Reducing the influence of a transition process in field calibration of hydrophones at low frequencies with the use of quadrature-added harmonic signals

A method of reducing the signal settling time in a transmitter–receiver system in field calibration of a hydrophone at low frequencies in a non-anechoic water tank based on correction of the radio frequency response is considered. The advantage gained with the use of the radiation of quadrature-added harmonic signals in precise low-frequency calibration of hydrophones by comparison with pulse-tone radiation is demonstrated.     

Comparing hydrophone calibration results for Russian and Chinese standards

Russian and Chinese national standards have been compared by exchanging hydrophones for calibration in the frequency range from 1 Hz to 630 kHz. The results agree very closely, which confirms that the estimates made of the errors in the two standards are reliable. Deceased. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 63–67, June, 2000.     

Two approaches to the continuous-radiation field calibration of a hydrophone in a nonanechoic water tank

A comparative analysis is carried out of a time-delay spectrometry method and a proposed method for the sliding complex weighted averaging of the frequency dependence of the transfer impedance of a radiator and receiver, which provide different approaches to the free-field continuous-radiation calibration of hydrophones in a nonanechoic water tank. The advantages of the second method are demonstrated.     

用偶极子换能器驻波场校准系统校准声压水听器

我们研究了采用偶极子接收换能器的驻波场校准系统,通过调整该系统水小箱中的驻波形式,实现局部空间内的均匀声场,从而可以用来进行声压水听器的比较法校准,并与振动液柱法校准结果相比较,从２０Ｈｚ～２０００Ｈｚ范围内两种方法测得的接收灵敏度偏差小于１ｄＢ。     

The results of the participation of the VNIIFTRI in the first international key comparisons of standards in the field of hydroacoustic measurements

The results of comparisons of the state special standard of the unit of sonic pressure in an aqueous medium, kept at the VNIIFTRI, are analyzed. These results were presented to the COOMET at the first international key comparisons in the field of the calibration of hydrophones in a free field, carried out in the period from 2002 to 2004 under the aegis of the Consultative Committee on Acoustics, Ultrasonics, and Vibrations. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 65–70, March, 2006.     

Primary calibration of hydrophones with extended frequency range 1 to 70 MHz using optical interferometry

A technique for the primary calibration of hydrophones based on an optical principle is presented. An interferometer determines the displacement of a pellicle mounted on the surface of the tank fluid perpendicular to the sound propagation axis; the known acoustic field is then measured using the hydrophone. The application range extends from 1 to 50 MHz and, with a lesser accuracy, to 70 MHz. The loaded and the open-circuit sensitivity are obtained pointwise, and the frequency and the number of the measurement points can be arbitrarily chosen. As an example, two membrane hydrophones with a spot diameter of 0.5 mm are calibrated, and the comparison with a theoretical model describing the acoustic and electrical properties of the hydrophone shows good agreement.     

水听器复数灵敏度的激光法校准

利用激光测振技术直接检测声场作用下的水介质质点振速,通过推算得到声场中该点声压的幅值和相位,从而可精确校准水听器的复数灵敏度.利用该技术,我们在10～100 kHz频段建立了一套水听器复数灵敏度的校准装置.本文简要介绍了装置的校准原理、方法以及各组成部分,并对Φ20球形水听器进行实验测试.结果表明,激光测振技术是一种有效的校准水听器复数灵敏度的方法,校准结果具有很高的精度.     

中俄标准水听器在0.01～1Hz频段的双边比对校准

叙述中国杭州应用声学研究所和俄罗斯全俄物理技术与无线电测量科学研究院的标准水听器在0．01～1Hz频率范围内的双边比对校准方法和结果。在15个频率点上双方分别对5个不同水听器测得的开路电压灵敏度之差的平均值最小为0．02dB,最大也只有0．21dB,远小于双方合成的总扩展不确定度,这证明了两国在此频段内的水声声压标准装置都有很高的准确度。     

Optimization of the underwater structures employed when calibrating hydrophones in a free field

The results of investigations of the distribution of sources of reflections on the bars employed to position hydrophones under water during free-field measurements are analyzed. It is established experimentally that the sources of reflections are formed on parts of the bars where its reflective power changes sharply. It is shown that structures, designed taking into account the mechanism of the distribution of sources of reflection, enable the interference distortions of the acoustic field to be reduced considerably. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 60–63, January, 2007.     

