Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/22—Details, e.g. general constructional or apparatus details
  • G01N29/30—Arrangements for calibrating or comparing, e.g. with standard objects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
  • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
  • G01S7/52046—Techniques for image enhancement involving transmitter or receiver

Definitions

• the present invention relates to a method and an apparatus for generating short ultrasonic pulses.
• Ultrasonic echo pulses are widely used nowadays in medical diagnosis. This diagnostic technique is bas- ed upon reflections of ultrasonic energy from boundary surfaces between media having different acoustic impe ⁇ dance.
• the time interval or delay between the emission of a pulse and the reception of an echo is a measure of the distance from the ultrasonic emitter/receiver (transducer) to the reflecting surface.
• the same transducer is usually employed for both emission and reception.
• the signal pro ⁇ cessing utilized has comprised the analogue or digital inverse filtration of the electric signals emitted by the transducer in response to received echo pulse signals.
• the results obtained with this technique have not been entirely satisfactory, inter alia because the impulse response of the ultrasonic transducer has a
• short ultrasonic pulses are generated by imparting to the method and the appa- ratus the special features which are stated in the ap ⁇ pended claims.
• Fig. 1 illustrates the basic principle of this invention in an apparatus according to the inven tion directed towards a specific test object.
• Figs. 2a and 2b show the impulse response and the associated frequency function of an ultrasonic transducer.
• Figs. 3a and 3b show the impulse response and frequency charac- teristic of a pulse shaping filter of the weighted least squares- type.
• Fig. 4 is a block diagram of a test equip ⁇ ment incorporating the invention.
• Figs. 5a and 5b show examples of echo signals obtained respectively without and with preshaping of the excitation pulse of the ultra sonic transducer.
• the apparatus according to the invention comprises a signal generator 1 which is coupl ed to an ultrasonic transducer 2 for the excitation thereof.
• the ultra sonic emitter 2 emits its pulses in a water tank towards two blocks 3, 4 of the plexiglass, each having a thick ⁇ ness of 15 mm and being spaced apart a distance of 2 mm. It should be mentioned in this connection that the ve ⁇ locity of sound in plexiglass is twice as high as in water, or approximately 3000 m/s.
• the signal generator 1 is adapted to generate an excitation signal which substantially constitutes a weighted least squares signal to the transducer proper. More particularly, this excitation signal is generated preferably by means of a pulse shaping filter which preshapes the excitation signal to the ultrasonic transducer 2.
• Fig. 2a shows an Example of the impules response s(t) for an ultrasonic transducer 2 having a centre frequency of about 2 MHz.
• the corresponding frequency spectrum is shown in Fig. 2b illustrating the narrow bandpass characteristic typical of an ultrasonic trans ⁇ ducer.
• the excitation signal of the ultrasonic trans ⁇ ducer 2 instead is given the shape u(t) which is shown in Fig. 3a
• an echo signal of the shape shown in Fig. 5b is obtained.
• the signal shown in Fig. 3a constitutes the impulse response from a weighted least squares filter ( LS filter) .
• the frequency characteristic of the WLS filter is shown in Fig. 3b.
• the WLS filter may be defined as a filter which minimises a cost function of the form
• s(t) is the impulse response of the ultrasonic transducer
• u(t) is the impulse response of the WLS filter
• the WLS filter In designing the WLS filter, the resolution para ⁇ meter T and the parameter w which pays regard to the in put signal noise, must be determined. However, these pa- rameters affect the filter independently of one another. It should be mentioned in the context that the WLS filter is related both to the pure inverse filter and to the signal-adapted filter. Actually, these two filters are special cases of the WLS filter.
• the pure inverse filter is obtained by defining both w and T as 0.
• the signal-adapted filter is obtained by select ⁇ ing a large value for either T or w .
• a WLS filter intro ⁇ quizzed into the signal generator 1 will improve the axial resolution of the received echo signal.
• Fig. 4 illu ⁇ strates a test equipment for producing a suitable i - pulse response u(t) for preshaping the excitation pulse.
• This equipment comprises a shift register 6 for digital storage of the impulse response of the WLS filter.
• the output of the shift register 6 is coupled, via a digital to-analogue converter 7 and a power amplifier 8, to the input of the ultrasonic transducer 2.
• the transducer 2 emits its pulses towards a target 9 and receives echo signals therefrom.
• OMPI trical form by the transducer 2 are supplied, via a preamplifier 10 and an analogue-to-digital converter 11, to a logic unit 12.
• a computer 13 con ⁇ nected to the logic unit 12, the echo signal can be evaluated, and the impulse response u(t) stored in the shift register 6 can be adjusted.
• Fig. 4 shows an oscilloscope 14 connected to the output of the con ⁇ verter 7 and the input of the converter 11.
• the shift register 6 it is possible to utilise, for example, a programmable read ⁇ only memory (PROM) or the like in which the suitable filter signal may thus be stored digitally.
• PROM programmable read ⁇ only memory

Landscapes

• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Computer Networks & Wireless Communication (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Ultra Sonic Daignosis Equipment (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20345341

Family Applications (1)

Country Status (6)

Cited By (4)

Families Citing this family (6)

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• 1981
  • 1981-12-22 SE SE8107731A patent/SE425996B/sv not_active IP Right Cessation
• 1982
  • 1982-12-20 JP JP83500170A patent/JPS58502164A/ja active Pending
  • 1982-12-20 WO PCT/SE1982/000431 patent/WO1983002330A1/en not_active Application Discontinuation
  • 1982-12-20 EP EP83900081A patent/EP0096690A1/en not_active Withdrawn
  • 1982-12-20 US US06/527,576 patent/US4520670A/en not_active Expired - Fee Related
• 1983
  • 1983-08-11 DK DK3657/83A patent/DK365783D0/da not_active Application Discontinuation

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