Micromechanical Tuning Research Articles

Effect of nonlinearity and axial force on frequency drift of a T-shaped tuning fork micro-resonator

In this paper, the effect of nonlinearity on axial force sensitivity is investigated in a T-shaped micromechanical tuning fork resonator. Firstly, a unified model of this resonator for both in-phase and anti-phase modes is established, in which the quadratic and cubic nonlinearities are considered. The validity of this proposed model is verified by the experimental results. Then, the effects of the axial force on the frequency shift and of the nonlinearity on the axial force sensitivity are analyzed theoretically and experimentally. The sensitivity to frequency shift caused by the axial force is observed to be slightly enhanced by soft spring nonlinearity. These results can be used to provide reference for some practical applications, e.g. electrometers, force sensors, etc.

C-band optical filters with micromechanical tuning

Tunable optical filters that cover the entire range of the C-band (1530–565 nm) are designed by utilizing the Vernier effect, i.e. series coupling of microring resonators of different sizes, and the micromechanical tuning method. The micromechanical tuning method employs lateral comb-drive actuators to control evanescent coupling between the resonators and index modulators. Single crystalline silicon is used as the material for all of the main components including bus waveguide cores, resonators, index modulators, and comb-drive actuators. A finite-difference time-domain method is used for optical analysis of the filter. The simulation results show good agreement with those by analytical methods, previously reported. The width of the index modulator is found to play an important role to the filter characteristics. A wider modulator (e.g., width: 100 nm) can cover the full tuning range of 35 nm without switching among different bands owing to stronger effective index change effect, but induces significant loss to the filter, especially when it is brought close to the resonator. While a narrow modulator (e.g., width: 50 nm), on the other hand, induces moderate loss to the filter, it requires hopping among multiple bands to cover the full range since the effective index change incurred is again moderate. In order to achieve linear tuning characteristics in the cascaded-resonator filters, the shaped-finger comb-drive actuator design method is applied. The design method based on two-dimensional slice approximation is further examined by three-dimensional finite element analysis for verification. It is shown that the design method can also work for the cascaded-resonator filters, even for the one that requires band hopping. Effects of fabrication imperfections to the designed device characteristics are studied as well.

Auditory capabilities of birds in relation to the structural diversity of the basilar papilla

The basilar papilla length increases systematically with body mass for 41 species from more than 10 avian orders and this relation does not differ between phylogenetic groups. Audiograms of 25 non-strigiform and 12 owl species, normalized relative to best frequency and best threshold, were used to compare audiogram shapes. The analysis revealed that the high frequency flank of the audiogram was remarkably similar across non-strigiform species. The high-frequency limit was on average 1.1 octaves above the best frequency, the low-frequency flank was less steep and showed much more species dependent variability. Audiogram shape in owls was much more variable. Morphological gradients along the basilar papilla revealed a small species dependent variability for the basal region of the basilar papilla and an increasing degree of variability towards the apex. In non-strigiform species, frequency selectivity for 2 and 4 kHz varied systematically with the space on the basilar papilla devoted to processing the corresponding frequency range. Space on the papilla did not vary systematically with frequency selectivity at 1 kHz. This difference between test frequencies might be related to the transition from electrical hair-cell tuning, that dominates below 1–2 kHz, to micromechanical tuning at higher frequencies.

What have lizard ears taught us about auditory physiology?

The structure of the basilar papilla of the inner ear of lizards is the most diverse among all vertebrates. Research on a variety of lizard ears, animals that are remarkably robust under laboratory conditions, has provided the field of auditory research with valuable information, particularly on the minimum structural requirements for sensitive, selective hearing and on the importance of the tectorial membrane and active processes in this regard. Despite the absence of a tuned basilar membrane, lizard ears produce highly frequency selective hearing through micromechanical tuning of small, resonant hair-cell-tectorial units or of free-standing hair bundles. These units are driven by an active process that also underlies spontaneous and other otoacoustic emissions. Lizard ears provided the first in vivo evidence that the active process is calcium-sensitive and lies within the stereovillar bundles of the hair cells.

Cochlear mechanisms from a phylogenetic viewpoint.

The hearing organ of the inner ear was the last of the paired sense organs of amniotes to undergo formative evolution. As a mechanical sensory organ, the inner-ear hearing organ's function depends highly on its physical structure. Comparative studies suggest that the hearing organ of the earliest amniote vertebrates was small and simple, but possessed hair cells with a cochlear amplifier mechanism, electrical frequency tuning, and incipient micromechanical tuning. The separation of the different groups of amniotes from the stem reptiles occurred relatively early, with the ancestors of the mammals branching off first, approximately 320 million years ago. The evolution of the hearing organ in the three major lines of the descendents of the stem reptiles (e.g., mammals, birds-crocodiles, and lizards-snakes) thus occurred independently over long periods of time. Dramatic and parallel improvements in the middle ear initiated papillar elongation in all lineages, accompanied by increased numbers of sensory cells with enhanced micromechanical tuning and group-specific hair-cell specializations that resulted in unique morphological configurations. This review aims not only to compare structure and function across classification boundaries (the comparative approach), but also to assess how and to what extent fundamental mechanisms were influenced by selection pressures in times past (the phylogenetic viewpoint).

