Multiple ultrasonic transducer with remote selector

An ultrasonic scanning system utilizing a selectively rotatable reflector permitting selective use of multiple transducers mounted around the periphery of a water jet for flaw detection in composite materials.

TECHNICAL FIELD 
This invention relates to ultrasonic inspection, and more particularly, to 
a system and method of switching between different transducers while 
checking for flaws in composite materials with an ultrasonic scanning 
system. 
BACKGROUND OF THE INVENTION 
Ultrasonic testing is used for a variety of different applications from 
thickness measurements to flaw detection in aerospace and structural 
materials. The transducers used for these tests must be selected carefully 
to obtain the required spatial resolution and penetration. Damping, 
frequency, and focal properties required for a specific test often require 
the use of separate transducers. Transducers have heretofore been changed 
manually in order to obtain the characteristics desired for different 
tests. This is a time-consuming operation, particularly for multichannel 
testing and rapid inspection of large test pieces. 
Since ultrasound is strongly reflected at air/solid or air/liquid 
interfaces, test pieces are often immersed in water or streams of water 
supplied by jets or bubblers to provide the coupling medium. 
Various scanning techniques to provide pulsed laser radiation beams on a 
unitary path are exemplified in the prior art, for example U.S. Pat. No. 
3,924,937. 
Use of rotatable reflecting mirrors for light beams are known in the prior 
art as shown for example in U.S. Pat. No. 3,475,552. 
Reflector means for reflecting ultrasonic energy from a plurality of 
transducers is known in the prior art from U.S. Pat. No. 3,107,521. 
SUMMARY OF THE INVENTION 
In accordance with preferred embodiments of the present invention, separate 
ultrasonic transducers are mounted around a rotating element. The end of 
the rotating element acts as a reflector that redirects the ultrasound 
from a transducer toward the inspection surface. A stepper motor coupled 
to the rotator permits selection of the transducer. 
It is accordingly an object of the present invention to provide an 
ultrasonic scanning system which may be used with either immersion, 
bubbler, or water jet coupling of ultrasound to provide switching between 
different test modes of operation.

DETAILED DESCRIPTION OF THE INVENTION 
A preferred embodiment of the present invention is shown in cross section 
in FIG. 2 wherein first and second ultrasonic transducers 12 and 14 are 
shown mounted around the periphery of and extending radially from the 
water jet traveling along the central axis with a sound path 30 of the 
present multiple ultrasonic transducer. Rotating reflector element 16 is 
coaxially disposed about the central axis and sound path diagrammed at 30. 
The end surface of rotating reflector 16 reflects and redirects the 
ultrasound from transducers 12 and 14 along the principal axis of the 
water jet which includes sound path 30. Stepper motor 10 is coupled to 
rotating reflector 16 and permits remote selection of whichever transducer 
12 or 14 is to be activated. The apparatus of FIG. 2 comprising the first 
embodiment of the present invention utilizes a highly damped 5 MHz 
transducer 12 extending radially from the central axis, of the apparatus 
of FIG. 2 and is utilized for inspection of graphite composite laminates. 
Such pulse-echo inspection is effective for detection of certain foreign 
materials that may be inadvertently included in composite structures. 
Second transducer 14 also radially extending from the central axis of the 
apparatus of FIG. 2 comprises an undamped 1 MHz element utilized for 
through-transmission inspection over an extended dynamic range. Such 
transducer 14 is effective in the testing of thick honeycomb structures as 
well as metal bond components. Utilizing a water jet 34 exiting from jet 
nozzle 32 to transmit sound path 30 to a test piece 36, tests were 
conducted utilizing either pulse-echo transducer 12 activation or 
through-transmission testing utilizing transducer 14. Alternately, by 
switching the rotating reflector 16 between transducers 12 and 14 through 
stepper motor 10, a dual mode test was conducted to acquire both types of 
data during a single testing procedure. In the latter dual mode testing, 
through-transmission data was collected while the jet 34 was moving along 
the scan lines away from the scan start point. At the end of the initial 
scan line rotating reflector 16 was automatically switched and pulse-echo 
data was collected as the jet moved towards the start point on test piece 
36. Upon returning to the start point, rotating reflector 16 was again 
moved to cause through-transmission transducer 14 to be active. After 
returning to the scan start point, the jet was indexed laterally and the 
cycle resumed until the area of interest on test piece 36 had been 
scanned. 
For the test conducted with the two transducer jet, it was possible to have 
both the pulse-echo and through-transmission electronics (not shown) 
active simultaneously. The curved rear surface of the support for the 
reflector prevents sound from reaching the transducer that is active at a 
given time. In other words, the through-transmission transducer 14 can be 
active in generating high level 1 MHz sound pulses and not interfere with 
the 5 MHz pulse-echo tests conducted at the same time. 
While only first and second transducers 12 and 14 were utilized in the 
apparatus of FIG. 2, several transducers may be arranged radially around 
the central axis of the jet 34. In such a case, a programmable stepper 
controller would select the appropriate transducer element for scanning 
each portion of a complex structure. Turning now to FIG. 3 it may be 
observed that first and second transducers 12 and 14 have their axes 
parallel to the central axis of the apparatus shown in FIG. 3 as might be 
utilized for immersion testing. A stationary reflector 20 is associated 
with each of transducers 12 and 14 in the apparatus of FIG. 3 with the 
rotary reflector 16 selecting the active transducer.