Reference Arm Research Articles

Single-pixel coherent diffractive imaging based on super-pixel holography

Quantitative phase imaging (QPI) is a powerful approach to study dynamics associated with both thickness and refractive index fluctuations. In this work, we propose a coherent diffractive QPI scheme based on single-pixel imaging structure and coherent modulation imaging. In this scheme, digital micro-mirror device with high refresh rate is employed for structured illumination. Synchronously, a single point detector is used to perform mode selected measurement of diffraction intensity. Based on the illumination structure and point signals, phase imaging is realized using a reweighted amplitude flow phase retrieval algorithm. Non-interference modality omits the reference arm, which simplifies the apparatus and improves the system robustness. This proposed technique is demonstrated by QPI of both digital binary and grayscale objects. The three-dimensional profile measurement of a plano-convex lens shows the possibility of phase retrieval for real objects. Accordingly our technique will promote the application of single-pixel phase imaging to biomedical imaging, x-ray diffraction imaging and three-dimensional profilometry.

Analysis of BCB and SU 8 photonic waveguide in MZI architecture for point-of-care devices

The proposed refractive index-based biosensor made of cost-effective polymer material in Mach-Zehnder configuration with novel horizontal slot waveguide structure offers high sensitivity. Due to the recent demand for low-cost point-of-care biosensor, silicon wafer-based polymer material has the potential for developing new hybrid waveguides for sensors. Hence we designed BenzoCycloButene (BCB), SU8 material as the core, and polymethyl methacrylate (PMMA) clad on a silicon wafer. The novelty of proposed BCB and SU8 horizontal slot waveguide structure of 2.5 μ m wide and 1.8μ m thick with a slot height of 400 ​nm, which handles the analyte effectively without any external sample holder. In Mach-Zehnder Interferometer architecture, reference arm 1 ​cm and sensing arm at a length of 1.1 ​cm with analyte refractive index of cancer cell (RI ​= ​1.401) and Influenza A type virus (RI ​= ​1.48) are used. Effective mode index of BCB core and SU8 are investigated through Finite-difference time domain (FDTD) analysis, and sensitivity results are calculated. Detection of disease are plotted in the transmission spectrum with reference to normal human serum (RI ​= ​1.35). This horizontal slot waveguide of BCB core achieves a sensitivity of 19280 nm/RIU and SU8 horizontal slot core waveguide provides a sensitivity of 16500 nm/RIU, which is higher in this polymer based refractive index biosensing.

High sensitivity photonic crystal sensor based on transition between photonic bands

In this work, we performed a study of an interferometric high sensitivity photonic crystal (PhC) sensor applied to measure glucose concentration in human urine samples. The architecture of the photonic sensor numerically simulated is based on a Mach–Zehnder interferometer formed by a coupled waveguide-cavity system. The sensor operates using photonic mode transitions detected from the photonic band diagram analysis, driven by changes in the glucose concentration in the urine samples that affect the refractive index of the optical sampling cavity. The photonic mode transition causes a phase shift between the wave traveling in the reference arm of the interferometer and the propagating electromagnetic wave in the sensing cavity containing the probing sample. As a consequence, the transmittance at the output of the interferometer can be modulated, making it extremely sensitive to changes in the refractive index of the sensing cavity. Since the PhC sensor studied works under variations in transmittance, we proposed a sensitivity coefficient as a function of the change in transmittance per unit change in the refractive index. The sensitivity achieved by the photonic sensor presents a value of 7000%/RIU, which indicates a variation in transmittance of 70% for changes in the refractive index of 0.01. These results demonstrate the feasibility of using photonic transitions between modes as a sensing tool in integrated photonic devices.

Single-arm tool for assessment of anomalous head posture.

