The iMic is a piezoelectric displacement sensor that detects the motion of the umbo, which is the tip of the malleus that attaches to the underside of the eardrum. When sound waves enter the ear canal and hit the eardrum, they cause the membrane to vibrate, which in turn moves the umbo. The umbo displaces the piezoelectric iMic, resulting in a measurable charge accumulation. The umbo’s motion is large and unidirectional, making it a better place to target than other parts of the ossicular chain.

The iMic is shaped like a triangular diving board and is made from two layers of the piezoelectric thin-film, polyvinylidene fluoride (PVDF). This type of cantilever shaped structure with two active layers is known as a bimorph. The output from our sensor is the difference in charge between the top and bottom layer when the sensor is bent. We amplify this signal with our custom low-noise differential charge amplifier. A differential measurement is advantageous over a single ended measurement because it reduces common mode noise and thus boosts the signal to noise ratio. One of our previous designs used only a single layer of PVDF and it suffered from high noise and electromagnetic interference.

We test all of our iMic sensors in fresh cadaveric specimens provided by Mass Eye and Ear. The specimens are prepared in a manner similar to the surgery used for cochlear electrode insertion. This surgery allows access to the middle ear cavity, through which we can insert our sensor to contact the umbo.

We’ve demonstrated through extensive testing that the iMic has high sensitivity and a bandwidth up to at least 7 kHz. Its equivalent input noise is very low, comparable to that of commercially available hearing aids.

Our team is preparing to implant the iMic in live sheep as an animal model. Concurrently, we are working towards making the iMic biocompatible and robust to years of wear in the body. Choosing a robust and flexible encapsulation layer is key to the longevity of the implanted device, and we are studying various methods of encapsulation using accelerated aging.

Additionally, our team is iterating on a stable fixation device for holding the sensor inside of the middle ear canal. The related figure here shows a current locking ball joint design printed in titanium. Finally, we are considering redesign of the amplifier such that it is smaller and low power.

This difference in human anatomy relates to its difference in function: the osseous spiral lamina is able to move like a diving board, compared to in animal where it is relatively immobile. In collaboration with Sunil Puria’s lab, Paul Secchia is using optical coherence tomography to measure submicron motion of the cochlear partition structures.

The ears are the primary way to perceive sound, but the skull provides another pathway for sound to be interpreted by the sensory organ in the ear. Bone conduction has been used as a diagnostic tool and treatment for hearing loss since the 17th century. Recently there has been a growing popularity of bone conduction devices which allow for audio communication without blocking sound entering through the ear canal. With the innovative miniature pressure sensors, we are able to study the mechanisms of bone conduction. We also have an interest in understanding effects of diseases, such as otosclerosis and semicircular canal dehiscence, on bone conduction hearing.

Our lab specializes in intracochlear pressure sensor measurements and we’ve accumulated enough data from many ears to create an impedance model of the middle and inner ear. Analyses of intracochlear pressures in the scala vestibuli (SV) and scala tympani (ST), as well as velocities of the middle ear, enables us to quantify the frequency-dependent impedances in the middle ear and cochlear system. Our analyses also further the understanding of air conduction (AC, pictured) and RW stimulation by quantifying the volume velocities of various paths of sound during different stimulation modes.

It is widely believed that the hearing range of humans is between 20 Hz to 20 kHz (as described above). However, there is compelling evidence that infrasound (frequencies below 20 Hz) does enter the ear and even alter sound processing in the cochlea. Especially in industrialized nations, people are frequently exposed to high-energy, low-frequency sounds radiated by heavy machinery, making exposure to infrasound a possible public health concern. Yet the transmission of infrasound to and within the inner ear is not well described.

We measured the motion of middle ear bones and the round window membrane (part of the inner ear) for frequencies between 1 Hz and 2000 Hz and show that the middle ear considerably limits the sound energy transmitted to the inner ear at such low frequencies. However, inner ear pathologies such as semicircular canal dehiscence (SCD) decreases the velocity of the round window membrane in a predictable, frequency-dependent manner, demonstrating that acoustic energy is shunted through and exciting the vestibular system. Our findings suggest that mechanical perturbations of the inner ear could lead to vestibular hypersensitivity to infrasound.

First described by Minor and colleagues in 1998, superior canal dehiscence (SCD) is a disorder characterized by a defect in the bony covering of the superior semicircular canal in the inner ear. Patients with SCD experience a range of auditory and/or vestibular complaints. Although believed to be rare, knowledge and awareness of SCD among physicians has increased over the past decade. However, the diagnosis is difficult to establish as the presentation of SCD often mimics symptoms of other common ear pathologies. As a consequence, patients may wait years before getting their diagnosis and have often receive incorrect treatment for other pathologies.  

Our lab is interested in understanding the underlying mechanics of the inner and middle ear in patients with SCD and to develop methods to establish the diagnosis of SCD in patients. We perform wideband acoustic immittance and laser Doppler vibrometry in patients diagnosed with SCD at our institution. Furthermore, we compare measurements before and after surgery to assess the mechanical effect of surgery on SCD. In our lab, we model the SCD in fresh human temporal bone specimens. The basic science work seeks to improve our understanding of the mechanisms behind SCD and to quantitatively study the effects of different surgical approaches to improve SCD treatment.