Surface Acoustic Wave Oscillator Research Articles

A SAW oscillator for monitoring particulate matter in air

A cyclone impactor has been modified to include an ionizing radiation source and a SAW device in place of the usual filter. The SAW has been incorporated in an oscillator circuit and, with a chemical treatment of the collection plate, the real time response to particulate matter is demonstrated.

A comparative analysis of one-port Colpitt and two-port Pierce SAW oscillators for DMMP vapor sensing

This paper reports an experimental study on chemical sensitivity and noise behavior of Colpitt and Pierce SAW oscillators based on 433.92 MHz one-port and two-port SAW resonator devices, respectively. The oscillators are characterized for phase noise as well as Allan variance. The sensitivity for DMMP (di-methyl methyl phosphonate) vapor is imparted by providing a diallyl-bisphenol polymer precursor as a selective interface coated on to both the SAW devices in an identical manner. Comparative vapor sensing experiments are carried out under simultaneous exposure to the same DMMP vapor stream in different ranges of vapor concentration and duration. A new data acquisition method is employed which is wireless and automated. It uses an antenna pickup at the input of a spectrum analyzer with PC control interface. The results show that the two-port Pierce oscillator is more stable but less sensitive than the one-port Colpitt oscillator. It is found that under the conditions of analyte exposure durations longer than 30 s the one-port Colpitt oscillator yields higher signal to noise ratios. The results are interpreted in terms of phase response characteristics and different sensitivities of the one-port and two-port SAW devices towards mass loading and viscoelastic effects.

위상변화를 이용한 표면탄성파 가스센서

This paper describes the development of a surface acoustic wave gas sensor that is designed to detect volatile gas by monitering phase change of output signal as a function of time. The sensor consists of SAW oscillators with a center frequency of 100 MHz fabricated on <TEX>$128^{\circ}$</TEX> Y-Z <TEX>$LiNbO_{3}$</TEX> substrates. Experimental results, which show the phase change of output signal under the absorption of volatile gas onto sensors, are presented. The proposed sensor has the properties of high sensitivity compare to the conventional SAW gas sensor and chemical selectivity. Thus, it is thought these results are applicable for use in sensor array of an high performance electronic nose system.

A 300-MHz-Band, Sub-1 V and Sub-1 mW CMOS SAW Oscillator Suitable for Use in RF Transmitters

An ultra low power CMOS SAW oscillator in the 300MHz-band that operates on a sub-1 V supply voltage and at sub-1 mW power consumption has been developed. The SAW oscillator is fabricated in a 0.35-μm fully depleted SOI (FD-SOI) process with low voltage operation capability. The SAW oscillator is configured as a type of Colpitts oscillator but consists of 3 cascaded amplifiers instead of a single amplifier. Although the circuit configuration is quite similar to the conventional Colpitts oscillator, this proposed configuration generates an excessively high negative resistance that even exceeds the theoretical limit of the conventional one.

Fine-tuning of the resonant frequency using a hybrid coupler and fixed components in SAW oscillators for gas detection

A method for fine-tuning of the resonant frequency of a typical delay line (DL) SAW oscillator by means of a procedure simple and widely used in microwave circuits is presented. It consists of a quadrature hybrid coupler in whose coupled ports, two identical terminations are placed. Each of them is composed of a set formed by a fixed capacitor C and a fixed inductor L in series. In this way no variable components are used. Therefore the phase can be adjusted for every sensor once the polymer film is deposited and measured. The output signal has the same amplitude than the input one and its phase is changed depending on the value of C and L. The oscillator designed in this way exhibits stable frequency response and operates with a wide range of coatings in measurements with volatile organic compounds (VOCs).

P2-54 A Balanced SAW Oscillator for Short Range Transmitters(Short presentation for poster)

P2-54 A Balanced SAW Oscillator for Short Range Transmitters(Short presentation for poster)

Dependence of AlGaN-based SAW oscillator frequency on temperature

A SAW delay-line oscillator based on an Al/sub x/Ga/sub 1-x/N-on-sapphire structure is presented, and its frequency dependence on temperature has been measured. The temperature coefficient of frequency -69 ppm/K has been found for the Al/sub x/Ga/sub 1-x/N layer thickness 1.7 /spl mu/m, Al molar amount x=0.5, and operation frequency 226 MHz.

Highly sensitive ultraviolet detector based on ZnO/LiNbO3 hybrid surface acoustic wave filter

Fabrication of a highly-sensitive UV detector based on the surface-acoustic-wave (SAW) principle is reported. The output voltage of the SAW oscillator constructed with a ZnO/LiNbO3 hybrid SAW filter was found to decrease linearly with increasing UV light intensity, and a very low intensity UV light of 10 μW/cm2 was detected easily. Our results show its potential use in wireless UV measurement systems.

