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01:11 Sep-17-2003
Richard
bathymetric transducer construction

I'm writing a thesis about sonar.
It's hard to find information about the construction
of the transducers used.
I was wondering what kind of backing these transducers use,
or if they even use backing.
And what kind of housing and what is in the housing.
I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?


 
03:31 Sep-18-2003
Joerg Schulze-Clewing
Re: bathymetric transducer construction Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:

http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf

Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.

Greetings (Groetjes...),

Joerg
joergsch pacbell net

----------- Start Original Message -----------
: I'm writing a thesis about sonar.
: It's hard to find information about the construction
: of the transducers used.
: I was wondering what kind of backing these transducers use,
: or if they even use backing.
: And what kind of housing and what is in the housing.
: I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
09:10 Sep-18-2003
Suszanne Thwaites
Re: bathymetric transducer construction ----------- Start Original Message -----------
: I'm writing a thesis about sonar.
: It's hard to find information about the construction
: of the transducers used.
: I was wondering what kind of backing these transducers use,
: or if they even use backing.
: And what kind of housing and what is in the housing.
: I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------

The National Physical Laboratory (NPL)in the UK is a useful source of info on sonar transducers and also the USRD in the USA. Both have good web pages.


 
02:46 Sep-24-2003
Richard
Re: bathymetric transducer construction Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, not technical detailed, but I'll keep searching. .

Groetjes
Richard

----------- Start Original Message -----------
: Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: Greetings (Groetjes...),
: Joerg
: joergsch pacbell net
: : I'm writing a thesis about sonar.
: : It's hard to find information about the construction
: : of the transducers used.
: : I was wondering what kind of backing these transducers use,
: : or if they even use backing.
: : And what kind of housing and what is in the housing.
: : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
02:00 Sep-26-2003
Joerg Schulze-Clewing
Re: bathymetric transducer construction Richard, there are two other sources that might work if you can't find anything useful on the net.

One is the IEEE-UFFC society. If you or a friend of yours is a member you could look through tons of publications. Your university library should have the Transactions as well but it is easier to do an electronic search.

Another would be Penn State University (www.psu.edu). They have a very substantial research group on ultrasound and transducers and should be willing to help a colleague. Also, in your country the TU Delft and Erasmus Universiteit in Rotterdam are studying ultrasound but I believe most of their research is medical ultrasound.

All the best, Joerg.

----------- Start Original Message -----------
: Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
: also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, no technical detailed, but I'll keep searching. .
: Groetjes
: Richard
: : Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: : http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: : Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: : Greetings (Groetjes...),
: : Joerg
: : joergsch pacbell net
: : : I'm writing a thesis about sonar.
: : : It's hard to find information about the construction
: : : of the transducers used.
: : : I was wondering what kind of backing these transducers use,
: : : or if they even use backing.
: : : And what kind of housing and what is in the housing.
: : : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
02:58 Sep-29-2003
Richard
Re: bathymetric transducer construction Can't find the information on there either. Can someone however explain to me how a short pulse (from a transducer) increases the bandwidth of the transducer? What is the explanation for this, and why on the same note does a long pulse create better sound propagation through the medium.?
Does anyone have some clear explanation?
Thanks
Richard

