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A nitrogen dioxide (NO 2 ) gas sensor using dual track surface acoustic wave (SAW) device was developed and fabricated in this paper. The dual track architecture and the MSCs were skillfully applied to the sensor. The external perturbations were eliminated by the dual track architecture, and the bulk acoustic wave (BAW) was suppressed by Multistrip coupler (MSC). The input IDT apodized by Morlet wavelet function can improve the side lobe rejection compared with uniform IDT. Utilizing Tungsten powders, hydrogen peroxide, absolute methanol and polyvinylpyrrolidone as raw materials, the micro-porous network Tungsten trioxide (WO 3 ) film sensitive to NO 2 gas was fabricated in measurement acoustic track of dual track SAW device. Experiments results confirm that the NO 2 gas sensor using dual track SAW device has good response characteristics to different concentrations NO 2 gas from 0.5 ppm to 10 ppm. Furthermore, the NO 2 gas sensor using dual track SAW device has good reproducibility and stability.

In this paper, a sensor architecture of a dual track surface acoustic wave (SAW) gas sensor using three-interdigitated transducers (IDTs) and two-multistrip couplers (MSCs) is proposed. The dual track SAW gas sensor consists of three IDTs and two MSCs fabricated on 128degY-X LiNbO3 piezoelectric substrate. Dual track structure and MSCs are incorporated into the sensor, thus the perturbations of the measurement signal from external environment are eliminated, and spurious responses caused by bulk acoustic waves (BAWs) are suppressed. Furthermore, the side lobe rejection is better than that of SAW sensors with uniform IDTs due to input IDT apodized by Morlet wavelet function. An experiment of dual track SAW gas sensor coated with polyaniline film sensitive to SO2 gas is presented. Experiment results confirm that the sensor has good reproducibility and response properties to SO2 gas at different concentrations. In the measurement ranging from 312 ppb to 20 ppm, the sensor has good linearity, and its sensitivity is approximately 6.8 KHz/ppm.

In this paper, the relationship between the center frequency and radius of bandwidth and its effect on the frequency band characteristics of dyadic wavelet processor array using surface acoustic wave (SAW) devices are studied, and an optimal frequency band design scheme is proposed. For an arbitrary scale wavelet processor, we proposed that the center frequency is defined to three times of the radius of frequency bandwidth. The frequency band design scheme ensures that the frequency band coverage factor is equal to 100% at -3 dB, which avoid the signal loss caused by the discrete frequency band and the device waste caused by the redundant frequency band. With the frequency band design scheme, an experiment of implementing a dyadic wavelet processor array using SAW devices with five scales is presented. Experimental results confirm that the frequency band coverage factor equals 100% at -3 dB without discrete and redundant frequency band.

In this paper, we propose dual track architecture and time synchronous scheme for wavelet reconstruction processor using surface acoustic wave (SAW) device based on multistripe coupler (MSC). An arbitrary scale wavelet reconstruction processor with dual track architecture consists of a wavelet interdigital transducer (IDT) apodized by the envelope of wavelet function, two MSCs, and two reconstruction wavelet IDTs apodized by the envelope of identical reconstruction wavelet function. The SAW launched by wavelet IDT is bidirectional. Two reconstruction wavelet IDTs with identical design parameter are symmetrically deposited on the dual track of wavelet reconstruction processor. Therefore, the performances of wavelet reconstruction processor were improved due to bidirectional SAW received by two reconstruction wavelet IDTs. Furthermore, the delay time characteristic of SAW propagating on crystals substrate surface was skillfully applied to compensate the time asynchronous problem among wavelet reconstruction processor. This means ensures that all scale processors in wavelet reconstruction processor have identical response time. An experiment of wavelet reconstruction processor with dual track architecture and time synchronous scheme was presented. Experimental results confirm that the performances of wavelet reconstruction processor are improved, and time synchronous is realized in this wavelet reconstruction processor with three scales.

In this paper, we propose a sulfur hexafluoride (SF6) gas sensor using a dual track surface acoustic wave (SAW) device based on multi-wall carbon nanotubes (MWCNTs). The sensor consists of a dual track SAW device and MWCNT film sensitive to SF6 gas. The measurement acoustic track of the sensor is coated with an MWCNT film treated by an acid process which selectively absorbs SF6 gas, while the reference acoustic track is uncoated. Experimental results confirm that the SF6 gas sensor using a dual track SAW device based on multi-wall CNTs has good response characteristics to different concentrations of SF6 gas from 0.5 to 20 ppm. The sensor has good linearity and reproducibility, and its sensitivity is approximately 7.4 kHz ppm−1. Furthermore, the sensor has a smaller cross-sensitivity for SO2 and HF.