A delay differential equation model for surface acoustic wave sensors

This paper presents a functional differential equation model for surface acoustic wave (SAW) devices. Closed-loop SAW delay line oscillators are modeled as differential equations with multiple delays. Stable oscillations of the circuit are associated with Hopf bifurcations. Conditions for Hopf bifurcations to occur are used to predict the mode number of the oscillator and its operating frequency. It is found that the operating frequency is close to the center frequency of the open-loop filter but is modulated by the effective separation distance between the generator and the receptor. The frequency relationship is applied to a tunable SAW oscillator to provide a phenomenological understanding of the mode jumping that is reported in experiments.

Composite substrate material for surface acoustic-wave oscillator

Surface acoustic-wave (SAW) oscillators have advantageous features compared with other technologies. The Y-128° LiNbO3 is a well-known, high electromechanical-coupling SAW material, but its usefulness is limited because of its poor temperature-stability property. The AlN films have some excellent characteristics, such as high SAW velocity, stable chemical properties, and high-temperature stability. In this research, different thickness AlN films were sputtered on Y-128° LiNbO3 to be a composite substrate for the SAW oscillator. As AlN film thickness increased, the temperature coefficient of frequency (TCF) value of the oscillator varied from −76.32 ppm/°C to −28.81 ppm/°C giving an improvement in the TCF of 62.25%. The oscillator frequency at 25°C also varied from 40.0909 MHz to 41.6221 MHz, giving an improvement in the oscillator frequency of 3.8%. The composite substrate (AlN/Y-128° LiNbO3) can enhance the oscillator frequency and effectively improve the poor temperature stability for the SAW oscillator.

A direct digital synthesis system for acoustic wave sensors

Current designs for acoustic wave sensor system electronics are typically based on surface acoustic wave (SAW) oscillators, phase detectors, or phase-locked loops to measure changes in SAW velocity. The advantage of oscillators is a high resolution frequency output, as compared to phase detection systems which are more stable and can more easily provide amplitude information. Phase-locked loops (PLL) offer advantages of both the oscillator and phase detection systems but have the disadvantages of a fixed frequency range and the need for frequency counting circuitry. The objectives of this work were to study the performance of a direct digital synthesis (DDS) based PLL system with the advantages of a programmable frequency range, elimination of the need for frequency counting circuitry, and tolerance of large SAW sensor insertion losses. The DDS system tested had a resolution of 4 Hz and a range of 80 to 120 MHz in SAW humidity and temperature sensing applications indicating that the DDS based PLL is a practical electronic system for SAW sensors.

Interdigital transducer analysis using equivalent PSpice model

Interdigital transducers generating surface acoustic waves have found numerous applications. The present paper deals with an equivalent model of a single interdigital transducer as well as an SAW filter complying with the PSpice programme for the analysis of electronic systems. The suggested model makes it possible to take into account such effects as interelectrode reflections, losses along the acoustic path and the electromagnetic coupling between the transducers. The obtained results of the analysis of an interdigital transducer comply with the results obtained basing on an admittance model and δ-function model. The final aim is to model an SAW oscillator.

Visible–blind photoresponse of GaN-based surface acoustic wave oscillator

We describe the photoresponse of GaN-based surface acoustic wave (SAW) delay-line oscillator operating in the 200 MHz range. The decrease in oscillator frequency under ultraviolet illumination of GaN transducer is caused by the SAW velocity decrease due to the acoustoelectronic interaction with photoconductivity electrons. The oscillator frequency shift reaches its maximum value at 365 nm and drops to zero above 400 nm with visible/ultraviolet rejection ratio more than 100. The optical quenching of the photoconductivity in GaN was observed. These results demonstrate the potential of the GaN-based SAW oscillators for applications as visible–blind remote UV sensors.

Radio frequency response of GaN-based SAW oscillator to UV illumination by the Sun and man-made source

A new solar-blind UV detector based on a GaN surface acoustic wave delay line oscillator is reported. The illumination by an artificial UV source in the presence of sunlight increased the RF spectral line width of the oscillator by almost an order of magnitude, which we attribute to the different noise spectra of these light sources. The output of this detector is a radio signal, which makes it especially attractive for remote sensing applications.

