Longbiao He

Uncertainty evaluation of piezoelectric constant measurement based on dynamic resonance method

The piezoelectric strain constant d33 plays a pivotal role in characterizing the energy conversion efficiency of piezoelectric materails. The dynamic resonance method is the reference method to measure the constant. To evaluate the uncertainty, a measurement system based on impedance analyzer iwas set up. A labview programme is written to achieve automatic measurements and data analysis. Based on the mathematical models, the sweeping frequency step was optimized, and the characteristic parameters of piezoelectric ceramic NCE51 cylinders were tested and finally the uncertainty is evaluated. For 15 mm thick samples, the relative expanded uncertainty of d33 measurement of piezoelectric ceramic is 0.96% (k=2), when the frequency step is selected as 50 Hz. Thus the sample measured by dynamic resonance method can be used as reference material to calibrate the commercial d33 measurement apparatus, which uncertainty is about 2% to 5%.

Three-Dimensional Reconstruction of Ultrasound Images Based on Area Iteration

Ultrasonic C scan technique has been extensively applied in nondestructive testing (NDT) in recent years. Aiming at ultrasonic C scanning original data, this paper presents a 3D reconstruction algorithm for ultrasonic C scanning image based on area iteration. Because the distance between two neighboring slices is small, the area chance between two neighboring images is also few. Therefore, we design an iterative rule on the area of the object to detect and extract the target contour of each image. After preprocessing of ultrasonic C image, we extract the contour of the object scanned by ultrasonic transducer. Then, we reconstruct the 3D ultrasonic C scanning image using marching cube algorithm. In experiments, we implement the proposed method for ultrasonic scanning data of tissue-mimicking phantom including a liver model, and we compare the proposed method with other methods. The results show that the proposed method can more accurately display the edge information of the scanned object, and improve the precision of region detection, especially suitable when the edge has the incomplete information.

Discussion on the absolute calibration of piezoelectric acoustic emission sensors

The calibration of acoustic emission sensor is important for acoustic emission quantitative evaluation. To carry out the sensor calibration, one way is to find a reference acoustic emission source, such as a falling solid ball, a fracturing pencil lead, with energy evaluation to obtain the characteristics of the reference source. One way is to use a reference sensor to measure the pressure or the normal velocity at the surface, including the capacitive transducer and the laser interferometer. The other is using reciprocity method. Frequency characteristics of amplitude of absolute sensitivity of both the Rayleigh and longitudinal waves could be determined by purely electrical measurement without the use of mechanical sound sources of reference transducers. In this paper, the progress of the methods of the AE sensor calibration was given. The principles and the merits and faults of each method are discussed. In this paper the rapid calibration method by pulse exciting transducer was also discussed in different wave mode, as well as Face to Face method.

Heterodyne System for Measuring Frequency Response of Photodetectors in Ultrasonic Applications

The heterodyne interferometer using acousto-optic modulation is presented to measure the frequency response of photodetectors (PDs) utilized in ultrasonic applications by optical methods. The heterodyne signal is served as the excitation source. The measurement frequency more than 150 MHz can be achieved by two serial or parallel connected acousto-optic frequency shifters (AOFSs) in the interferometer. The frequency shift of AOFSs can be adjusted continuously, so that the frequency resolution of the measurement better than 500 kHz is easy to realize. The experimental results for two PDs with bandwidth 150 and 50 MHz are discussed. The presented scheme can also be used to characterize the PDs in the frequency range of megahertz for other optical measurement applications.

Consistency of surface pulse and reciprocity calibration of piezoelectric AE sensors

The calibration of piezoelectric acoustic emission sensors mainly includes two methods, reciprocity method and surface pulse method. The former uses the principle of electro-acoustic reciprocity of piezoelectric sensors, and the latter needs a reference capacitance or laser system for displacement or velocity measurement. Prior studies have indicated that the two methods had some consistency, but some scholars still questioned the reciprocity calibration of piezoelectric acoustic emission sensors. In this paper the equivalent and real reciprocity coefficient were calculated and compared to test their consistency. Experimental system was established to test and verify the results. The test results showed that the reciprocity and surface pulse method had good agreement.

Objective evaluation system for noise reduction performance of hearing aids

Hearing aid is a device, which can acquire, process and feedback acoustic signal in real-time, it is portable and has low power consumption. Its many technologies will influence the effect of hearing, such as manufacturing technology, adjusting procedure. The key technology that influences the effect of hearing is the noise reduction technology. The performance of noise reduction seriously affects the intelligibility of speech, even the physical and mental health of the people who have diminished or defective hearing. So studying on the evaluation for noise reduction performance of hearing aids has a very important significance. However, there is not a clear system to evaluate the noise reduction of hearing aids in the domestic. In this paper, a complete set of objective evaluation scheme is put forward. At first, acoustic signal will be acquired though the experiment system designed in our work which can simulate real working conditions, then signal-to-noise ratio (SNR) and segmental signal-to-noise ratio (segSNR) of signal will be calculated after aligning the output signal and input signal to evaluate the noise reduction performance of hearing aids. The simulation results show that the evaluation method proposed here can evaluate hearing aids automatically and conveniently.

Factors and uncertainty evaluation of quasi-static method for measuring piezoelectric constant

Quasi-static method is recommended by international standards to measure the piezoelectric constant d33 of piezoelectric ceramics. To calibrate the quasi-staticapparatus, a system directly based on quasi-static force and electric charge measurement was developed. The factors were studied and the uncertainty was evaluated. The test results showed that the static force had different effect on hard and soft ceramics materials, and the frequency and the amplitude of driving force made significant impact. The uncertainty evaluation indicated that the d33 measurement of quasi-static method is no more than 4 % (k=2) for PZT4 and PZT5 materials.

Measurement of microphone parameters based on high-pressure calibration system

This paper presents a method for measuring a few microphone parameters based on the high-pressure calibration system. The high pressure calibration apparatus and method are first given. Then the linearity-deviations of three microphones are measured, the uncertainties of three microphones are estimated, and the dynamic range limits of three microphones at high sound pressure levels (SPL) are measured. In this study, the range of the linearity-deviations is from -0.02dB to +0.02dB, and that of the uncertainties is less 0.05dB. The dynamic range limit of three microphones is 149dB, 147dB and 162dB, respectively. Compared with the manufacturer parameters, experimental results are consistent with manufacturer data.