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辐射压力法与声光法测定超声功率 总被引:2,自引:0,他引:2
本文介绍两种相互独立的超声功率绝对测量方法——辐射压力法和声光法,并对同一标准超声源进行测量,以验证声光法的可靠性。一、两种测量方法的原理及测量装置辐射压力法的测量原理是:在小振幅平面超声场中,两种媒质交界面上出现的时间平均单向压力即辐射压力,其值等于界面两边声能密度的差值。由此产生的辐射压力可用一个置于超声场中的靶来测定。超声换能器所辐射的总功率w与作用在全反射靶上的辐射力之间的关系为: W=CF/2cos~2θ (1)式中,W——总声功率,W; F——沿超声波轴线方向作用于靶上的力,N; c——超声在液体中的传播速度,m/s; θ——靶面法线与入射声束之间的夹角。瓦级超声功率所产生的辐射力约为零点几至几十毫牛顿。 相似文献
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中国计量科学研究院1982年研制建立的毫瓦级超声功率到基准,采用辐射力法获得总声功率值。当超声波通过交界面的不同介质时,在此交界面上产生辐射压力,通过对此压力的测量就可以计算出超声的功率。该装置是由电子微量天平和消声水槽反射靶悬吊系统组成,标准超声源产生的高频激励电压供给超声换能器,以发射超声束,超声束作用在靶上,所产生的辐射力由电子微量天平读取。毫瓦级超声功率副基准1986年被批准为国家副基准,1982年曾荣获广东省科技二等奖。其技术指标为平均声功率测量范围:门一Woo)mw;频率范围:(1-500)MHz;不确定… 相似文献
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发射率分布测量是评价大口径辐射源辐射均匀性的重要基础,但目前针对相关参数的研究较为匮乏。基于全半球激光积分反射方案,设计搭建了基于积分球反射法的红外辐射源发射率分布特征测量系统;开展了测量系统的性能研究,评价了激光光源子系统的稳定性,并在3 W的激光器功率下开展了面辐射源发射率分布特征测量实验。结果表明:建立的测量系统的稳定性良好,以标准金板表面为研究对象,多次测量结果的重复性为0.30%;开展了碳基面辐射源发射率分布实验测量,获得面辐射源发射率的分布云图,发射率的均匀性为98.1%。 相似文献
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瓦级超声功率基准装置基于辐射压力原理制成,超声换能器所辐射的总声功率P与作用在全反射靶上的辐射力F之间的关系式为: P=cF/2cos~7θ (1)式中c为超声在液体中传播速度,单位是m/s;θ为靶面法线与入射声束之间的夹角,单 相似文献
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本文就超声功率标准中的反射靶和换能器的安装误差对测量精度的影响进行数学分析,推导出在存在安装误差的情况下计算超声功率的数学解析式及其二阶近似式,并用计算机算出一些常用条件下反射声压的精确值,从而可以修正由安装误差引起的超声功率测量误差。 相似文献
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换能器的聚焦特性等声学性能是治疗超声系统的重要参数之一,在出厂前和日常维护中须精确测量。目前常用的水听器测量法结果准确,但受声压幅度及测量效率的限制,高功率量程的声功率计造价较高;而基于声全息的表面振动模式测量法可作为高声压下水听器和声功率计测量法的补充,测量小声压平面并对高幅度声压焦域进行重建。为评估声全息法的准确性,文章研究了在小声压下使用基于声全息的表面振动模式测量法对声场进行测量和重建,分析该方法与水听器测量结果之间的功率和声压误差,以及影响误差的重要参数。结果表明,基于声全息的表面振动模式测量法可重建得到与水听器直接测量相近的结果,有望对高声压下工作的换能器的声场特性进行评估。 相似文献
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Tang SC Clement GT 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(2):359-367
The aim of this study is to evaluate the feasibility of using harmonic cancellation for a therapeutic ultrasound transducer excited by a switched-mode power converter without an additional output filter. A switching waveform without the third harmonic was created by cascading two switched-mode power inverter modules at which their output waveforms were pi/3 phase shifted from each other. A PSPICE simulation model for the power converter output stage was developed. The simulated results were in good agreement with the measurement. The waveform and harmonic contents of the acoustic pressure generated by a 1-MHz, self-focused piezoelectric transducer with and without harmonic cancellation have been evaluated. Measured results indicated that the acoustic third harmonicto- fundamental ratio at the focus was small (-48 dB) with harmonic cancellation, compared to that without harmonic cancellation (-20 dB). The measured acoustic levels of the fifth harmonic for both cases with and without harmonic cancellation also were small (-46 dB) compared to the fundamental. This study shows that it is viable to drive a piezoelectric ultrasound transducer using a switched-mode power converter without the requirement of an additional output filter in many high-intensity focused ultrasound (HIFU) applications. 相似文献
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Kelli Hoover Mahesh Bhardwaj Nancy Ostiguy Owen Thompson 《Materials Research Innovations》2002,6(5-6):291-295
Conventional wisdom stipulates that high power ultrasound without direct or indirect transducer contact with the medium to
be treated is not possible. This seemingly correct notion is based upon two major hurdles: inefficient transmission of ultrasound
from the piezoelectric material into air/gases and exorbitant attenuation of ultrasound by gases. The latter is a natural
phenomenon about which nothing can be done, and the former requires an un-conventional approach to transducer design. After
many years of R& D in this area, we have finally succeeded in producing transducers that generate immense acoustic pressure
in air in the frequency range of ∼50 kHz→10 MHz. By using these transducers without any contact with the material, we demonstrate
destruction of 99.9% of dried bacterial spore samples of a close relative of anthrax, Bacillus thuringiensis. Following further refinement of the transducers and the mechanism of their excitation, we anticipate that non-contact ultrasound
will have numerous applications including inactivation of agents of bioterrorism and sterilization of medical and surgical
equipment, food materials, and air-duct systems of buildings, airplanes, space stations, and others.
