Frequency dependence and harmonic distortion of stapes displacement and intracochlear pressure in response to very high level sounds.

Previous reports have suggested that intracochlear pressures (PIC) measured at the base of the cochlea increase directly proportionally with stapes displacement (DStap) in response to moderately high (<130 dB SPL) level sounds. Consistent with this assumption, we have reported that for low frequency sounds (<1 kHz), stapes displacement and intracochlear pressures increase linearly with sound pressure level (SPL) for moderately high levels (<130 dB SPL), but saturate at higher exposure levels (>130 dB SPL). However, the magnitudes of each response were found to be frequency dependent, thus the relationship between DStap and PIC may vary at higher frequencies or higher levels. In order to further examine this frequency and level dependence, measurements of DStap and PIC were made in cadaveric human temporal bones prepared with a mastoidectomy and extended facial recess to expose the ossicular chain. PIC was measured in scala vestibuli (PSV) and scala tympani (PST) simultaneously with SPL in the external auditory canal (PEAC) and laser Doppler vibrometry (LDV) measurements of stapes velocity (VStap). Consistent with prior reports, DStap and PSV increased proportionally with sound pressure level in the ear canal up to a frequency-dependent saturation point, above which both DStap and PSV showed a distinct deviation from proportionality with PEAC, suggesting that their relationship may remain constant at these high frequencies. Likewise, while the asymptotic value, and SPL at which saturation occurred were frequency dependent in both DStap and PSV, the reduction in gain with increasing SPL above this level was constant above this level at all frequencies, and the magnitude of responses at harmonics of the driving frequency increased with increasing level, consistent with harmonic distortion via peak clipping. Importantly, this nonlinear distortion shifts the energy arriving at the inner ear to higher frequencies than are present in incident stimulus, thus exposing the high frequency sensitive components of the auditory system to more noise than would be expected from measurement of that stimulus on its own. Overall, responses suggest that the cochlear representation of very high-level air conducted stimuli is limited by nonlinearities in the middle ear, and that this peak limiting leads to increased high frequency cochlear exposures than are present in the driving stimulus.

Dynamic X-ray Microtomography vs. Laser-Doppler Vibrometry: A Comparative Study.

Purpose: There are challenges in understanding the biomechanics of the human middle ear, and established methods for studying this system show significant limitations. In this study, we evaluate a novel dynamic imaging technique based on synchrotron X-ray microtomography designed to assess the biomechanical properties of the human middle ear by comparing it to laser-Doppler vibrometry (LDV). Methods: We examined three fresh-frozen temporal bones (TB) using dynamic synchrotron-based X-ray microtomography for 256 Hz and 512 Hz, stimulated at 110 dB and 120 dB SPL. In addition, we performed measurements on these TBs using 1D LDV, a well-established method. Results: The normalized displacement values (µm/Pa) at the umbo and the posterior crus of the stapes are consistent or within 5-10 dB differences between all LDV and dynamic microtomography measurements and previously reported literature references. In general, the overall behavior is similar between the two measurement techniques. Conclusion: In conclusion, our results demonstrate the suitability of dynamic synchrotron-based X-ray microtomography in studying the middle ear's biomechanics. However, this study shows that better standardization regarding acoustic stimulation and measurement points is needed to better compare the two measurement techniques.

Operational Deflection Shape Measurements on Bladed Disks with Continuous Scanning Laser Doppler Vibrometry.

The continuous scanning laser Doppler vibrometry (CSLDV) technique is usually used to evaluate the vibration operational deflection shapes (ODSs) of structures with continuous surfaces. In this paper, an extended CSLDV is demonstrated to measure the non-continuous surface of the bladed disk and to obtain the ODS efficiently. For a bladed disk, the blades are uniformly distributed on a given disk. Although the ODS of each blade can be derived from its response data along the scanning path with CSLDV, the relative vibration direction between different blades cannot be determined from those data. Therefore, it is difficult to reconstruct the complete vibration mode of the whole blade disk. In order to measure the complete ODS of the bladed disk, a method based on ODS frequency response functions (ODS FRFs) has been proposed. While the ODS of each blade is measured by designing the suitable scanning paths in CSLDV, an additional response signal is obtained at a fixed point as the reference signal to identify the relative vibration phase between the blade and the blade of the bladed disk. Finally, a measurement is performed with a simple bladed disk and the results demonstrate the feasibility and effectiveness of the proposed extended CSLDV method.

