Amplitude Measurements Research Articles

Self-sensing model of low-frequency magnetostrictive composites actuator based on Jiles-Atherton theory

Giant magnetostrictive powder composites (GMPCs) have important applications in electric current sensing, stress sensing, vibration damping, actuation, health monitoring and other fields. Most of the research discussed the actuation or sensing function of GMPCs merely. In this paper, GMPCs based actuator with a self-sensing function is proposed to realize direct measurement of the deformation amplitudes of the actuator in low frequency, through monitoring the voltage signal of the driving circuit. It also means the actuator can be used as a compressive stress and magnetostriction sensor. The self-sensing actuator avoids the dependence on extra sensors for actuation detection, which complements the self-sensing technique in GMPC-based actuators. It is helpful not only in the designing and controlling of self-sensing applications in actuators, but also in expanding the applications of GMPCs in the field of integrated devices.

Development of Amplitude Measurement System for Ultrasonic Vibration Assisted Micro Forming

Microforming is a process that involves forming a material through plastic deformation at a micro level. However, this method encounters an issue at the micro-scale known as the size effect. There are several new approaches to overcome these difficulties, one of which is using Ultrasonic Vibration Assisted (UVA) micro forming. UVA micro forming is a forming method by applying high-frequency vibrations to the workpiece to reduce forming forces, increase smooth zone, reduce surface roughness, and increase accuracy. A bolted Langevin transducer is needed to produce vibration, which converts electrical signals into acoustic signals in the ultrasonic frequency range. Therefore, the vibration characteristics must be considered in detail to find the best parameters in the micro forming process. This study aims to develop an amplitude measurement system for UVA micro forming. Several things that need to be considered in designing a measurement system are pre-stress characteristics, resonant frequency of the machine, and the amplitude of the vibration generated by the system. Firstly, a pre-stress test was carried out by tightening the pre-stress bolt slowly until the resonant frequency did not change. Then, the resonant frequency is measured using signal generator, oscilloscope, transducer, and resistor to determine the system’s resonant frequency. Finally, the vibration amplitude is measured by observing the displacement at the end of the punch using a digimatic indicator. The result shows that the resonance frequency that produces longitudinal vibration for UVA micro forming system is 28,720 Hz, with a pre-stress of 30 MPa with torque of 14.36 Nm, and total displacement on the normal axis is 9 μm.

Enhanced-Reach Polarization Optical Time-Domain Reflectometry Technique for Fibre Optical Infrastructure Monitoring

Abstract This interdisciplinary research is focused on constructing and demonstrating enhanced-reach polarization optical time-domain reflectometer (POTDR) for monitoring single-mode fibre optical communication lines. An optical signal state of polarization measurements enables several new possibilities for real-time monitoring solutions in fibre optics. However, there is no commercial equipment available to determine the location in fibre optical cable where the light polarization state changes. The authors present a monitoring technique of an optical signal state of polarization based on reflected signal time-amplitude analysis with improved operation parameters, namely, timing resolution (2 to 3 ps RMS) and amplitude measurement resolution of nanosecond scale pulses (8 to 10 bits) for monitoring of fibre optical communication lines. Additionally, the demonstrated POTDR provides a considerable optical fibre line measurement reach of up to 40 km.

Using Moment Tensor Inversions for Rapid Seismic Source Detection and Characterization: Application to the North Korean Nuclear Tests

AbstractThe rapid detection and source characterization of any type of seismic events including earthquakes and nuclear explosions is one of the missions of many seismological laboratories. Most often, the techniques used are based on phase picking and amplitude measurements for detecting and locating events, and for estimating magnitudes. From these parameters, especially for anthropogenic sources, event screening is then done empirically, and this may lead to misinterpretations of the source nature. However, it is known that seismic waveform inversion for the determination of the moment tensor has proven to be a reliable source physics-based method for event characterization. Here, we present a technique already used for earthquake monitoring in tectonically active regions, and we test it on very shallow natural and anthropogenic events recorded in the vicinity of the Democratic People’s Republic of Korea (DPRK). From a grid of potential locations and by scanning continuous seismic waveforms, it is possible to implement a rapid detector of seismic events providing the full information of the sources (origin time, location, magnitude, mechanism, and source decomposition). We show its overall performances on all past DPRK nuclear tests and regional earthquakes. From such an approach fast complete event screening is achieved. Source uncertainties can also be estimated. This stand-alone detector and identifier of seismic events may help monitoring seismological agencies to provide a rapid and complete alert for any events within a region of interest before more in-depth discrimination analysis can be run.