Micromechanical tuning elements in a 620-GHz monolithic integrated circuit

While monolithic integrated-circuit technology promises a practical means for realizing reliable reproducible planar millimeter and submillimeter-wave circuits, conventional planar circuits do not allow for critical post-fabrication optimization of performance. A 620-GHz quasi-optical monolithic detector circuit is used here to demonstrate the performance of two integrated micromechanical planar tuning elements. This is the first reported demonstration of integrated micromechanical tuning at submillimeter wavelengths. The tuning elements, called sliding planar backshorts (SPBs), are used to adjust the electrical length of planar transmission-line tuning stubs to vary the power delivered between a substrate-lens coupled planar antenna and a thin-film bismuth detector over a range of nearly 15 dB. The circuit performance agrees with theoretical calculations and microwave measurements of a -0.06-dB reflection coefficient made for a scale model of the integrated tuners. The demonstrated tuning range for the SPB tuners indicates that they can be valuable for characterizing components in developmental circuits and for optimizing the in-use performance of various millimeter and submillimeter-wave integrated circuits.

Widely tunable 1.5 µm micromechanical opticalfilter usingAlO x /AlGaAs DBR

The authors demonstrate, for the first time, a wavelength tunable optical filter at 1.55 /spl mu/m using micromechanical tuning of a Fabry-Perot resonator with an AlO/sub x//AlGaAs distributed Bragg reflectors (DBR). The use of thermally oxidised AlAs layers, resulting an ultrawide bandwidth, dramatically increased the tuning range and efficiency of the resonator. Very efficient continuous tuning of >50 nm with only a 0.95 V tuning voltage was achieved. The tuning range, limited by our test laser, is expected to be expandable to hundreds of nm.

Contactless Surface Measurement with a New Acoustic Sensor

A standard diamond tip fixed to a micromechanical tuning fork (32 kHz) is guided by piezo-electric actuators in a controlled distance of about 100 nm along the inspected surface. The small acoustic fork oscillation (constantly excited) is (mainly) damped by the air gap between diamond tip and surface. Thus, constant output signal of the high-Q oscillatory circuit indicates that the tip traces the surface roughness in a constant distance. First results carried out at roughness standards, map the profiles obtained mechanically. Difficult materials like laquers, glasses, ceramics were investigated.

The effects of quinine on the cochlear mechanics in the isolated temporal bone preparation

Quinine is known to induce a reversible hearing loss and to evoke motile responses of isolated outer hair cells. To study the effect of quinine, mechanical tuning curves of the Hensen's cells were measured in the isolated cochlea preparation in response to acoustical stimuli applied to the ear before and after application of the drug. It was shown that 0.5–4 mM quinine increased the vibration amplitude at the peak of the mechanical resonance curves and increased the sharpness of tuning. The time course of the event depended on whether the scala media was opened or not. The results show that quinine alters the micromechanical tuning of the organ of Corti.

Connections between stereocilia in auditory hair cells of the alligator lizard

The interconnections between stereocilia within individual tufts of auditory hair cells in the basilar papilla of the alligator lizard were examined with a transmission electron microscope. An elaborate array of fibers near the base of each stereocilium (where it tapers to anchor into the cuticular plate) connected it to each of its neighboring stereocilia. The tips of individual stereocilia, which were slightly larger in diameter than their shaft, contacted adjacent stereocilia. Fibers also connected the tip of the kinocilium to neighboring stereocilia in the first row. The remaining regions of the stereocilia were relatively free of connecting fibers. The integrity of these connecting fibers are likely to be important in maintaining the normal micromechanical tuning and mechanoelectric transduction in these auditory hair cells. The addition of 0.1 % ruthenium red to the primary fixative enhanced the preservation of the connecting structures, implying the presence of glycosaminoglycans.

Quantitative light and scanning electron microscopic study of the developing auditory organs in the bullfrog: implications on their functional characteristics.

During postmetamorphic development in the bullfrog, there is a downward shift in the distributions of best excitatory frequencies (BEFs) of the three populations of primary auditory fibers. This decrease in BEF distribution suggests that concurrent morphological changes occur in the peripheral auditory system during postmetamorphic growth. The postmetamorphic development of the auditory organs in the bullfrog was quantitatively investigated with light and scanning electron microscopy. In the basilar papilla, there are dramatic increases in the lumen volume, contact membrane area, and mass of the tectorial membrane (TM). The area of the sensory epithelium and the total number of hair cells also increase slightly. In the amphibian papilla, the mass of the TM is spatially graded in a step-wise fashion along the length of the organ in both juvenile and adult bullfrogs, but there is an increase in the absolute mass of the TM throughout the papilla with age. The height of the tallest stereocilia of the predominant hair cell type systematically decreases caudally in the juvenile amphibian papilla, but is uniform throughout the adult papilla. The increase in stereociliary height in the caudal end of the organ presumably results in a decrease in stereociliary stiffness with postmetamorphic age. The length of the amphibian papilla sensory epithelium and the number of hair cells also increase during postmetamorphic development. Theoretically, the observed morphological changes alter the micromechanical tuning properties of the auditory organs so that there is a decrease in the BEFs of the auditory fibers that innervate the two papillae.

A micromechanical contribution to cochlear tuning and tonotopic organization.

The response properties of hair cells and nerve fibers in the alligator lizard cochlea are frequency selective and tonotopically organized with longitudinal position in the organ. The lengths of the hair-cell hair bundles also vary monotonically with longitudinal position. In this study, quantitative measurements were made of the motion of individual hair bundles in an excised preparation of the cochlea stimulated at auditory frequencies. The angular displacement of hair bundles is frequency selective and tonotopically organized, demonstrating the existence of a micromechanical tuning mechanism.