Electronic Publication 相似文献
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Corbett SS 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1988,35(2):162-167
Miniature polyvinylidene fluoride (PVDF) hydrophones used in determining the power and intensity output of ultrasonic fields, including those radiated from diagnostic ultrasound equipment, were calibrated under a variety of field conditions using the planar scanning technique. A diagnostic B-scan piston-type transducer was used as a source, and the output intensity (spatial-peak pulse-average, or SPPA) was varied from 2 to 30 W/cm(2) while the total power was kept constant. The higher-intensity waveforms were significantly nonlinear in the focal region of the source. When the lateral beam profiles of the source (as measured by the hydrophone to be calibrated) were determined by positive-peak-detecting the ultrasonic pulse, the calibrated pressure sensitivity of the hydrophone systematically decreased as the field became progressively more nonlinear. When the beam profiles were measured using the pulse intensity integral, no systematic dependence of the calibration on field linearity was noted. These results imply that measured values of power and intensity of ultrasound diagnostic equipment may be dependent on the methodology utilized to map the lateral beam profiles of the transducer being measured, and the extent of nonlinear effects in the field under characterization. 相似文献
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Willatzen M 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1999,46(5):1164-1174
A general set of modeling equations for lossless one-dimensional multilayer ultrasound transducers is presented based on first principles. In particular, a direct relationship between ultrasound transducer results and the underlying physical principles of electroacoustics is given. As such, the model may provide better physical understanding for designers not fully versed in electrical circuits theory or in linear system analyses. The model is suitable for time-domain analysis and monofrequency design. Special attention is given to the determination of the time-dependent voltage across the receiver electrodes subject to a general voltage input, but information on any (dynamic) variable of interest is provided. The basic equations governing the dynamics of the multilayer structure acting as transmitter as well as receiver are solved by Fourier analysis and by imposing continuity of velocity and pressure between layers. Sound transmission between the two piezoelectric circuits is assumed to take place in a water bath such that the Rayleigh equation can be used to obtain the incoming pressure at the receiver aperture from the acceleration of the opposing transmitter aperture. Comparison with experimental results is possible by allowing coupling to external electric impedances. A numerical test case using a multilayered 1-MHz transducer for flow meter applications was considered and good agreement with experiments was obtained in terms of voltage signals. The transducer contains a half-wavelength stainless steel layer needed to resist corrosion, the ability to operate at temperatures in a wide range from 20 to 150 degrees Celsius, resistance to impact from flowing particles in the medium, high pressure or vacuum, and pH values up to 10 in some locations. The influence of epoxy glue and grease acoustic coupling layers-between the piezoceramics and the stainless steel layer-in the range from 1 to 70 mum was examined. It was shown that, for the same layer thickness, epoxy glue is preferred as compared with grease, both in terms of signal shapes and amplitudes. Finally, inclusion of appropriate electric impedances in the transmitter and receiver circuits is found to affect signal pulses strongly. 相似文献
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介绍了一种基于量热法的平面换能器声功率测量的方法。先将超声辐射入真空绝热容器内的蓖麻油中,使其温度升高。用热电偶并联测量蓖麻油的平均温升值,计算出蓖麻油所吸收的热能,进而求得换能器的声功率。测量结果表明,在换能器两端电压峰峰值为120V时,用本方法重复10次测得声功率的平均值为5.09W,相应的用辐射力法测得声功率的平均值为6.06W,两者相差16%。该方法的其综合不确定度为±9.3%。此方法使用设备简单且准确性较好,是超声功率测量的一种简单有效的途径。 相似文献
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Wu X Worthington AE Gertner MR Hunt JW Sherar MD 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(5):1028-1035
Strongly focused large aperture transducers used in high-intensity focused ultrasound treatments are prone to manufacturing defects and degradation. Current methods for evaluating transducer quality measure only bulk physical changes of transducers. We have determined the pressure distribution at the transducer surface, using the angular spectrum method, to detect defects of the transducer. Three therapeutic transducers were investigated. The pressure distribution at the focal plane of each transducer was measured and input into a back-projection algorithm to calculate the pressure distribution at the transducer surface. A number of scan window sizes were used for the pressure distribution measurement at the focal plane to determine the effect on the resolution of the calculated pressure distribution at the transducer surface. Results showed that one transducer might have suffered manufacturing defects. The second transducer degraded over 1 year of use with one half of the transducer suffering a partial loss of efficiency. The third transducer remained unchanged over 1 year. The scan window of 40 mm X 40 mm at the focal plane was required to identify defects 6 mm in diameter on the transducer surface. The results demonstrate that the angular spectrum method could be a useful tool for evaluating transducer quality. 相似文献
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Transmitting electric energy through a metal wall by acoustic waves using piezoelectric transducers 总被引:3,自引:0,他引:3
Hu Y Zhang X Yang J Jiang Q 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(7):773-781
The feasibility of transmitting electric energy through a metal wall by propagating acoustic waves using piezoelectric transducers is examined by studying the efficiency of power transmission and its dependence upon the relevant system parameters for a simplified system consisting of an elastic plate sandwiched by two piezoelectric layers. One of these layers models the driving transducer for generating acoustic wave, and the other layer models the receiving transducer for converting the acoustic energy into electric energy to power a load circuit. The output voltage, the output power, and the efficiency of this system are expressed as explicit functions of the system parameters. A numerical example is included to illustrate the dependence of the system performance upon the physical and geometrical parameters. 相似文献