Re: Can a vibrating unit be made from piezo ceramics?

It seems like you are on the right track.

By "similar vibration to that of an insect" I assume you mean the type of 
sound made by insect wings (such as flies) it is conceivable you may 
design a device to imitate a cricket as well, although that may be more 
difficult.

Assuming you want to emmulate a fly, the maximum dimensions force you to 
use a piezo powered by one or two watch batteries. The piece of the 
puzzle that remains is the circuit. The sound of a fly is comparable to 
that of a saw tooth wave with varying pitch and amplitude. So you need to 
build a very small saw wave sinthesizer, powered by a watch battery, 
coupled to a piezo. Depending on how far you go in sophistication, you 
may reduce the project to simply producing a sawtooth wave, and make the 
pitch or amplitude variable externally (make a mini theremin) or simply 
fixed. Yet, a higher level of sophistication would involve varying the 
pitch and amplitude automatically in a random fashion.

Because the circuit needs to be very small I will just give you some tips 
on how to make a fixed pitch/amplitude sawtooth sinthesizer using a small 
integrated circuit: the 555 timer. It's small enough (just an 8 pin DIP 
package), takes little power, and it only needs a few additional 
components.

By just putting the words '555' and 'sawtooth' in www.google.com I found 
this link which will be helpful to you in this project:
 http://www.electronic-circuits-
diagrams.com/oscillatorsimages/oscillatorsckt2.shtml

They have full schematics and instructions on how to select the resistor 
and capacitor for a desired frequency (something between 200 and 400 Hz 
seems reasonable). Although the schematics suggest a supply voltage of 
5.0V you might succeed with just 4.5 (a voltage commonly attained with 
batteries) Three 1.5 volt batteries (or one 4.5V) will be needed 
(hopefully it will still fit within the specified dimensions.) You could 
power the circuit with slightly higher voltage with no adverse effects.

Remember to try your prototype out on a bread board first, and good luck!

-Aurelio R. Ramos, Your Mad Scientist.