View
233
Download
1
Category
Preview:
Citation preview
7/30/2019 Characteristics of Piezoelectric Transducers
1/50
Characteristics of Piezoelectric
Transducers
The transducer incorporates apiezoelectric element, whichconverts electrical signals intomechanical vibrations(transmit mode) andmechanical vibrations intoelectrical signals (receivemode).
7/30/2019 Characteristics of Piezoelectric Transducers
2/50
Composition
Zirconato titanato de plomo Titanato de bario Metaniobato de plomo
Sulfato de litio Quarzo Niobato de litio
7/30/2019 Characteristics of Piezoelectric Transducers
3/50
Band width and frequency
Bandwidth, or range of frequencies. The frequencynoted on a transducer is the central or center frequencyand depends primarily on the backing material.
Highly damped transducers will respond to frequenciesabove and below the central frequency.
The broad frequency range provides a transducer with
high resolving power.Less damped transducers will exhibit a narrowerfrequency range and poorer resolving power, but greaterpenetration
7/30/2019 Characteristics of Piezoelectric Transducers
4/50
US BEAMThe intensity of the sound is indicated by color, with
lighter colors indicating higher intensity.
7/30/2019 Characteristics of Piezoelectric Transducers
5/50
Acoustic pressure and far field
xxD
senPP
21
22
042
Acoustic pressure at the beam axis
)12(4
)12( 222
m
mDX m
Far field: m= 0,1,2,3 Far field pressure: X > 3.7N
7/30/2019 Characteristics of Piezoelectric Transducers
6/50
Far field
7/30/2019 Characteristics of Piezoelectric Transducers
7/50
Near field and far field
7/30/2019 Characteristics of Piezoelectric Transducers
8/50
Ultrasonic field for a straight probe
Campo en eje de palpador (excitacin con pulsos
7/30/2019 Characteristics of Piezoelectric Transducers
9/50
Transducer Beam Spread
Beam spread is largely determined by the frequency and diameter of thetransducer. Beam spread is greater when using a low frequency transducer thanwhen using a high frequency transducer. As the diameter of the transducerincreases, the beam spread will be reduced.
7/30/2019 Characteristics of Piezoelectric Transducers
10/50
Near Field- Far Field- Divergence
The nearfield
BeamDivergence
7/30/2019 Characteristics of Piezoelectric Transducers
11/50
Angulo medio de divergencia del
hazTheoretical value of the half angle d in relation to thediameter and the frequency of the transducer for asound velocity of 1500 m/s (water).
7/30/2019 Characteristics of Piezoelectric Transducers
12/50
Beam characteristics
7/30/2019 Characteristics of Piezoelectric Transducers
13/50
The US beam
Beam Diameter Focal Zone
7/30/2019 Characteristics of Piezoelectric Transducers
14/50
Transducer Types
Contact transducers are generally hand manipulated. They have elementsprotected in a rugged casing to withstand sliding contact with a variety ofmaterials. These transducers have an ergonomic design so that they are easy to gripand move along a surface. They often have replaceable wear plates to lengthen theiruseful life.
7/30/2019 Characteristics of Piezoelectric Transducers
15/50
Immersion transducers
Do not contact the component.These transducers are designed
to operate in a liquid
environment and all connections
are watertight.
7/30/2019 Characteristics of Piezoelectric Transducers
16/50
Dual element transducers
Contain two independently
operated elements in a singlehousing. One of the elementstransmits and the otherreceives the ultrasonic signal
7/30/2019 Characteristics of Piezoelectric Transducers
17/50
Delay line transducers
Provide versatility with a varietyof replaceable options.Removable delay line, surfaceconforming membrane, and
protective wear cap options canmake a single transducereffective for a wide range ofapplications. As the nameimplies, the primary function of
a delay line transducer is tointroduce a time delay betweenthe generation of the sound
wave and the arrival of anyreflected waves.
7/30/2019 Characteristics of Piezoelectric Transducers
18/50
Angle beam transducers
Angle beam and wedges aretypically used to introduce arefracted shear wave into thetest material. Transducerscan be purchased in a varietyof fixed angles or inadjustable versions where the
user determines the angles ofincidence and refraction.
7/30/2019 Characteristics of Piezoelectric Transducers
19/50
Couplant
A couplant is a material(usually liquid) that facilitatesthe transmission of ultrasonic
energy from the transducerinto the test specimen.In contact ultrasonic testing athin film of oil, glycerin or
water is generally usedbetween the transducer andthe test surface.
7/30/2019 Characteristics of Piezoelectric Transducers
20/50
The ultrasonic flaw detector
7/30/2019 Characteristics of Piezoelectric Transducers
21/50
Data Presentation
The three most common formats are knowin the NDT world asA-scan, B-scan and C-scan presentations.
A-Scan Presentation
The A-scan presentation displays the amount of
received ultrasonic energy as a function of time.Most instruments with an A-scan display allow thesignal to be displayed in its natural radio frequencyform (RF), as a fully rectified RF signal, or as eitherthe positive or negative half of the RF signal. In the
A-scan presentation, relative discontinuity size canbe estimated by comparing the signal amplitudeobtained from an unknown reflector to that from aknown reflector. Reflector depth can be determinedby the position of the signal on the horizontalsweep.
