resonance! - Electronic Circuits Projects Diagrams Free

epilot · 27th April 2006, 01:30 AM

Hello,

I need to measure the resonance frequency of an ultrasonic transducer,
I had a test with a transmitter and a receiver ultrasonic sensor that I knew
their resonance freq (about 40kHz ,)
I connected the receiver ultrasonic sensor to my oscilloscope probe while my transmitter sensor was near it, the oscillator circuit for transmitter had a volume and it was able to generate a freq between 30 to 50kHz., so I was able to see the change in the wave on the scope, when the volume was set at 40 kHz I had the max of wave form.
Well unfortunately with this way I am able to measure the resonance only at 40kHz because the T and R ultrasonics are designed to make resonance at that freq,
But I have a piezo and a tweeter that have another freq (between 22 to 50kHz)
Now I have a big problem to measure their resonance freq,

Any idea about solving my problem would be very very appreciated

Papabravo · 27th April 2006, 02:09 AM

I'm confused about something. A piezo and a tweeter need to be excited by an AC signal. Each of these devices will have a "response" across a range of frequencies. The frequency at which a maximum response occurs may or may not be a resonance. Is this correct?

That said there are instruments called Gain-Phase Meters which will automate this process, by sweeping a signal source across a frequency range and measuring the response. This is exactly analogous to measuring the response of an RC filter, or any other filter for that matter.

The results are often displayed on a Bode Plot which separates the magnitude of the response from the phase of the response.

audioguru · 27th April 2006, 04:28 AM

In an audio speaker or a piezo membrane usually a resonant frequency results in a peak in the output level.
A woofer resonates with the air in its enclosure at a low frequency where lower frequencies quickly drop off, then another resonance occurs at about 4kHz to 6kHz where the higher frequencies quickly drop off.
A tweeter resonates at about 18kHz so that it still responds to 20kHz.
A Piezo membrane resonates at many frequencies and its resonance produces the highest output if the enclosure resonates at the same frequency.

**Nigel Goodwin** · 27th April 2006, 09:28 AM

Assuming these are audio devices?, the resonance will either be fairly low amplitude, or outside it's normal operating frequencies. It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency.

As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance).

epilot · 27th April 2006, 01:38 PM

Quote:

Originally Posted by Nigel Goodwin

Assuming these are audio devices?, the resonance will either be fairly low amplitude, or outside it's normal operating frequencies. It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency.

As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance).

Sorry Nigel i could not understand your mean with my broken english can you explain your mean in other way please?

**Nigel Goodwin** · 27th April 2006, 02:55 PM

Quote:

Originally Posted by epilot

Quote:

Originally Posted by Nigel Goodwin

Assuming these are audio devices?, the resonance will either be fairly low amplitude, or outside it's normal operating frequencies. It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency.

As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance).

Sorry Nigel i could not understand your mean with my broken english can you explain your mean in other way please?

Which part, about tweeters or ultrasonic transducers?

epilot · 27th April 2006, 05:18 PM

Which part, about tweeters or ultrasonic transducers?[/quote]

you said "It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency"

like "audioguru" said the main part for a piezo to make resonant is the enclosure, even an ultrasonic sensor uses a piezo with a "suitable" diaphragm or something like that ( don't know its name) i mean the piezo in the ultrasonic sensor has a resonant freq near 40kHz because of that diphragm.

by the way i could not understand this:
"
As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance)."
i made a test but with no results becuase i think i could not understand something in your text

Hero999 · 27th April 2006, 05:30 PM

Piezo beeper elements are usally have a resonance at 2.8kHz which they are most comonly operated at, but I've tested this and there's also another very sharp hi Q peek at 32kHz so you could also use it as a cheap ultrasonic transducer.

**Nigel Goodwin** · 27th April 2006, 05:56 PM

Quote:

Originally Posted by epilot

you said "It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency"

Sorry, a typo! - should have read "If it's a piezo beeper, these are sharply resonant, and should be operated at that frequency"

Quote:

by the way i could not understand this:
"
As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance)."
i made a test but with no results becuase i think i could not understand something in your text

Connect it like this:

audioguru · 27th April 2006, 07:03 PM

I have some piezo transducers (speakers) taken from alarm clocks. Their sound output varies very much with frequency, but they are much louder at certain frequencies when the back of the transducer is near an acousic chamber like a thimble or a big bottle cap.
Piezo beepers that I have are mounted in an acoustic chamber for resonance.

Piezo beepers have a built-in oscillator with feedback from the piezo, so they oscillate at the high output resonance of the piezo transducer in its acoustic chamber.

epilot · 27th April 2006, 08:04 PM

Quote:

Originally Posted by Hero999

Piezo beeper elements are usally have a resonance at 2.8kHz which they are most comonly operated at, but I've tested this and there's also another very sharp hi Q peek at 32kHz so you could also use it as a cheap ultrasonic transducer.

how could you make a test at that freq?

epilot · 27th April 2006, 08:05 PM

Connect it like this:[/quote]

ok i'll do the test and see what will happen, thanks.

do you know what is the standard device to measure the resonance of a transducer?

epilot · 27th April 2006, 08:20 PM

Quote:

Originally Posted by audioguru

Piezo beepers have a built-in oscillator with feedback from the piezo, so they oscillate at the high output resonance of the piezo transducer in its acoustic chamber.

can you give me more info about that?

by the way i have read that there is something called "PVDF"(Polyvinylidene Fluoride) that has a property like a piezo(produce sound when there is a voltage and produce power when there is a pressure),
i heard it can handle lot of frequencies, with a good resonance
i wanted to use it because i heard that it is easy working with but could not find any source here for it.

it would be good if someone could give us more info about it.

audioguru · 27th April 2006, 08:41 PM

Piezo tweeters in cheap speakers take a lot of abuse without burning out, but sound like a whistle. Only their few resonant frequencies are heard. People with tin ears think they sound great!

