Pulse Rate Monitor Transducer Datasheet Request from EEWeb Extreme Circuits Diagram

can you give me the datasheet of the transducer in the diagrame below in the link

i can't find it

thank you

https://www.eeweb.com/blog/extreme_circuits/pulse-rate-monitor

It says there that it uses an electret microphone but did not specify what type. maybe this can help you further with your research. They use electret condenser microphone for detecting pulses. "Human pulse detection using multiple silicon microphones toward estimation of physical condition("Human pulse detection using multiple silicon microphones toward estimation of physical condition")":http://scialert.net/fulltext/?doi=itj.2012.476.479&org=11#f1

thank you