This explains the pressure waves:
<https://www.knowyourparts.com/technical-resources/electrical/measuring-o2-sensor-signals/>

1. The oxygen sensor monitors the content of the pressure waves as they
pass the sensor. With each pressure wave the sensor sends a rich
or lean mixture voltage to the engine controller.

2. At temperature, the sensor changes resistance as the air/fuel ratio
changes. But instead of a gradual change, it switches very quickly
from low resistance (less than 10 K ohms when the mixture is rich),
to more than 20 K (ohms when the mixture is lean).

3. The engine controller supplies a base reference voltage of one volt
to the sensor.

4. Lambda1 is the reference voltage of 450 mV, which represents an
air-fuel ratio of 14.7:1 or stoichiometric.

5. The sensor is capable of generating a one-volt signal when there
is no oxygen in the exhaust stream.