An Influence of Actuator Gluing on Elastic Wave Excited in the Structure.

In this article, the practical issues connected with guided wave measurement are studied: (1) the influence of gluing of PZT plate actuators (NAC2013) on generated elastic wave propagation, (2) the repeatability of PZT transducers attachment, and (3) the assessment of the possibility of comparing the results of Laser Doppler Vibrometry (LDV) measurement performed on different 2D samples. The consideration of these questions is crucial in the context of the assessment of the possibility of the application of the guided wave phenomenon to structural health-monitoring systems, e.g., in civil engineering. In the examination, laboratory tests on the web of steel I-section specimens were conducted. The size and shape of the specimens were developed in such a way that they were similar to the elements typically used in civil engineering structures. It was proved that the highest amplitude of the generated wave was obtained when the exciters were glued using wax. The repeatability and durability of this connection type were the weakest. Due to this reason, it was not suitable for practical use outside the laboratory. The permanent glue application gave a stable connection between the exciter and the specimen, but the generated signal had the lowest amplitude. In the paper, the new procedure dedicated to objective analysis and comparison of the elastic waves propagating on the surface of different specimens was proposed. In this procedure, the genetic algorithms help with the determination of a new coordinate system, in which the assessment of the quality of wave propagation in different directions is possible.

Influence of the Intracranial Contents on the Head Motion under Bone Conduction.

INTRODUCTION: The mechanism of non-osseous bone conduction pathways, involving the intracranial contents (ICC) of the skull, is still not well understood. This study aimed to investigate the influence of the ICC on the skull bone wave propagation, including dependence on stimulation location and coupling. METHODS: Three Thiel-embalmed whole-head cadaver specimens were studied before and after the removal of the ICC. Stimulation was via the electromagnetic actuators from commercial bone conduction hearing aids. Osseous pathways were sequentially activated by mastoid, forehead, and bone-anchored hearing aid location stimulation via a 5-Newton steel headband or percutaneously implanted screw. Non-osseous pathways were activated by stimulation on the eye and dura via a 5-Newton steel headband and a custom-made pneumatic holder, respectively. Under each test condition, the 3D motion of the superior skull bone was monitored at ∼200 points. RESULTS: The averaged response of the skull surface showed limited differences due to the removal of the ICC. In some isolated cases, the modal pattern on the skull surface showed a trend for an upshift (∼1/2 octave) in the observed natural frequencies for drained heads. This was also consistent with an observed trend for an upshift in the transition frequency in the estimated deformation across the lateral surfaces of the temporal bones. Such changes were consistent with the expected reduction in mass and damping due to the absence of the ICC. CONCLUSION: Overall, the ICC affect to a limited extent the motion of the skull bone, with a limited trend for a reduction of its natural frequencies.

Stress and strain calculation method for orthotropic polymer composites under axial and bending ultrasonic fatigue loads.

Accelerated fatigue testing is one potential solution to evaluate the very high cycle fatigue behavior of composite materials within a reasonable amount of time. The ultrasonic fatigue testing methodology can be adopted to realize fatigue experiments up to 109 cycles at 20 kHz, compared to conventional fatigue experiments usually carried out between 5-50 Hz. The determination of cyclic stresses during ultrasonic loading remains to be one of the major challenges. The cyclic stresses during ultrasonic fatigue loading were investigated for a carbon fiber 5H satin fabric reinforced in Polyetherketoneketone (CF-PEKK) composite material. Two experimental setups were developed to perform ultrasonic testing under uni-axial and three-point bending loading conditions. A 3D-Scanning Laser Doppler Vibrometer (3D-SLDV) and a single-point Laser Doppler Vibrometer (LDV) were integrated into the test systems to measure the oscillation displacement of the CF-PEKK specimens during ultrasonic cyclic loading. These displacement measurements were used to calculate the resulting strains and stresses under elastic loading conditions. The experimental results were found to be in good agreement with those obtained from finite element models, providing evidence for applying the proposed method.

