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

Ultraminiature Piezoelectric Implantable Acoustic Transducers for Biomedical Applications

Miniature piezoelectric acoustic transducers have been developed for numerous applications. Compared to other transduction mechanisms like capacitive or piezoresistive, piezoelectric transducers do not need direct current (DC) bias voltage and can work directly exposed to fluid. Hence, they are good candidates for biomedical applications that often require the transducer to work in water based fluid. Among all piezoelectric materials, aluminum nitride (AlN) is a great choice for implantable sensors because of the high electrical resistance, low dielectric loss, and biocompatibility for in vivo study. This thesis presents the design, modeling, fabrication, and testing of the AlN acoustic transducers, miniaturized to be implantable for biomedical applications like hearing or cardiovascular devices. To design and model the transducer in air and in water, a 3D finite element analysis (FEA) model was built to study the transducer in a viscous fluid environment. An array of AlN bimorph cantilevers were designed to create a multi-resonance transducer to increase the sensitivity in a broad band frequency range. A two-wafer process using microelectricalmechanical systems (MEMS) techniques was used to fabricate the xylophone transducer with flexible cable. Benchtop testing confirmed the transducer functionality and verified the FEA model experimentally. The transducer was then implanted inside a living cochlea of a guinea pig and tested in vivo. The piezoelectric voltage output from the transducer was measured in response to 80-95 dB sound pressure level (SPL) sinusoidal excitation spanning 1-14 kHz. The phases showed clear acoustic delay. The measured voltage responses were linear and above the noise level. These results demonstrated that the transducer can work as a sensor for a fully implantable cochlear implant. The second generation device, an ultraminiature diaphragm transducer, was designed to be smaller, and yet with an even lower noise floor. The transducer was designed and optimized using a 2D axial-symmetric FEA model for a better figure of merit (FOM), which considered both minimal detectable pressure (MDP) and the diaphragm area. The low-frequency sensitivity was increased significantly, because of the encapsulated back cavity. Because of this merit, cardiovascular applications, which focus on low frequency signals, were also investigated. The diaphragm transducers were fabricated using MEMS techniques. Benchtop tests for both actuating and sensing confirmed the transducer functionality, and verified the design and model experimentally. The transducer had a better FOM than other existing piezoelectric diaphragm transducers, and it had a much lower MDP than the other intracochlear acoustic sensors.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147673/1/chumingz_1.pd

Interfacing biomimetics and nanomaterials for next generation wearables

With the steady rise in average life expectancy across the globe in the last century, lifestyle related diseases are causing a burden on existing healthcare infrastructure. Emerging complex diseases cause significant impact on productive man hours and burden the existing healthcare system. For instance, people suffering from progressive neurodegenerative disorders like Parkinson’s disease, multiple sclerosis, and Huntington’s disease must be monitored frequently to track the progress of the diseases. Due to the life altering nature of these neurodegenerative diseases, it becomes very difficult for the patients to return to their daily routine, considering the fact that a significant amount of their time is spent in hospital-based diagnostic and rehabilitation centres. Other less serious complications, like sleep apnoea, post-trauma recovery, and similar conditions also need regular progress tracking and medical intervention (if necessary) and can cause disruptions to daily life due to frequent hospital stays. Inexpensive, accurate, and power efficient wearable sensors will be playing a major role in facilitating the health 3.0 in the foreseeable future. Particularly, the onslaught of COVID-19 pandemic since late 2019 have fuelled the demand for wearable sensors capable of human physiological vitals monitoring.The need of the hour is efficient, non-invasive, wearable sensors capable of gathering vital human physiological parameters round the clock and store the data in cloud for remote access by healthcare specialists. However, for any sensor to be considered seriously in healthcare space, parameters like sensitivity, ease of use, cost effectiveness, long term reliability and most importantly, low power budget are of paramount importance. Other than applications in human physiological monitoring, flexible sensors are relevant for applications involving artificial skins for next generation prosthesis, soft human-machine interface, and robotics assisted medical facilities.Nature is full of unique designs to tackle interesting problems we encounter daily. For instance, the seamless entry of a Kingfisher from a low resistance medium (air) to a high resistance medium (water) is nothing short of an extraordinary aerodynamic design marvel. Interfacing nanotechnology with biomimetics is important in the context of next generation wearables as it can lead to the development of a class of highly reliable and inexpensive wearable sensors tailored to cater the urgent needs of physiological parameter monitoring.This thesis has been a humble effort towards creating a seamless integration between the concepts of bioinspiration and Microsystems-enabled miniaturized sensors for tackling a wide variety of problems we encounter in our daily life. Two most widely used and traditional mechanisms of sensing entailing piezoresistive and capacitive sensing were investigated and a bioinspiration approach was taken to device next generation flexible and wearable devices. A wide variety of practical problems ranging from human gait monitoring to low powered flow sensing has been tackled taking inspiration from nature

