# Wave from the piezoelectric material is not what I expected. Did I miss a step? [closed]

The wave from the piezoelectric material may be

1. sine wave (classmate told me )

2. AC wave (but not sine, I suppose it from the paper)

3. DC wave (from the oscilloscope it seems like a DC wave, not AC wave)

Steps:

Red oscilloscope line connects to the red line. Black oscilloscope line connects to the black line. No load (resistor or capacitor), as in the picture shown below

Here are the wave situations, shown in the oscilloscope

1. no press: a horizontal wave which has noise
2. at the time I press: the horizontal wave goes down
3. at the time i release: the horizontal wave goes up

After that, the horizontal wave returns back to the original, and this is the reason: I think the wave produced from the piezoelectric material is a DC wave, because there is no AC wave, only DC. However, I read some papers and articles from the internet, and they all said that the wave from the piezoelectric material is definitely not a DC wave. So, did I miss any steps before I tested the wave with the oscilloscope1?

I saw a waveform from this pdf ( Chinese version), and in Fig 14 & 15 there is a voltage waveform, as shown below.

1I’m using a WaveRunner-8000 oscilloscope.

• hold it down longer. You may be using 1M input load. The time it takes to drop 64% is the capacitance in uF. DC is not a wave. Mar 10, 2018 at 9:14
• DC is displayed as a straight line that does not move up or down .... any motion in vertical direction, even if it is slow, means that there is a signal Mar 10, 2018 at 9:31
• not the same as i know ... you did not say what it is that you know ... how is your observation different from what you know? Mar 10, 2018 at 9:34
• @jsotola as i know,the wave is not the DC wave Mar 10, 2018 at 9:41
• @TonyStewart.EEsince'75 This time,i press it longer,but only the second i press,the wave goes up horizontally,and than back to the original,i didn't see any AC Mar 10, 2018 at 12:23