Feasibility of 3D-printed middle ear prostheses in partial ossicular chain reconstruction.

Despite advances in prosthesis materials, operating microscopes and surgical techniques during the last 50 years, long-lasting hearing improvement remains a challenge in ossicular chain reconstruction. Failures in the reconstruction are mainly due to inadequate length or shape of the prosthesis, or defects in the surgical procedure. 3D-printed middle ear prosthesis might offer a solution to individualize treatment and obtain better results. The aim of the study was to study the possibilities and limitations of 3D-printed middle ear prostheses. Design of the 3D-printed prosthesis was inspired by a commercial titanium partial ossicular replacement prosthesis. 3D models of different lengths (1.5-3.0 mm) were created with Solidworks 2019-2021 software. The prostheses were 3D-printed with vat photopolymerization using liquid photopolymer Clear V4. Accuracy and reproducibility of 3D printing were evaluated with micro-CT imaging. The acoustical performance of the prostheses was determined in cadaver temporal bones with laser Doppler vibrometry. In this paper, we present an outline of individualized middle ear prosthesis manufacturing. 3D printing accuracy was excellent when comparing dimensions of the 3D-printed prostheses and their 3D models. Reproducibility of 3D printing was good if the diameter of the prosthesis shaft was 0.6 mm. 3D-printed partial ossicular replacement prostheses were easy to manipulate during surgery even though they were a bit stiffer and less flexible than conventional titanium prostheses. Their acoustical performance was similar to that of a commercial titanium partial ossicular replacement prosthesis. It is possible to 3D print functional individualized middle ear prostheses made of liquid photopolymer with good accuracy and reproducibility. These prostheses are currently suitable for otosurgical training. Further research is needed to explore their usability in a clinical setting. In the future, 3D printing of individualized middle ear prostheses may provide better audiological outcomes for patients.

Intracochlear pressure and temporal bone motion interaction under bone conduction stimulation.

BACKGROUND: Under bone conduction (BC) stimulation, the otic capsule, and surrounding temporal bone, undergoes a complex 3-dimentional (3D) motion that depends on the frequency, location and coupling of the stimulation. The correlation between the resultant intracochlear pressure difference across the cochlear partition and the 3D motion of the otic capsule is not yet known and is to be investigated. METHODS: Experiments were conducted in 3 fresh frozen cadaver heads, individually on each temporal bone, resulting in a total of 6 samples. The skull bone was stimulated, via the actuator of a BC hearing aid (BCHA), in the frequency range of 0.1-20 kHz. Stimulation was applied at the ipsilateral mastoid and the classical BAHA location via a conventional transcutaneous (5-N steel headband) and percutaneous coupling, sequentially. Three-dimensional motions were measured across the lateral and medial (intracranial) surfaces of the skull, the ipsilateral temporal bone, the skull base, as well as the promontory and stapes. Each measurement consisted of 130-200 measurement points (∼5-10 mm pitch) across the measured skull surface. Additionally, intracochlear pressure in the scala tympani and scala vestibuli was measured via a custom-made intracochlear acoustic receiver. RESULTS: While there were limited differences in the magnitude of the motion across the skull base, there were major differences in the deformation of different sections of the skull. Specifically, the bone near the otic capsule remained primarily rigid across all test frequency (above 10 kHz), in contrast to the skull base, which deformed above 1-2 kHz. Above 1 kHz, the ratio, between the differential intracochlear pressure and the promontory motion, was relatively independent of coupling and stimulation location. Similarly, the stimulation direction appears to have no influence on the cochlear response, above 1 kHz. CONCLUSIONS: The area around the otic capsule appears rigid up to significantly higher frequencies than the rest of the skull surface, resulting in primarily inertial loading of the cochlear fluid. Further work should be focused at the investigation of the solid-fluid interaction between the bony walls of the otic capsule and the cochlear contents.