Rayleigh wave attenuation tomography based on ambient noise interferometry: methods and an application to Northeast China

SUMMARY Although ambient noise interferometry has been extensively utilized for seismic velocity tomography, its application in retrieving attenuation remains limited. This study presents a comprehensive workflow for extracting Rayleigh wave amplitude and attenuation from ambient noise, which consists of three phases: (1) retrieval of empirical Green's functions (EGFs), (2) selection and correction of amplitude measurements and (3) inversion of attenuation, site amplification and noise intensity terms. Throughout these processes, an ‘asynchronous’ temporal flattening method is used to generate high-quality EGFs while preserving relative amplitudes between stations. Additionally, a novel ‘t-symmetry’ criterion is proposed for data selection along with the signal-to-noise ratio. Furthermore, 2-D sensitivity kernels are utilized to estimate the focusing/defocusing effect, which is then corrected in amplitude measurements. These procedures are designed to deliver reliable attenuation measurements while maintaining flexibility and automation. To validate the effectiveness of the proposed noise-based attenuation tomography approach, we apply it to a linear array, NCISP-6, located in NE China. The obtained results correlate reasonably well with known geological structures. Specifically, at short periods, high attenuation anomalies delineate the location of major sedimentary basins and faults; while at longer periods, a notable rapid increase of attenuation is observed beneath the Moho discontinuity. Given that attenuation measurements are more sensitive to porosity, defect concentration, temperature, melt and volatile ratio than seismic velocities, noise-based attenuation tomography provides important additional constraints for exploring the crustal and upper mantle structures.

Differences in resting-state brain activity in first-episode drug-naïve major depressive disorder patients with and without suicidal ideation.

Despite altered brain activities being associated with suicidal ideation (SI), the neural correlates of SI in major depressive disorder (MDD) have remained elusive. We enrolled 82 first-episode drug-naïve MDD patients including 41 with SI and 41 without SI, as well as 41 healthy controls (HCs). Resting-state functional and structural MRI data were collected. The measures of fractional amplitude of low-frequency fluctuation (fALFF) and grey matter volume (GMV) were calculated and compared. Compared with HCs, patients with SI exhibited increased fALFF values in the right rectus gyrus and left medial superior frontal gyrus, middle frontal gyrus and precuneus. Decreased GMV in the right parahippocampal gyrus, insula and middle occipital gyrus and increased GMV in the left superior frontal gyrus were detected in patients with SI. In addition, patients without SI demonstrated increased fALFF values in the right superior frontal gyrus and decreased fALFF values in the right postcentral gyrus. Decreased GMV in the left superior frontal gyrus, right medial superior frontal gyrus, opercular part of inferior frontal gyrus, postcentral gyrus, fusiform gyrus and increased left supplementary motor area, superior occipital gyrus, right anterior cingulate gyrus and superior temporal gyrus were revealed in patients with SI. Moreover, in comparison with patients without SI, increased fALFF values were identified in the left precuneus of patients with SI. However, no significant differences were found in GMV between patients with and without SI. These findings might be helpful for finding neuroimaging markers predicting individual suicide risk and detecting targeted brain regions for effective early interventions.

Single-protein optical holography

Light scattering by nanoscale objects is a fundamental physical property defined by their scattering cross-section and thus polarizability. Over the past decade, a number of studies have demonstrated single-molecule sensitivity by imaging the interference between scattering from the object of interest and a reference field. This approach has enabled mass measurement of single biomolecules in solution owing to the linear scaling of image contrast with molecular polarizability. Nevertheless, all implementations so far are based on a common-path interferometer and cannot separate and independently tune the reference and scattered light fields, thereby prohibiting access to the rich toolbox available to holographic imaging. Here we demonstrate comparable sensitivity using a non-common-path geometry based on a dark-field scattering microscope, similar to a Mach–Zehnder interferometer. We separate the scattering and reference light into four parallel, inherently phase-stable detection channels, delivering a five orders of magnitude boost in sensitivity in terms of scattering cross-section over state-of-the-art holographic methods. We demonstrate the detection, resolution and mass measurement of single proteins with mass below 100 kDa. Separate amplitude and phase measurements also yield direct information on sample identity and experimental determination of the polarizability of single biomolecules.

A prototype scintillator real-time beam monitor for ultra-high dose rate radiotherapy.

