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MEASURE AND VIZUALIZATION IN THE NEAR ZONES OF TRANSIENT ULTRASONIC FIELDS GENERATED BY BROADBAND TRANSDUCERS IN
LIQUID MEDIA
E. Riera-Franco de Sarabia, A. Ramos-Fernandez, L . Gomez-Ullate
To cite this version:
E. Riera-Franco de Sarabia, A. Ramos-Fernandez, L . Gomez-Ullate. MEASURE AND VIZUAL-
IZATION IN THE NEAR ZONES OF TRANSIENT ULTRASONIC FIELDS GENERATED BY
BROADBAND TRANSDUCERS IN LIQUID MEDIA. Journal de Physique Colloques, 1990, 51 (C2),
pp.C2-603-C2-606. �10.1051/jphyscol:19902142�. �jpa-00230438�
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Colloque C2, supplément au n°2, Tome 51, Février 1990 C2-603 1er Congrès Français d'Acoustique 2990
M E A S U R E AND V I S U A L I Z A T I O N IN THE NEAR ZONES OF TRANSIENT U L T R A S O N I C FIELDS GENERATED B Y BROADBAND TRANSDUCERS IN L I Q U I D M E D I A
E . RIERA-FRANCO DE SARABIA, A. RAMOS-FERNANDEZ and L. GOMEZ-ULLATE*
Institute de Rcustica, CSIC, Serrano 144, SP-28006 Madrid, Spain
* I n s t i t u t o de Automatics Industrial. CSIC, Rrganda, Madrid, Spain
Résumé - Le but de cet article est de montrer une technique expérimentale pour l'analyse sur la zone proche de la propagation de le champ ultrasonique transitoire émis par des disques résonnants en épaisseur, en bande large. L'amplitude de crête du signal reçu en les transducteurs, pour éléments focalisés et non focalisés, est mesurée en déplaçant des fenêtres temporelles étroites. Des enregistrements de la pression en 3D et 2D ont été réalisés, et ils permettent la visualisation du front d'onde de l'impulsion, et aussi ils donnent des informations sur d'éventuelles anomalies produites sur les disques piézoélectriques lors de la construction des émeteurs.
Abstract - This paper presents an experimental technique for analyzing the propagation of transient ultrasonic patterns generated by broadband thickness-resonant discs in water over the near zones. The amplitude peak detection of the received signals from' focused and unfocused single element transducers is made by using shifting narrow temporal gates. The 3D and 2D pressure plots obtained, allow the snapshot visualization of the pulsed wavefronts, they also provide information on the vibration pattern of the transducer face, which results in the detection of possible constructed anomalies on the piezoelectric disc of the emitters.
1 - INTRODUCTION
In a previous work 111, an analysis in the temporal domain of the broadband pressure signals generated in water by thickness vibrating circular sources was presented. Some discrepances between the experimental results and the temporal behaviour predicted by the radiating piston theory, in some particular points of the field, were discussed. Two non-predicted components,
"head wave" type, were observed with characteristics similar to those shown by other workers
|2|, |3l, |4|> l5lj in very thick piezoelectric transducers. Through out the present work, we will focus our attention on the obtention of pressure-plots related to: very near zones of the transducer surface (plane aperture case), and regions close to the focus (curved aperture case). The temporal components of the transversal beam profile, in the focus line, will be detected through a chopping process performed every 50 ns. In this way, some effects of certain importance in high spatial and temporal resolution imaging systems, which remain hidden in conventional plots, will be detected.
2 - THE VISUALIZATION AND MEASURE SYSTEM
A full account of the experimental system used, to make ^measurements and visualizations of transient ultrasonic wavefronts, is available as a previous publication |6|, and only a brief description is given here. A broadband pulse generator drives the transducer 171 with spike-voltages ranging up to 500 v and rise-times of 10 ns. The transmitting transducers studied were manufactured from heavily damped discs of lead metaniobate (PMN) and lead zirconate titanate (PZT-5A). The PMN emitter is commercially available from Panametrics (A305; J2=19 mm; fr=2.25 MHz) as long as PZT-5A focused (0=28 mm; f =4 MHz) and unfocused (0=26 mm; f =3 MHz) sources were made in our laboratory. The small receiving probes used to make field point pressure measurements were a PZT needle type hydrophone with an active diameter of 0.3 mm and a PVDF microprobe of about 0.8 mm in diameter. These are broadband microtransducers usable in the frequency range 0.5-10 MHz.