Lead Zirconate Titanate Transducers Embedded in Composite Laminates: The Influence of the Integration Method on Ultrasound Transduction.

In the context of an embedded structural health monitoring (SHM) system, two methods of transducer integration into the core of a laminate carbon fiber-reinforced polymer (CFRP) are tested: cut-out and between two plies. This study focuses on the effect of integration methods on Lamb wave generation. For this purpose, plates with an embedded lead zirconate titanate (PZT) transducer are cured in an autoclave. The embedded PZT insulation, integrity, and ability to generate Lamb waves are checked with electromechanical impedance, X-rays, and laser Doppler vibrometry (LDV) measurements. Lamb wave dispersion curves are computed by LDV using two-dimensional fast Fourier transform (Bi-FFT) to study the quasi-antisymmetric mode (qA0) excitability in generation with the embedded PZT in the frequency range of 30 to 200 kHz. The embedded PZT is able to generate Lamb waves, which validate the integration procedure. The first minimum frequency of the embedded PZT shifts to lower frequencies and its amplitude is reduced compared to a surface-mounted PZT.

Effect of freezing and embalming of human cadaveric whole head specimens on bone conduction.

BACKGROUND AND AIMS: Conserved specimens do not decay and therefore permit long-term experiments thereby overcoming limited access to fresh (frozen) temporal bones for studies on middle ear mechanics. We used a Thiel conservation method which is mainly based on a watery solution of salts. In contrast to pure Formalin, Thiel conservation aims to preserve the mechanical proprieties of human tissue. The aim of this study is to examine the effect of Thiel conservation on bone conduction in the same specimen before and after conservation. METHODS: Nine ears of five defrosted whole heads were stimulated with a direct, electrically driven, bone anchored hearing system (Baha, Baha SuperPower). The motion produced by bone conduction stimulation was measured with a single point laser Doppler vibrometer (LDV) at the promontory, the ossicular chain, and the round window through a posterior tympanotomy. After the initial experiments, the entire whole heads were placed in Thiel solution. In order to enable direct comparison between fresh frozen and Thiel specimens, our Thiel conservation did not include intravascular and intrathecal perfusion. The measurements were repeated 3 and 12 months later. To determine the effect of freezing, defrosting, and embalming on the whole heads, CT scans were performed at different stages of the experimental procedure. Additionally, three extracted temporal bones were stimulated a Baha, motion of the promontory measured by LDV and embalmed in Thiel solution to investigate the direct impact of Thiel solution on the bone. RESULTS: The averaged magnitude of motion on the promontory increased in whole head specimens by a mean of 10.3 dB after 3 months of Thiel embalming and stayed stable after 12 months. A similar effect was observed for motion at the tympanic membrane (+7.2 dB), the stapes (+9.5 dB), and the round window (+4.0 dB). In contrast to the whole head specimens, the motion of the extracted temporal bones did not change after 3 months of Thiel embalming (-0.04 dB in average). CT scans of the whole heads after conservation showed a notable brain volume loss mostly >50% as well as a remarkable change in the consistency and structure of the brain. Partial changes could already be observed before the Thiel embalming but after 1-2 days of defrosting. In an additional experiment, a substitution of brain mass and weight by Thiel fluid did not lead to new deterioration in sound transmission. In contrast, a frozen (non-defrosted) whole head showed a distinctively reduced magnitude of promontory motion before defrosting. DISCUSSION: For our setup, the vibration of the ear due to bone conduction in the same whole head specimens significantly increased after Thiel conservation. Such an increase was not observed in extracted temporal bone specimens. Due to brain changes in the CT scans, we investigated the consequences of the brain volume changes and structure loss on the frozen brain before defrosting. The loss of brain volume alone could not explain the increase of ear vibrations, as we did not observe a difference when the volume was replaced with Thiel fluid. However, freezing and defrosting of the entire brain seems to have a major influence. Beside the destructive effect of freezing on the brain, the modified conservation method without perfusion changed the brain structure. In conclusion, bone conduction in whole heads depends on the physical condition of the brain, rather than on the conservation.

