Also known as the thumb piano, the mbira is an African musical instrument that has been around in one form or another for at least 3,000 years. Now, however, scientists have developed a new version that – when combined with a smartphone – can detect toxic substances and possibly even counterfeit medication.
A traditional mbira consists of multiple metal tines of varying sizes, mounted on a wooden sounding board. When one of those tines is plucked by the user's thumb, it produces a specific musical note. The different tines produce different notes based on their size, although their density also affects their sound.
Led by Dr. William Grover, a team from the University of California, Riverside recently created an mbira that has just a single, hollow, U-shaped tine. When that tine contains nothing but air, it produces a note of G-sharp when plucked. If the tine is filled with water, though, that note drops to an F-sharp.
While the difference between those two notes is easily heard, the sound frequencies produced by Grover's mbira are also subtly affected by the density of the liquid inside the tine. These differences in frequency can't be detected by the human ear, but they can be detected by a free web-based smartphone app.
In lab tests, that app was easily able to distinguish between the sounds made by similar-looking samples of non-toxic glycerol and toxic diethylene glycol, plus it could tell the difference between solutions containing varying concentrations of sodium chloride. On the other hand, when it was used to analyze six samples of cold medication from different production lots and with different expiration dates, it confirmed that they were all the same legitimate substance.
In field tests, the instrument has also been used to measure the fat content of bison milk in India, and to indicate sediment levels of river water in California.
Grover now hopes that the device will find use in developing nations, where it could reportedly be built from scrap materials, and be easily used with little training. It can be seen and heard in use, in the following video.
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