Thin film piezoelectric acoustic transducer for fully implantable cochlear implants

This paper reports the development of a single cantilever thin film PLD-PZT transducer prototype. The device was experimentally characterized by attaching it on an acoustically vibrating membrane resembling the behavior of the eardrum. Acceleration characteristic of the sensor attached on the membrane was obtained by using a Laser Doppler Vibrometer (LDV) as the output voltage was measured by an oscilloscope. A voltage output of 114 mV was obtained, when the device was excited at 110 dB Sound Pressure Level (SPL) at 1325 Hz. This is the highest value for a thin film piezoelectric transducer in the literature to our knowledge. Using the results of a finite element analysis for this single-channel prototype, which are within 92% agreement with the experimental results, we performed an optimization study to propose a multi-frequency acoustic sensor to be placed on the eardrum for fully-implantable cochlear implant (FICI) applications. The proposed multi-channel transducer consists of eight cantilever beams. Each of these beams resonates at a specific frequency within the daily acoustic band (250–5000 Hz), senses the eardrum vibration and generates the required voltage output for the stimulation circuitry. The total volume and mass of the transducer are 5 × 5×0.2 mm3 and 12.2 mg, respectively. High sensitivity of the transducer (391.9 mV/Pa @900 Hz) enables transmission of strong signals to be the readout circuit, which can easily be processed. Expected to satisfy all the requirements (volume, mass, and stimulation signal at the hearing band) of FICI applications for the first time in literature, the proposed concept has a groundbreaking nature and it can be referred to as the next generation of FICIs since it revolutionizes the operational principle of conventional CIs.