Fast frequency discrimination and phoneme recognition using a biomimetic membrane coupled to a neural network

In the human ear, the basilar membrane plays a central role in sound recognition. When excited by sound, this membrane responds with a frequency-dependent displacement pattern that is detected and identified by the auditory hair cells combined with the human neural system. Inspired by this structure, we designed and fabricated an artificial membrane that produces a spatial displacement pattern in response to an audible signal, which we used to train a convolutional neural network (CNN). When trained with single frequency tones, this system can unambiguously distinguish tones closely spaced in frequency. When instead trained to recognize spoken vowels, this system outperforms existing methods for phoneme recognition, including the discrete Fourier transform (DFT), zoom FFT and chirp z-transform, especially when tested in short time windows. This sound recognition scheme therefore promises significant benefits in fast and accurate sound identification compared to existing methods.Comment: 7 pages, 4 figure

Review of the applications of principles of insect hearing to microscale acoustic engineering challenges

When looking for novel, simple, and energy-efficient solutions to engineering problems, nature has proved to be an incredibly valuable source of inspiration. The development of acoustic sensors has been a prolific field for bioinspired solutions. With a diverse array of evolutionary approaches to the problem of hearing at small scales (some widely different to the traditional concept of "ear"), insects in particular have served as a starting point for several designs. From locusts to moths, through crickets and mosquitoes among many others, the mechanisms found in nature to deal with small-scale acoustic detection and the engineering solutions they have inspired are reviewed. The present article is comprised of three main sections corresponding to the principal problems faced by insects, namely frequency discrimination, which is addressed by tonotopy, whether performed by a specific organ or directly on the tympana; directionality, with solutions including diverse adaptations to tympanal structure; and detection of weak signals, through what is known as active hearing. The three aforementioned problems concern tiny animals as much as human-manufactured microphones and have therefore been widely investigated. Even though bioinspired systems may not always provide perfect performance, they are sure to give us solutions with clever use of resources and minimal post-processing, being serious contenders for the best alternative depending on the requisites of the problem

An overview on structural health monitoring: From the current state-of-the-art to new bio-inspired sensing paradigms

In the last decades, the field of structural health monitoring (SHM) has grown exponentially. Yet, several technical constraints persist, which are preventing full realization of its potential. To upgrade current state-of-the-art technologies, researchers have started to look at nature’s creations giving rise to a new field called ‘biomimetics’, which operates across the border between living and non-living systems. The highly optimised and time-tested performance of biological assemblies keeps on inspiring the development of bio-inspired artificial counterparts that can potentially outperform conventional systems. After a critical appraisal on the current status of SHM, this paper presents a review of selected works related to neural, cochlea and immune-inspired algorithms implemented in the field of SHM, including a brief survey of the advancements of bio-inspired sensor technology for the purpose of SHM. In parallel to this engineering progress, a more in-depth understanding of the most suitable biological patterns to be transferred into multimodal SHM systems is fundamental to foster new scientific breakthroughs. Hence, grounded in the dissection of three selected human biological systems, a framework for new bio-inspired sensing paradigms aimed at guiding the identification of tailored attributes to transplant from nature to SHM is outlined.info:eu-repo/semantics/acceptedVersio

Piezoelectric/Triboelectric Nanogenerators for Biomedical Applications

Bodily movements can be used to harvest electrical energy via nanogenerators and thereby enable self-powered healthcare devices. In this chapter, first we summarize the requirements of nanogenerators for the applications in biomedical fields. Then, the current applications of nanogenerators in the biomedical field are introduced, including self-powered sensors for monitoring body activities; pacemakers; cochlear implants; stimulators for cells, tissues, and the brain; and degradable electronics. Remaining challenges to be solved in this field and future development directions are then discussed, such as increasing output performance, further miniaturization, encapsulation, and improving stability. Finally, future outlooks for nanogenerators in healthcare electronics are reviewed