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The difference here is that the 100 dB limit isn't some fundamental law of physics. It's one of the currently accepted standards for safe use of ultrasound. Tak

The difference here is that the 100 dB limit isn't some fundamental law of physics. It's one of the currently accepted standards for safe use of ultrasound. Taking a look through the literature, though, you can find various numbers that say ultrasound several orders of magnitude stronger have had no observable long-term adverse effects. Basically, there's an intensity level that we're pretty sure is harmful, and an intensity level that we're pretty sure is safe, and, as it happens, the intensity level necessary to make uBeam useful is somewhere in between. Investing in uBeam requires a calculated wager that the threshold for ultrasound safety is a fair bit higher than 100 dB. It's a risky position to take, and I'm not sure how to calculate it, but it's not pure lunacy.

nitro20045 12y ago
No, 100 dB SPL is not a fundamental law of physics, but it's certainly a fundamental limit of human tolerance (it's about the same sound pressure as standing next to an operating jackhammer), and even if you can't hear it at ~20 kHz, any small animal in the vicinity will likely be tortured (seriously, PETA should take an interest in this technology). And since we're talking about investing in a consumer technology, any fundamental limit in human tolerance or even FDA guidance should be a deal breaker from a business perspective. My objection is that no one did such a sanity check before investing a large sum into this concept.