Finger Tissue Research Articles

Design and analysis of a metamaterial based biosensor to determine blood glucose concentration

In this paper, a biosensor utilizing metamaterials is designed and simulated to detect blood glucose concentration. The proposed sensor comprised of a microstrip patch antenna designed on a Rogers RT5880 substrate. A circular-shaped complementary split ring resonator (CSRR) cell is integrated onto the patch of the antenna which acts as the sensing region. The sensor is analyzed in order to ascertain the blood glucose concentration ranging from 50-300 mg/dL in a human finger model. The sensing parameter is amplitude of reflection coefficient, which exhibits variation in response to alterations in the dielectric characteristics of the sample being tested. The Cole-Cole relaxation model is employed to predict the dielectric properties of different finger tissues. An analysis of the characteristics of the CSRR was conducted to illustrate its significance in the realm of glucose detection. The glucose level is determined through the utilization of a linear regression model that describes the relationship between the reflection coefficient of the sensor and glucose level. The sensor demonstrates an impressive sensitivity of 1.792 dB per (mgdL<sup>-1</sup>) and has the ability of determining glucose levels with a good accuracy, as verified by the application of Clarke error grid. This sensor exhibits enhanced performance compared to some other recent glucose sensors.

Exploring the bias: how skin color influences oxygen saturation readings via Monte Carlo simulations.

Our goal is to understand the root cause of reported oxygen saturation ( ) overestimation in heavily pigmented skin types to devise solutions toward enabling equity in pulse oximeter designs. We aim to gain theoretical insights into the effect of skin tone on curves using a three-dimensional, four-layer tissue model representing a finger. A finger tissue model, comprising the epidermis, dermis, two arteries, and a bone, was developed using a Monte Carlo-based approach in the MCmatlab software. Two skin tones-light and dark-were simulated by adjusting the absorption and scattering properties within the epidermal layer. Following this, curves were generated in various tissue configurations, including transmission and reflection modes using red and infrared wavelengths. In addition, the influence of source-detector (SD) separation distances on both light and dark skin tissue models was studied. In transmission mode, curves did not deviate with changes in skin tones because both pulsatile and non-pulsatile terms experienced equal attenuation at red and infrared wavelengths. However, in reflection mode, measurable variations in curves were evident. This was due to differential attenuation of the red components, which resulted in a lower perfusion index at the red wavelength in darker skin. As the SD separation increased, the effect of skin tone on curves in reflection mode became less pronounced, with the largest SD separation exhibiting effects similar to those observed in transmission mode. Monte Carlo simulations have demonstrated that different light pathlengths within the tissue contribute to the overestimation of in people with darker skin in reflection mode pulse oximetry. Increasing the SD separation may mitigate the effect of skin tone on readings. These trends were not observed in transmission mode; however, further planned research using more complex models of the tissue is essential.

Intractable painful great toe – A diagnostic enigma

ABSTRACT Glomus bodies are highly specialized arteriovenous anastomoses that are responsible for thermoregulation by regulating the blood flow. Glomus tumor consists of vascular channels and glomus piles separated by connective tissue stroma. Approximately, 75% of all tumors occur in subungual tissues of fingers. Glomus tumors in foot are uncommon. We report a case of glomus tumor in a young male who is having pain in the left great toe since 5 years duration. For diagnosis, MRI and excisional biopsy were done. After excision of tumor, the complaints of the patient were relieved.

Human Mesenchymal Stem Cells Improve Angiogenesis and Bone Formation in Severed Finger Rats through SIRT1/Nrf2 Signaling.

This study employed a severed finger rat model to analyze the effects of human mesenchymal stem cells (MSCs) on angiogenesis, inflammatory response, apoptosis, and oxidative stress, to evaluate the possible mechanism of the repair effect of MSCs on severed finger (SF) rats. Sixty Sprague-Dawley (SD) rats were categorized into five groups (n = 12). The pathological changes of severed finger tissues were investigated by Hematoxylin and eosin (H&E) staining on day 14 after the rats were sacrificed. The levels of inflammatory factors and oxidative stress factors were detected by ELISA. Terminal Deoxynucleotidyl Transferase (TdT) dUTP Nick End Labeling (TUNEL) was employed to assess the apoptosis of chondrocytes in severed finger tissues. The expression of osteocalcin (OCN), osteopontin (OPN), Collagen I (Col-1), and CD31 were detected by immunohistochemistry or immunofluorescence assay, respectively. The expression levels of related proteins were determined by western blot. Our study presented evidence that MSCs treatment improved pathological changes of skin and bone tissue, diminished the inflammatory response, prevented oxidative stress injury, suppressed chondrocyte apoptosis, and promoted angiogenesis, and bone formation compared to the model group. In addition, EX527 treatment attenuated the effect of MSCs, SRT1720 and ML385 co-treatment also attenuated the effect of MSCs. Importantly, the MSCs treatment increased the expression of Sirtuin 1(SIRT1)/Nuclear factor erythroid2-related factor 2(Nrf2) relate proteins. Our study indicated that the mechanism of the effect of MSCs on a severed finger was related to the SIRT1/ Nrf2 signaling pathway.

