Frequency Modulation Detection Research Articles

Noise in combined optical microscopy and dynamic force spectroscopy: Toward in vivo hydration measurements

Noncontact atomic force microscopy (AFM) using frequency modulation (FM) detection allows atomic resolution to be obtained in vacuum on a variety of insulating surfaces and molecular deposits. This technique has recently been extended to liquid environments, and, in addition to atomic scale contrast, FM-AFM in liquid allows measurement of ordered liquid layers above surfaces. The role of water and ions in biological processes is of great interest and in order to localize fluorescently tagged structures, such as proteins, optical microscopy combined with AFM provides an invaluable tool. Thus, to take advantage of the wealth of optical identification techniques available in biology, the AFM must be coupled to an optical microscope. Such systems are commercially available, but mechanical noise due to vibrations is a major concern compared with the compact, specialized instruments used to measure hydration structure to date. In this article the authors demonstrate, through both modeling and measurement, that hydration structure can be measured on such a commercial “bio-AFM,” despite the additional noise sources present in these instruments and that with the addition of a bandpass filter and amplifier it can be done “out-of-the-box” using only commercial electronics and tips. Thus, hydration structure measurements are accessible to virtually any laboratory with such a system.

Global or local shape discrimination of radial frequency patterns?

Purpose. Color vision performs below luminance vision on global shape discrimination measured with radial frequency patterns (Mullen & Beaudot, Vision Research, 2002). This effect might reflect a genuine deficit of color on global shape processing, or it might originate from the fact that color vision is poorer at encoding local orientation. In a series of experiments we test and compare the role of local orientation cues in the shape discrimination of radial frequency (RF) patterns for chromatic and achromatic vision. Methods. Stimuli are contours described by the 4th derivative of a gaussian and form radial patterns (global task) or parts of the pattern (local task). We designed the following tasks in order to separate the role of local-orientation and global cues in the shape discrimination task: 1) we compare performance for the discrimination of local parts (corners or sides) of a RF pattern versus circular arcs of the same radius; 2) we compare the performance for the detection of line modulation versus radial frequency modulation for otherwise identical contours; 3) we compare the effect on shape discrimination of varying the spatial frequencies of the contour of the radial frequency pattern. Data were fitted with a model that uses changes in local curvature to discriminate shape. Results. We find very little performance difference between the local-orientation based tasks and the global shape discrimination task, regardless of whether stimuli were chromatic or achromatic. Conclusions. We conclude that performance on the shape discrimination of radial frequency patterns is limited by local orientation cues in our experiments. While RF patterns presumably exploit a global shape processing mechanism, this affords little or no performance advantages in the task.

Signal-to-noise ratios in high-signal-transfer-rate read heads composed of spin-torque oscillators

An application of spin-torque oscillators (STOs) to high-signal-transfer-rate read heads beyond 3 Gbits/s is considered and the signal-to-noise ratios (SNRs) of the output signals under the thermal magnetization fluctuations are calculated by using the results of recent nonlinear theories. The STO head senses the media field as a modulation in the oscillation frequency, enabling high signal transfer rates beyond the limit of ferromagnetic relaxation. The output (digital) signal is obtained by frequency modulation (FM) detection, which is commonly used in communication technologies. As the problem of rapid phase diffusion in nonlinear STOs caused by the thermal fluctuations is overcome by employing a delay detection method, the sufficiently large SNRs are obtained even in nonlinear STOs less than 30×30 nm2 in size.

Suprathreshold auditory processing and speech recognition in noise for hearing-impaired listeners.

Suprathreshold distortions in auditory processing contribute to speech recognition deficits for hearing-impaired (HI) listeners in noise. Outer hair cell damage and attendant reductions in frequency selectivity and peripheral compression may contribute to these deficits. Reduced sensitivity to spectral or temporal modulations or temporal fine structure (TFS) information may also play a role. Eight normal-hearing and 18 HI listeners were tested in psychoacoustic tasks to assess frequency selectivity (notched-noise), peripheral compression (temporal masking curves), TFS sensitivity [frequency modulation (FM) detection in the presence of random amplitude modulation], and spectrotemporal modulation (STM) sensitivity (spectral-temporal “ripple” detection). Performance was examined at 500, 1000, 2000, and 4000 Hz at several presentation levels. Listeners were also tested on sentence recognition in stationary and modulated noise (92-dB sound pressure level signal level; −6-, −3-, 0-, and +3-dB SNRs). HI listeners with similar audiometric thresholds showed a wide range of speech scores. Estimates of FM and STM sensitivity at 500 and 1000 Hz were significantly correlated with speech scores and with each other. Frequency selectivity and compression measures were not clearly associated with speech performance. Implications for models of HI speech intelligibility are discussed. [Work supported by the Oticon Foundation.]