FLASH Radiotherapy (RT) is an emergent cancer RT modality where an entire therapeutic dose is delivered at more than 1000 times higher dose rate than conventional RT. For clinical trials to be conducted safely, a precise and fast beam monitor that can generate out-of-tolerance beam interrupts is required. This paper describes the overall concept and provides results from a prototype ultra-fast, scintillator-based beam monitor for both proton and electron beam FLASH applications. A FLASH Beam Scintillator Monitor (FBSM) is being developed that employs a novel proprietary scintillator material. The FBSM has capabilities that conventional RT detector technologies are unable to simultaneously provide: (1) large area coverage; (2) a low mass profile; (3) a linear response over a broad dynamic range; (4) radiation hardness; (5) real-time analysis to provide an IEC-compliant fast beam-interrupt signal based on true two-dimensional beam imaging, radiation dosimetry and excellent spatial resolution. The FBSM uses a proprietary low mass, less than 0.5mm water equivalent, non-hygroscopic, radiation tolerant scintillator material (designated HM: hybrid material) that is viewed by high frame rate CMOS cameras. Folded optics using mirrors enable a thin monitor profile of ∼10cm. A field programmable gate array (FPGA) data acquisition system generates real-time analysis on a time scale appropriate to the FLASH RT beam modality: 100-1000Hz for pulsed electrons and 10-20kHz for quasi-continuous scanning proton pencil beams. An ion beam monitor served as the initial development platform for this work and was tested in low energy heavy-ion beams (86Kr+26 and protons). A prototype FBSM was fabricated and then tested in various radiation beams that included FLASH level dose per pulse electron beams, and a hospital RT clinic with electron beams. Results presented in this report include image quality, response linearity, radiation hardness, spatial resolution, and real-time data processing. The HM scintillator was found to be highly radiation damage resistant. It exhibited a small 0.025%/kGy signal decrease from a 216 kGy cumulative dose resulting from continuous exposure for 15 min at a FLASH compatible dose rate of 237Gy/s. Measurements of the signal amplitude versus beam fluence demonstrate linear response of the FBSM at FLASH compatible dose rates of >40Gy/s. Comparison with commercial Gafchromic film indicates that the FBSM produces a high resolution 2D beam image and can reproduce a nearly identical beam profile, including primary beam tails. The spatial resolution was measured at 35-40µm. Tests of the firmware beta version show successful operation at 20000Hz frame rate or 50 µs/frame, where the real-time analysis of the beam parameters is achieved in less than 1 µs. The FBSM is designed to provide real-time beam profile monitoring over a large active area without significantly degrading the beam quality. A prototype device has been staged in particle beams at currents of single particles up to FLASH level dose rates, using both continuous ion beams and pulsed electron beams. Using a novel scintillator, beam profiling has been demonstrated for currents extending from single particles to 10 nA currents. Radiation damage is minimal and even under FLASH conditions would require ≥50 kGy of accumulated exposure in a single spot to result in a 1% decrease in signal output. Beam imaging is comparable to radiochromic films, and provides immediate images without hours of processing. Real-time data processing, taking less than 50 µs (combined data transfer and analysis times), has been implemented in firmware for 20kHz frame rates for continuous proton beams.

Quartz as an accurate high-field low-cost THz helicity detector

Emerging concepts employing angular momentum of THz light for ultrafast material control rely on the measurement of undistorted intense THz fields and on the precise knowledge about sophisticated THz helicity states. Here, we establish z-cut α-quartz as a precise electro-optic THz detector for full amplitude, phase, and polarization measurement of highly intense THz fields, all at a fraction of costs of conventional THz detectors. We experimentally determine its detector response function, in excellent agreement with our modeling. Thereupon, we develop a swift and reliable protocol to precisely measure arbitrary THz polarization and helicity states. This two-dimensional electro-optic sampling in α-quartz fosters rapid and cost-efficient THz time-domain ellipsometry and enables the characterization of polarization-tailored fields for driving chiral or other helicity-sensitive quasi-particles and topologies.

The Voice of the People: Populism and Donald Trump’s Use of Informal Voice

Many studies have examined characteristic verbal aspects of Donald J. Trump’s political communication, from his authoritarian rhetoric to his preference for short words and simple sentences, as expressions of his populism. This article focuses on his use of non-verbal voice quality. In analyzing the “Trump rallies” and other materials from his successful campaigning before the 2016 United States presidential election, I argue that Trump’s evocative and meaningful uses of pitch, amplitude, speech rate, rhythm, and other vocal measures combine to make his paralanguage exceptionally and counter-normatively informal, and that this informality amplifies his explicitly populist messaging. I conclude by suggesting that Trump’s informal voice solves an important problem for him: It allows him to express his populism with a deeply personal undertone, and thereby potentially to make his claims to popular identification ring intuitively true.

