Bee Counters: Measuring a nest's occupation by its capacitance [Resources_Hands On

Abstract

Bees are important: they pollinate dozens of crops, including almonds, cacao, and coffee. While there has been a lot of attention paid to Western honeybees owing to colony collapse disorder, this specific disease and others like it are really measurable only once a colony collapses. And in any case, honeybees are not the only important bee pollinators. What we need is the ability to measure and monitor bee activity as it happens. · Historically, such monitoring was the purview of undergraduates armed with clipboards. More recently, optical sensors have allowed for the automatic detection of bees entering and exiting the hive. But placing optical sensors in a habitat of pollen, mud, and other hive debris drastically degrades their effectiveness. What if there was a better way? · A solution suggested itself when the two of us--a field applications engineer for Analog Devices and an amateur bee enthusiast--were working together on a previous project that involved capacitive sensing. Teachman (the bee enthusiast) commented to Perrault (the applications engineer) that the sensitivity of the AD7746 capacitance-to-digital conversion chip was better than he had expected, and wondered, Do you think we could measure bees with this? All else being equal, the capacitance between two electrodes depends on the dielectric constant of the substance between them. Air has a dielectric constant of roughly 1, while water comes in at around 80. As living cells are mostly water, a bee should have a detectable dielectric signature. Intrigued by the idea, we developed a custom sensor setup to measure just that.