Measuring and testing – Vibration – By mechanical waves
Patent
1982-06-22
1984-11-13
Birmiel, Howard A.
Measuring and testing
Vibration
By mechanical waves
73625, 73628, 307262, 307320, G01N 2900
Patent
active
044818238
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to ultrasonic probing for exploring a part or an organ to be analysed, more especially although not exclusively, in depth, i.e. by echography B.
There is described in French Pat. No. 2 472 753 and corresponding U.S. Pat. No. 4,351,038, an ultrasonic sonic probing device of the type comprising n elementary transducers spaced apart at even intervals, a generator associated with the transducers through members adapted to supply, on different channels, from the same pulse of the generator, pulses delayed by time .tau. and multiples of .tau., means for storing the distribution over n successive elementary transducers of the delays corresponding to focusing at a given distance from the line, means for connecting a group of n transducers to the phase-shift means and to the generator in accordance with the distribution selected by the storage means, and a receiver associated with the transducers.
The device described by way of example in French Pat. No. 2 472 753 uses, for reception, switching means which comprise a multiplexer (which is also generally used for emission) associated with each transducer and connected, by a common bus line having a channels in which are inserted phase-shift means, to a summing circuit for summing the reception signals, each multiplexer comprising a multibit control input connected to a respective stage of a phase-shift register associated with a clock for moving said stored distribution along the register. These phase-shift means are formed by several separate phase-shifters or delay lines.
The a phase shifts may be spaced evenly apart, but in some cases it is more advantageous to provide different intervals, for example so as to take into account the variation of the slope of the curve representative of the phase as a function of the distance to the centre of the group of n transducers.
The present invention aims at providing an ultrasonic probing device of the above-defined kind, which is simple but allows however fine sampling of the phase or of the delay, focusing without a secondary lobe of a prohibitive level and continuous dynamic cocusing (also called tracking focusing) and not simply by discrete steps as in the case of the embodiment described in French Pat. No. 2 742 753.
To this end, the invention proposes more especially a device of the above-defined kind, in which the receiver associated with the transducers comprises a single delay line having multiple taps, closed upstream across an iterative impedance formed of progressively variable delay cells and in which the transducers are connected to said taps through voltage-current amplifiers.
The use of the same multitap delay line for emission and reception is known per se see French Pat. No. 1 163 092, but using an arrangement which only allows the delays to be varied by switching. The use of a variable-delay line for each transducer for focusing at reception is disclosed in the French Pat. No. 1 163 092 but in a form which cannot be implemented in practice.
The delay line may be formed of identical LC cells connected together, each comprising an adjustable-impedance element. This adjustable impedance element is formed for example by a VARICAP diode. The diodes of all the cells then receive the same control voltage. So that the delay line may remain closed in all cases on its iterative impedance, the line may be looped upstream across a series of LC cells each comprising a VARICAP diode. All the diodes are then biased by a line to which there is applied, at the upstream end, a fixed voltage and, at the downstream end, the voltage for controlling the VARICAP diodes. A resistance bridge is placed across the cells forming the iterative impedance so as to ensure the correct spacing out of the voltages over the VARICAP diodes and the iterative impedance.
The focusing distance may be controlled manually by operating a control voltage generator: thus, a medium may be examined in depth by focusing, at reception, on the interesting zone. There may also be provided in the device a control-voltage gener
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Birmiel Howard A.
Centre National de la Recherche Scientific
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