Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Patent
1986-06-04
1988-03-29
Kyle, Deborah L.
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
181113, G01V 100
Patent
active
047348941
DESCRIPTION:
BRIEF SUMMARY
This invention concerns an electroacoustic pulse source for high-resolution seismic prospectings.
TECHNICAL FIELD
The device can greatly interest industry owing to the manifold application fields involved. It can have useful exploitation in archaeological explorations where acoustic techniques have not yet met with success up to now. Further, the device can be considered a valid means for location of water tables, inland water contour exploration, study of characteristics and behaviours of soils planned for building up operas such as foundations, tunnels, dams and nuclear power plants.
BACKGROUND ART
Sources for deep seismic explorations are very expensive and often not suitable for shallow prospectings for which higher resolutions are required. The most common seismic sources are explosive charges, vibrators, and weight-dropping devices. In near-surface prospectings such as the archaeological one, explosives, although of reduced power, had to be excluded because they do not guarantee a non destructive exploration and require an expensive handling such as security measures, shot-hole drilling and so on. Under many aspects seismic vibrators would represent an adequate means, but their cost is too high. The most simple and economic mechanical devices, usually utilized for shallow prospecting, suffer from several shortcomings; the energy supplied by them is lost in most part, like surface waves and shear waves and is limited to lower frequencies, and the shot repetition rate is too low.
This latter type of source, already experienced at IDAC (G. B. Cannelli, "Geoacoustic Measurement of p-Wave Velocity by Seismic Refraction Technique", Riv. Ital. di Acustica, 8(1), 39-57, 1984), allows only rough prospectings on land.
DISCLOSURE OF THE INVENTION
The seismic wave source, according to this invention, mainly aims at improving the resolution in the acoustic prospectings of shallow underground (from some meters to a few hundred meters). Shallow depths are almost completely ignored in mining research prospectings which are interested to depths of the order of thousand meter and over. These latter are considered more remunerative, and on the other hand, do not acquire high resolutions owing to the macroscopic disomogeneities involved. The seismic wave source according to this invention comprises an electroacoustic transducer carried out so that inside a metallic structure, substantially shaped like a bell, closed at the base by an elastic diaphragm and filled with a liquid having an high electric resistivity and a relatively low dielectric strength, two main electrodes, with adjustable positioning, are set around the focus of the paraboloid and an auxiliary electrode is put between the first ones; a set of capacitors supplied by a high-voltage power supply, and electrically connected, to the main electrodes; a trigger pulse generator electrically connected to one of the main electrodes and to the auxiliary electrode; a synchronization pulse generator which controls the trigger pulse generator and generates the electric pulses necessary to pilot a seismograph and a control oscilloscope, a remote control to drive the synchronism signals by means of a manual operated pushbutton. The above mentioned metallic structure of the electroacoustic transducer is preferably shaped like an empty round paraboloid.
In order to generate a seismic wave by means of the source of this invention, a high voltage discharge is primed between the main electrodes around the paraboloid focus. The produced acoustic pulse is transmitted via the liquid medium to the soil on which the base of the transducer is fixed through the diaphragm that assures the seal of the liquid inside the transducer so as not to cause the contact with the earth surface.
The main advantages of the invention consist in the fact that it carries out a seismic source of "nondestructive" type and that it produces P-waves (longitudinal waves) with such frequency characteristics, directivity patterns and energy, that it allows a good resolution of underground inhomoge
REFERENCES:
patent: 2167536 (1939-07-01), Suits
patent: 2559227 (1951-07-01), Rieber
patent: 3106982 (1963-10-01), Wade
patent: 3356178 (1967-12-01), Nash
patent: 3895188 (1975-07-01), Ingraham
patent: 4369395 (1983-01-01), Stempeck
patent: 4398127 (1983-08-01), Bahn et al.
Cannelli Giovanni B.
D'Ottavi Enrico
Santoboni Silvio
Consiglio Nazionale Delle Ricerche
Kyle Deborah L.
Steinberger Brian S.
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