Stepped electrode designs of TSM langasite resonators for high-temperature applications.

In this paper, we report the simulation and fabrication of thickness-shear mode langasite resonators with stepped elliptical electrode designs to investigate their effects on energy trapping and suppression of spurious modes at elevated temperatures. Finite element analysis was conducted to analyze the design of a stepped elliptical electrode on a contoured langasite crystal. Based on the simulation findings, langasite resonators with stepped electrodes were fabricated, and their displacement profiles and frequency-temperature properties were characterized using network analysis and laser Doppler vibrometry. Results demonstrate improved frequency separation between the resonant and spurious modes, and enhanced spurious mode suppression at both room and higher temperatures, suggesting that stepped elliptical electrode designs can effectively enhance the sensing performance of langasite resonators.

Real-time measurement of stapes motion and intracochlear pressure during blast exposure.

Blast-induced auditory injury is primarily caused by exposure to an overwhelming amount of energy transmitted into the external auditory canal, the middle ear, and then the cochlea. Quantification of this energy requires real-time measurement of stapes footplate (SFP) motion and intracochlear pressure in the scala vestibuli (Psv). To date, SFP and Psv have not been measured simultaneously during blast exposure, but a dual-laser experimental approach for detecting the movement of the SFP was reported by Jiang et al. (2021). In this study, we have incorporated the measurement of Psv with SFP motion and developed a novel approach to quantitatively measure the energy flux entering the cochlea during blast exposure. Five fresh human cadaveric temporal bones (TBs) were used in this study. A mastoidectomy and facial recess approach were performed to identify the SFP, followed by a cochleostomy into the scala vestibuli (SV). The TB was mounted to the "head block", a fixture to simulate a real human skull, with two pressure sensors - one inserted into the SV (Psv) and another in the ear canal near the tympanic membrane (P1). The TB was exposed to the blast overpressure (P0) around 4 psi or 28 kPa. Two laser Doppler vibrometers (LDVs) were used to measure the movements of the SFP and TB (as a reference). The LDVs, P1, and Psv signals were triggered by P0 and recorded simultaneously. The results include peak values for Psv of 100.8 ± 51.6 kPa (mean ± SD) and for SFP displacement of 72.6 ± 56.4 µm, which are consistent with published experimental results and finite element modeling data. Most of the P0 input energy flux into the cochlea occurred within 2 ms and resulted in 10-70 µJ total energy entering the cochlea. Although the middle ear pressure gain was close to that measured under acoustic stimulus conditions, the nonlinear behavior of the middle ear was observed from the elevated cochlear input impedance. For the first time, SFP movement and intracochlear pressure Psv have been successfully measured simultaneously during blast exposure. This study provides a new methodology and experimental data for determining the energy flux entering the cochlea during a blast, which serves as an injury index for quantifying blast-induced auditory damage.

A Partial Ossicular Replacement Prosthesis With a Concentric Ball Joint in the Headplate.

