Changchun Zhu

The theoretical analysis on damping characteristics of resonant microbeam in vacuum

Abstract This paper takes into account the differences in the number and the velocity distribution of moleculae impacting on two sides of a resonant microbeam and modifies the velocity distribution of the moleculae given by Kadar et al. [Z. Kadar, W. Kindt, A. Bossche, J. Mollinger, Quality factor of torsional resonators in the low-pressure region, Sensors and Actuators A, 53 (1996) 299–303]. By a modified model, the damping characteristics of the resonant microbeam vibrating in vacuum are analysed. New results reduce the deviation between the experimental data and the old theoretical values by 1.5 times, therefore the new model will be beneficial to design the optimal structural parameters of resonant microbeam. This paper also considers the coupling effect between the intrinsic damping and the impact of moleculae in the high vacuum, so a break point occurring in this region by means of the old method is eliminated, and the theoretical values show good agreement with the experimental ones.

Solving Three Key Problems of Wavelet Transform Processor Using Surface Acoustic Wave Devices

Abstract-In this paper, we present the bulk acoustic wave (BAW), the sound-electricity reclamation (SER), and the insertion loss as the three key problems of a wavelet transform processor using surface acoustic wave devices. The solutions to these problems are achieved in this study. The more the number of electrode pairs for the interdigital transducer (IDT) is, the weaker the excited BAW is, so the BAW can be eliminated when the number of electrode pairs for IDT is large enough. The substrate material of a small electromechanical coupling coefficient (ECC) k2 and the low-impedance load of IDT can eliminate SER. When the output ends of the wavelet transform processors are respectively connected to the amplifiers, their insertion losses can be compensated. X-112oY LiTaO3 (small ECC k2) is used as a substrate material to fabricate the wavelet transform processor.

Study of gas sensor with carbon nanotube film on the substrate of porous silicon

A new method of obtaining extremely high electric fields in a very small region near the tip of a carbon nanotube, with diameter of nanometer order, is studied. This method makes the self-sustaining dark discharge voltage decrease to less than 220 V, which is in the safe range. The carbon nanotube array film is used as a cathode to form a new kind of gas sensor based on the gas discharge. The discharge current at room temperature and atmospheric pressure increases from the order of nanoamperes to that of microamperes. The electrical characteristics of several gases at atmospheric pressure are studied. The self-sustaining dark discharge voltages of different gases vary, as do the discharge currents. Porous silicon is selected as the substrate for the carbon nanotubes. This can improve the adhesion of the nanotube on the substrate and so prolong the lifetime of the cathode.

Optimal Frequency Band Design Scheme of Dyadic Wavelet Processor Array Using Surface Acoustic Wave Devices

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.

Implementing wavelet inverse-transform processor with surface acoustic wave device

The objective of this research was to investigate the implementation schemes of the wavelet inverse-transform processor using surface acoustic wave (SAW) device, the length function of defining the electrodes, and the possibility of solving the load resistance and the internal resistance for the wavelet inverse-transform processor using SAW device. In this paper, we investigate the implementation schemes of the wavelet inverse-transform processor using SAW device. In the implementation scheme that the input interdigital transducer (IDT) and output IDT stand in a line, because the electrode-overlap envelope of the input IDT is identical with the one of the output IDT (i.e. the two transducers are identical), the product of the input IDTs frequency response and the output IDTs frequency response can be implemented, so that the wavelet inverse-transform processor can be fabricated. X-112(0)Y LiTaO(3) is used as a substrate material to fabricate the wavelet inverse-transform processor. The size of the wavelet inverse-transform processor using this implementation scheme is small, so its cost is low. First, according to the envelope function of the wavelet function, the length function of the electrodes is defined, then, the lengths of the electrodes can be calculated from the length function of the electrodes, finally, the input IDT and output IDT can be designed according to the lengths and widths for the electrodes. In this paper, we also present the load resistance and the internal resistance as the two problems of the wavelet inverse-transform processor using SAW devices. The solutions to these problems are achieved in this study. When the amplifiers are subjected to the input end and output end for the wavelet inverse-transform processor, they can eliminate the influence of the load resistance and the internal resistance on the output voltage of the wavelet inverse-transform processor using SAW device.

Solving Three Key Problems of the SAW Yarn Tension Sensor

In this brief, we propose to implement a new method of the yarn tension sensor with a surface acoustic wave (SAW) oscillator. When the yarn tension is subjected to the piezoelectric substrate of SAW oscillator, the oscillation frequency of SAW oscillator varies with yarn tension so that the goal of measuring yarn tension is reached. We present the temperature compensation of the SAW yarn tension sensor, establishment of the functional relationship between the yarn tension and the output frequency shift of the yarn tension sensor, and suppression of the sidelobes for the frequency characteristic curve of the SAW oscillator as the three key problems of the SAW yarn tension sensor. The solutions to these problems are achieved in this brief.

Solution to the influence of the MSSW propagating velocity on the bandwidths of the single-scale wavelet-transform processor using MSSW device.

The objective of this research was to investigate the possibility of solving the influence of the magnetostatic surface wave (MSSW) propagating velocity on the bandwidths of the single-scale wavelet transform processor using MSSW device. The motivation for this work was prompted by the processor that -3dB bandwidth varies as the propagating velocity of MSSW changes. In this paper, we present the influence of the magnetostatic surface wave (MSSW) propagating velocity on the bandwidths as the key problem of the single-scale wavelet transform processor using MSSW device. The solution to the problem is achieved in this study. we derived the function between the propagating velocity of MSSW and the -3dB bandwidth, so we know from the function that -3dB bandwidth of the single-scale wavelet transform processor using MSSW device varies as the propagating velocity of MSSW changes. Through adjusting the distance and orientation of the permanent magnet, we can implement the control of the MSSW propagating velocity, so that the influence of the MSSW propagating velocity on the bandwidths of the single-scale wavelet transform processor using MSSW device is solved.

A Novel Dual Track SAW Gas Sensor Using Three-IDT and Two-MSC

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.

A SF6 gas sensor using a dual track SAW device based on multi-wall carbon nanotubes

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.

Compensated SAW Yarn Tension Sensor

The measurement and control of yarn tension is important in textile technology. This paper presents a two channel architecture surface acoustic wave yarn tension sensor, which is able to provide a sensitivity about two times bigger than the previous one. The design and the fabrication of the devices are also presented. A mathematical analysis shows that the output frequency of the sensor varies linearly with the yarn tension. To test the performance of the sensor, an experiment is carried out to obtain the output frequencies in different yarn tension. The results show that the sensor has a sensitivity of 8234 Hz/N (80.75 Hz/gf), and the sensor is capable of measuring a range of 0-0.196 N (20 gf) yarn tension with a relative error of 2% and a hysteresis error of 3%.