Abstract
The paper presents a comprehensive review of mechanical energy harvesters and microphone sensors for totally implanted hearing systems. The studies on hearing mechanisms, hearing losses and hearing solutions are first introduced to bring to light the necessity of creating and integrating the in vivo energy harvester and implantable microphone into a single chip. The in vivo energy harvester can continuously harness energy from the biomechanical motion of the internal organs. The implantable microphone executes mechanoelectrical transduction, and an array of such structures can filter sound frequency directly without an analogue-to-digital converter. The revision of the available transduction mechanisms, device configuration structures and piezoelectric material characteristics reveals the advantage of adopting the polymer-based piezoelectric transducers. A dual function of sensing the sound signal and simultaneously harvesting vibration energy to power up its system can be attained from a single transducer. Advanced process technology incorporates polymers into piezoelectric materials, initiating the invention of a self-powered and flexible transducer that is compatible with the human body, magnetic resonance imaging system (MRI) and the standard complementary metal-oxide-semiconductor (CMOS) processes. The polymer-based piezoelectric is a promising material that satisfies many of the requirements for obtaining high performance implantable microphones and in vivo piezoelectric energy harvesters.
Highlights
The ear and brain work together in the hearing process
For developing the implantable microphones, we have seen that the incorporation of the ear drum and middle ear bones with the microphone sensor is favoured for sound conduction as these structures can naturally pick up sound and process it
Unimorph and bimorph piezoelectric transducers have shown interesting outputs with the inorganic piezoelectric polymers surmount as the suitable material for an implantable microphone
Summary
The ear and brain work together in the hearing process. Sound energy in the audible frequency range (20 Hz–20 kHz) propagates through air medium as an acoustical mechanical wave which enters from the outer ear towards the middle ear to vibrate the eardrum. FMT converts the electrical signals into mechanical vibrations that set the middle ear structures into motion and subsequently transfer the vibrations to the cochlea At this stage, the cochlea may proceed with its natural functionalities by which the BM mechanically filters the sound vibration and the hair cells transform the vibration into bioelectrical potentials. These signals are transmitted to the RF receiver coil (2) which has been surgically positioned transcutaneously under the skin around the temporal bone. We have found that a piezoelectric/polymer combination material satisfies many of the requirements and future opportunities include the development of a biocompatible, electromagnetic-compatible, CMOS-compatible fully implanted hearing device system in the ear cavity
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