Microconfigured piezoelectric artificial materials for hydrophones

Piezoelectric PZT–air composites with a complex design optimized for hydrophones were fabricated as arrays of hundreds of 60 μ units using a microfabrication technique involving coextrusion of mixtures of thermoplastic with PZT powder or carbon powder. The measured piezoelectric coefficient was 300 pC/N with a figure of merit of 18 pm²/N, in excellent agreement with the predicted properties.     

250Hz～8kHz频率范围水听器自由场校准补充比对

介绍了以杭州应用声学研究所作为主导实验室与俄罗斯国立物理技术和无线电工程测量研究院开展COOMET.AUV.W-S1:250 Hz~8 kHz频率范围水听器自由场校准国际补充比对的结果。比对校准了两只标准水听器TC 4033和GI 55。互易法和比较法及其校准装置被用于评估中俄两国在水听器自由场低频校准方面的当前水平。结果显示,中俄两国得到的两只标准水听器的自由场灵敏度校准结果具有很好的一致性,绝大多数频率点的校准结果与参考值的差值小于0.40 dB,最大偏差为0.59 dB。结果证明,中俄两国的自由场水听器校准低限可扩展至250 Hz。     

Effect of platinum oxidation on the characteristics of standard platinum resistance thermometers

Platinum oxidation in PTS-10 and PTS-25 standard platinum resistance thermometers has been studied. The experimental results show that heat treatment of a thermometer at 100–300°C can increase its resistance at the triple point of water by the equivalent of 1.5 mK. A procedure for calibration in the range 0–450°C is recommended. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 41–44, July, 1996.     

The effective frequency band for free-field measurements under laboratory hydroacoustic tank conditions

The principle of free-field measurements under continuous radiation conditions, based on the use of the properties of the transfer function of a hydroacoustic tank, is analyzed. The radiator can excite signals with a complex spectrum and harmonic signals. The effect of reflections is eliminated by complex averaging of the frequency dependence of the transfer impedance of the converters. The result of these measurements is the value of the free-field transfer impedance, averaged over the effective frequency band of the measuring tank. __________ Translated from Izmeritel’naya Tekhnika, No. 11, pp. 46–51, November, 2006.     

Comparison of the National Standards of Russia and China in the Infrasound Frequency Range

The Russian and the Chinese Underwater Pressure National Standards in the frequency range 0.01 Hz to 1 Hz were compared by exchanging hydrophones and the results of calibration. The reproducibility of the calibration results confirmed the high-level metrological characteristics of both standards.     

An ultrasonic time-delay spectrometry system employing digital processing

Time-delay spectrometry (TDS) is a swept-frequency technique that has proven useful in several ultrasonic applications. Commercial TDS systems are available, but only in the audio frequency range. Several ultrasonic research TDS systems have been constructed, and they have been used effectively for substitution calibration of hydrophones and for measurement of attenuation and sound velocity in materials. Unfortunately these systems depend on features of commercial equipment no longer manufactured, so a new system has been designed using modern equipment and straightforward signal processing. This system requires a frequency source with a reasonably linear sweep of frequency versus time, audio frequency filters, a standard double-balanced mixer, a power splitter, a waveform digitizer capable of handling audio frequency signals, and a personal computer. An optional implementation that shifts the signal to a lower frequency for more convenient digitization and easier velocity measurements additionally requires an audio frequency oscillator and an audio-range analog multiplier. The processing steps are performed with standard signal processing software. To demonstrate the operation of the system, substitution calibration measurements of hydrophones as well as attenuation measurements on a tissue mimicking material were obtained and compared to a custom TDS system previously described by the authors. The data from these two TDS systems agree to within +/- 0.5 dB in the 1-10 MHz frequency range used. Higher frequency source transducers could be used to extend this range.     