Ultrasonic evaluation of additively manufactured components with embedded structures

In recent years, the use of ultrasonic nondestructive evaluation (NDE) for in situ and ex situ assessment of Additive Manufacturing (AM) parts has garnered interest due to its proficiency in defect detection and material characterization. This study focuses on evaluating the ability to resolve internal structures created by AM and hybrid AM using ultrasonic NDE as well as assessing the impact of microstructure heterogeneity. For this purpose, first the parameter space for laser powder bed fusion (LPBF) of SS316L is mapped in a Lumex Avance 25 system. Based on this parameter mapping, optimal process parameters are identified and sets of process parameters are selected to vary the thermal history of the samples, while minimizing the influence of porosity. Two groups of samples are printed with these parameter sets: a solid group of samples, and a group with internal structures, such that each internal structure sample has an equivalent solid sample. Measurements of ultrasonic velocity, attenuation, and backscatter amplitude are collected and compared against the intended geometry to assess the impact of non-optimal processing on the ability to resolve internal structures with ultrasound. The viability and limitations of using ultrasound to assess internal features created with AM are discussed.

Quantum Spectral Analysis by Continuous Measurement of Landau-Zener Transitions.

We demonstrate the simultaneous estimation of signal frequency and amplitude by a single quantum sensor in a single experimental shot. Sweeping the qubit splitting linearly across a span of frequencies induces a nonadiabatic Landau-Zener transition as the qubit crosses resonance. The signal frequency determines the time of the transition, and the amplitude its extent. Continuous weak measurement of this unitary evolution informs a parameter estimator retrieving precision measurements of frequency and amplitude. Implemented on radio-frequency-dressed ultracold atoms read out by a Faraday spin-light interface, we sense a magnetic signal with estimated sensitivities to amplitude of 11 pT/sqrt[Hz], frequency 0.026 Hz/Hz^{3/2}, and phase 0.084 rad/sqrt[Hz], in a single 300ms sweep from 7 to 13kHz. The protocol realizes a swept-sine quantum spectrum analyzer, potentially sensing hundreds or thousands of channels with a single quantum sensor.

The Danish Nationwide Electrocardiogram (ECG) Cohort

The electrocardiogram (ECG) is a non-invasive diagnostic tool holding significant clinical importance in the diagnosis and risk stratification of cardiac disease. However, access to large-scale, population-based digital ECG data for research purposes remains limited and challenging. Consequently, we established the Danish Nationwide ECG Cohort to provide data from standard 12-lead digital ECGs in both pre- and in-hospital settings, which can be linked to comprehensive Danish nationwide administrative registers on health and social data with long-term follow-up. The Danish Nationwide ECG Cohort is an open real-world cohort including all patients with at least one digital pre- or in-hospital ECG in Denmark from January 01, 2000, to December 31, 2021. The cohort includes data on standardized and uniform ECG diagnostic statements and ECG measurements including global parameters as well as lead-specific measures of waveform amplitudes, durations, and intervals. Currently, the cohort comprises 2,485,987 unique patients with a median age at the first ECG of 57 years (25th–75th percentiles, 40–71 years; males, 48%), resulting in a total of 11,952,430 ECGs. In conclusion, the Danish Nationwide ECG Cohort represents a novel and extensive population-based digital ECG dataset for cardiovascular research, encompassing both pre- and in-hospital settings. The cohort contains ECG diagnostic statements and ECG measurements that can be linked to various nationwide health and social registers without loss to follow-up.

Frequency response of the non-polarization-maintaining depolarized sagnac interferometer based on maximum fringe contrast

The Sagnac Interferometer offers a promising solution to the speckle problem in interferometric detection due to its insensitivity to environmental low-frequency interference, making it well-suited for applications such as laser ultrasonic detection. Control of the polarization state of light is imperative for achieving high sensitivity in optical fiber interferometer and ensuring optimal quiescent operating conditions. This study employed the coherence matrix method to analyze the theory of optimal polarization control in a non-polarization-maintaining depolarized Sagnac Interferometer, encompassing the deduction of the stable π/2 initial phase bias and the maximum fringe contrast of 50% in theory. In experimental observations during PZT simulated large amplitude ultrasound experiments, the fringe contrast reached 48.4%. Furthermore, the system's amplitude-frequency response was evaluated using an electro-optics phase modulator, demonstrating its capability to detect high-frequency signals within 100 MHz These findings provide essential insights into optimizing the Sagnac Interferometer's performance for laser ultrasonic detection and its potential applications in high-frequency signal detection and ultrasonic amplitude measurement.