Anomalous head posture (AHP) measurement is crucial in the management of nystagmus and incomitant strabismus and also during follow-up assessments. The types of AHP include chin posture, head tilt, and face turn. Goniometer is a low-cost tool widely used to measure head posture. This has two arms: one reference arm and one measuring arm. The drawback of this device is that the examiner has to maintain the reference arm exactly parallel or perpendicular to the floor and the other arm has to align the AHP. Since not all the examiners are comfortable in aligning both the arms simultaneously, the measurements obtained by a goniometer end up being less accurate. A device named cervical range of motion (CROM) is more reliable but expensive. There is an iOS application created for the purpose of head posture assessment, but an iPhone is expensive. To demonstrate a low-cost, innovative, reliable single-arm tool (SAT) for assessment of AHP. A clinometer is a device that is used to measure the heights of buildings. In this device, the gravitational force of the earth determines the reference line. We have modified a clinometer into a SAT by incorporating a long plastic arm to it, which is used to measure head tilt and chin up/down measurements. For the purpose of face-turn measurement, we modified a compass for direction into another type of SAT by fitting a yoke dial and a long plastic arm to measure face turn. Here, the principle is to have the line of direction as a reference. The direction of the patient's seating arrangement is determined and taken as the reference direction. The amount of the patient's face turn is measured by finding out the angle between reference direction and direction of the nose. This video shows the method of making SAT in a do-it-yourself manner and also demonstrates the method of measuring AHP. SAT is a reliable and low-cost device. https://youtu.be/UwoHARok85c.

Multi-wavelength off-axis digital holographic microscopy with broadly tunable low-coherent sources: theory, performance and limitations

Multi-wavelength digital holographic microscopy (MDHM) is widely used in biological and industrial applications because of increased unambiguous height measurement range and the ability to measure concentration from the spectral dependence of phase delay. Acousto-optic tunable filters (AOTFs) provide the simultaneous selection of several bands with tunable central wavelengths to create a multiplexed hologram, but may limit the field of view (FOV) in off-axis holography because of the short coherence length of the filtered light. We analyzed the performance of the AOTF-based off-axis MDHM setup with a diffraction grating or a prism in the reference arm necessary to increase the efficiency of angular multiplexing. This allows varying the number of spectral channels selected simultaneously without setup realignment. Mathematical description relates the spectral bandwidth of the AOTF, tilt of the coherence plane induced by the angular dispersion of a prism or a grating, width of the FOV determined by interference pattern visibility, spatial resolution, and optimal intermediate wavelengths. We theoretically and experimentally demonstrated that the FOV may be expanded by changing the angle of light incidence on the AOTF and that the prism changes the wavelength dependence of the FOV. We validated this technique by single-shot acquisition of the height maps of the transparent test chart at four wavelengths with an error similar to that of four sequentially captured single-wavelength holograms. The results may be helpful for multiple applications of MDHM using spectrally tunable light sources.

Understanding efficacy-safety balance of biologics in moderate-to-severe pediatric psoriasis.

BackgroundPsoriasis is a chronic immune-mediated inflammatory skin disease affecting both adults and children. To better understand the efficacy-safety profile of biologics in children with moderate-to-severe psoriasis, this study aimed to analyze efficacy and safety data of randomized controlled trials (RCTs) performed in pediatric psoriasis and to compare efficacy outcomes in children with those in adults.MethodsRCTs investigating biologics in children with moderate-to-severe psoriasis were identified in a systematic literature review. PASI75/90 treatment responses at weeks 11/12 were analyzed comparing biologics with control arms. Serious adverse events (SAEs) were analyzed at the end of each study. Efficacy data from RCTs in adults with psoriasis were selected for the same biologics. Risk ratios (RR) of selected RCTs were pooled together in a statistical random effects model using the inverse variance method.ResultsFor children, there were 1 etanercept, 2 secukinumab, 1 ixekizumab and 1 ustekinumab placebo-controlled RCTs and 1 adalimumab RCT using methotrexate as reference arm at weeks 11/12. For adults, out of 263 RCTs, 7 adalimumab and 15 etanercept (TNF inhibitors) and 4 ixekizumab and 12 ustekinumab (IL-17 and IL-12/23 inhibitors) RCTs reported PASI75/90 efficacy responses at weeks 11/12. Regarding efficacy, all biologics showed improved PASI responses over control arms. RRs ranges were 2.02–7.45 in PASI75 and 4.10–14.50 in PASI90. The highest PASI75 responses were seen for ustekinumab 0.375 mg/kg (RR = 7.25, 95% CI 2.83–18.58) and ustekinumab 0.75 mg/kg (RR = 7.45, 95% CI 2.91–19.06) in the CADMUS study. The highest PASI90 response was seen for ixekizumab (RR = 14.50, 95% CI 4.82–43.58) in the IXORA-PEDS study. SAE incidences in pediatric and adult arms with biologics were 0 to 3% except for a pediatric arm with adalimumab 0.40 mg/kg (8%). For adults, pooled RR also showed improved PASI responses over placebo for all biologics, with highest PASI75 response observed for ixekizumab (pooled RR = 16.18, 95% CI 11.83–22.14).ConclusionBoth adults and children with psoriasis show superior efficacy with biologics compared to control arms after 3 months of treatment with SAE incidences in the low percentages. Additional longer-term clinical studies are warranted to fully understand the overall efficacy-safety profile of biologics in children with moderate-to-severe psoriasis.

