If you plan to use an ultra sound receiver, then you will need to amplifiy its signal from it maximum output of +-10mV to something like +-3V. How do you do this if you only have positive power supply. You will need to raise the signal level from its +-10mV with an offset of +10mV so that the signal moves between 0 and +20mV. This signal can then be amplified and placed between 0V and 3V. From here, you only need to filter the output with a high-pass filter that eliminates the amplified offset of 1.5V. The result is the green curve.
