Surface acoustic wave sensor

The simplest SAW sensor is a two-terminal transmission (delay) line in which the acoustic (mechanical) wave is piezoelectrically launched in one oscillator, called the transmitter. It travels along the surface of the substrate and is then transformed back into an electrical signal by the reverse piezoelectric effect at the receiving oscillator (Fig. 4.18). 

As shown in Fig. 4.19, in anisotropic medium, a surface acoustic wave represents a combined longitudinal (4.19a) and shear (4.19b) motion of the lattice in the y-(0)-z plane this is the saggital plane. In anisotropic media, in certain multilayer structures and at some interfaces, the surface wave velocity exceeds the velocity of the shear wave and the energy continuously leaks from the surface to the bulk of the material. In such cases, we talk about pseudo- or leaky waves. Various energy-loss 

Most SAW sensors employ a resonator arrangement a sensor delay line and the reference line are combined on one substrate with one generator in the center and two receivers at the ends (D Amico et al., 1982/83 Fig. 4.20) terminated by two reflectors. 

0E is the phase shift introduced by the compensating (stretched) line, lr and ls are the length of the reference and of the sensing channel, respectively, and vr and vs are the acoustic velocities in the two channels. The output of the sensor (Vo) is then 

The addition of mass due to the interaction with the sample causes the change of the acoustic velocity vs in the sensing line. Therefore, the sensitivity S of the device is obtained by differentiating (4.36) with respect to the concentration of gas Cgas. 

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The methods and means for ecological diagnostics make rapid strides among all the NDT and TD developing areas. To provide the atmosphere monitoring recently the good results were achieved in the development of surface-acoustics wave sensors (SAW), laser measuring systems, infrared detectors and systems based on other physical principles. 

A new chemical sensor based on surface transverse device has been developed (99) (see Sensors). It resembles a surface acoustic wave sensor with the addition of a metal grating between the tranducer and a different crystal orientation. This sensor operates at 250 mH2 and is ideally suited to measurements of surface-attached mass under fluid immersion. By immohi1i2ing atra2ine to the surface of the sensor device, the detection of atra2ine in the range of 0.06 ppb to 10 ppm was demonstrated. 

The surface-acoustic-wave sensor is also commercially available, either as a single sensor or as a part of an entire sensing system. The authors hope that informing potential users about acoustic sensors may stimulate the wider use of all the sensors that we discuss. 

Matsushita, K., Sekiguchi, H., Seto, Y. (2005). Performance of portable surface acoustic wave sensor array chemical agent detector. Bunseki Kagaku 54 83-8. 

In this entry, we focus on the discussion of the platform technology for electrochemical sensors, metal oxide semiconductive (MOS) sensors, and piezoelectric based quartz crystal microbalance (QCM) sensors. There are other types of chemical sensors, such as optical sensors, Schottky diode based sensors, calorimetric sensors, field-effect transistor (FET) based sensors, surface acoustic wave sensors, etc. Information of these specific sensors can be found elsewhere and in current journals on sensor technologies. Because of the increasing importance of microfabricated sensors, a brief discussion of microsensors is also given. 

Chemical sensors for gas molecules may, in principle, monitor physisorp-tion, chemisorption, surface defects, grain boundaries or bulk defect reactions [40]. Several chemical sensors are available mass-sensitive sensors, conducting polymers and semiconductors. Mass-sensitive sensors include quartz resonators, piezoelectric sensors or surface acoustic wave sensors [41-43]. The basis is a quartz resonator coated with a sensing membrane which works as a chemical sensor. 

G. Schmera, L.B. Kish, "Surface diffusion enhanced chemical sensing by surface acoustic waves", Sensors and Actuators B 93 (2003) 159-163. 

Grate J W, Rose-Pehrsson S L, Venezky D L, Klusty M and Wohltjen H 1993 Smart sensor system for trace organophosphorus and organosulfur vapor detection employing a temperature-controlled array of surface acoustic wave sensors, automated sample preconcentration and pattern recognition Anal. Chem. 65 1868... 

Hill and Martin (2002) presented a review of conventional analytical methods for CWAs. They discussed various. sensors, such as surface acoustic wave sensors, electrochemical sen.sors, spectrophotometric sensors, immunochemical sen.sors, and IMS detector. For OP nerve agents. FPD and MS are the detectors of choice when coupled with GC or LC. Miniature ion trap ma.ss spectrometer has been described for the detection of nerve agents in the field (Patterson et at., 2002 Riter et al., 2002). A book published by the Institute of Medicine and the National Research Council explains the use of various types of detectors for nerve agents as well as CWAs (lOM, 1999). 

A Modeling of Surface Acoustic Wave Sensor Response... 

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