----------- Start Original Message -----------
: Richard, there are two other sources that might work if you can't find anything useful on the net.
: One is the IEEE-UFFC society. If you or a friend of yours is a member you could look through tons of publications. Your university library should have the Transactions as well but it is easier to do an electronic search.
: Another would be Penn State University (www.psu.edu). They have a very substantial research group on ultrasound and transducers and should be willing to help a colleague. Also, in your country the TU Delft and Erasmus Universiteit in Rotterdam are studying ultrasound but I believe most of their research is medical ultrasound.
: All the best, Joerg.
: : Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
: : also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, no technical detailed, but I'll keep searching. .
: : Groetjes
: : Richard
: : : Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: : : http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: : : Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: : : Greetings (Groetjes...),
: : : Joerg
: : : joergsch pacbell net
: : : : I'm writing a thesis about sonar.
: : : : It's hard to find information about the construction
: : : : of the transducers used.
: : : : I was wondering what kind of backing these transducers use,
: : : : or if they even use backing.
: : : : And what kind of housing and what is in the housing.
: : : : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
01:34 Sep-30-2003
Joerg Schulze-Clewing
Re: bathymetric transducer construction Richard, the bandwidth of a transducer is given. You can't
really change it. For maximum use of the bandwidth it is
customary to use a "matching" number of pulses with the
center frequency of these "pulse trains" being the same
as the transducer frequency. For example, if you had a
PZT ceramic and with the chosen backing material the
resulting transducer would offer 50% bandwidth then you
would send a pulse train consisting of two or three
pulses for good resolution.

Longer pulse trains are used if you need more penetration
but can sacrifice some resolution. Then you get more energy
transmitted (assuming same pulse voltage) and also you
can receive with a narrower bandwidth filter which will
lead to better signal to noise ratio. The trick is always
to make sure that the bandwidth of the receiver filter
matches the bandwidth of the outgoing pulse burst.

There are some tricks to achieve a better compromise
between energy (penetration) and resolution but that
would take a lot to explain, plus some of those tricks
are proprietary anyway.

Regards, Joerg.

----------- Start Original Message -----------
: Can't find the information on there either. Can someone however explain to me how a short pulse (from a transducer) increases the bandwidth of the transducer? What is the explanation for this, and why on the same note does a long pulse create better sound propagation through the medium.?
: Does anyone have some clear explanation?
: Thanks
: Richard
: : Richard, there are two other sources that might work if you can't find anything useful on the net.
: : One is the IEEE-UFFC society. If you or a friend of yours is a member you could look through tons of publications. Your university library should have the Transactions as well but it is easier to do an electronic search.
: : Another would be Penn State University (www.psu.edu). They have a very substantial research group on ultrasound and transducers and should be willing to help a colleague. Also, in your country the TU Delft and Erasmus Universiteit in Rotterdam are studying ultrasound but I believe most of their research is medical ultrasound.
: : All the best, Joerg.
: : : Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
: : : also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, no technical detailed, but I'll keep searching. .
: : : Groetjes
: : : Richard
: : : : Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: : : : http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: : : : Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: : : : Greetings (Groetjes...),
: : : : Joerg
: : : : joergsch pacbell net
: : : : : I'm writing a thesis about sonar.
: : : : : It's hard to find information about the construction
: : : : : of the transducers used.
: : : : : I was wondering what kind of backing these transducers use,
: : : : : or if they even use backing.
: : : : : And what kind of housing and what is in the housing.
: : : : : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
09:43 Sep-30-2003
Richard
Re: bathymetric transducer construction Hello Joerg,

I don't understand your first paragraph,
for good resolution the center frequency dictates
the numer of pulses?
Why, for a 50% bandwidth does the pulse train consists
of 2 or 3 pulses, for good resolution?

What I understand:
The backing material creates the bandwidth, so if you
raise the damping the bandwidth increases.The difference between the center frequency and the resonance frequency is the damping. (?)

If you have two transducers with the same frequency, than the one with the shortest pulse wil have the broather bandwidth?

I read somewhere:
Short pulses contain multiple frequency components and can only be produced by broadband transducers. The pulse length is roughly determined by frequency and number of cycles in the electronic pulse that is applied to the transducer. The bandwidth of the array will also control the pulse length.

Do longer pulses contain less frequency components, and if you raise the number of cycles from the pulse generator you canincrease pulse length?

I still don't thoroughly understand how the bandwidth determains the pulse length.
Can you give it one more try?

