# Creating Vibrations using a Small Device

1. Aug 3, 2015

### BillIsTheDill

I'm creating something as a side-project, but I've encountered a problem in a field I'm not well-versed in.
There is a material I am looking to excite with a resonance frequency of 50 Hz.
I need the smallest possible device to create the largest amount of vibration, I've looked into some small sound emitters (a few centimeters/inches) but I'm concerned that they won't make large enough vibrations (again, I don't know much about this). Something that could be incorporated into a circuit would be fantastic.
Price is not a concern.
Does anybody know of any devices or ideas that would satisfy my needs?

2. Aug 3, 2015

### Staff: Mentor

I could suggest a motor with an unbalanced shaft, or a tiny speaker, or a piezioelectric crystal.

You have to define numerically how small is small and how much vibration is much before we can give you a better answer.

Edit: a single water melcule in a magentic field might qualify as smallest.

3. Aug 3, 2015

### BvU

Could you tell a little more about why you sasy "resonance frequency of 50 Hz" instead of "frequency of 50 Hz" ? If the natural vibration frequency of whatever it is you want to excite is 50 Hz already, a small force of 50 Hz may already be enough (all you have to compensate for is the damping). Anorlunda's (bass) speaker seems a good idea to me, but you only need the driving parts: a small coil and a magnet.

4. Aug 3, 2015

5. Aug 3, 2015

### Jeff Rosenbury

What about skipping the speaker part and just going for a solenoid and a stiff spring to reset it? Of course there would be a lot of wear, but that's good ... right?

It could be scaled up to pile driver size if needed, or made tiny.

6. Aug 3, 2015

### Staff: Mentor

What do cell phones use for vibrations?

7. Aug 3, 2015

See post #4

8. Aug 3, 2015

### Staff: Mentor

Ah, thanks! I missed that.

9. Aug 3, 2015

### BillIsTheDill

I mentioned in my original post that it should be at most a few centimeters or inches. Thanks for the cell phone motor idea, I'll be trying that one out. The more vibrations, the better though :P

10. Aug 3, 2015

### BillIsTheDill

@BvU I just realized, is there any sort of "magnitude" in vibrations (again, not my field)? Like if I had a 50 hz vibration (since that is the resonance frequency), if I change the amount/size of vibration, is there any difference in the output?

11. Aug 3, 2015

### Staff: Mentor

The cell phone vibrators come in sizes rated by the G force they can produce.

12. Aug 3, 2015

### rootone

I don't know why the 50Hz frequency is important, but it would be easy enough to make a simple oscillator circuit for this frequency,
then amplify it as much as you need and feed it into a coil/magnet setup, just a repurposed loudspeaker coil should do.

13. Aug 3, 2015

### stedwards

What's your target application?

14. Aug 4, 2015

### BvU

In first order 'all' systems are linear and response is proportional to excitation (see the wiki oscilator links). But around resonance non-linearities come in to limit that proportionality. In other words: it depends...

15. Aug 4, 2015

### sophiecentaur

If that were the 'best' solution then that's what all the highly paid design Engineers would have put in their phones. The point about using a motor and an eccentric wheel is that the system is very well matched (acoustic impedance) to the body of the phone. It is Efficient. The 'dis'advantage could be that the frequency would be pretty well fixed.

16. Aug 4, 2015

### rootone

I'm not suggesting it's the most efficient solution, just an easy and inexpensive one.
I don't know what the end purpose for the device is.

17. Aug 4, 2015

### sophiecentaur

If this device is to be as tiny as the OP seems to indicate then the efficiency could be very low indeed. And I'm not talking about Running Costs; I'm talking about conversion of Electrical Power to mechanical power. The size of magnet and voice coil needed would be considerable. The good thing about a motor is that the energy builds up over a number of cycles, reducing the running power required for the actuator (motor). Needless to say, if he wants a 1kHz beeper, the motor would not be the right solution.

18. Aug 4, 2015

### Nidum

Depends really whether OP wants a device which is small in total or just small at point of application and on what the actual usage is to be .

Many ways of having a powerful sound/vibration generator in a relatively large unit and then conducting sound/vibration to point of application .

At crudest an old fashioned buzzer mechanism and a lightweight drive rod .

Need to know more otherwise guessing in the dark .