OBJECTIVE: In passive middle ear prosthetics, rigid implants have proven successful in reconstructing the ossicular chain. However, these cannot fully replicate the physiology of the ossicular chain. Pressure fluctuations cause high stresses in rigid passive prostheses, which can result in dislocation, protrusion, and pre-tension in the annular ligament resulting in unsatisfactory hearing results. METHODS: In collaboration with MED-EL, we developed a new passive middle ear prosthesis that features a balanced, centered ball joint between the headplate and shaft of the prosthesis. We compared the sound transmission properties of this new prosthesis with those of a standard rigid prosthesis. Using Laser-Doppler-Vibrometry, we measured the sound-induced velocity of the stapes footplate relative to a given acoustic stimulus. RESULTS: The new prosthesis showed equivalent sound transmission characteristics compared to the rigid prosthesis, whereas retaining the ability to compensate for pressure fluctuations due to its ball joint. This ensures good transmission properties even during displacements of the tympanic membrane. CONCLUSION: This development is a further step toward a physiological reconstruction of the ossicular chain. LEVEL OF EVIDENCE: NA Laryngoscope, 133:1717-1721, 2023.

Creation of an incus recess for a middle-ear microphone using a drill or laser ablation: a comparison of equivalent noise level and middle ear transfer function.

PURPOSE: Studies have assessed the trauma and change in hearing function from the use of otological drills on the ossicular chain, but not the effects of partial laser ablation of the incus. A study of the effectiveness of a novel middle-ear microphone for a cochlear implant, which required an incus recess for the microphone balltip, provided an opportunity to compare methods and inform a feasibility study of the microphone with patients. METHODS: We used laser Doppler vibrometry with an insert earphone and probe microphone in 23 ears from 14 fresh-frozen cadavers to measure the equivalent noise level at the tympanic membrane that would have led to the same stapes velocity as the creation of the incus recess. RESULTS: Drilling on the incus with a diamond burr created peak noise levels equivalent to 125.1-155.0 dB SPL at the tympanic membrane, whilst using the laser generated equivalent noise levels barely above the baseline level. The change in middle ear transfer function following drilling showed greater variability at high frequencies, but the change was not statistically significant in the three frequency bands tested. CONCLUSIONS: Whilst drilling resulted in substantially higher equivalent noise, we considered that the recess created by laser ablation was more likely to lead to movement of the microphone balltip, and therefore decrease performance or result in malfunction over time. For patients with greatly reduced residual hearing, the greater consistency from drilling the incus recess may outweigh the potential benefits of hearing preservation with laser ablation.

Electrical and Optical Characterization of SAW Sensors Coated with Parylene C and Their Analysis Using the Coupling-of-Modes (COM) Theory.

In this paper, we present how complementary characterization techniques, such as electrical measurements with a vector network analyzer (VNA), optical measurements with a laser Doppler vibrometer (LDV), and numerical simulations with the finite element method, coupled with spectral domain analysis (FEMSDA), allow us to independently access different properties of a SAW device and fully characterize its operation using the coupling-of-modes theory (COM). A set of chemical SAW sensors coated with parylene C layers of different thicknesses (1, 1.5, and 2 µm) and an uncoated sensor were used as test samples. The sensors represent dual-channel electroacoustic delay lines operating in the vicinity of 77 MHz. The IDTs consist of split aluminum electrodes deposited on a AT-cut quartz substrate. The thickness-dependent influence of the parylene C layer was observed on the operating frequency (SAW velocity), static capacitance, attenuation, crosstalk, and reflection coefficient. COM parameters were reported for the four cases considered; measured and simulated data show good agreement. The presented approach is suitable for the design, characterization, and validation of polymer film-coated SAW sensors.

Detecting Defects in Composite Polymers by Using 3D Scanning Laser Doppler Vibrometry.

