where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -
848 views
Technical Discussions
Doug Niessen
Doug Niessen
02:52 Sep-29-1998
PVDF face mtl.

I have a requirement to build a PVDF transducer for pulse echo work at low kilohertz freq.s.
The transducer will be coming in contact with sand and other earth materials. What material is
sugested to be used as a protective face?

Tank you,

Doug


    
 
 Reply 
 
Yoseph Bar-Cohen
R & D,
Jet Propulsion Lab (JPL), USA, Joined Nov 1998, 26

Yoseph Bar-Cohen

R & D,
Jet Propulsion Lab (JPL),
USA,
Joined Nov 1998
26
03:22 Sep-30-1998
Re: PVDF face mtl.
: I have a requirement to build a PVDF transducer for pulse echo work at low kilohertz freq.s.
: The transducer will be coming in contact with sand and other earth materials. What material is
: sugested to be used as a protective face?

: Thank you,

: Doug

--------------
Doug,

While PVF2 can induce waves at a broad frequency range it is not
an effective transmitter material for the low KHz frequency range. Generally,
the protective material that is located between the transmitter piezoelectric
material and the test medium needs to have the following properties:
- To reduce reflection losses its impedance value should be between the two media
- It should have minimum internal and bonding flaws and have low attenuation
- In case of contact transducer: good ware characteristics, chemical
resistance, formability and easy to process.

Since the frequency is low you can use thin homogeneous material to minimize
the effect of attenuation. There are not going to be much internal reflections to
interfere with your signal analysis.

Yosi




    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
04:44 Sep-30-1998
Re: PVDF face mtl.
: I have a requirement to build a PVDF transducer for pulse echo work at low kilohertz freq.s.
: The transducer will be coming in contact with sand and other earth materials. What material is
: sugested to be used as a protective face?

: Tank you,

: Doug

Doug:
I suspect you will be struggling to find a suitable material for a PVDF facing to use under the conditions you described.
Yosi pointed out, PVDF is a poor transmitter (only about 6.9 efficiency compared to 1 for quartz and 70 for PZT-5A).
But even worse is its receiver characteristics, normalising whith quartz as 1.0 again we find PVDF only 1.35. But
this is good compared to PZT-5A at 0.21. Combining the efficiencies of the transmit-receive PVDF still comes up short
with the Loop gain of PVDF 9.3 and PZT-5A 14.6.

Since the output of the pulse is relativley broadband and you are working in a VERY lossy medium you are going to lose
much of the upper frequency components so the broadband helps you very little.

The other item Yosi mentioned is the impedance matching matching effect. Most manufacturers use hard materials for
face plates (like Boron Silicate). For work on steel using standard PZT elements this is effective as the high acoustic
impedance of the face plate matches the impedance of the steel AND the PZT. In your application you again run into problems with
a low acoustic impedance in PVDF and a relatively high impedance for sand. You would normally want to find something in the middle
range between the sand and the PVDF. If the material you chose is too "hard" your losses due to reflections will be high and a
hard face of too high a density will also load the PVDF causing the bandwidth to broaden and amplitue displacement will drop causing
even further losses.

As a COMPROMISE, if you must use PVDF I would suggest you look for a thin durable plastic or rubber to bond to the front of the PVDF
probe. Your centre frequency is low so if the rubber is thin enough the losses in the material should be minimised and the loading
effect on the PVDF will be reduced. Also, you should be able to find rubbers and plastics will probably be closer matched in
acoustic impedance to the PVDF.

I do not know the application you have in mind but if you need to penetrate soils you might also want to consider microwaves.

Good luck!


    
 
 Reply 
 

Product Spotlight

PROlineTOP Plug & Play Ultrasonic inspection device

As Plug & Play solution it units all control and operation elements in a small housing and therefo
...
re replaces the typical control cabinet...
>

NOVO Armor 15 & NOVO Armor 22

The Armor Kit Contains the NOVO Armor, which provides additional mechanical protection to the NOVO 1
...
5WN & NOVO 22WN Detectors, the Armor Stand and a traveling soft cover. - Newest shock absorbent technology case - Water resistant design - Supports wired & wireless communication - Multiple positioning options - Tripod connection using the Built-in 1/4” threads - Simple Detector battery replacement
>

AIS229 - Multipurpose Real Time System

Latest standard & automatic real time system developed by Balteau. The AIS229 has been designed to
...
do series inspection in a wide variety of industry. Composed of a shielded cabinet, 5 axis manipulator, x-ray generator and tubehead from 160kV to 225kV, a fl at panel & much more, the AIS229 is most certainly one of the most multipurpose RTR system available on the market.
>

FAAST-PA! OEM Patented phased Array for high speed UT inspection

Multiangle, Multifocus, Multifrequency, Multibeam. Instead of stacking UT electronics and having m
...
any PA probes, FAAST-PA is able to transmit all delay laws within ONE single shot in Real time.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window