Both acoustic emitter and receiver are located in an automatic scanning water tank which gives positional resolution of up to 20 ym, and an accuracy of ± 1 pm by means of numerical control equipment. The amplitude of the pulsed waveforms is detected by an adjustable gated peak detection stage, through a wideband head amplifier. 3D-plots were made by recording the detected pressure amplitude as the Y-coordinate on an analog XY-recorder. In parallel, the reset of the holder circuit in the peak detection process can be externally controlled by an IBM PC/AT computer. This allows the obtention of acoustic patterns from different perspectives, normalization of the pressure values, contour plots, ... etc.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19902142
COLLOQUE DE PHYSIQUE
3
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EXPERDENTAL PROCEDUREA s it was shown i n (61, a c o u s t i c methods produce f i e l d q u a n t i t a t i v e p l o t s by measuring t h e peak of t h e i n d i v i d u a l pressure or i n t e n s i t y values a t each point of a XY-plane ( p a r a l l e l t o t h e emitter v i b r a t i n g s u r f a c e ) or XZ-plane (beam p a t t e r n ) . The amplitude gated d e t e c t i o n of t h e highest peak of t h e pulsed waveforms is made by using temporal windows wide enough t o c o n t a i n t h e whole time evolution of t h e u l t r a s o n i c t r a n s i e n t s i g n a l s . In t h e s e c a s e s it has been confirmed by us t h a t important a s p e c t s about wavefront behaviour can remain masked i n many zones. T h i s is owing t o t h e f a c t t h a t t h e conventional t y p e 2D-plots use t o be t h e p r o j e c t i o n over a plane of events happened in a r e l a t i v e l y long i n t e r v a l of time, t h u s preventing information belonging t o i n s o n i f i c a t i o n s , t h a t can be non-simultaneous, t o be appreciated. For t h e s e reasons we propose t h e use of s h i f t i n g narrow temporal g a t e s with which w e have been a b l e t o observe, s p a t i a l y , c e r t a i n sequences of a c o u s t i c e v e n t s t h a t occur, through a p a r t i c u l a r plane of a focused c i r c u l a r source, according t o our temporal results. Through t h i s procedure some analogies between t h e temporal and s p a t i a l progressions of t h e t r a n s i e n t wavefronts have been analyzed, and t h e non-simultaneity of information r e l a t e d t o d i f f e r e n t p o i n t s of a p l o t , a t t h e f o c a l zones, from a focused c i r c u l a r t r a n s m i t t e d transducer can a l s o be s t u d i e d when t h e usual broader g a t e s a r e used. F i n a l l y , c e r t a i n constructed anomalies w e r e d e t e c t e d i n t h e a c o u s t i c behaviour of some p i e z o e l e c t r i c t r a n s d u c e r s . The evaluation of t h e s e a c o u s t i c d e f e c t s i s very important t o v a l i d a t e u l t r a s o n i c echographic devices.
4 - RESULTS
This s e c t i o n p r e s e n t s s e l e c t e d r e s u l t s f o r t h e s i n g l e element t r a n s d u c e r s (A) 4 MHz-focused, (B) 3 MHz and (C) 2.25 MHz-unfocused, o p e r a t i n g i n a pulse mode. The 3D-experimental p l o t s w e r e c a r r i e d out thro* a f i n e c o n t r o l of t h e v i s u a l i z a t i o n system g a t e (only negative half-cycles of pressure values have been p l o t t e d ) , where t =50 ns is its lower temporal width which corresponds t o a (1/9-1/5) of t h e s i g n a l "equivalenEl1 periods. I n Fig. 1 and analog ZX view of a t r a v e l i n g wavefront, generated by e m i t t e r (A) a t an i n s t a n t t -20.3
u s
(td=delaytime from t h e mainbang) of its propagation, is shown. This agrees with %e passing of t h e pulse by t h e f o c a l point (0,0,21) mm (Z i s r e f e r e d t o t h e transducer edge), being a l s o remarkable t h e analogy, along Z-axis, between s p a t i a l (Fig. l a ) and temporal progressions (Fig. I b ) of t h e t r a n s i e n t s i g n a l , and t h e s h o r t time needed t o make t h e analog-record. In Figs. 2 and 3, on t h e c o n t r a r y , 3D and 2D-snapshots were obtained through t h e computer with s p a t i a l sampling i n t e r v a l s of Az=0.1 mm and Ax=0.5 mm, i n t h e very near f i e l d ( t = l 0 us; Fig.