7/30/2019 Characteristics of Piezoelectric Transducers
22/50
Data Presentation
In the B-scan, the time-of-flight (traveltime) of the sound energy is displayed along
the vertical axis and the linear position ofthe transducer is displayed along thehorizontal axis. From the B-scan, the depthof the reflector and its approximate lineardimensions in the scan direction can bedetermined
7/30/2019 Characteristics of Piezoelectric Transducers
23/50
Data PresentationC-Scan PresentationThe C-scan presentation provides a plan-type view of thelocation and size of test specimen features. The plane ofthe image is parallel to the scan pattern of the transducer.C-scan presentations are produced with an automateddata acquisition system, such as a computer controlledimmersion scanning system. Typically, a data collectiongate is established on the A-scan and the amplitude orthe time-of-flight of the signal is recorded at regularintervals as the transducer is scanned over the test piece.The relative signal amplitude or the time-of-flight is
displayed as a shade of gray or a color for each of thepositions where data was recorded. The C-scanpresentation provides an image of the features thatreflect and scatter the sound within and on the surfacesof the test piece.
7/30/2019 Characteristics of Piezoelectric Transducers
24/50
Phase array
7/30/2019 Characteristics of Piezoelectric Transducers
25/50
7/30/2019 Characteristics of Piezoelectric Transducers
26/50
Normal Beam Inspection
Pulse-echo ultrasonic measurements can determine the locationof a discontinuity in a part or structure by accurately measuringthe time required for a short ultrasonic pulse generated by atransducer to travel through a thickness of material, reflect fromthe back or the surface of a discontinuity, and be returned to the
transducer. In thickness gauging, ultrasonic techniques permit quick and
reliable measurement of thickness without requiring access toboth sides of a part. Accuracy's as high as 1 micron.
It is possible to measure most engineering materials
ultrasonically, including metals, plastic, ceramics, composites,epoxies, and glass as well as liquid levels and the thickness ofcertain biological specimens.
7/30/2019 Characteristics of Piezoelectric Transducers
27/50
Angle Beams
Angle Beam Transducers and wedges are typically used to introduce ashear wave into the test material.
7/30/2019 Characteristics of Piezoelectric Transducers
28/50
Calibration
Calibration refers to the act of evaluating and adjustingthe precision and accuracy of measurement equipment
7/30/2019 Characteristics of Piezoelectric Transducers
29/50
AWS V1 or IIW
7/30/2019 Characteristics of Piezoelectric Transducers
30/50
Bloque V2
7/30/2019 Characteristics of Piezoelectric Transducers
31/50
Multiple reflections at the edge of
a plate
7/30/2019 Characteristics of Piezoelectric Transducers
32/50
Test on pipes
D
d21sin
))tan(2( dfs s
)cos
2
(
d
fw ws
7/30/2019 Characteristics of Piezoelectric Transducers
33/50
7/30/2019 Characteristics of Piezoelectric Transducers
34/50
Weld testing
7/30/2019 Characteristics of Piezoelectric Transducers
35/50
Weld testing
Ecodynamic curves
7/30/2019 Characteristics of Piezoelectric Transducers
36/50
Ecodynamic curves
Envolvente?
7/30/2019 Characteristics of Piezoelectric Transducers
37/50
7/30/2019 Characteristics of Piezoelectric Transducers
38/50
Flaw location
7/30/2019 Characteristics of Piezoelectric Transducers
39/50
Flaw location and sizing
7/30/2019 Characteristics of Piezoelectric Transducers
40/50
7/30/2019 Characteristics of Piezoelectric Transducers
41/50
7/30/2019 Characteristics of Piezoelectric Transducers
42/50
Crack Tip Diffraction
When the geometry ofthe part is relativelyuncomplicated and the
orientation of a flaw iswell known, the length(a) of a crack can bedetermined by a
technique known as tipdiffraction
7/30/2019 Characteristics of Piezoelectric Transducers
43/50
Tips for U.S. scanning
7/30/2019 Characteristics of Piezoelectric Transducers
44/50
Reflection from small reflectors
7/30/2019 Characteristics of Piezoelectric Transducers
45/50
AVG Diagram
7/30/2019 Characteristics of Piezoelectric Transducers
46/50
7/30/2019 Characteristics of Piezoelectric Transducers
47/50
7/30/2019 Characteristics of Piezoelectric Transducers
48/50
Sound attenuation
7/30/2019 Characteristics of Piezoelectric Transducers
49/50
Calibracin de sensibilidad
7/30/2019 Characteristics of Piezoelectric Transducers
50/50
Curvas DAC
Distance Amplitude Correction (DAC)Acoustic signals from the same reflecting surface will havedifferent amplitudes at different distances from the transducer.Distance amplitude correction (DAC) provides a means ofestablishing a graphic reference level sensitivity as a function of
sweep distance on the A-scan display
Recommended