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 -

LECOEUR ELECTRONIQUE
The Specialist of electronics for ultrasonic testing.

7137 views
Career Discussions
Sandy
Sandy
07:22 Dec-03-2003
Resonance and crystal thickness

Hello, can anyone please help me with my question?
I read somewhere:
Resonance frequency (Fr)= (speed of sound in crystal)/(2xthickness of the crystal)

I can't really believe this because what I understand is that the crystal vibrates via voltage and then produces vibration,
or do they mean the impedance of the material?

Also I read:The so-called "fundamental resonant frequency" of an ultrasound transducer is the transmit frequency that corresponds to the half-wavelength crystal thickness.
So that:
Fr = 2 x christal thickness

So my question is:
Is the Fr of the crystal obtained when the crystal has a diameter equal to exactly half the wavelength of the ultrasound that is produced by the crystal.

Or does this depend on the acoustic impedance, or speed of sound in the crystal? Do does the Fr depend on the material?

Can someone please give me the correct information on this
or point me in the good direction?

Many thanks!




    
 
 
Paul A. Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul A. Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
09:21 Dec-03-2003
Re: Resonance and crystal thickness
Hello Sandy,
The fundamental mechanical resonance occurs when the thickness of the crystal is 1/2 wavelength thick.
Let
lambda = wavelength
c = acoustic velocity
f = frequency


thickness = lambda/2 (at fundamental resonance)

and

lambda = c/f

then

thickness= c/(2*f)

solving for f

f=c/(2 * thickness)

This refers to the mechanical free resonance of the crystal which is achieved by deforming it and allowing it to resonate...much like striking a tuning fork or a piano string.

If you drive the crystal with an electrical signal, the response will be at the driving frequency. The amplitude of the output will vary with driving frequency...as you approach the resonant frequency of the crystal, the output amplitude will increase.

The piezoelectric element used in a transducer has many resonances, some related to the thickness, and some related to the lateral dimensions. Most transducers are designed so that the unwanted resonances are suppressed and the fundamental dominates theoutput.

So, to answer your question, Fr depends on the thickness and and the acoustic velocity of the crystal.

I hope this answers your question.
Paul
----------- Start Original Message -----------
: Hello, can anyone please help me with my question?
: I read somewhere:
: Resonance frequency (Fr)= (speed of sound in crystal)/(2xthickness of the crystal)
: I can't really believe this because what I understand is that the crystal vibrates via voltage and then produces vibration,
: or do they mean the impedance of the material?
: Also I read:The so-called "fundamental resonant frequency" of an ultrasound transducer is the transmit frequency that corresponds to the half-wavelength crystal thickness.
: So that:
: Fr = 2 x christal thickness
: So my question is:
: Is the Fr of the crystal obtained when the crystal has a diameter equal to exactly half the wavelength of the ultrasound that is produced by the crystal.
: Or does this depend on the acoustic impedance, or speed of sound in the crystal? Do does the Fr depend on the material?
: Can someone please give me the correct information on this
: or point me in the good direction?
: Many thanks!
------------ End Original Message ------------




    
 
 
Sandy
Sandy
05:30 Dec-09-2003
Re: Resonance and crystal thickness
Thank you very much Paul, forgot to thank you,it answers perfectly well my question,
and still another little question(S)

It is stated that for a gaussian pulse shape the bandwidth;
df x t pulse = 1

what do they mean with gaussian?
So the bandwidth x the pulse time = 1

hz x time = 1 ?

Sandy

----------- Start Original Message -----------
: Hello Sandy,
: The fundamental mechanical resonance occurs when the thickness of the crystal is 1/2 wavelength thick.
: Let
: lambda = wavelength
: c = acoustic velocity
: f = frequency
:
: thickness = lambda/2 (at fundamental resonance)
: and
: lambda = c/f
: then
: thickness= c/(2*f)
: solving for f
: f=c/(2 * thickness)
: This refers to the mechanical free resonance of the crystal which is achieved by deforming it and allowing it to resonate...much like striking a tuning fork or a piano string.
: If you drive the crystal with an electrical signal, the response will be at the driving frequency. Theamplitude of the output will vary with driving frequency...as you approach the resonant frequency of the crystal, the output amplitude will increase.
: The piezoelectric element used in a transducer has many resonances, some related to the thickness, and some related to the lateral dimensions. Most transducers are designed so that the unwanted resonances are suppressed and the fundamental dominates the output.
: So, to answer your question, Fr depends on the thickness and and the acoustic velocity of the crystal.
: I hope this answers your question.
: Paul
: : Hello, can anyone please help me with my question?
: : I read somewhere:
: : Resonance frequency (Fr)= (speed of sound in crystal)/(2xthickness of the crystal)
: : I can't really believe this because what I understand is that the crystal vibrates via voltage and then produces vibration,
: : or do they mean the impedance of the material?
: : Also I read:The so-called "fundamental resonant frequency" of an ultrasound transducer is the transmit frequency that corresponds to the half-wavelength crystal thickness.
: : So that:
: : Fr = 2 x christal thickness
: : So my question is:
: : Is the Fr of the crystal obtained when the crystal has a diameter equal to exactly half the wavelength of the ultrasound that is produced by the crystal.
: : Or does this depend on the acoustic impedance, or speed of sound in the crystal? Do does the Fr depend on the material?
: : Can someone please give me the correct information on this
: : or point me in the good direction?
: : Many thanks!
------------ End Original Message ------------




    
 
 
Paul A, Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul A, Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
01:01 Dec-10-2003
Re: Resonance and crystal thickness
Hi Sandy,

A continuous wave signal has only one frequency component and that signal will continue for all time. A pulse can be represented as a summation of continuous wave signals of various frequency and amplitude. The Fourier or frequency spectrum of a pulse shows the distribution of energy as a function of frequency necessary to create the prescribed pulse. The Gaussian shape you reference means that the frequency spectrum has a Gaussian, or "normal", distribution with frequency. This is the same "normal" distribution you encounter in statistics.