Saturation of Fishbone Instability by Self-Generated Zonal Flows in Tokamak Plasmas.

Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas find that self-generated zonal flows can dominate the nonlinear saturation by preventing coherent structures from persisting or drifting in the energetic particle phase space when the mode frequency down-chirps. Results from the simulation with zonal flows agree quantitatively, for the first time, with experimental measurements of the fishbone saturation amplitude and energetic particle transport. Moreover, the fishbone-induced zonal flows are likely responsible for the formation of an internal transport barrier that was observed after fishbone bursts in this DIII-D experiment. Finally, gyrokinetic simulations of a related ITER baseline scenario show that the fishbone induces insignificant energetic particle redistribution and may enable high performance scenarios in ITER burning plasma experiments.

(125) Measurement of Clitoral Pulse Amplitude with a Wearable Device

Abstract Introduction Penile erection is well understood and has been extensively studied. The Erectile Hardness Score is a commonly used tool to quantify the strength of an erection. Few such measurement tools exists for women. This study builds on the work done by Mechelmans et al exploring Clitoral Pulse Amplitude (CPA) as a marker for physical arousal in women. CPA has been shown to be related to clitoral blood volume, erection, and engorgement of the clitoris. The erection in the clitoris is homologous to penile erection. Objective To test a new, wearable, clitoral pulse sensor designed for at-home use for correlation with subjective arousal for proof of concept. To test the comfort and usability of such a device configured with an internal (vaginal) portion and a clitoral portion. Methods 20 healthy female participants were shipped the device and completed the study from their home with an online module which guided them through the study material. Participants wore the device while watching a control (non-arousing) video and during progressively more sexually arousing activities. They were allowed to choose their own materials to watch, read, or listen to for arousal. A masturbation phase was included for additional information. Participants also reported their subjective arousal after each phase. After the test, participants were also surveyed about the comfort and usability of the device. Results The pulse sensor successfully detected CPA. Results show that most participants had increasing levels of subjective arousal correlating with increasing CPA. Statistical correlation between CPA and arousal was positive but low, which could be attributed to differences of sensor calibration and/or device placement by participants. Overall, this positive relationship indicates that a commercially available pulse sensor could be integrated into a future device to measure physical arousal in women, a metric which was previously not widely available. Participants reported high satisfaction with the comfort and usability of the device. These insights validate that this device shape will be comfortable and usable in further iterations, with the ultimate goal of producing a device which would give clitoris-owners greater insight into their sexual health and provide valuable information to their healthcare providers. Conclusions This study showed a positive relationship between Clitoral Pulse Amplitude and subjective sexual arousal using an at-home wearable device, opening possibilities for future measurement devices. Participants felt the device was very comfortable and easy to use, suggesting this form factor with vaginal (internal) and clitoral (external) portions is a viable configuration for further development. We anticipate improving both the pulse sensing system and device usability as the device is further commercialized. Disclosure Yes, this is sponsored by industry/sponsor: FirmTech. Clarification: Industry initiated, executed and funded study. Any of the authors act as a consultant, employee or shareholder of an industry for: FirmTech.

Feedback control of collective dynamics in an oscillator population with time-dependent connectivity.

We present a numerical study of pulsatile feedback-based control of synchrony level in a highly-interconnected oscillatory network. We focus on a nontrivial case when the system is close to the synchronization transition point and exhibits collective rhythm with strong amplitude modulation. We pay special attention to technical but essential steps like causal real-time extraction of the signal of interest from a noisy measurement and estimation of instantaneous phase and amplitude. The feedback loop's parameters are tuned automatically to suppress synchrony. Though the study is motivated by neuroscience, the results are relevant to controlling oscillatory activity in ensembles of various natures and, thus, to the rapidly developing field of network physiology.

