kV and frequency of 20 kHz. Artificial load able to dissipate up to 6 kW of continuous power was designed to simulate ultrasonic transducer. Power measurements were performed on the mains supply of the generator using accurate true RMS power meter and load side measurements were performed using specially built power metering system able to measure high voltage 20 kHz signals based on calibrated high voltage resistive divider and high frequency current transducer.
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