Ultrasonic range

For short wave vectors (or long wavelengths) corresponding to waves in the acoustic or ultrasonic range, eq. (8.17) reduces to... 

These applications of ultrasonics constitute only a small portion of the total scope of sonic technology which is presented in specialized references (Refs 9 11). Strictly speaking, the ultrasonic range should begin above 16kHz, the limit of human auditory capacity, but as the limits of only a few applications have been extensively explored, the range of ultrasonics of interest here must be chosen somewhat wider. Moreover, the choice of the human auditory... 

Electromagnetic radiation in the ultraviolet range or X-rays can form a source of ignition as well as acoustic waves, especially in the ultrasonic range. It is only a question of power density in the radiation field. 

Mobility of blind individuals is complicated, especially in unfamiliar territory, by hazards that cannot be easily sensed with a long cane, such as overhanging tree limbs. A few devices have appeared that convert the output of sonar-like ultrasonic ranging sensors to discriminable audio displays. For example, the Wormald Sonicguide uses interaural intensity differences to indicate the azimuth of an object and frequency to indicate distance (Cook, 1982) subtle information such as texture can sometimes also be discriminated. 

The frequency range of AE phenomena in the broadest sense extends from the infrasonic range (less than 16 Hz) far into the ultrasonic range (higher... 

Piezoelectric transducers are the most common devices employed for the generation of ultrasound and utilise ceramics containing piezoelectric materials such as barium titanate or lead metaniobate. The piezoceramic element commonly used in ultrasonic cleaners and for probe systems is produced in the form of a disk with a central hole. Ceramic transducers are potentially brittle and so it is normal practice to clamp them between metal blocks. This serves both to protect the delicate crystalline material and to prevent it from overheating by acting as a heat sink. Usually two elements are combined so that their overall mechanical motion is additive (Figure 10.4). Piezoelectric transducers are better than 95% electrically efficient and can operate over the whole ultrasonic range. 

The frequency dependence of 33 over a frequency range of more flian eight decades can be obtained by utilizing two methods, namely, a step-response and an interferometric technique (Zhang et al. 2004). The step-response measurement is based on the quasistatic method utilizing the direct piezoelectric effect and employs, for data evaluation, a Fourier analysis of the temporal electrical response to fire appUcation of a pressure step. This method yields useful data in the frequency range from 10 Hz to several Hz. For frequencies from 1 Hz to 300 kHz, an interferometer can be utilized. In addition, acoustic method can also be used to obtain the frequency dependence of 33 in audio and ultrasonic ranges. 

Ultrasonic absorption is used in the investigation of fast reactions in solution. If a system is at equilibrium and the equilibrium is disturbed in a very short time (of the order of 10"seconds) then it takes a finite time for the system to recover its equilibrium condition. This is called a relaxation process. When a system in solution is caused to relax using ultrasonics, the relaxation lime of the equilibrium can be related to the attenuation of the sound wave. Relaxation times of 10" to 10 seconds have been measured using this method and the rates of formation of many mono-, di-and tripositive metal complexes with a range of anions have been determined. 

The technique presented above has been extensively evaluated experimentally using ultrasonic data acquired from a test block made of cast stainless steel with cotirse material structure. Here we briefly present selected results obtained using two pressure wave transducers, with refraction angles of 45° and 0°. The -lOdB frequency ranges of the transducers were 1.4-2.8 MHz and 0.7-1.4 MHz, respectively. The ultrasonic response signals were sampled at a rate of 40 MHz, with a resolution of 8 bits, prior to computer processing. 

Fokker Bond Tester. An ultrasonic inspection technique commonly used for aircraft structures is based on ultrasonic spectroscopy [2]. Commercially available instruments (bond testers) used for this test operate on the principle of mechanical resonance in a multi-layer structure. A piezoelectric probe shown in Figure 3b, excited by a variable frequency sine signal is placed on the surface of the inspected structure. A frequency spectrum in the range of some tens of kHz to several MHz is acquired by the instrument, see Figure 3a. 

During the inspection of an unknown object its surface is scanned by the probe and ultrasonic spectra are acquired for many discrete points. Disbond detection is performed by the operator looking at some simple features of the acquired spectra, such as center frequency and amplitude of the highest peak in a pre-selected frequency range. This means that the operator has to perform spectrum classification based on primitive features extracted by the instrument. 

Projection radiography is widely used for pipe inspection and corrosion monitoring. Film digitisation allows a direct access to the local density variations by computer software. Following to a calibration step an interactive estimation of local wall thickness change based on the obtained density variation is possible. The theoretical model is discussed, the limitations of the application range are shown and examples of the practical use are given. The accuracy of this method is compared to results from wall thickness measurements with ultrasonic devices. 

Papoulis, A. and Chamzas, C., Improvement of range resolution by spectral extrapolation. Ultrasonic Imaging /, pp. 121-135 (1979)... 

This paper describes the development of a novel system for improving the quality of information provided by manual ultrasonic examination of welds, while retaining the flexibility of the human operator to apply the techniques to components of a wide range of geometries and dimensions. The system, known as CamuS (Computer Aided Manual UltraSonics) provides assistance to the manual operator in two separate areas ... 

Assessment variations ranging from 2 to 3 dB are normal, even with well-trained ultrasonic inspectors. With longer work assignments or adverse external influences (cold, heat, dust, noises, etc.) considerably higher variations (12 dB and more) are often observed due to lack of concentration and to tiredness [1]. 

In this paper, the following aspects have been studied (A) Flaw detection can be made directly on the surface of the pipes, (B) The defects within the range of wall thickness can be tested out, that is to say, the ultrasonic testing without dead zone for the pipe wall can be realized and (C) Testing the defects of FBH as our testing. Objects, we may make the testing... 

In order to test a wide range of materials a series of ultrasonic pulser/receiver boards has been developed. In combination with an ADC-board (analogue-to-digital converter) a PC can be converted to a high performance ultrasonic system not only for manual testing but also for automatic testing and imaging systems. 

The HILL-SCAN 30XX boards enable ultrasonic inspections from 50 kHz (concrete inspections) to 35 MHz (inspection of thin layers) with a signal to noise ratio up to 60 dB. The gain setting range of the receiver is 106 dB. High- and low pass filters in the receiver can be combined to band-passes, so that optimal A-scans are displayed. 

MAPPscan is a manual ultrasonic testing system connected to an acoustic positioning system.. The system is developed as a consequence of the increased radiation doses in nuclear plants The system has the same flexibility as manual scanning with the same accuracy and the possibilties to collect, store and evaluate the UT data as with mechanised Ultrasonic systems The positioning system is based on spatial acoustic triangulation and have an accuracy of better than 1.0 mm within its recommended range. 

The UT-Acquisition system hardware consists of a 1 channel ultrasonic board, for puls/echo, one or two crystal probes It operates within a frequency range of 0,5 - 15 Mhz and with variable sampling frequencies in steps of 20,40 or 80 MHz... 

The range of ultrasonic, eddy-current and magnetic defectoscopes, structuroscopes and thickness gauges for metals and coatings are continuously modernized. 

Besides large-diameter pipes, ultrasonic testing is used for checking the welded joints of drill bits, components of wind-driven electric plants, welded joints of light alloys and non-metallic materials, for an integrated inspection of various objects. A range of training aids developed at the Institute allows the operators to be trained effectively. 

There is a very wide range of designs for nebulizers, but most are based on some form of gas/liquid sprayer or on ultrasonics. 

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