2) and behind t h e focus zone (td=40 us; Fig. 3 ) . Two curved wavefronts c l e a r l y appear d corresponding t o t h e transducer curved shape, and t h e s p h e r i c a l pulse-form i n t h e f a r f i e l d region. S l i g k t l y d i f f e r e n t results a r e presented i n Figs. 4 and 5, where XZ-plots a r e shown.
These graphics were made maintaining t h e g a t e p o s i t i o n a s before ( i n Figs. l a and 3a), but with sampling i n t e r v a l s of Ax=0.2 mm and Az=0.2 mm. A temporal sequence of t h e d i v e r s e spatial-forms adopted by t h e beam p r o f i l e along t h e X-axis, a t a f i x e d depth of z=21 mm, can be seen i n Fig. 6 a ) . The c o n t r i b u t i o n s t o t h e i n t e g r a t e d p a t t e r n obtained, with t = 50 ns, appear i n d i v i d u a l i z e d and can be compared with t h e p l o t performed (Fig. 6b) by usi% a wide temporal g a t e ( t =3.5 v s ) . F i n a l l y , in Fig. 7, t h e .XY-plots of t h e sound f i e l d near t o t h e e m i t t e r s u r f a c e w(z=0.5 mm) were c a r r i e d out f o r t h e t r a n s d u c e r s (B) and (C), providing d e t a i l e d information on t h e v i b r a t i o n p a t t e r n of t h e transducer f a c e . I n c a s e ( B ) it is e a s i l y seen t h a t t h e r e is a @ = l 5 mm lump of t i n s o l d e r on t h e d i s c of t h e transducer, whereas i n c a s e (C) t h e presence of a diametral e l e c t r o d e on t h e d i s c is a l s o c l e a r l y detected.
5 - CONCLUSIONS
This work has demonstrated t h e a p p l i c a b i l i t y of t h e measure and v i s u a l i z a t i o n system and t h e usefulness of s h i f t i n g narrow temporal g a t e s with t =SO ns, in t h e obtention of 3D and 2D-snapshot p l o t s of u l t r a s o n i c t r a n s i e n t wavefronts,
%I
t h e frequency range 0.5-10 MHz. The experimental procedure h e r e presented a l s o provides information on t h e v i b r a t i o n p a t t e r n of t h e e m i t t e r s u r f a c e , which permits t h e d e t e c t i o n of whether constructed anomalies a r e presented o r not on t h e p i e z o e l e c t r i c d i s c of t h e transducers.1. E. Riera and A. Ramos, Anales de F i s i c a , S e r i e A 85 ( l ) , 1989, (13-27).
2. M.R. Layton and E.F. Carome, J. Acoust. Soc. Am. 64 ( l ) , 1978, (250-256).
3. A . J . Hayman and J . P . Weigkt, J. Acoust. Soc. Am. 66 (41, 1979, (945-951).
4. G.R. H a r r i s , E.F. Carome and H.D. Dardy, IEEE SU-30 ( 5 ) , 1983, (295-303).
5. J . C . Babow, F. Lakestani and M. Perdrix, U l t r a s o n i c s I n t e r n a t i o n a l , 1979, (462-467).
6. E. Riera, A. Ramos and L. Gomez-Ullate, Ultrasonics InCernational, 1989 ( t o be published).
7. A. Ramos, P.T. Sanz and F. Montero de Espinosa, Ultrasonics, 25 ( 4 ) , 1987, (221-228).
F i g u r e 1 F i g u r e 2
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Figure
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Figure5
Figure
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X
TransducerB
)X Transducer C
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Figure
7.
(X-Y) p l o t s of Ppeak f o r Z =0.5
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ACKNOWLEDGEMENTST h i s work was supported by CICYT/PRONTIC 1989. We a r e g r a t e f u l t o D r . Montero de Espinosa and MS A. Garcia-Olias f o r t h e i r helpfulness i n t h e construction of t h e transducers used i n t h i s work.