Corrosion and electrochemical properties of the steel of exploited oil tanks in bottom water

We have detected a distinction in the corrosion and electrochemical behavior of St3sp steel of different parts of an oil storage tank in under-product water of different oil refineries depending on preliminary contact between the metal and working media of different corrosiveness. Due to long-term contact of the steel with a corrosive working medium (under-product or condensed water), its corrosion resistance decreases substantially. We have established that a medium with an oil-water interface has the greatest corrosiveness, and oil-water emulsion has the lowest. The intensity of electrochemical processes is higher on the steel of those domains of the oil storage which contacted with under-product or condensed water as compared with the metal contacted with oil. The least mineralized under-product water is also the least corrosive. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 1, pp. 104–108, January–February, 2008.     

Infrared spectroscopic study of water in mesoporous silica under supercritical conditions

The structure of water under high temperature–pressure conditions in mesospace was investigated by measuring the infrared spectra of water in mesoporous silica. Absorption peaks attributed to OH-stretching vibration of water in mesoporous silica were detected at lower wavenumbers as compared with bulk water, and the absorption peak positions were dependent on pore diameter. For small pore diameters (3–20 nm), absorption peak positions of water were detected at lower wavenumbers (ca. 3,300 cm⁻¹) at 400 °C, while for larger pore diameters (30–50 nm) the peaks were detected at higher wavenumbers (ca. 3,500 cm⁻¹). We attribute these features to the effects of mesoporous silica surface structure on the structural and vibrational modes of water. Furthermore, absorption peak positions changed significantly at different pore sizes (20 and 30 nm), indicating that the structure of water in small pores approaches a more ice-like structure. Based on our experimental results, the structured water layer in mesoporous silica is estimated to be at least 10 nm thick, which is thicker than that previously documented in molecular dynamic simulation studies where the thickness of structured water was found to be two or three layers from the surface.     

Resonator measurements: The area under the resonance curve as informative parameter

It is shown that the method of measurement using the area under the resonance curve in resonator sensors as the informative parameter is considerably more sensitive to the quantity being measured than the method based on measurement of the resonance frequency. An example of the use of the method to determine the level of a dielectric liquid in a tank using a radio-wave resonator sensor is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 56–58, May, 2006.     

Characteristics of piezoceramic and 3–3 piezocomposite hydrophones evaluated by finite element modelling

The transducer characteristics of hydrophones manufactured from porous 3–3 piezocomposites are compared with dense piezoceramic disc hydrophones using finite element modelling. Due to the complex porous structure of the 3–3 piezocomposites, a real-size 3-dimensional model was developed while a 2-dimensional axisymmetric model was constructed for the simple dense disc hydrophone. The electrical impedance and receiving sensitivity of the hydrophones in water were evaluated in the frequency range 10–100 kHz. The model results were compared with the experimental results. The sharp resonance peaks observed for the dense piezoceramic hydrophone were broadened to a large extent for porous piezocomposite hydrophones due to weaker coupling of the structure. The receiving sensitivity of piezocomposite hydrophones is found to be constant over the frequency range studied. The flat frequency response suggests that the 3–3 piezocomposites are useful for wide-band hydrophone applications.     

Extending the frequency range of the National Physical Laboratory primary standard laser interferometer for hydrophone calibrations to 80 MHz

A method for the primary calibration of hydrophones in the frequency range up to 60 MHz is described. The current National Physical Laboratory (NPL) primary standard method of calibrating ultrasonic hydrophones from 500 kHz to 20 MHz is based on optical interferometry. The acoustic field produced by a transducer is detected by an acoustically transparent but optically reflecting pellicle. Optical interferometric measurements of pellicle displacement at discrete frequencies in tone-burst fields are converted to acoustic pressure, and the hydrophone for calibration is substituted at the same point, allowing sensitivity in volts per pascal to be obtained directly. For calibrations up to 60 MHz, the interferometer is capable of measuring the displacement of the pellicle as a function of frequency in a harmonically rich nonlinear field up to and including the 12th harmonic of the shocked field generated by a 5 MHz focusing transducer, allowing hydrophones to be calibrated by substitution in the same field. Sources of uncertainty in the new method have been investigated. Best combined random and systematic uncertainties at the 95% confidence level for the new method are 7% at 20 MHz, 11% at 40 MHz, and 16% at 60 MHz.