Proposal of hydrostatic pressure sensor integrated in a dual-core hollow optical fiber

In this paper, a novel dual-core hollow optical fiber (DHOF) based Mach-Zehnder interferometer (MZI) is proposed for hydrostatic pressure sensing. For the proposed fiber, two cores of the dual-core fiber are separated by a large air hole, and a D-type platform is fabricated adjacent one core. The existence of the central large air hole enhances the pressure-induced refractive index change of the dual-core fiber and ensures the independent transmission of the guiding light in the two fiber cores. Meanwhile, the D-type platform ensures that the dual-core fiber is subjected to asymmetric hydrostatic pressure, which results in the pressure-induced guiding mode phase change. For the dual-core hollow optical fiber, Mach-Zehnder interferometer (MZI) can be integrated in the fiber. One core is to measure the external environment as a sensing arm, and the other core is used as a reference arm. Furthermore, a dual-platform dual-core hollow optical fiber (DDHOF) is proposed, which further improves the asymmetry of the hydrostatic pressure on the dual-core fiber to continuously increase the sensing sensitivity. The mode field distribution and light guiding properties of DHOF and DDHOF under different hydrostatic pressures are analyzed by the finite element method and beam propagation method. The results show that the DHOF has a sensitivity of 2.4125 nm/MPa for the measurement range from 0 MPa to 100 MPa and the temperature cross-sensitivity is − 0.0886 nm/ ℃, the DDHOF has a sensitivity of 9.23 nm/MPa for the measurement range from 5 MPa to 10 MPa. The proposed DHOF and DDHOF can achieve different ranges of hydrostatic pressure sensing and possess extremely low temperature cross-sensitivity, which is suitable for the field of deep-sea exploration. Furthermore, the sensors possess a flexible structure, low temperature cross-sensitivity, can be integrated in the fiber, is easy to manufacture, and have other advantages.

Backflow-assisted time-resolved phase modulation in nematic liquid crystal Pi-Cells

By monitoring the time-dependent phase modulation behavior, we demonstrate the benefits of backflow on the phase modulation depth of nematic liquid crystal (LC) pi-cells in comparison to the phase modulation observed for other nematic LC device configurations. Specifically, results are presented for the time-resolved phase modulation of three different nematic LC device configurations under a range of electric field conditions: pi-cell (parallel-rubbed alignment layers), Fréedericksz cell (anti-parallel rubbed alignment layers), and a hybrid aligned nematic (HAN) device. The time-dependent behavior is obtained experimentally with a Michelson interferometer with a piezoelectric scanning mirror in the reference arm, which provides a continuous phase ramp in the reference signal. By recording the interference signal intensity, it is then possible to extract the change in optical phase as a function of time. It is shown that both the pi-cell and Fréedericksz cell exhibit a modulation that is greater than π radians for a double-pass configuration (2π radians for a four-pass configuration), with the lowest voltage amplitude corresponding to π phase modulation being observed for the pi-cell. Through the time-resolved response, it is shown that the presence of backflow hinders the dynamic phase response of the Fréedericksz device but does not negatively impact the behavior of the pi-cell. These results are found to be in good agreement with simulations of the phase modulation for the three nematic devices when backflow is taken into consideration.

Single-stage, three-arm, adaptive test strategies for non-inferiority trials with an unstable reference.

For indications where only unstable reference treatments are available and use of placebo is ethically justified, three-arm "gold standard" designs with an experimental, reference and placebo arm are recommended for non-inferiority trials. In such designs, the demonstration of efficacy of the reference or experimental treatment is a requirement. They have the disadvantage that only little can be concluded from the trial if the reference fails to be efficacious. To overcome this, we investigate novel single-stage, adaptive test strategies where non-inferiority is tested only if the reference shows sufficient efficacy and otherwise -superiority of the experimental treatment over placebo is tested. With a properly chosen superiority margin, -superiority indirectly shows non-inferiority. We optimize the sample size for several decision rules and find that the natural, data driven test strategy, which tests non-inferiority if the reference's efficacy test is significant, leads to the smallest overall and placebo sample sizes. We proof that under specific constraints on the sample sizes, this procedure controls the family-wise error rate. All optimal sample sizes are found to meet this constraint. We finally show how to account for a relevant placebo drop-out rate in an efficient way and apply the new test strategy to a real life data set.