Long-interval afferent inhibition measurement using two different methods: Normative values, repeatability and reliability

BackgroundThe mechanism of Short-Latency Afferent Inhibition (SAI) is relatively well understood. In contrast, Long-Latency Afferent Inhibition (LAI) has not been as extensively studied as SAI, and its underlying mechanism remains unclear. Objective/HypothesisThis study had two primary objectives: first, to determine the optimal ISIs for LAI measured by amplitude changes (A-LAI) using high-resolution ISI ranges; and second, to compare measurements of LAI by threshold-tracking (T-LAI). MethodsTwenty-eight healthy volunteers (12 males aged 24- 45 years) participated in the study. Paired peripheral electrical and transcranial magnetic stimulation (TMS) stimuli (TS1mv) were applied at varying (ISIs)- 100, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 800, 900, 1000 ms. ResultsBoth A-LAI and T-LAI showed that LAI decreased progressively from a peak at 200 or 250 ms to 1000 ms. Using the A-LAI method, pronounced inhibition was observed at three specific ISIs: 100 ms, 250 ms and 450 ms. When A-LAI values were converted to equivalent threshold changes, they did not differ significantly from T-LAI. Reliability at distinguishing individuals, as indicated by intraclass correlation coefficient (ICC) was greater for A-LAI, with a peak value of 0.82 at 250 ms. Conclusion(s)The study demonstrates that ISIs of 100 ms and 250 ms can be reliably used in amplitude measurement LAI. The study demonstrates that both LAI measurements record a similar decline of inhibition with increasing ISI.

Processing of VLF Amplitude Measurements: Deduction of a Quiet Time Seasonal Variation

AbstractThe amplitude of Very Low Frequency (VLF) transmissions propagating from transmitter to receiver between the Earth's surface and the ionospheric D‐region is a useful measurement to detect changes in the ionization within the D‐region ranging from 60 to 90 km. The VLF signal amplitude is disturbed by geomagnetic, solar, and atmospheric phenomena. To be able to identify perturbations in the VLF signal amplitude, we determine its averaged seasonal variation under quiet solar and geomagnetic conditions. Here it is challenging, that long time series of the VLF signal amplitude show significant jumps and outliers, which are caused artificially by technical adjustments/maintenance work. This paper presents a new approach for processing long VLF data time series over multiple years resulting in level 2 data. The new level 2 data enables the consideration of time series with artificial jumps since the jumps are leveled. Moreover, the outliers are removed by a robust and systematic 2‐step outlier filtering. The average seasonal and diurnal variation for different transmitter‐receiver combinations can be computed with the new level 2 data by applying a composite analysis. A subsequently applied polynomial fit obtains the quiet time lines for daytime and nighttime, representing the typical seasonal variation under undisturbed conditions of the VLF signal amplitude for each considered link. The developed quiet time lines may serve as a tool to determine perturbations of the VLF signal amplitude with solar and geomagnetic as well as atmospheric origin. Also, they allow comparison of the VLF signal amplitude variation for different transmitter‐receiver links.

Comparison of proximal and minus lens autorefraction techniques to measure monocular accommodative amplitude.

This study provides a faster method for objectively measuring accommodative amplitude with an open-field autorefractor in a research setting. Objective measures of accommodative amplitude with an autorefractor take time because of the numerous stimulus demands tested. This study compares protocols using different amounts and types of demands to shorten the process. One hundred participants were recruited for four age bins (5 to 9, 10 to 14, 15 to 19, and 20 to 24 years) and monocular amplitude measured with an autorefractor using three protocols: proximal, proximal-lens (letter), and proximal-lens (picture). For proximal, measurements were taken as participants viewed a 0.9 mm "E" placed at 13 demands (40 to 3.3 cm = 2.5 to 30 D). The other protocols used a target (either the "E" or a detailed picture) placed at 33 and 12.5 cm followed by 12.5 cm with a series of lenses (-2, -4, and -5.5 D). Adjustments were made for lens effectivity for the three lens conditions, which were thus 9.6, 11.1, and 12.0 D for individuals without additional spectacle lenses. Accommodative amplitude was defined as the greatest response measured with each technique. One-way analysis of variance was used to compare group mean amplitudes across protocols and differences between letter protocols by age bin. Amplitudes were significantly different between protocols (p < 0.001), with proximal having higher amplitudes (mean ± standard deviation, 8.04 ± 1.70 D) compared with both proximal-lens protocols (letter, 7.48 ± 1.42 D; picture, 7.43 ± 1.42 D) by post hoc Tukey analysis. Differences in amplitude between the proximal and proximal-lens (letter) protocol were different by age group (p = 0 .003), with the youngest group having larger differences (1.14 ± 1.58 D) than the oldest groups (0.17 ± 0.58 and 0.29 ± 0.48 D, respectively) by post hoc Tukey analysis. The proximal-lens protocols took less time and identified the maximum accommodative amplitude in participants aged 15 to 24 years; however, they may underestimate true amplitude in younger children.