We completed a quick proof of concept: The photonic fence project has been using an expensive lens and large area photodiode in order to detect wing beat frequency. We knew on paper that this could be replaced cheaply, however, it seemed worth while to do some quick validation. I ordered some $3 fresnel lenses from Ebay, and replaced our large area photo diode with a much cheaper/smaller part. Not only did it work , but we had a AMAZING signal to noise ratio on wing beat signal – - due to the large (8.5×11″) area of the fresnel lens. Total effort of validation: 40 minutes and some tape. Due to X/Y movement of the retroreflected signal from the laser, we will need one more additional (inexpensive) optical element to keep the signal aligned with the photodiode.