Method of Merging the Divergence Sparsity and Simplified Acousto-Optic Interferometry to Sense an Acoustic Wave Field

This paper proposes a method of sensing an acoustic wave field by merging the divergence sparsity and the acousto-optic interferometry. For simplicity, we call this method the Compressed Acousto-optic Interferometry. Specifically, the Compressed Acousto-optic Interferometry refers to the integration of compressed tomography with acousto-optic interferometry, which is a potential solution for the real-time capture of an acoustic wave field that will apply in building future sonar systems. In this sensing regime, two important improvements to the preceding works are: (1) using a specific diffraction order of the sensing laser caused by the acousto-optic effect to establish the interferometer, which omits the reference arms broadly adopted in conventional experiments; (2) using the sparse extremums of a cross-section of the acoustic wave field as the features to integrate the compressed sensing into the construction of an acoustic wave field, which will reduce the number of necessary lasers and photodetectors. Detailed construction of the corresponding mathematical model, simulations and experiments are presented in this paper. The results show that the Compressed Acousto-optic Interferometry proposed is potentially an effective method for capturing the acoustic wave field in real-time, maintaining the accuracy of the reconstruction, as well as reducing the number of laser-photodetector pairs by more than 30%.

Integrated Slow-Light Enhanced Silicon Photonic Modulators for RF Photonic Links

An integrated RF-photonic link that consists of a slow-light enhanced silicon (Si) electro-optic modulator, a single mode Si optical waveguide and a silicon-germanium (SiGe) photodetector was fabricated using a Si photonic standard foundry service. The third-order intermodulation distortion (IMD3) of the RF signals and the link spur-free dynamic range (SFDR) were characterized through a two-tone test method. The Si Mach-Zehnder modulator architecture is designed to have unequal arms to operate on a simplified driving scheme. As a result, on-chip thermal heaters can be omitted, and the modulator can configure near its quadrature point by adjusting the wavelength to the modulator. Owning to enhanced light-matter interaction in the slow-light region, an increased slope efficiency is observed in the modulator. By selecting the optimal DC bias to the grating and the reference arms of the modulator, a SFDR of 96 dB/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> can be obtained in the RF link at the slow light region. The slow-light modulator also displays increased modulation efficiency, allowing for a reduced footprint for large array integration.

High-Speed Balanced-Detection Visible-Light Optical Coherence Tomography in the Human Retina Using Subpixel Spectrometer Calibration.

Increases in speed and sensitivity enabled rapid clinical adoption of optical coherence tomography (OCT) in ophthalmology. Recently, visible-light OCT (vis-OCT) achieved ultrahigh axial resolution, improved tissue contrast, and provided new functional imaging capabilities, demonstrating the potential to improve clinical care further. However, limited speed and sensitivity caused by the high relative intensity noise (RIN) in supercontinuum lasers impeded the clinical adoption of vis-OCT. To overcome these limitations, we developed balanced-detection vis-OCT (BD-vis-OCT), which uses two calibrated spectrometers to cancel RIN and other noises. We analyzed the RIN to achieve robust subpixel calibration between the two spectrometers and showed that BD-vis-OCT reduced the A-line noise floor by up to 20.5 dB. Metrics comparing signal-to-noise-ratios showed similar image qualities across multiple reference arm powers, a hallmark of operation near the shot-noise limit. We imaged healthy human retinas at an A-line rate of 125 kHz and a field-of-view up to 10 mm ×4 mm. We found that BD-vis-OCT revealed retinal anatomical features previously obscured by the noise floor.

