It is certainly an odd idea, but a rather effective one: Power a medical implant, with the beats of whatever song you happen to be listening to at the time. That in a nutshell is what Purdue university researchers have done with their latest prototype sensing device.

What the device senses doesn't actually matter. It could be a diabetics monitor, or an incontinence warning device. The base mechanics are the same, and it is literally powered by sound. Specifically bass sounds.

Created as a joint venture by doctoral student Albert Kim, research scientist Teimour Maleki and Professor Babak Ziaie, the sensor is a microelectromechanical system which is based on a vibrating cantilever. Basically, it is a thin beam attached to a larger sensor at one end like a miniature diving board. Music within a certain range of frequencies, from 200-500 hertz, causes the cantilever to vibrate, generating electricity on piezoelectric principles. This charge is then stored in a capacitor.

It could charge perfectly happily from a plain tone sounded at the correcrt frequency, and placed a few inches from the patient. However, that would quickly get on the patient's nerves. So, If they are going to use sound, why not use something a bit more pleasant to listen to?

Professor Ziaie stated as much. "A plain tone is a very annoying sound. We thought it would be novel and also more aesthetically pleasing to use music."

"The music reaches the correct frequency only at certain times, for example, when there is a strong bass component," he said. "The acoustic energy from the music can pass through body tissue, causing the cantilever to vibrate."
When the frequency falls outside of the proper range, the cantilever stops vibrating, automatically sending the electrical charge to the sensor, which takes a pressure reading and transmits data as radio signals. Because the frequency is continually changing according to the rhythm of a musical composition, the sensor can be induced to repeatedly alternate intervals of storing charge and transmitting data.
"You would only need to do this for a couple of minutes every hour or so to monitor either blood pressure or pressure of urine in the bladder," Ziaie said. "It doesn't take long to do the measurement."

It doesn't even matter which songs you play, so long as they broadcast within the sensitive frequency range, at least part of the time. Listen to enough songs with a personal music player, and the device is fully charged.

In fact, the researchers experimented with four types of music: rap, blues, jazz and rock.

"Rap is the best because it contains a lot of low frequency sound, notably the bass," Ziaie said.
However, even the 'less than optimal' other types still worked, they just took longer. If rap was not your musical taste, you would just have to listen tio more music each day to get the same charge.

The sensor is capable of monitoring pressure in the urinary bladder and in the sack of a blood vessel damaged by an aneurism. Such a technology could be used in a system for treating incontinence in people with paralysis by checking bladder pressure and stimulating the spinal cord to close the sphincter that controls urine flow from the bladder. More immediately, it could be used to diagnose incontinence. The conventional diagnostic method now is to insert a probe with a catheter, which must be in place for several hours while the patient remains at the hospital.
"A wireless implantable device could be inserted and left in place, allowing the patient to go home while the pressure is monitored," Ziaie said.

In theory, the implant could be left in place permanently; only powering up when the patient hears music, and transmitting its data in between the valid frequency range pulses. If you listen to radio in the car whilst commuting each day, that is more than enough to keep it powered.

Findings are detailed in a paper, “A Novel Electromechanical Interrogation Scheme for Implantable Passive Transponders” to be presented during the IEEE MEMS conference.

References

Rap music powers rhythmic action of medical sensor