Hello,
My classmates an I are working on senior design project which incorporates 2 piezo discs. The first disc is supplied by the function generator with a 6.5 kHz square wave and 3 VPP. The second disc which is connected to the oscillscope is used to pick up the generated signal. We ultimately would like to be able to place a small structure in between the 2 discs ( for example a 3" nail placed 1.5" in a 2x4), then power first disc for a set period of time and collect the signal once the disc if powered off. Are problem is that we are only a able to get a signal through the pick up disc when its face to face with the powered disc, or when we tap on the pick up disc. We alo do not want the discs to touch the object placed in between them, we are afraid this will add stability to the structure and skew are readings.
Any help will be greatly appreciated.
Thanks,
Ray

 

I assume that you are making a sonar circuit that detects the range of an object by its reflection of ultrasonic sound.

A piezo disc resonates for a long time after its signal is turned off. Also because it resonates then it takes some time for it to receive a signal.
Many years ago, Polaroid used ultrasonic transducers to auto-focus their camera but the minimum distance was much farther than yours.

 

As well as the long mechanical time constant, at 6.5KHz the wavelength as getting on for two inches and the resolution of anything with dimension much under that will be very poor.

Have a look at 40KHz (or higher) ultrasonic transducers.

These are intended to give good response in transmit/receive applications and you will get a much finer object resolution.