Regards, Richard


----------- Start Original Message -----------
: Richard, the bandwidth of a transducer is given. You can't
: really change it. For maximum use of the bandwidth it is
: customary to use a "matching" number of pulses with the
: center frequency of these "pulse trains" being the same
: as the transducer frequency. For example, if you had a
: PZT ceramic and with the chosen backing material the
: resulting transducer would offer 50% bandwidth then you
: would send a pulse train consisting of two or three
: pulses for good resolution.
: Longer pulse trains are used if you need more penetration
: but can sacrifice some resolution. Then you get more energy
: transmitted (assuming same pulse voltage) and also you
: can receive with a narrower bandwidth filter which will
: lead to better signal to noise ratio. The trick is always
: to make sure that the bandwidth of the receiver filter
: matches the bandwidth of the outgoing pulse burst.
: There are some tricks to achieve a better compromise
: between energy (penetration) and resolution but that
: would take a lot to explain, plus some of those tricks
: are proprietary anyway.
: Regards, Joerg.
: : Can't find the information on there either. Can someone however explain to me how a short pulse (from a transducer) increases the bandwidth of the transducer? What is the explanation for this, and why on the same note does a long pulse create better sound propagation through the medium.?
: : Does anyone have some clear explanation?
: : Thanks
: : Richard
: : : Richard, there are two other sources that might work if you can't find anything useful on the net.
: : : One is the IEEE-UFFC society. If you or a friend of yours is a member you could look through tons of publications. Your university library should have the Transactions aswell but it is easier to do an electronic search.
: : : Another would be Penn State University (www.psu.edu). They have a very substantial research group on ultrasound and transducers and should be willing to help a colleague. Also, in your country the TU Delft and Erasmus Universiteit in Rotterdam are studying ultrasound but I believe most of their research is medical ultrasound.
: : : All the best, Joerg.
: : : : Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
: : : : also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, no technical detailed, but I'll keep searching. .
: : : : Groetjes
: : : : Richard
: : : : : Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: : : : : http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: : : : : Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: : : : : Greetings (Groetjes...),
: : : : : Joerg
: : : : : joergsch pacbell net
: : : : : : I'm writing a thesis about sonar.
: : : : : : It's hard to find information about the construction
: : : : : : of the transducers used.
: : : : : : I was wondering what kind of backing these transducers use,
: : : : : : or if they even use backing.
: : : : : : And what kind of housing and what is in the housing.
: : : : : : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
06:58 Sep-30-2003

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
780
Re: bathymetric transducer construction Dear Richard,

A short pulse has many frequencies as you can see when you run it through a frequency-domain analyser. So, a short pulse increases the frequencies generatd by the transducer and will need a wide-band amplifier on the reciever side. A long pulse on the other hand forces the crystal to oscilalte at a given frequency - closer to its natural frequncy for a longer period. And the amplitude of the resulting sound wave will be much higher than say for the wave resulting from a short pulse. Thus high power Pulsers will use long pulses while high frequency pulsers use a very short pulse. A short pulse gets dampened very fast unlike a long pulse. That also explains the better propagation of sound through a given medium.

Swamy

----------- Start Original Message -----------
: Can't find the information on there either. Can someone however explain to me how a short pulse (from a transducer) increases the bandwidth of the transducer? What is the explanation for this, and why on the same note does a long pulse create better sound propagation through the medium.?
: Does anyone have some clear explanation?
: Thanks
: Richard
: : Richard, there are two other sources that might work if you can't find anything useful on the net.
: : One is the IEEE-UFFC society. If you or a friend of yours is a member you could look through tons of publications. Your university library should have the Transactions as well but it is easier to do an electronic search.
: : Another would be Penn State University (www.psu.edu). They have a very substantial research group on ultrasound and transducers and should be willing to help a colleague. Also, in your country the TU Delft and Erasmus Universiteit in Rotterdam are studying ultrasound but I believe most of their research is medical ultrasound.
: : All the best, Joerg.
: : : Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
: : : also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, no technical detailed, but I'll keep searching. .
: : : Groetjes
: : : Richard
: : : : Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: : : : http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: : : : Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: : : : Greetings (Groetjes...),
: : : : Joerg
: : : : joergsch pacbell net
: : : : : I'm writing a thesis about sonar.
: : : : : It's hard to find information about the construction
: : : : : of the transducers used.
: : : : : I was wondering what kind of backing these transducers use,
: : : : : or if they even use backing.
: : : : : And what kind of housing and what is in the housing.
: : : : : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
00:09 Oct-01-2003