Experimental Investigation of the Electrical Parameter Changes of Tuning Fork Crystal Oscillators Exposed to Air

We performed frequency response measurements of commercially available tuning fork crystal oscillators and analyzed their measured electrical equivalent circuit parameters of R, L, CS, and CP in vacuum and in air. We observed that R and L components increased as the tuning forks were exposed to air while the capacitance components CS and CP decreased. Of the changes of the electrical parameters for all the tested tuning forks, the resistance R showed the most significant change. These results seem to indicate that an amplitude modulation detection scheme is advantageous over a frequency modulation detection scheme in sensor applications in gaseous environment.

Anelastic Phenomena and Cr<sub>2</sub>N Precipitation in a High Nitrogen Austenitic Steel

Internal friction (IF) and dynamic modulus measurements on a high nitrogen (0.8 wt%) austenitic steel in the temperature range from room temperature to 800 °C have been carried out by using a vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations in the frequency range of kHz. The IF spectrum of the as-prepared material shows a broad peak superimposed to an exponentially increasing background. The discontinuous precipitation of Cr2N phase changes the characteristics of the peak. The results have been discussed by considering interstitial-substitutional (i-s) interactions.

Higher harmonic detection employing wavelength modulation spectroscopy and near infrared diode lasers: An undergraduate experiment

Frequency modulation and harmonic detection are extensively employed in a variety of experimental techniques and offer a detection sensitivity limited only by quantum noise. We discuss a simple experiment using wavelength modulation spectroscopy and near infrared diode lasers operating in the 780 nm region to detect rubidium hyperfine spectra. Modulation spectroscopy techniques are employed to improve the signal to noise ratio for the detection of weak signals and thus significantly improve the sensitivity and specificity for detection. By using quantum cascade lasers and wavelength modulation spectroscopy, one can detect trace species at sub-ppm level, which has numerous applications in diverse areas such as medical diagnostics, food processing, industrial applications, and environmental monitoring.

Relations between frequency selectivity, temporal fine-structure processing, and speech reception in impaired hearing

Frequency selectivity, temporal fine-structure (TFS) processing, and speech reception were assessed for six normal-hearing (NH) listeners, ten sensorineurally hearing-impaired (HI) listeners with similar high-frequency losses, and two listeners with an obscure dysfunction (OD). TFS processing was investigated at low frequencies in regions of normal hearing, through measurements of binaural masked detection, tone lateralization, and monaural frequency modulation (FM) detection. Lateralization and FM detection thresholds were measured in quiet and in background noise. Speech reception thresholds were obtained for full-spectrum and lowpass-filtered sentences with different interferers. Both the HI listeners and the OD listeners showed poorer performance than the NH listeners in terms of frequency selectivity, TFS processing, and speech reception. While a correlation was observed between the monaural and binaural TFS-processing deficits in the HI listeners, no relation was found between TFS processing and frequency selectivity. The effect of noise on TFS processing was not larger for the HI listeners than for the NH listeners. Finally, TFS-processing performance was correlated with speech reception in a two-talker background and lateralized noise, but not in amplitude-modulated noise. The results provide constraints for future models of impaired auditory signal processing.

Frequency modulation detection, frequency selectivity, and speech recognition in noise by hearing‐impaired listeners.

Reduced ability to make use of temporal fine structure (TFS) information may contribute to deficits among hearing impaired (HI) listeners for speech recognition in competing background sounds. The broad tuning typically observed in HI listeners will produce more complex patterns of TFS as input to the auditory nerve, and these patterns may be more difficult to encode and/or interpret by higher auditory centers. In the current study, we tested HI listeners on a frequency‐modulation (FM) detection task thought to require the use of TFS cues, on tone detection in notched‐noise to assess frequency selectivity, and on speech recognition in continuous and modulated background sounds. Performance on the psychoacoustic tasks was tested at four frequencies (500, 1000, 2000, and 4000 Hz) at levels between 60 and 85 dB SPL (approximating the range of third‐octave band levels in the speech stimuli). HI listeners with similar audiometric thresholds showed clear differences in frequency tuning, FM detection thresholds, and speech performance. Relationships between the psychoacoustic measures in the four frequency regions and between these measures and speech performance will be discussed.

