The driving bass rhythm of rap music can be harnessed to power a new type of miniature medical sensor designed to be implanted in the body.
The heart of the sensor is a vibrating cantilever, a thin beam attached at one end like a miniature diving board. Music within a certain range of frequencies causes the cantilever to vibrate, generating electricity and storing a charge in a capacitor, said Babak Ziaie, a Purdue University professor of electrical and computer engineering and biomedical engineering.
"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. Nothing happens when you stop playing music," says Babak Ziaie. The implant works only when exposed to specific frequencies. And because of design constraints that dictate the length of the vibrating lever, those frequencies are most often found in rap music.
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.
(A new type of miniature pressure sensor, shown above, designed to be implanted in the body is generating a charge to power the sensor from acoustiv waves.)
The device is an example of a microelectromechanical system, or MEMS, and was created in the Birck Nanotechnology Center. The cantilever beam is made from a ceramic material called lead zirconate titanate, or PZT, which is piezoelectric, meaning it generates electricity when compressed. The sensor is about 2 centimeters long. A receiver that picks up the data from the sensor could be placed several inches from the patient.
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.
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.
"A wireless implantable device could be inserted and left in place, allowing the patient to go home while the pressure is monitored," Ziaie said.
The new technology offers potential benefits over conventional implantable devices, which either use batteries or receive power through a property called inductance, which uses coils on the device and an external transmitter.