Linas Svilanis

R & D,
Kaunas University of Technology,
Lithuania,
Joined Nov 1998
66
Re: bathymetric transducer construction ----------- Start Original Message -----------
Dear Richard,

I think I can also add my comments to your discussion.

One of your questions was:
: Do longer pulses contain less frequency components, and if you raise the number of cycles from the pulse generator you can increase pulse length?
I am not sure whether you distinguish between pulse and "cycles". The "cycles" is usually used when we speak about gated continuous wave(CW), that is when you have the sinus signal and gate it to have some limited number of cycles at the output.
Theory:
CW signal bandwidth is 0(zero)
gated CW bandwidth is 1/gatewidth x 2

Therefore one can say that gated CW (sometimes called radio or CW burst) bandwidth depends on its duration or number of CW cycles fitted into gate.

Since ultrasonic transducer is exhibiting the bandpass filter properties, it is more convenient to excite it with square wave (pulse train) instead of sinus. Therefore sometimes "cycles" are mixed with "pulses".
The simplest way to produce square wave mathematically is to do sign operation on gated CW. One important moment - you will notice that every individual pulse in the train will have duration half of CW frequency period.


Actually Exciting pulse bandwidth and transducer bandwidth have nothing incomon. One can use long burst to excite wide bandwidth transducer or vise versa.
Anyway, it seems wise to match the bandwidth of transducer and the exciting signal.

Here comes your next question:
: I still don't thoroughly understand how the bandwidth determains the pulse length.

Actually the bandwidth determines the pulse train length (gate lenght), not the individual pulse length. Word "determines" may be misleading. Better to use "require" or "recommend". That is: transducer bandwidth "requires"
a pulse train of particular length.
Nothing terrible will happen if pulse train is shorter - just some of energy which is out of transducer passband will be lost. But it is not wise to loose energy just because someone did not thing to "match" the transducer and signal bandwidth.
Also, nothing terrible will happen if pulse train is longer - longer train will have more narrow bandwidth, so all energy will be transmitted through transducer- just not efficiently - and this is another discussion...


 
01:14 Oct-02-2003

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
780
Re: bathymetric transducer construction Dear Richard,

I posted the following in the forum, which seems to have escaped your attention. I am reproducing the same below.

Dear Richard,

A short pulse has many frequencies as you can see when you run it through a frequency-domain analyser. So, a short pulse increases the frequencies generatd by the transducer and will need a wide-band amplifier on the reciever side. A long pulse on the other hand forces the crystal to oscilalte at a given frequency - closer to its natural frequncy for a longer period. And the amplitude of the resulting sound wave will be much higher than say for the wave resulting from a short pulse. Thus high power Pulsers will use long pulses while high frequency pulsers use a very short pulse. A short pulse gets dampened very fast unlike a long pulse. That also explains the better propagation of sound through a given medium.

Swamy

I will add a few more points for your consideration.

The backing of the trasducer changes the rigidity and thus the damping of the crystal. So, a short electrical pulse needs to be matched with a properly, in this case, heavily damped crystal. To anlyse the echo from the medium, we need a broadband (wideband) amplifier.

A longer duration pulse applied to the crystal forces the crystal to vibrate at a given frequncy. The frequncy of the mechanical vibration generated depends upon the natural frequncy, the frequency of the electrical signal and the damping. But generally such transducers are driven closer to their natural frequncy so that a large amplitude mechanical vibration is generated and sent into the material. The need for such a situation is in heavily absorbing media.