Frequency noise in frequency modulation atomic force microscopy

Atomic force microscopy (AFM) using the frequency modulation (FM) detection method has been widely used for atomic/molecular-scale investigations of various materials. Recently, it has been shown that high-resolution imaging in liquids by the FM-AFM is also possible by reducing the noise-equivalent displacement in the cantilever displacement sensor and by oscillating the cantilever at a small amplitude even with the extremely reduced Q-factor due to the hydrodynamic interaction between the cantilever and the liquid. However, it has not been clarified how the noise reduction of the displacement sensor contributes to the reduction in the frequency noise in the FM-AFM in low-Q environments. In this article, the contribution of the displacement sensor noise to the frequency noise in the FM-AFM is described in detail to show how it is important to reduce the noise-equivalent displacement in the displacement sensor especially in low-Q environments.

High temperature damping behaviour of Ti6Al4V–SiC f composite

The Ti6Al4V–SiC f composite, reinforced by unidirectional SiC fibres (SCS-6), has been investigated by internal friction (IF) and dynamic modulus measurements in the temperature range 300–1173 K. Experiments have been carried out by using a vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations in the frequency range from 600 to 1800 Hz. For comparison the monolithic Ti6Al4V alloy has been submitted to the same experiments. The IF spectrum of the composite exhibits a relaxation peak at about 870 K superimposed to an exponentially increasing background. The peak, not present in the spectrum of matrix alloy, has activation energy H = 186 kJ mol −1 and relaxation time τ 0 = 2.3 × 10 −15 s. The peak has been explained by an interstitial-substitutional pair reorientation mechanism in the α phase of Ti6Al4V matrix around the fibres.

Single crystal PWA 1483 superalloy: Dislocation rearrangement and damping phenomena

The structural stability of the single-crystal PWA 1483 superalloy has been investigated by internal friction (IF) and dynamic modulus measurements from room temperature to 1073 K. The examined samples were in the solubilized state. The vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations has been employed. Frequency was ∼350 Hz. IF spectra recorded in successive test runs on the same samples show a Q −1 maximum (M1) above 623 K, whose intensity and position change from one run to another; in correspondence with M1 the modulus undergoes a slow decrease followed by a sudden increase. Sometimes another maximum (M2) has been observed at lower temperature (∼523 K). After each run the values of the modulus and of Q −1 change indicating that a progressive irreversible transformation occurs. Damping phenomena have been attributed to the rearrangement of dislocation structures in the disordered matrix. This rearrangement modifies the density and the average distance of pinning points. This explanation is supported by transmission electron microscopy (TEM) observations.

Maturation of Visual and Auditory Temporal Processing in School-Aged Children

To examine development of sensitivity to auditory and visual temporal processes in children and the association with standardized measures of auditory processing and communication. Methods Normative data on tests of visual and auditory processing were collected on 18 adults and 98 children aged 6-10 years of age. Auditory processes included detection of pitch from temporal cues using iterated rippled noise and frequency modulation detection at 2 Hz, 40 Hz, and 240 Hz. Visual processes were coherent form and coherent motion detection. Test-retest data were gathered on 21 children. Performance on perceptual tasks improved with age, except for fine temporal processing (iterated rippled noise) and coherent form perception, both of which were relatively stable over the age range. Within-subject variability (as assessed by track width) did not account for age-related change. There was no evidence for a common temporal processing factor, and there were no significant associations between perceptual task performance and communication level (Children's Communication Checklist, 2nd ed.; D. V. M. Bishop, 2003) or speech-based auditory processing (SCAN-C; R. W. Keith, 2000). The auditory tasks had different developmental trajectories despite a common procedure, indicating that age-related change was not solely due to responsiveness to task demands. The 2-Hz frequency modulation detection task, previously used in dyslexia research, and the visual tasks had low reliability compared to other measures.

Computational Auditory Scene Analysis: Principles, Algorithms and Applications

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Applications of Atomic Force Microscopy to Surface Investigations in Liquids

Atomic force microscopy (AFM) using frequency modulation (FM) detection has been widely used for the atomic scale investigations of various materials. However, high-resolution imaging in liquids by FM-AFM is severely hindered by the extreme reduction of the Q-factor due to the hydrodynamic interaction between the cantilever and the liquid. Recently the use of the small amplitude mode and the large noise reduction in the cantilever deflection sensor brought a great progress in FM-AFM imaging in liquids. In this article the details of the problems in FM-AFM imaging in liquids as well as the general directions of the improvements are described. The present status of the high-resolution FM-AFM imaging is also presented. Furthermore, future prospects and possible applications of FM-AFM in liquids are discussed.