However, if I understand your question, it refers to a different situation. You can calculate the frequency spectrum of a pulse through the use of a mathematical process called a Fourier Transform. With the advent of digital computers an approximation algorithm was developed that calculates the transform at discrete frequencies rather that as a continuous function. For practical purposes, this is sufficient and much quicker computationally. In thatresult, the frequency increment (df) calculated is equal to 1/(length of pulse in time). Rearranging this equation yields: df x t pulse = 1 I do not believe that a Gaussian spectrum shape is necessary for this equation to be true.

Thanks,
Paul

----------- Start Original Message -----------
: Thank you very much Paul, forgot to thank you,it answers perfectly well my question,
: and still another little question(S)
: It is stated that for a gaussian pulse shape the bandwidth;
: df x t pulse = 1
: what do they mean with gaussian?
: So the bandwidth x the pulse time = 1
: hz x time = 1 ?
: Sandy
: : Hello Sandy,
: : The fundamental mechanical resonance occurs when the thickness of the crystal is 1/2 wavelength thick.
: : Let
: : lambda = wavelength
: : c = acoustic velocity
: : f = frequency
: :
: : thickness = lambda/2 (at fundamental resonance)
: : and
: : lambda = c/f
: : then
: : thickness= c/(2*f)
: : solving for f
: : f=c/(2 * thickness)
: : This refers to the mechanical free resonance of the crystal which is achieved by deforming it and allowing it to resonate...much like striking a tuning fork or a piano string.
: : If you drive the crystal with an electrical signal, the response will be at the driving frequency. The amplitude of the output will vary with driving frequency...as you approach the resonant frequency of the crystal, the output amplitude will increase.
: : The piezoelectric element used in a transducer has many resonances, some related to the thickness, and some related to the lateral dimensions. Most transducers are designed so that the unwanted resonances are suppressed and the fundamental dominates the output.
: : So, to answer your question, Fr depends on the thickness and and the acoustic velocity of the crystal.
: : I hope this answers your question.
: : Paul
: : : Hello, can anyone please help me with my question?
: : : I read somewhere:
: : : Resonance frequency (Fr)= (speed of sound in crystal)/(2xthickness of the crystal)
: : : I can't really believe this because what I understand is that the crystal vibrates via voltage and then produces vibration,
: : : or do they mean the impedance of the material?
: : : Also I read:The so-called "fundamental resonant frequency" of an ultrasound transducer is the transmit frequency that corresponds to the half-wavelength crystal thickness.
: : : So that:
: : : Fr = 2 x christal thickness
: : : So my question is:
: : : Is the Fr of the crystal obtained when the crystal has a diameter equal to exactly half the wavelength of the ultrasound that is produced by the crystal.
: : : Or does this depend on the acoustic impedance, or speed of sound in the crystal? Do does the Fr depend on the material?
: : : Can someone please give me the correct information on this
: : : or point me in the good direction?
: : : Many thanks!
------------ End Original Message ------------




    
 
 

Product Spotlight

Aerospace Systems - Automated Ultrasonic Inspection

USL are specialists in the design and manufacture of turnkey ultrasonic inspection systems for aer
...
ospace applications. From monolithic composites to complex honeycomb structures. This video shows just a few examples of what is possible, find out more at: www.ultrasonic-sciences.co.uk
>

ISAFE3 Intrinsically Safe Sensor System

ISAFE3 intrinsically safe sensor system of Vallen Systeme is especially targeted at the petrochemica
...
l - as well as oil and gas transportation industry. The sensor system is designed for permanent monitoring or periodic inspection tasks. Sensors are available for different AE-frequency ranges optimized for corrosion and fatigue crack detection and other applications. The ISAFE 3 sensor system consists of an AE-sensor (model ISAS3) certified according to ATEX/IEC for installation in zone 0, gas group IIC, IP68, 20 to +60 °C, and a signal isolator (model SISO3) certified for installation in zone 2. An ISAS3 sensor can be mounted in atmosphere or submerged, e.g. in water or crude oil. It is supported by mounting tools for temporary (magnets) or permanent (welded) installation. ISAFE3 supports automatic sensor coupling test and can be used with any AE signal processor supporting 28V supply at 90 mA peak, e.g. Vallen Systeme ASIP-2/A.
>

HARDNESS TESTER TKM-459CE combi

TKM-459CE combi applies 2 methods of hardness control: UCI and Leeb. It provides high-accuracy tes
...
ting of metals and alloys as well as items of different sizes and configurations, their hardened layers and galvanic coatings. Device represents results in HB, HRC, HV and others. Shock-, dust- and water-proof housing with intuitive software make this gauge easy to use in all working conditions.
>

Lyft™: Pulsed Eddy Current Reinvented

PEC Reinvented—CUI Programs Redefined Corrosion under insulation (CUI) is possibly the greatest u
...
nresolved asset integrity problem in the industry. Current methods for measuring wall thickness with liftoff, without removing insulation, all have severe limitations. Eddyfi introduces Lyft — a reinvented, high-performance pulsed eddy current (PEC) solution. The patent- pending system features a state-of-the-art portable instrument, real- time C-scan imaging, fast data acquisition with grid-mapping and dynamic scanning modes, and flexibility with long cables. It can also scan through thick metal and insulation, as well as aluminum, stainless steel, and galvanized steel weather jackets. Who else but Eddyfi to reinvent an eddy current technique and redefine CUI programs. Got Lyft?
>

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