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Technical Discussions
xinyuanwanli
Student
NEU, China, Joined Oct 2009, 5

xinyuanwanli

Student
NEU,
China,
Joined Oct 2009
5
04:48 Dec-18-2009
sin wave and ultrasonic transducer

hi,
I desigen a sin wave producing circuit, but when I connect the ultrasonic transducer and the circuit, the wave has not been sin wave.Is the frequency not right or other reason? Who can explantion it for me? Thanks.

 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 304

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
304
09:48 Dec-18-2009
Re: sin wave and ultrasonic transducer
In Reply to xinyuanwanli at 04:48 Dec-18-2009 (Opening).

Hi,
If your circuit is producing a sine wave when unloaded, have you taken into account the loading that the circuit will see from the cable characteristic impedance and the transducer itself?
The transducer (if commercially manufactured) will have some form of inductive or capacitive tuning added accross the crystal, and the crystal itself is likely to have its own inductive, resistive and capacitive components, which of course will be frequency dependent.
Godfrey

 
 Reply 
 
Linas Svilainis
R & D,
Kaunas University of Technology, Lithuania, Joined Nov 1998, 67

Linas Svilainis

R & D,
Kaunas University of Technology,
Lithuania,
Joined Nov 1998
67
11:08 Dec-18-2009
Re: sin wave and ultrasonic transducer
In Reply to xinyuanwanli at 04:48 Dec-18-2009 (Opening).

Hi,

without examination of the circuit it is hard to tell the reason: you may want to post the scope screenshot of the signal and the circuitry used.
For now such are my thoughts:
1. As Godfrey have indicated transducer posses several resonances. To put it simple, there are at least two: serial resonance (minimal impedance at the resonance) and parallel (max Z). Serial is good for transmission, parallel for reception. If same transducer is used for Tx and Rx then useful frequency is somewhere in between.
2.It depends whether your sine generator is using the load impedance to adjust the frequency or not. And which (serial or par) resonance.
3. You might have decided to use square signal to excite, expecting to have sine wave after. Actually this is almost the case in high efficiency excitation. But the sharp edges excite transducer's resonance and transducer oscillates at it's resonance frequency and you also have fundamental from your exciting generator. They interfere with each other and as the result you have distorted wave.
4. You might have nonlinearity in propagation path

Linas

 
 Reply 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 265

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
265
11:58 Dec-18-2009
Re: sin wave and ultrasonic transducer
In Reply to xinyuanwanli at 04:48 Dec-18-2009 (Opening).

If the transducer is working in resonance, you will get pretty good sinus wave. If not, and the circuit is not a perfect generator with very low impedance, it is not to expect.

 
 Reply 
 
xinyuanwanli
Student
NEU, China, Joined Oct 2009, 5

xinyuanwanli

Student
NEU,
China,
Joined Oct 2009
5
14:19 Dec-20-2009
Re: sin wave and ultrasonic transducer
In Reply to xinyuanwanli at 04:48 Dec-18-2009 (Opening).

Thanks for everyone's help! With the help the question has been solved. The reason is that the tunableness inductive do not work well. Now I am testing the recieving circuit. Thanks everyone again.
xinyuanwanli

 
 Reply 
 

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