I do hope it is a little clearer now. Pl. feel free to contact for any further help.

Swamy


----------- Start Original Message -----------
: Hello Joerg,
: I don't understand your first paragraph,
: for good resolution the center frequency dictates
: the numer of pulses?
: Why, for a 50% bandwidth does the pulse train consists
: of 2 or 3pulses, for good resolution?
: What I understand:
: The backing material creates the bandwidth, so if you
: raise the damping the bandwidth increases.The difference between the center frequency and the resonance frequency is the damping. (?)
: If you have two transducers with the same frequency, than the one with the shortest pulse wil have the broather bandwidth?
: I read somewhere:
: Short pulses contain multiple frequency components and can only be produced by broadband transducers. The pulse length is roughly determined by frequency and number of cycles in the electronic pulse that is applied to the transducer. The bandwidth of the array will also control the pulse length.
: Do longer pulses contain less frequency components, and if you raise the number of cycles from the pulse generator you can increase pulse length?
: I still don't thoroughly understand how the bandwidth determains the pulse length.
: Can you give it one more try?
: Regards, Richard
:
: : Richard, the bandwidth of a transducer is given. You can't
: : really change it. For maximum use of the bandwidth it is
: : customary to use a "matching" number of pulses with the
: : center frequency of these "pulse trains" being the same
: : as the transducer frequency. For example, if you had a
: : PZT ceramic and with the chosen backing material the
: : resulting transducer would offer 50% bandwidth then you
: : would send a pulse train consisting of two or three
: : pulses for good resolution.
: : Longer pulse trains are used if you need more penetration
: : but can sacrifice some resolution. Then you get more energy
: : transmitted (assuming same pulse voltage) and also you
: : can receive with a narrower bandwidth filter which will
: : lead to better signal to noise ratio. The trick is always
: : to make sure that the bandwidth of the receiver filter
: : matches the bandwidth of the outgoing pulse burst.
: : There are some tricks to achieve a better compromise
: : between energy (penetration) and resolution but that
: : would take a lot to explain, plus some of those tricks
: : are proprietary anyway.
: : Regards, Joerg.
: : : Can't find the information on there either. Can someone however explain to me how a short pulse (from a transducer) increases the bandwidth of the transducer? What is the explanation for this, and why on the same note does a long pulse create better sound propagation through the medium.?
: : : Does anyone have some clear explanation?
: : : Thanks
: : : Richard
: : : : Richard, there are two other sources that might work if you can't find anything useful on the net.
: : : : One is the IEEE-UFFC society. If you or a friend of yours is a member you could look through tons of publications. Your university library should have the Transactions as well but it is easier to do an electronic search.
: : : : Another would be Penn State University (www.psu.edu). They have a very substantial research group on ultrasound and transducers and should be willing to help a colleague. Also, in your country the TU Delft and Erasmus Universiteit in Rotterdam are studying ultrasound but I believe most of their research is medical ultrasound.
: : : : All the best, Joerg.
: : : : : Thank you for responding although this isn't a typical ndt topic. There's a lot about transducers on the net,
: : : : : also from ultrasonic imaging, but indeed not about the materials used. From multibeam manufacturers you get the standard commercial folders, no technical detailed, but I'll keep searching. .
: : : : : Groetjes
: : : : : Richard
: : : : : : Richard, there are many published papers available on the web about construction of the transducers and their properties, such as:
: : : : : : http://www.wai.com/AppliedScience/Software/Pzflex/Papers/pzflexieee971.pdf
: : : : : : Also, manufacturers might help if you are doing a university research project. However, being from the medical ultrasound world myself I know that the details of backing material formulation are often a closely guarded trade secret so it might be tough.
: : : : : : Greetings (Groetjes...),
: : : : : : Joerg
: : : : : : joergsch pacbell net
: : : : : : : I'm writing a thesis about sonar.
: : : : : : : It's hard to find information about the construction
: : : : : : : of the transducers used.
: : : : : : : I was wondering what kind of backing these transducers use,
: : : : : : : or if they even use backing.
: : : : : : : And what kind of housing and what is in the housing.
: : : : : : : I know in the early days of the quartz-element it used to be castor oil, but what material is used for ceramic or polymer piëzo-electric elements?
------------ End Original Message ------------




