ABSTRACT
A dual-channel directional digital hearing aid front end using microelectromechanical-systems microphones, and an adaptive-power analog processing signal chain are presented. The analog front end consists of a double differential amplifier-based capacitance-to-voltage conversion circuit, 40-dB variable gain amplifier (VGA) and a power-scalable continuous time sigma delta analog-to-digital converter (ADC), with 68-dB signal-to-noise ratio dissipating 67 µ W from a 1.2-V supply. The MEMS microphones are fabricated using a standard surface micromachining technology. The VGA and power-scalable ADC are fabricated on a 0.25-µ m complementary metal-oxide semciconductor TSMC process.
ABSTRACT
The volatile constituents of the aerial parts of Lallemantia iberica growing wild in Iran have been examined by GC-FID and GC-MS. Altogether, 11 compounds were identified, constituting approximately 97.2% of the oil. The oil of L. iberica consisted mainly of germacrene-D (33.7%), delta-3-carene (19.0%), iso-caryophyllene (12.8%), sabinene (11.1%), alpha-terpinene acetate (6.5%) and limonene (4.4%).
Subject(s)
Lamiaceae/chemistry , Oils, Volatile/isolation & purification , Plant Extracts/isolation & purification , Gas Chromatography-Mass Spectrometry , Iran , Oils, Volatile/chemistry , Plant Extracts/chemistryABSTRACT
A microelectromechanical-systems (MEMS)-based electromagnetically actuated loudspeaker to reduce form factor, cost, and power consumption, and increase energy efficiency in hearing-aid applications is presented. The MEMS loudspeaker has multilayer copper coils, an NiFe soft magnet on a thin polyimide diaphragm, and an NdFeB permanent magnet on the perimeter. The coil impedance is measured at 1.5 Omega, and the resonant frequency of the diaphragm is located far from the audio frequency range. The device is driven by a power-scalable, 0.25-mum complementary metal-oxide semiconductor class-D SigmaDelta amplifier stage. The class-D amplifier is formed by a differential H-bridge driven by a single bit, pulse-density-modulated SigmaDelta bitstream at a 1.2-MHz clock rate. The fabricated MEMS loudspeaker generates more than 0.8-mum displacement, equivalent to 106-dB sound pressure level (SPL), with 0.13-mW power consumption. Driven by the SigmaDelta class-D amplifier, the MEMS loudspeaker achieves measured 65-dB total harmonic distortion (THD) with a measurement uncertainty of less than 10%. Energy-efficient and cost-effective advanced hearing aids would benefit from further miniaturization via MEMS technology. The results from this study appear very promising for developing a compact, mass-producible, low-power loudspeaker with sufficient sound generation for hearing-aid applications.
ABSTRACT
The volatile constituents of the aerial parts of Eremostachys macrophylla growing in the wild in Iran have been examined by GC-FID and GC-MS. Altogether, 16 compounds were identified, constituting approximately 96.4% of the oil. The oil of E. macrophylla consisted mainly of germacrene-D (47.1%), germacrene-B (17.8%), gamma-elemene (9.1%), myrcene (6.7%), beta-elemene (2.7%), and beta-phellandrene (2.6%).