Rapid design of SAW oscillator electronics for sensor applications

This paper presents electronic techniques and a general methodology for the rapid design of two-port surface acoustic wave oscillators. By using a methodical approach, the stability problems and much of the time-consuming experimentation common to radio frequency (RF) oscillator design was avoided. Several oscillators in the range of 200 MHz to 1 GHz were designed using variations of the same basic circuit. Circuit designs included both two-port resonator and delay line SAW devices. The electronics were small in size ( 1.75 cm×1.75 cm ) and inexpensive (<US$ 10 in part cost). The active circuit element of the oscillators was a radio frequency integrated circuit (RFIC) wide-band amplifier. The first step of this systematic method was to identify a readily available RFIC amplifier that met the specifications of the oscillator. The specifications included amplifier gain, bandwidth and maximum input power. Choice of the proper amplifier allowed the same circuit to be used for several SAW oscillators spanning a large frequency range. Next a passive LC filter was designed to limit the open loop gain to a small frequency region around the SAW device’s fundamental frequency. This filter eliminates the problems of mode hopping and oscillation at harmonics. The S-parameters of the oscillator were then measured in an open-loop configuration to determine the phase shift requisite for the closed loop oscillation condition of 0° phase shift. To achieve stable oscillation, a passive LC phase-shifting filter was designed. Using the properties of Butterworth filters and a simple computer program, filters of exact phase shift were designed. The last step of design was the use of microstrip layout techniques to reduce wave reflections and susceptibility to electromagnetic interference.

GaN-based SAW delay-line oscillator

An SAW oscillator based on a GaN-sapphire acoustic delay line is reported. The oscillation frequency is determined by the GaN sound velocity and transducer period and is sensitive to temperature and to ultraviolet radiation. Our results show that GaN-based structures offer the possibility of integrating the acoustic and electronic elements on a single chip capable of operating at relatively high temperatures.

Development of a SAW microgas sensor for monitoring SO2 gas

We have developed a new type SO2 gas sensor applying a particular inorganic thin film on SAW devices. The sensor consists of twin SAW oscillators of the center frequency of 54 MHz fabricated on LiTaO3 piezoelectric single crystals. One delay line of the sensor is coated with a CdS thin film that selectively adsorbs and desorbs SO2, while the other is uncoated for use as a stable reference. Deposition of CdS thin film has been carried out by the spray pyrolysis method using an ultrasonic nozzle. Mass loading induced by the SO2 gas adsorbed onto the CdS film results in corresponding frequency shifts directly proportional to the gas concentration. The relative change in the frequency of the two oscillators is monitored with a digital signal processing circuit. SO2 sensor properties investigated include selectivity, sensitivity, response time, and repeatability. The sensor shows promising performance as a microsensing tool and is capable of measuring concentrations in air less than 200 parts per billion of SO2.

Reference SAW oscillator on quartz-on-silicon (QoS) wafer for polylithic integration of true single chip radio

The authors present an electro-acoustic circuit fabricated on quartz directly bonded on the processed silicon wafer (QoS), which allows us to polylithically integrate high precision passives with integrated circuits. We first fabricated a prototype SAW resonator and oscillator on thick QoS. The SAW resonator on QoS shows Q about 10,000 and 11 dB insertion loss at 289 MHz, and SAW oscillator on QoS shows phase noise of as small as -120 dBc at 100 kHz offset, demonstrating the feasibility of true single chip radio.

A surface acoustic wave mercury vapor sensor

A sensor for the in situ detection and measurement of low concentrations of gaseous mercury is presented. The sensor is based upon a dual delay line SAW oscillator with a gold-coated delay path. Gaseous mercury interacts rigorously with the gold film, forming an amalgam. The resulting increase in film mass is manifested as a decrease in oscillation frequency. Measurement of gas concentration is achieved by differentiating the sensor response at room temperature or by operating the sensing element at a temperature where gas-film reaction kinetics result in equilibrium rates of mercury amalgamation and desorption. This equilibrium value of amalgamated mercury is highly dependent upon the gas concentration. Thus, the delay line oscillation frequency is a sensitive measure of gaseous mercury concentration. Responses of this sensor to gaseous mercury concentrations in the ppb range are presented. The sensor response features are analyzed in terms of response shape, response magnitude, response time, and linearity at 25/spl deg/C and 200/spl deg/C.

Synthesis and evaluation of fluoropolyol isomers as saw microsensor coatings: role of humidity and temperature

A surface acoustic wave (SAW) organophosphorus gas detector has been designed, fabricated and tested. The gas detector consists of a dual delay line fabricated on a single quartz substrate. Each delay line is connected into the feedback path of a radio-frequency amplifier, to realize a SAW oscillator. The propagation path of one delay line is coated with fluoropolyol (FPOL). These polymers offer an interesting way to detect organophosphorus compounds like GB at low concentration levels. The absorption of vapors induces phase variations due to mass loading and stress effects. These variations result in corresponding frequency shifts. In this work, we have synthesised the four FPOL isomer combinations separately and characterized these materials by physico–chemical analysis. A series of SAW sensors have been coated with these materials and experimental results as a function of vapor concentration are presented. The influence of coating thickness, temperature and humidity are examined. Results showed on one hand that frequency variations are linear with GB gas concentrations from 0.5 to 10 ppm and on the other hand that sensitivity to organophosphorus compounds is two times greater in wet atmospheres (RH=60%) than in dry air. The sensitivity was also better at a working temperature close to the glass transition point ( T G) of the polymer. Above T G, the modification of the polymer structure induced a great radiation of the acoustic energy in the coating.