 
09:26 Oct-02-2003
Joerg Schulze-Clewing
Re: bathymetric transducer construction Swamy, Richard, and others,

There may be a little bit of misunderstanding here.
By long pulse it is probably meant to be a long burst of
pulses, not just one long on-off cycle.

PZT, no matter how dampening the backing, has a specific
center frequency which for most transducers is determined
by material properties and by the thickness. So if you would
excite it with a pulse that is much too long it will still
operate around its center frequency. In case of excessively
long single pulses it will generate one sound wave on the
rising edge and another one later on the falling edge.

If we want to radiate more energy this can only be done
by exciting the transducer with a burst of pulses where
the frequency matches the transducer. So for a
transducer of 10MHz center frequency the pulses within such
a burst would have to be about 100 nsec apart each. If
they were more apart we would sacrifice energy and saddle
the pulse transmitter with a pretty serious mismatch in
impedance.

Regards, Joerg.


 
03:17 Oct-02-2003
Richard
Re: bathymetric transducer construction Thanks for your reactions,

Multibeam sonars are pulsed ultrasound systems.
As I understand this means no gated continuous wave(CW).

For as I understand it now:
Pulse length=synonym for Pulse width =synonym for Pulse Duration.
The spatial pulse length is equal to the number of waves (cycles) in the pulse multiplied by their wavelength. The pulse length is determined by the Q factor of the transducer crystal and by the characteristics of the backing block of the transducer.

By chanching the backing block you can chance the bandwidth and with that the pule length.

A lot of manufacturers have multibeam sonars with variable Pulse lengths, so it is possible to change the pulse length with a given transducer.

So I think an answer to my question of how pulse length invluences the bandwidth is;
Short pulses contain more frequenties and therefore have a larger bandwidth.
The pulse length in the time domain corresponds with bandwidth in the frequency domain.

I even read somwhere; Pulse Length = 1/Bandwidth
( )

----------- Start Original Message -----------
: Dear Richard,
: I think I can also add my comments to your discussion.
: One of your questions was:
: : Do longer pulses contain less frequency components, and if you raise the number of cycles from the pulse generator you can increase pulse length?
: I am not sure whether you distinguish between pulse and "cycles". The "cycles" is usually used when we speak about gated continuous wave(CW), that is when you have the sinus signal and gate it to have some limited number of cycles at the output.
: Theory:
: CW signal bandwidth is 0(zero)
: gated CW bandwidth is 1/gatewidth x 2
: Therefore one can say that gated CW (sometimes called radio or CW burst) bandwidth depends on its duration or number of CW cycles fitted into gate.
: Since ultrasonic transducer is exhibiting the bandpass filter properties, it is more convenient to excite it with square wave (pulse train) instead of sinus. Therefore sometimes "cycles" are mixed with "pulses".
: The simplest way to produce square wave mathematically is to do sign operation on gated CW. One important moment - you will notice that every individual pulse in the train will have duration half of CW frequency period.
:
: Actually Exciting pulse bandwidth and transducer bandwidth have nothing incomon. One can use long burst to excite wide bandwidth transducer or vise versa.
: Anyway, it seems wise to match the bandwidth of transducer and the exciting signal.
: Here comes your next question:
: : I still don't thoroughly understand how the bandwidth determains the pulse length.
: Actually the bandwidth determines the pulse train length (gate lenght), not the individual pulse length. Word "determines" may be misleading. Better to use "require" or "recommend". That is: transducer bandwidth "requires"
: a pulse train of particular length.
: Nothing terrible will happen if pulse train is shorter - just some of energy which is out of transducer passband will be lost. But it is not wise to loose energy just because someone did not thing to "match" the transducer and signal bandwidth.
: Also, nothing terrible will happen if pulse train is longer - longer train will have more narrow bandwidth, so all energy will be transmitted through transducer- just not efficiently - and this is another discussion...
------------ End Original Message ------------




