Mechanical Energy Sensing and Harvesting in Micromachined Polymer-Based Piezoelectric Transducers for Fully Implanted Hearing Systems: A Review

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.

The remaining obstacles for a totally implantable cochlear implant

“…CIs are already considered low-power electronic devices, consuming only 10mW [15 ▪ ]. With the recent development of silicone microelectromechanical systems (MEMS) [16] and low-power speech processing strategies [17], the energy requirements of TICIs could be reduced even further.…”

Frequency Selectivity via Inner Boundary Conditions for A Self‐Powered Multiresonant Acoustic Sensing Array with Broad Bandwidth

“…The filtered mechanical vibration is converted into electrical pulses by the multichannel hair cells (≈15 000) to stimulate corresponding auditory nerves, [ 5 ] imparting frequency selectivity in a broad bandwidth. [ 6,7 ]…”

“…The filtered mechanical vibration is converted into electrical pulses by the multichannel hair cells (≈15 000) to stimulate corresponding auditory nerves, [5] imparting frequency selectivity in a broad bandwidth. [6,7] Sensorineural hearing loss should be treated via CIs, which consist of external microphones, batteries, signal processing units, and a linear array of electrodes. [6] Because conventional microphones exhibit a flat frequency response within the range of audible acoustic waves (20 Hz-20 kHz), [8] additional signal processing is required to filter and separate the frequency information to activate the surviving neurons at a specific position in the BM through the implanted electrodes (Figure S1, Supporting Information).…”

“…[6,7] Sensorineural hearing loss should be treated via CIs, which consist of external microphones, batteries, signal processing units, and a linear array of electrodes. [6] Because conventional microphones exhibit a flat frequency response within the range of audible acoustic waves (20 Hz-20 kHz), [8] additional signal processing is required to filter and separate the frequency information to activate the surviving neurons at a specific position in the BM through the implanted electrodes (Figure S1, Supporting Information). [6] Despite the functional imitation of CIs, high hearing fidelity, speech recognition under noise, and broader bandwidth remain challenges.…”

“…[6] Because conventional microphones exhibit a flat frequency response within the range of audible acoustic waves (20 Hz-20 kHz), [8] additional signal processing is required to filter and separate the frequency information to activate the surviving neurons at a specific position in the BM through the implanted electrodes (Figure S1, Supporting Information). [6] Despite the functional imitation of CIs, high hearing fidelity, speech recognition under noise, and broader bandwidth remain challenges. [4,9] Furthermore, the energy for driving microphones and signal processing units requires an external power supply, making CIs bulky, aesthetically unsatisfactory, and inconvenient for patients.…”