The technique of 3D scanning laser Doppler vibrometry has recently appeared as a promising tool of nondestructive evaluation of discontinuity-like defects in composite polymers. The use of the phenomenon of local defect resonance (LDR) allows intensifying vibrations in defect zones, which can reliably be detected by means of laser vibrometry. The resonance acoustic stimulation of structural defects in materials causes compression/tension deformations, which are essentially lower than the material tensile strength, thus proving a nondestructive character of the LDR technique. In this study, the propagation of elastic waves in composites and their interaction with structural inhomogeneities were analyzed by performing 3D scanning of vibrations in Fast Fourier Transform mode. At each scanning point, the in-plane (x, y) and out of plane (z) vibration components were analyzed. The acoustic stimulation was fulfilled by generating a frequency-modulated harmonic signal in the range from 50 Hz to 100 kHz. In the case of a reference plate with a flat bottom hole, the resonance frequencies for all (x, y, and z) components were identical. In the case of impact damage in a carbon fiber reinforced plastic sample, the predominant contribution into total vibrations was provided by compression/tension deformations (x, y vibration component) to compare with vibrations by the z coordinate. In general, inspection results were enhanced by analyzing total vibration patterns obtained by averaging results at some resonance frequencies.

A Normalized Model of a Microelectromechanical Relay Calibrated by Laser-Doppler Vibrometry.

This work presents a behavioral model for a microelectromechanical (MEM) relay for use in circuit simulation. Models require calibration, and other published relay models require over a dozen parameters for calibration, many of which are difficult to extract or are only available after finite element analysis. This model improves on prior work by taking advantage of model normalization, which often results in models that require fewer parameters than un-normalized models. This model only needs three parameters extracted from experiment and one dimension known from device fabrication to represent its non-contact behavior, and two additional extracted parameters to represent its behavior when in contact. The extracted parameters-quality factor, resonant frequency, and the pull-in voltage-can be found using laser Doppler vibrometry. The device dimension is the actuation gap size, which comes from process data. To demonstrate this extraction process, a series of velocity step responses were excited in MEM relays, the measured velocity responses were used to calibrate the model, and then then simulations of the model (implemented in Verilog-A) were compared against the measured data. The error in the simulated oscillation frequency and peak velocity, two values selected as figures of merit, is less than 10% across many operating voltages.

Beyond the exponential horn: a bush-cricket with ear canals which function as coupled resonators.

Bush-crickets have dual-input, tympanal ears located in the tibia of their forelegs. The sound will first of all reach the external sides of the tympana, before arriving at the internal sides through the bush-cricket's ear canal, the acoustic trachea (AT), with a phase lapse and pressure gain. It has been shown that for many bush-crickets, the AT has an exponential horn-shaped morphology and function, producing a significant pressure gain above a certain cut-off frequency. However, the underlying mechanism of different AT designs remains elusive. In this study, we demonstrate that the AT of the duetting Phaneropterinae bush-cricket Pterodichopetala cieloi function as coupled resonators, producing sound pressure gains at the sex-specific conspecific calling song frequency, and attenuating the remainder-a functioning mechanism significantly different from an exponential horn. Furthermore, it is demonstrated that despite the sexual dimorphism between the P. cieloi AT, both male and female AT have a similar biophysical mechanism. The analysis was carried out using an interdisciplinary approach, where micro-computed tomography was used for the morphological properties of the P. cieloi AT, and a finite-element analysis was applied on the precise tracheal geometry to further justify the experimental results and to go beyond experimental limitations.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps.

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40 µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10 dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1 kHz) decreased monotonically as the pressure became more negative except for a dip (about 500 Pa wide) that occurred between - 700 and - 1800 Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.

Miniaturization of Laser Doppler Vibrometers-A Review.

Laser Doppler vibrometry (LDV) is a non-contact vibration measurement technique based on the Doppler effect of the reflected laser beam. Thanks to its feature of high resolution and flexibility, LDV has been used in many different fields today. The miniaturization of the LDV systems is one important development direction for the current LDV systems that can enable many new applications. In this paper, we will review the state-of-the-art method on LDV miniaturization. Systems based on three miniaturization techniques will be discussed: photonic integrated circuit (PIC), self-mixing, and micro-electrochemical systems (MEMS). We will explain the basics of these techniques and summarize the reported miniaturized LDV systems. The advantages and disadvantages of these techniques will also be compared and discussed.