 
00:27 Oct-04-2003
Joerg Schulze-Clewing
Re: bathymetric transducer construction Richard, Linas and others, just one suggestion regarding
the wording. It is customary in ultrasound and other
disciplines to refer to "pulse" as one single event, for
example one positive peak followed by one negative
peak. Or, in what is called a unipolar pulser just a peak
in one direction.

Multiple pulses in a row are usually referred to as
"bursts". It's the same in, for example, television
technology where the chroma carrier is transmitted as a
burst of just a few sine wave cycles. So they call that
the chroma burst.

I don't want to be a nitpicker here but this terminology
avoids confusion in a technical discussion.

Regards, Joerg.


 
00:42 Oct-07-2003

Linas Svilainis

R & D,
Kaunas University of Technology,
Lithuania,
Joined Nov 1998
66
Re: bathymetric transducer construction Dear Richard,

I fully agree with Joerg as regarding the naming.
I have noticed that this "misnaming" have introduced a lot of errors in explanations which have accumulated and now we have a complete mess.
So, trying to place things back into their places:
"pulse" is just a swing of a signal into + or - direction and then - back.
"burst" is a gated CW piece or a train of multiple "pulses"
Anyway, both "pulse" and "burst" total length determines the bandwidth of signal spectra.
Furthemore - "pulse" length determines the "optimal" frequency for excitation (usually length is 1/2 of optimal frequency period).
For a "burst" it's almost obvious - individual pulse duration is half the pulses repatition frequency - only then excitation is optimal.
Do not want to mess things further, but sometimes pulse duration is varied from "optimum" deliberately, in order to artificially increase the transducer bandwidth by introducing dynamical electrical dampeding.
One more thing to stress-on:
transducer bandwidth and exciting pulse bandwidth are independent on each other.
Same as sock and your feet.
but if you match them is the same as "putting the right sock".

Few statements which sounded here incorrectly for me:
"...A long pulse on the other hand forces the crystal to oscilalte at a given frequency - closer to its natural frequncy for a longer period. And the amplitude of the resulting sound wave will be much higher than say for the wave resulting from a short pulse..."
I hope "long" is ment a pulse train("burst") here. Only in case "burst" individual pulses repetition frequency is equal to transducer natural frequency ecitation is efficient and amplitude is the highest.
One can state that increasing the "burst" length amplitude will increase. But only up to the limit of 1/(transducer bandwith). Then it will stay constant.
Now to the next statement:
"...Thus high power Pulsers will use long pulses while high frequency pulsers use a very short pulse..."
Power does not depend on time, but energy does. And immediately to next statement:
"...A short pulse gets dampened very fast unlike a long pulse..."
I hope propagation in media is ment. The faster decay if pulse energy is the reason, because higher frequencies are usually more attenuated. So longer pulses can propagate larger distances because they have more energy (Energy=Power x time).
But again- if not right transducers are used there will be a little use of long "burst".
So statement "...By chanching the backing block you can chance the bandwidth and with that the pule length..." is not completely correct as it relates to pulse length. ANY length exciting pulse can be used. The only question what pulse to use is whather you want it matched to transducer bandwidth or not.
If not, we have to "bad" cases:
A:pulse is too short. Then a lot of energy will be lost and will not be radiated into media.
B:pulse is too long. Energy will be radiated into media but not as efficiently as would it have beed with wider bandwidth (less damped) transducer.

Huff...
Is it better now or even worse?

Regards,

Linas


 


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