An electronically tuneable inductance with extended frequency range
The extension of the usable frequency range of an electronically tuneable inductance circuit is investigated. By means of numerical and analytical studies, the transistor-internal reverse transfer capacitance can be identified as a frequency-limiting element, which must be minimised. This is achieved by circuitry-wise compensation of the capacitive effect by introducing an additional inductance. The concept is verified through measurements of the practical implementation and shows an extension of the frequency range by two octaves throughout the VHF range, which proves beneficial for applications such as broadband matched and tuneable transmission lines, amplifier circuits, oscillators, or filters.
Implementation of an Electronically Tuneable, Transistor-based, Passive, Symmetric RF Inductance
The concept of an electrically tuneable inductance based on a transistor circuit is introduced. Even though it incorporates an active circuit, passive, reciprocal behaviour is displayed at the output terminals. The resulting inductance value is tuneable through a variation of the biasing condition, constant for a wide frequency range, and it can be used in either series or parallel circuit configuration. Guidelines for the design of the circuit are presented and used to successfully simulate, build and measure the tuneable inductance. The inductance circuit is a promising approach to closing a long-existing gap, and thereby providing new possibilities of circuit design, e.g., in terms of miniaturisation through integrated circuits. It can prove beneficial for numerous applications, such as broadband matched and tuneable transmission lines, amplifier circuits, oscillators, or filters.
High-frequency hearing thresholds: effects of age, occupational ultrasound and noise exposure
AbstractPurpose
It has been suggested that high-frequency audiometry (HFA) could represent a useful preventive measure in exposed workers. The aim was to investigate the effects of age, ultrasound and noise on high-frequency hearing thresholds.MethodsWe tested 24 industrial ultrasound-exposed subjects, 113 industrial noise-exposed subjects and 148 non-exposed subjects. Each subject was tested with both conventional-frequency (0.125–8 kHz) and high-frequency (9–18 kHz) audiometry.ResultsThe hearing threshold at high frequency deteriorated as a function of age, especially in subjects more than 30 years old. The ultrasound-exposed subjects had significantly higher hearing thresholds than the non-exposed ones at the high frequencies, being greatest from 10 to 14 kHz. This hearing loss was already significantly evident in subjects with exposure <5 years and increased with years of exposure and advancing age. The noise exposure group had significantly higher hearing thresholds than the non-exposed group at the conventional frequencies 4 and 6 kHz and at the high frequency of 14 kHz. After stratification for age, there was a significant difference between the two groups at 9–10 and 14–15 kHz only for those under 30 years of age.ConclusionMultivariate analysis indicated that age was the primary predictor, and noise and ultrasound exposure the secondary predictors of hearing thresholds in the high-frequency range. The results suggest that HFA could be useful in the early diagnosis of noise-induced hearing loss in younger groups of workers (under 30 years of age).
