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Technical Discussions
Kyle Reed
Kyle Reed
03:55 Oct-12-1999
Mass Deposition Sensor for Coatings

I'm a research scientist working for a company in Atlanta Georgia and I'm having difficulty controlling a coating process.

What would be an appropriate technique to monitor the mass gain per unit area of a surface? I use a spray technique that sweeps across the substrate and the coating monitor would not have to be constantly impinged by the spray. The mass gain is small as I am making very thin films. The range of mass gain would be on the order of 25ug to 300ug per square centimeter.

Could a quartz crystal microbalance be adapted to the process? My thinking is that if I used a small piezoelectric bender (i.e. cantilever) transducer with an exposed platen of known area attached to the end. I could drive the transducer at the resonant frequency and determine mass gain by the decrease in frequency. The problem is that the bimorphs of the design dimensions I've considered would operate at only a few hundred hertz. The drop in resonant frequency I assume would follow:

f'=f*(Me/Me+X)^0.5

where Me is the effective mass of the transducer and X is the weight gain. I'm guessing that a weight gain of 25 ug/cm2 would only cause about a 0.1 Hz shift in resonant frequency for a transducer operating at a few hundred hertz. I base this on the use of a copper foil weighing 50mg/cm2 being used for the deposition platform attached to the end of the piezoelectric bender.

I feel I'd have a difficult time discerning a frequency shift of only 0.1 Hz in a laboratory environment that includes mechanical noise and temperature gradients. I might be able to calibrate the device and monitor the temperater of the sensor to do some form of temperature compensation, but I still feel it would be a difficult task. My thinking is I should reduce the effective mass of the sensor and increase it's frequency...does anyone have some suggestions?

Regards,

Kyle Reed
Microcoating Technologies, Inc.


    
 
 
Wieslaw Bicz
Wieslaw Bicz
03:05 Oct-13-1999
Re: Mass Deposition Sensor for Coatings
Me/Me+X)^0.5

: where Me is the effective mass of the transducer and X is the weight gain. I'm guessing that a weight gain of 25 ug/cm2 would only cause about a 0.1 Hz shift in resonant frequency for a transducer operating at a few hundred hertz. I base this on the use of a copper foil weighing 50mg/cm2 being used for the deposition platform attached to the end of the piezoelectric bender.

: I feel I'd have a difficult time discerning a frequency shift of only 0.1 Hz in a laboratory environment that includes mechanical noise and temperature gradients. I might be able to calibrate the device and monitor the temperater of the sensor to do some form of temperature compensation, but I still feel it would be a difficult task. My thinking is I should reduce the effective mass of the sensor and increase it's frequency...does anyone have some suggestions?

: Regards,

: Kyle Reed
: Microcoating Technologies, Inc.

Have you considered the possibility to measure the thickness of your coating instead of mass.

Using ultrasonic technique it would be relatively easy possible to measure thickness with accuracy, that could be better than 100nm.

For example: we have tested such measurements with our first UT card (see please: http://www.optel.com.pl/manual/english/osc.htm) and could easily measure the length differecies of at least 100nm.
We the newer card or even better equipment it must be possible to achieve much better results.

Wieslaw Bicz

http://www.optel.com.pl



    
 
 
Hermann Wüstenberg
R & D
BAM Berlin, Germany, Joined Nov 1998, 26

Hermann Wüstenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
04:00 Oct-14-1999
Re: Mass Deposition Sensor for Coatings
Me/Me+X)^0.5

: where Me is the effective mass of the transducer and X is the weight gain. I'm guessing that a weight gain of 25 ug/cm2 would only cause about a 0.1 Hz shift in resonant frequency for a transducer operating at a few hundred hertz. I base this on the use of a copper foil weighing 50mg/cm2 being used for the deposition platform attached to the end of the piezoelectric bender.

: I feel I'd have a difficult time discerning a frequency shift of only 0.1 Hz in a laboratory environment that includes mechanical noise and temperature gradients. I might be able to calibrate the device and monitor the temperater of the sensor to do some form of temperature compensation, but I still feel it would be a difficult task. My thinking is I should reduce the effective mass of the sensor and increase it's frequency...does anyone have some suggestions?

: Regards,

: Kyle Reed
: Microcoating Technologies, Inc.

If the ambience condition are allowing the use of PVDF foils as a piezoelectric transducer material, their application would give a much higher sensitivity for the change in masses deposited at one of the contacting electrodes.


    
 
 
Kyle Reed
Kyle Reed
04:31 Oct-14-1999
Re: Mass Deposition Sensor for Coatings
: If the ambience condition are allowing the use of PVDF foils as a piezoelectric transducer material, their application would give a much higher sensitivity for the change in masses deposited at one of the contacting electrodes.

The temperature of the deposition would be 200 C. Do you know the temperature limit of PVDF foils?

Thank you for the reply


    
 
 
Kyle Reed
Kyle Reed
05:25 Oct-14-1999
Re: Mass Deposition Sensor for Coatings
: Have you considered the possibility to measure the thickness of your coating instead of mass.

: Using ultrasonic technique it would be relatively easy possible to measure thickness with accuracy, that could be better than 100nm.

: For example: we have tested such measurements with our first UT card (see please: http://www.optel.com.pl/manual/english/osc.htm) and could easily measure the length differecies of at least 100nm.
: We the newer card or even better equipment it must be possible to achieve much better results.

: Wieslaw Bicz

: http://www.optel.com.pl

Thank you for the reply. What would be an appropriate device to generate the ultrasonic signal? The UT card has a sync output. Would I need a high priced pulse generator driven by this trigger to do the measurement?

Can you comment on what my options are for signal generation if I used a fast data aquisition card in a PC to collect the response signal?

Kyle Reed




    
 
 
Wieslaw Bicz
Wieslaw Bicz
08:07 Oct-14-1999
Re: Mass Deposition Sensor for Coatings

: : Have you considered the possibility to measure the thickness of your coating instead of mass.

: : Using ultrasonic technique it would be relatively easy possible to measure thickness with accuracy, that could be better than 100nm.

: : For example: we have tested such measurements with our first UT card (see please: http://www.optel.com.pl/manual/english/osc.htm) and could easily measure the length differecies of at least 100nm.
: : We the newer card or even better equipment it must be possible to achieve much better results.

: : Wieslaw Bicz http://www.optel.com.pl

: Thank you for the reply. What would be an appropriate device to generate the ultrasonic signal? The UT card has a sync output. Would I need a high priced pulse generator driven by this trigger to do the measurement?

: Can you comment on what my options are for signal generation if I used a fast data aquisition card in a PC to collect the response signal?

: Kyle Reed

You should use our signal generator (machtbox size) with the newer card version (see please: http://www.optel.com.pl/manual/english/osc2.htm). It costs together with the pulser@receiver 900 Euro.
We can also offer you a normal transducer with a short pulse (50 or 100ns length - see please: http://www.optel.com.pl/manual/english/transd.htm) for 140 Euro. We can also offer you a high temperature transducer (220°C) for 500 Euro.
If you want use it with a portable computer, it is possible to use our OPBOX with centronics interface and own power supply and battery (see please: http://www.optel.com.pl/manual/english/opbox.htm).

The accuracy of your measurement must be even higher.

Wieslaw Bicz

http://www.optel.com.pl



    
 
 

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