Take a piezo beeper with a built-in oscillator and change the size of its acoustic chamber. The frequency and loudness of its beep will also change. If the resonance of the piezo's element matches the resonance of the acoustic chamber it is mounted beside, then it will be extremely loud.

Dr.EM · 27th April 2006, 09:58 PM

Yes, I remember they demonstrated that effect in physics once with a speaker and measuring cylinder. It becomes louder because standing waves are formed which is where the orignal and reflected waves are perfectly in phase with each other, and so produce constructive superposition. This effectively doubles the amplitude of the signal.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

27th April 2006, 01:30 AM	(permalink)
epilot	resonance! Hello, I need to measure the resonance frequency of an ultrasonic transducer, I had a test with a transmitter and a receiver ultrasonic sensor that I knew their resonance freq (about 40kHz ,) I connected the receiver ultrasonic sensor to my oscilloscope probe while my transmitter sensor was near it, the oscillator circuit for transmitter had a volume and it was able to generate a freq between 30 to 50kHz., so I was able to see the change in the wave on the scope, when the volume was set at 40 kHz I had the max of wave form. Well unfortunately with this way I am able to measure the resonance only at 40kHz because the T and R ultrasonics are designed to make resonance at that freq, But I have a piezo and a tweeter that have another freq (between 22 to 50kHz) Now I have a big problem to measure their resonance freq, Any idea about solving my problem would be very very appreciated

27th April 2006, 02:09 AM	(permalink)
Papabravo	I'm confused about something. A piezo and a tweeter need to be excited by an AC signal. Each of these devices will have a "response" across a range of frequencies. The frequency at which a maximum response occurs may or may not be a resonance. Is this correct? That said there are instruments called Gain-Phase Meters which will automate this process, by sweeping a signal source across a frequency range and measuring the response. This is exactly analogous to measuring the response of an RC filter, or any other filter for that matter. The results are often displayed on a Bode Plot which separates the magnitude of the response from the phase of the response.

27th April 2006, 04:28 AM	(permalink)
audioguru	In an audio speaker or a piezo membrane usually a resonant frequency results in a peak in the output level. A woofer resonates with the air in its enclosure at a low frequency where lower frequencies quickly drop off, then another resonance occurs at about 4kHz to 6kHz where the higher frequencies quickly drop off. A tweeter resonates at about 18kHz so that it still responds to 20kHz. A Piezo membrane resonates at many frequencies and its resonance produces the highest output if the enclosure resonates at the same frequency. __________________ Uncle $crooge

27th April 2006, 09:28 AM	(permalink)
Nigel Goodwin	Assuming these are audio devices?, the resonance will either be fairly low amplitude, or outside it's normal operating frequencies. It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency. As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance). __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

27th April 2006, 05:18 PM	(permalink)
epilot	Which part, about tweeters or ultrasonic transducers?[/quote] you said "It's it's a piezo beeper, these are sharply resonant, and should be operated at that frequency" like "audioguru" said the main part for a piezo to make resonant is the enclosure, even an ultrasonic sensor uses a piezo with a "suitable" diaphragm or something like that ( don't know its name) i mean the piezo in the ultrasonic sensor has a resonant freq near 40kHz because of that diphragm. by the way i could not understand this: " As for ultrasonic transducers, stick the scope across one of them, and feed it from the signal generator via a resistor - this way you can test each one individually. Notice that the transmitter is series resonant (minimum amplitude at resonance), and the receiver is parallel resonant (maximum amplitude at resonance)." i made a test but with no results becuase i think i could not understand something in your text

27th April 2006, 05:30 PM	(permalink)
Hero999	Piezo beeper elements are usally have a resonance at 2.8kHz which they are most comonly operated at, but I've tested this and there's also another very sharp hi Q peek at 32kHz so you could also use it as a cheap ultrasonic transducer. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

27th April 2006, 07:03 PM	(permalink)
audioguru	I have some piezo transducers (speakers) taken from alarm clocks. Their sound output varies very much with frequency, but they are much louder at certain frequencies when the back of the transducer is near an acousic chamber like a thimble or a big bottle cap. Piezo beepers that I have are mounted in an acoustic chamber for resonance. Piezo beepers have a built-in oscillator with feedback from the piezo, so they oscillate at the high output resonance of the piezo transducer in its acoustic chamber. __________________ Uncle $crooge

27th April 2006, 08:05 PM	(permalink)
epilot	Connect it like this:[/quote] ok i'll do the test and see what will happen, thanks. do you know what is the standard device to measure the resonance of a transducer?

27th April 2006, 08:41 PM	(permalink)
audioguru	Piezo tweeters in cheap speakers take a lot of abuse without burning out, but sound like a whistle. Only their few resonant frequencies are heard. People with tin ears think they sound great! Take a piezo beeper with a built-in oscillator and change the size of its acoustic chamber. The frequency and loudness of its beep will also change. If the resonance of the piezo's element matches the resonance of the acoustic chamber it is mounted beside, then it will be extremely loud. __________________ Uncle $crooge

27th April 2006, 09:58 PM	(permalink)
Dr.EM	Yes, I remember they demonstrated that effect in physics once with a speaker and measuring cylinder. It becomes louder because standing waves are formed which is where the orignal and reflected waves are perfectly in phase with each other, and so produce constructive superposition. This effectively doubles the amplitude of the signal. __________________ Angry!? I'm absolutely electrolytic! Will have to make do with myspace now I guess...