Demystifying speckle field interference microscopy

Dynamic speckle illumination (DSI) has recently attracted strong attention in the field of biomedical imaging as it pushes the limits of interference microscopy (IM) in terms of phase sensitivity, and spatial and temporal resolution compared to conventional light source illumination. To date, despite conspicuous advantages, it has not been extensively implemented in the field of phase imaging due to inadequate understanding of interference fringe formation, which is challenging to obtain in dynamic speckle illumination interference microscopy (DSI-IM). The present article provides the basic understanding of DSI through both simulation and experiments that is essential to build interference microscopy systems such as quantitative phase microscopy, digital holographic microscopy and optical coherence tomography. Using the developed understanding of DSI, we demonstrated its capabilities which enables the use of non-identical objective lenses in both arms of the interferometer and opens the flexibility to use user-defined microscope objective lens for scalable field of view and resolution phase imaging. It is contrary to the present understanding which forces us to use identical objective lenses in conventional IM system and limits the applicability of the system for fixed objective lens. In addition, it is also demonstrated that the interference fringes are not washed out over a large range of optical path difference (OPD) between the object and the reference arm providing competitive edge over low temporal coherence light source based IM system. The theory and explanation developed here would enable wider penetration of DSI-IM for applications in biology and material sciences.

SA21 Using Reference-Arm Adjustment to Reduce Bias in Outcomes of Bucher Indirect Comparison: A Case Study

Indirect treatment comparison (ITC) has been widely used for investigating comparative effectiveness of target interventions when head-to-head studies are not available. Theoretically, ITC could produce valid estimations with assumptions in study homogeneity, similarity and evidence consistency. However, in an anchored ITC, relative effects of interventions to their reference arms could be influenced by unmeasured confounders and lead to biased comparison results. The aim of this study was to explore whether using reference-arm adjustment can help to reduce the biases in outcomes.

Quantum Asymmetry and Noisy Multimode Interferometry.

Quantum asymmetry is a physical resource that coincides with the amount of coherence between the eigenspaces of a generator responsible for phase encoding in interferometric experiments. We highlight an apparently counterintuitive behavior that the asymmetry may increase as a result of a decrease of coherence inside a degenerate subspace. We intuitively explain and illustrate the phenomena by performing a three-mode single-photon interferometric experiment, where one arm carries the signal and two noisy reference arms have fluctuating phases. We show that the source of the observed sensitivity improvement is the reduction of correlations between these fluctuations and comment on the impact of the effect when moving from the single-photon quantum level to the classical regime. Finally, we also establish the analogy of the effect in the case of entanglement resource theory.

Fiber-Optic Hydrophone Based on Michelson's Interferometer with Active Stabilization for Liquid Volume Measurement.

Sensing technologies using optical fibers have been studied and applied since the 1970s in oil and gas, industrial, medical, aerospace, and civil areas. Detecting ultrasound acoustic waves through fiber-optic hydrophone (FOH) sensors can be one solution for continuous measurement of volumes inside production tanks used by these industries. This work presents an FOH system composed of two optical fiber coils made with commercial single mode fiber (SMF) working in the sensor head of a Michelson’s interferometer (MI) supported by an active stabilization mechanism that drives another optical coil wound around a piezoelectric actuator (PZT) in the reference arm to mitigate external mechanical and thermal noise from the environment. A 1000 mL glass graduated cylinder filled with water is used as a test tank, inside which the sensor head and an ultrasound source are placed. For detection, amplitudes and phases are measured, and machine learning algorithms predict their respective liquid volumes. The acoustic waves create patterns electronically detected with resolution of 1 mL and sensitivity of 340 mrad/mL and 70 mvolts/mL. The nonlinear behavior of both measurands requires classification, distance metrics, and regression algorithms to define an adequate model. The results show the system can determine liquid volumes with an accuracy of 99.4% using a k-nearest neighbors (k-NN) classification with one neighbor and Manhattan’s distance. Moreover, Gaussian process regression using rational quadratic metrics presented a root mean squared error (RMSE) of 0.211 mL.

Effects of a Novel High-Quality Protein Infant Formula on Energetic Efficiency and Tolerance: A Randomized Trial.

Objectives:Protein overfeeding in infants can have negative effects, such as diabetes and childhood obesity; key to reducing protein intake from formula is improving protein quality. The impact of a new infant formula [study formula (SF)] containing alpha-lactalbumin, lactoferrin, partially hydrolyzed whey, and whole milk on growth and tolerance compared to a commercial formula (CF) and a human milk reference arm was evaluated.Methods:This randomized, double-blind trial included healthy, singleton, term infants, enrollment age ≤14 days. Primary outcome was mean daily weight gain. Secondary outcomes were anthropometrics, formula intake, serum amino acids, adverse events, gastrointestinal characteristics, and general disposition.Results:Non-inferiority was demonstrated. There were no differences between the formula groups for z scores over time. Formula intake [−0.33 oz/kg/day, 95% confidence interval (CI): −0.66 to −0.01, P = 0.05] and mean protein intake (−0.13 g/kg/day, 95% CI: −0.26 to 0.00, P = 0.05) were lower in the SF infants, with higher serum essential amino acid concentrations (including tryptophan) compared to the CF infants. Energetic efficiency was 14.0% (95% CI: 8.3%, 19.7%), 13.0% (95% CI: 6.0%, 20.0%), and 18.1% (95% CI: 9.4%, 26.8%) higher for weight, length, and head circumference, respectively, in SF infants compared to the CF infants. SF infants had significantly fewer spit-ups and softer stool consistency than CF infants.Conclusions:The SF resulted in improved parent-reported gastrointestinal tolerance and more efficient growth with less daily formula and protein intake supporting that this novel formula may potentially reduce the metabolic burden of protein overfeeding associated with infant formula.

