Wireless charging start-up uBeam has been accused of having a sham product by a former employee, TechCrunch reported Wednesday.

The company — launched in 2011 while its founder was a student at the University of Pennsylvania — says it has created a device that can wirelessly charge nearby devices, like mobile phones and laptops, using ultrasound waves. Its technology has been written about by The New York Times, Fortune and TechCrunch, among other media outlets.

This week, however, a blogger claiming to be uBeam's former vice president of engineering published a series of posts casting doubts on the company's product. The blogger, TechCrunch reported, said uBeam has yet to hold a public demonstration of its product because it does not work. (An independent science writer later confirmed that the blogger is an ex-uBeam employee.)

https://twitter.com/leegomes/status/730485599031857153

"While in theory [uBeam] may be possible in limited cases, the safety, efficiency, and economics of it mean it is not even remotely practical," the blogger wrote.