Development of Noncontact Atomic Force Microscopy Operating at Low Temperatures

Noncontact atomic force microscopy (NC-AFM) using frequency modulation detection method has been widely used to investigate the various surfaces with atomic resolution. In this paper, we introduce the measurement technique of NC-AFM operating at low temperatures (LTs). First, we theoretically discuss the enhancement of the force sensitivity in NC-AFM operating at LTs. Then, we present the design and performance of LT-NC-AFM using fiber optic interferometer with quick sample and cantilever exchange mechanism. We also show the present status of the LT-NC-AFM imaging. In detail, we show the experimental results to investigate the influence of the surface stress around an SA step of Si(001) surface onto the buckled dimer at 5 K. We demonstrate that the LT-NC-AFM has a capability to detect the surface stress with atomic resolution.

Dynamic force spectroscopy using cantilever higher flexural modes

By means of force spectroscopy measurements performed with the cantilever first and second flexural modes under the frequency modulation detection method, the authors corroborate the validity of the relation between tip-surface interaction force and frequency shift for force spectroscopy acquisition using higher cantilever eigenmodes. They estimate a cantilever effective stiffness for the second eigenmode 73 times larger than the static stiffness. This large effective stiffness enables them to perform force spectroscopy with a cantilever oscillation amplitude (A0) as small as 3.6Å. The authors provide experimental evidence that, at such small A0 values, normalized frequency shift curves deviate from a A03∕2 scaling and the signal-to-noise ratio is considerably enhanced.

Frequency modulation detection with simultaneous amplitude modulation by cochlear implant users

To better represent fine structure cues in cochlear implants (CIs), recent research has proposed varying the stimulation rate based on slowly varying frequency modulation (FM) information. The present study investigated the abilities of CI users to detect FM with simultaneous amplitude modulation (AM). FM detection thresholds (FMDTs) for 10-Hz sinusoidal FM and upward frequency sweeps were measured as a function of standard frequency (75-1000 Hz). Three AM conditions were tested, including (1) No AM, (2) 20-Hz Sinusoidal AM (SAM) with modulation depths of 10%, 20%, or 30%, and (3) Noise AM (NAM), in which the amplitude was randomly and uniformly varied over a range of 1, 2, or 3 dB, relative to the reference amplitude. Results showed that FMDTs worsened with increasing standard frequencies, and were lower for sinusoidal FM than for upward frequency sweeps. Simultaneous AM significantly interfered with FM detection; FMDTs were significantly poorer with simultaneous NAM than with SAM. Besides, sinusoidal FMDTs significantly worsened when the starting phase of simultaneous SAM was randomized. These results suggest that FM and AM in CI partly share a common loudness-based coding mechanism and the feasibility of "FM+AM" strategies for CI speech processing may be limited.

Multi-Probe Atomic Force Microscopy with Optical Beam Deflection Method

We developed a multi-probe atomic force microscope (AFM) having two AFM cantilevers independently controlled using the optical beam deflection method. We succeeded in simultaneously obtaining images with two independent probes by frequency modulation (FM) detection method. To evaluate the distance between the AFM tips of the cantilevers, we used a new the address-patterned sample, which was also developed for this study. The images obtained show that the distance between the probes was 2 µm. The development of the multi-probe AFM opens a wide variety of applications in the present nanoscience and engineering field.

Frequency modulation detection: Effects of age, psychophysical method, and modulation waveform

As part of an ongoing study of auditory aging, detection of sinusoidal and quasitrapezoidal frequency modulation (FM) was measured with a 5-Hz modulation frequency and 500- and 4000-Hz carriers in two experiments. In Experiment 1, psychometric functions for FM detection were measured with several modulation waveform time patterns in younger adults with normal hearing. Detection of a three-cycle modulated signal improved when its duration was extended by a preceding unmodulated cycle, an effect similar to adding a modulated cycle. In Experiment 2, FM detection was measured for younger and older adults with normal hearing using two psychophysical methods. Similar to frequency discrimination, FM detection was poorer in older than younger subjects and age-related differences were larger at 500 Hz than at 4000 Hz, suggesting that FM detection with low modulation frequencies and frequency discrimination may share common underlying mechanisms. One mechanism is likely related to temporal information coded by neural phase locking which is strong at low frequencies and decreases with increasing frequency, as observed in animals. The frequency-dependent aging effect suggests that this temporal mechanism may be affected by age. The effect of psychophysical method was sizable and frequency dependent, whereas the effect of modulation waveform was minimal.