Ultrasonic signal generator

A simple interferometer is illustrated in figure 6. The same basic components can be used for a c.w. experiment as for a pulsed experiment, i.e., a signal generator, a transducer, a measurement cell and an oscilloscope. Nevertheless, there function and arrangement are slightly different. The sample is contained in the measurement cell, between an ultrasonic transducer and a reflector plate which moves vertically through the sample. 

The signal generator applies a continuous sine wave of suitable frequency and amplitude to the transducer. The transducer generates an ultrasonic sine wave which propagates into the sample and is reflected back and forth between the reflector plate and transducer. Standing waves are set up in the sample, and the amplitude of the signal received by the transducer... 

The key elements of an ultrasonic measurement system are a transducer, which converts an electrical impulse into mechanical vibration, a signal generator to produce the original electrical excitation signal, and a display... 

Devices such as ultrasonic flow equipment use the Doppler frequency shift of ultrasonic signals reflected from discontinuities in the fluid stream to obtain flow measurements. These discontinuities can be suspended solids, bubbles, or interfaces generated by turbulent eddies in the flow stream. The sensor is mounted on the outside of the pipe, and an ultrasonic beam from a piezoelectric crystal is transmitted through the pipe wall into the fluid at an angle to the flow stream. Signals reflected off flow disturbances are detected by a second piezoelectric crystal located in the same sensor. Transmitted and reflected signals are compared in an electrical circuit, and the corresponding frequency shift is proportional to the flow velocity. 

Figure 2. Experimental apparatus for the investigations of acoustic cavitation in a liquid metal. (1) Signal-Generator (2) Amplifier (3) Ultrasonic Generator (4) Transducer (5) Frequency meter (6) Valve voltmeter (7) Sensor of a waveguide stick (8) Recorder (9) Cavitometer (10) Potentiometer (11) Probe (12) Crucible with a melt (13) Source of ultrasound (14) Receiving stick (15) Electric furnace (16) Detector of the first bubble.

Shade, R.E., Furgason, E.S., and Murdock, L.L. 1990. Detection of hidden infestations by feeding-generated ultrasonic signals. Am. Entomol. 36, 231-234. 

Ultrasonic measurement techniques applicable to food emulsions are reviewed extensively elsewhere (11—15) and only a brief introduction is presented here. Most ultrasonic measirrement systems require an electrical signal generator that is used to excite an ultrasonic transducer to produce an acoustic wave which, after passing through the emulsion, is detected by a second transducer (or the first after a reflection). Finally, a display system, usually a computer or oscilloscope, is used to record and store the elec-... 

Use bipolar cautery if possible. This type of system has a short current path, which greatly reduces the area of significant electrical signal generation to roughly a 6-in. circle centered on the site of electrocautery application. In addition, an ultrasonic scalpel may reduce EMI (22). If a unipolar cautery... 

UT crack detection tool generates an ultrasonic signal into the pipe wall that is reflected off the internal and outer surfaces of the pipe. If a crack is detected, the signal reflects back along the same path of the tool. Since a liquid couplant is required between the sensors and the pipe wall, this tool works only with liquid pipelines. 

Electromagnetic acoustic tools are particularly adapted to the detection of cracks in dry gas pipelines. This tool generates ultrasonic signals without requiring liquid couplant to transfer the ultrasound into the steel. These tools are new to the pipeline inspection industry, so their effectiveness has not yet been determined. 

Apparatus and principle of measurement For generation and detection of sonic and ultrasonic signals in the range of 0.5-135 kHz, an ELASTO-MAT 1.024 (made by Institut Dr. Forster, Reutlingen, FRG) and self constructed piezo-ceramic transmitter/receiver systems were used. A detailed description of the measurment technique is given in e.g. [7,8]. 

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

In Fig. 1.12, a typical experimental set-up of a bath-type reactor is shown. An electric signal with sinusoidal wave of a chosen ultrasonic frequency is generated by a function generator. The signal is amplified by a power amplifier. Then it is... 

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