Patent GB-1403241-A (GB)
Title: Ultrasonic inspection and diagnosis system
IPC: G01N29/28
Filed: 1972-09-26
Abstract: 1403241 Ultrasonic inspection devices T D SACHS 26 Sept 1972 [30 Sept 1971] 44497/72 Heading H4D A medium is inspected ultrasonically by focusing ultrasonic waves at a region in the medium to cause local heating, transmitting a sensing ultrasonic beam through the heated medium, and detecting the phase shift in the sensing beam caused by transmission through the heated medium. The invention is applicable to detecting defects or the relative amounts of heartwood and softwood in timber, to diagnostic examination of animal tissue, and to fluid flow measurement. In the Fig. 1 embodiment the output of a high stability oscillator 18 is gated at 22 to provide coherent RF bursts each comprising a digitally preset number of cycles. Transducer 10 is driven by the bursts and transmits the sensing beam, 11, through the test medium to receiving transducer 12 whose output is phase-compared at 20 with a signal fed from oscillator 18 over line 21 and phase shifter 24. For each burst the phase value from comparator 20 is digitized in an A-to-D converter 28. To obtain an average phase value over a set of bursts the digitized values of the set are added in arithmetic and memory unit 40. Transducer 14 is now energized by high power oscillator 19 to cause heating at a focal point 13 and is then switched off. The phase values for a further set of bursts are digitized at 28 and averaged at 40. The difference between the two averages is computed and represents a "perturbation" (P) value for point 13. By measuring the difference of averages for further sets of bursts, without reenergizing the heating transducer 14, a measure of the heating decay time (D value) is obtained for point 13. The P value is indicative of the temperature coefficient of acoustic velocity at point 13 and the D value is indicative of the rate at which heat can be conducted away from the point, hence of blood or sap flow. The medium is scanned in three dimensions by movement of transducers 10, 12, 14. P and D values for further points 13 are thus derived, transferred to storage and display system 41, and associated with the co-ordinates of the points. To compensate for changes in the acoustic path length between transducers 10 and 12 as the sensing beam is scanned, and so to avoid A-D converter 28 being driven over-scale by large phase shifts, logic 25 provides automatic phase control which tends to zero the phase comparator over a long period (a series of sense bursts). The logic 25 controls phase shifter 24 such that both a coarse delay change (in increments of one RF cycle of oscillator 18) and a fine delay change are provided. To ensure that each point 13 is given the same heating exposure, oscillator 19 output amplitude is varied according to the acoustic absorption of intervening medium, as determined by a preliminary measurement. If living tissue is being examined, the sensing bursts are initiated only when there is little movement of a patient and when interference on a mains supply line is low, the body functions and line being monitored by unit 30. Measurement disturbances are thereby reduced. The invention may be used for fluid flow rate measurement by acoustically heating a fluid portion at one point in the flow path and using the sensing beam to detect the arrival of the heated portion at a down-stream point. Details of the phase measurement and RF burst generation are given (Figs. 5 and 6, not shown).