Compact Mach-Zehnder Interferometer for Practical Vernier Effect Sensing System With High Extinction Ratio

Recently, Vernier effect is introduced into fiber optic interferometric sensors to enhance the sensitivity. To achieve a high-quality of the Vernier spectrum, the match of the free spectral range (FSR) and the extinction ratio (ER) in two arms is required. Furthermore, the reference arm should be designed to be different from the sensing arm to avoid crosstalk. In this work, a compact in-line Mach-Zehnder interferometer (MZI) by sandwiching a hollow capillary fiber (HCF) between two sections of no-core fiber (NCF) is proposed for the reference arm in Vernier effect based sensing system. FSR of the in-line MZI can be tuned by modulating the length of the HCF, while the ER can remain high up to ∼20 dB, which is equivalent to that of the polarization-maintaining fiber (PMF) based interferometers. Experimental results show that the MZI exhibits low sensitivity to temperature, strain, refractive index (RI) and torsion. When employed as the reference arm cascaded with PMF Sagnac interferometer (SI), the upper and lower envelope are with high extinction ratio (ER). The proposed MZI is a promising candidate for the reference arm in Vernier effect based sensing system with the merits of compact size, good spectral characteristics and insensitivity to ambient environment.

Optofluidic Micromachined Platform for Refractive Index Measurement

We present a combination of micromachined optofluidic platforms equipped with a fiber-optic sensing configuration based on a three-path Mach–Zehnder interferometer (MZI) for simultaneous measurement of the refractive index of liquids and the autocalibration in dynamic regime. The sensing principle is based on the low-coherence interferometry, characterized by a generation of Gaussian enveloped interferograms, for which the position of its maximum depends on the optical path difference (OPD) between the sensing and reference arm of the MZI. When liquid flows through the central microchannel of the optofluidic platform it crosses the light beam between the two optical fibers in the sensing arm causing the OPD change. An algorithm has been applied for the calculation of the refractive index of liquids out of the raw interference signals. We obtained a very good agreement between the experimental results and literature data of refractive indices of subjected fluids. The accuracy of refractive index measurement is approximately 1%, predominantly determined by the accuracy of reading the position of the mechanical scanner. The proposed sensor is attractive for the label-free biological, biochemical, and chemical sensing owing autocalibration and high sensitivity yet consuming a very small sample volume of 1 µL. It is capable to measure the refractive index of various liquids and/or gases simultaneously in the process.

Quantitative analysis and control of the torque profile of the upper limb using a kinetic model and motion measurements.

This paper investigates a new approach to the rapid control of an upper limb exoskeleton actuator. We used a mathematical model and motion measurements of a human arm to estimate joint torque as a means to control the exoskeleton's actuator. The proposed arm model is based on a two-pendulum configuration and is used to obtain instantaneous joint torques which are then passed into control law to regulate the actuator torque. Nine subjects volunteered to take part in the experimental protocol, in which inertial measurement units (IMUs) and a digital goniometer were used to measure and estimate the torque profiles. To validate the control law, a Simscape model was developed to simulate the arm model and control law in which measurement data from IMUs and a goniometer were fed into the suggested Simscape model. The arm torque profiles are key to the control approach and should be traced by torques produced by the exoskeleton actuators to provide comfort and flexibility for the subjects. A DC motor was used as an actuator for the exoskeleton, and its model was used in the physical Simscape model. To reduce the error in the driving torque compared with the reference arm torque, a PID controller was implemented. The results show the potential of our methodology for tracking and controlling the actuator's torque, in which the mean square error was reduced to less than 0.2 - a significantly low value.