Thin-Film PZT based Multi-Channel Acoustic MEMS Transducer for Cochlear Implant Applications

AuthorThis paper presents a multi-channel acoustic transducer that works within the audible frequency range (250-5500 Hz) and mimics the operation of the cochlea by filtering incoming sound. The transducer is composed of eight thin film piezoelectric cantilever beams with different resonance frequencies. The transducer is well suited to be implanted in middle ear cavity with an active volume of 5 mm × 5 mm × 0.62 mm and mass of 4.8 mg. Resonance frequencies and piezoelectric outputs of the beams are modeled with Finite Element Method (FEM). Vibration experiments showed that the transducer is capable of generating up to 139.36 mVpp under 0.1 g excitation. Test results are consistent with the FEM model on frequency (97%) and output voltage (89%) values. Device was further tested with acoustic excitation on an artificial tympanic membrane and flexible substrate. Under acoustic excitation, 50.7 mVpp output voltage generated under 100 dB Sound Pressure Level (SPL). Output voltages observed in acoustical and mechanical characterizations are the highest values reported to the best of our knowledge. Finally, to assess the feasibility of the transducer in daily sound levels, it was excited with a speech sample and output signal was recovered. Time-domain waveforms of the recorded and recovered signals showed close patterns

NİKEL MANGANİT ESASLI NTC TERMİSTÖRLERİN ELEKTRİKSEL ÖZELLİKLERİNE 0.15 VE 0.3 MOL CuO KATKISININ ETKİSİ

Endüstriyel uygulamalar için sıcaklık sensörü olarak kullanılan NTC termistörlerin ilgi çeken ana kompozisyonlarından biri nikel manganit’tir. Bu çalışmada nikel manganit esaslı NTC termistörlere bakır oksit katkısının elektriksel ve mikroyapı özelliklerine etkisi araştırılmıştır. Bu amaçla Ni0.5Co0.5CuxMn2-xO4 (x=0.15 ve 0.3) stokiometrisine uygun numuneler klasik seramik üretim yöntemi kullanılarak üretilmiştir. Numuneler 1300 oC'de 5 saat sinterlenmiştir. Numunelerin relatif bulk yoğunluklarının yaklaşık % 97 olduğu belirlenmiştir. Ni0.5Co0.5Cu0.15Mn1.85O4 numunesi için elektriksel özdirenç ve malzeme sabiti sırasıyla 286 Ω.cm ve 3355 K olarak bulunmuştur. CuO katkı miktarının artırılmasıyla ise elektriksel özdirenç ve malzeme sabiti değerlerinin azaldığı saptanmıştır. Ni0.5Co0.5Cu0.3Mn1.7O4 kompozisyonuna ait 1300 oC’de sinterlenen numunenin elektriksel özdirenç (ρ) ve malzeme sabiti (B) değerlerinin 61 Ω.cm ve 3124 K olduğu bulunmuştur.

Tamamen implante koklear implantlar için MEMS tabanlı çok kanallı pizeoelektrik akustik dönüştürücü.

This thesis presents multi-channel acoustic MEMS transducer that is able to work within the audible frequency range (250-5500 Hz) and mimic the operation of a cochlea by filtering incoming sound. This transducer is composed of eight thin film piezoelectric cantilever beams possessing different resonance frequencies. The transducer is well suited to be implanted in a middle ear cavity with an active volume of 5 x 5 x0.6 mm3 and 4.8 mg. Resonance frequencies and piezoelectric outputs of the beams are modeled by using Finite Element Method (FEM). Vibration experiments showed that the transducer was capable of generating up to 139.36 mVpp under 0.1 g excitation. Test results are consistent with FEM model on frequency (97%) and output voltage (89%) values. It was also tested with acoustical excitation in a test setup including artificial tympanic membrane and flexible connection equipment. In that case, it generated up to 50.7 mVpp under 100 dB Sound Pressure Level (SPL). Output voltages observed in acoustical and mechanical characterizations are the highest reported ones to the best of my knowledge. For the first time in the literature, acoustical transducer was excited with speech sound and recovered by using software. Spectrograms of recorded and recovered signals showed close patterns. Moreover, recovered sound was recognizable. Beside stand-alone tests, in-vivo and in-vitro tests have been conducted with stimulation circuits. This stimulation system can operate in 50 dB dynamic range. Finally, a new beam structure is proposed to improve hearing quality by expanding the covered bands as a future work.Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Electrical and Electronics Engineering