The effect of contact pressure on photoplethysmography

In the bioinformation photoplethysmography (PPG) measurement, the precision and repeatability could be impacted by the contact pressure between the optical sensor and the measurement site. Taking the finger’s geometrical, mechanical, and optical characteristics into consideration, finite element models and Monte Carlo (MC) simulation methods were used to quantitatively analyze the effects of the deformation of different finger layers under contact pressure on its optical parameters and PPG signals during fingertip spectroscopic detection. Firstly, a 3D axisymmetric finger model was established, pelican optimization was used to find the parameter lamp that caused the simulation to best match the finger pressing behavior, modeled the deformation of each layer, and quantified the changes in their absorption and scattering coefficient. Then, before and after pressure application, photon propagation in the reflectance and transmittance modalities within the diastolic and systolic finger tissues at 660 nm and 940 nm were studied by MC simulation. The result shows that contact pressure significantly altered the thickness of the dermis and subcutaneous tissues, a decrease in tissue thickness caused an increase in optical coefficient, which resulted in a reduction in normalized pulsatile reflectance and a boost in transmittance, and the change was dependent on wavelength.

DESIGN OF A NEW MINIATURE CIRCULAR BIOSENSOR FOR DETECTING GLUCOSE CONCENTRATION IN BLOOD

The research introduces a new small slotted circular biosensor for non-invasively measuring blood glucose levels. The proposed biosensor has an operating frequency of 5.15 GHz. Its overall dimensions are 27 mm × 23 mm × 1.6 mm, with a radius of 8 mm. It uses electromagnetic principles to detect changes in glucose levels without intrusive treatments. Using a cost-effective FR4 dielectric substrate, the biosensor simulates human finger tissue to accurately depict changes in glucose concentration. The results showed that the proposed biosensor can detect changes in glucose concentration by electromagnetic modeling, making it a potential option for continuous glucose monitoring in clinical settings.

Measurement Analysis of Non-Invasive Blood Glucose On Sensor Coplanar Waveguide Loaded Square Ring Resonator with Interdigital Coupling Capacitor

This study presents the experimental results of a system with a sensor structure detecting human blood glucose levels. A microwave-based sensor is used for non-invasive blood glucose monitoring. The sensor design uses an asymmetrically loaded CPW structure as a square ring resonator with an interdigital coupling capacitor on the ground side. Simulated with a load of artificial finger tissue made from gelatin, modeled in four layers. The first layer is the skin is the outermost tissue, the next layer is fat, blood and bone. Each layer of tissue has a certain thickness size; skin (0.3mm), fat (0.2mm), blood (1.5mm), and bone (4mm). The measurement simulation is used, HFSS as modeling simulation and VNA as a measurement of the physical representation of the design results with parametric optimization methods. To verify the correlation and the expected sensitivity, media with different dielectrics were mounted on the surface of the sensor resonator with blood glucose levels of 1mg/dl, 72mg/dl, 126mg/dl, 162mg/dl and 216mg/dl. Reflection factor S11 was observed based on dielectric constant blood glucose levels (dB) fluctuations. Analysis of the data on the graph between the independent variables, namely blood glucose concentration and the dependent variable levels of S11 has an “R” correlation value of 0.97. The sensitivity level of the sensor on the S11 reflection factor with HFSS simulation averages 73.36mdB/mgdl-1 and VNA reaches 82.39mdB/mgdl-1. The results are interesting for developing a more optimal glucose sensor system.

Measurement Analysis of Non-Invasive Blood Glucose On Sensor Coplanar Waveguide Loaded Square Ring Resonator with Interdigital Coupling Capacitor

This study presents the experimental results of a system with a sensor structure detecting human blood glucose levels. A microwave-based sensor is used for non-invasive blood glucose monitoring. The sensor design uses an asymmetrically loaded CPW structure as a square ring resonator with an interdigital coupling capacitor on the ground side. Simulated with a load of artificial finger tissue made from gelatin, modeled in four layers. The first layer is the skin is the outermost tissue, the next layer is fat, blood and bone. Each layer of tissue has a certain thickness size; skin (0.3mm), fat (0.2mm), blood (1.5mm), and bone (4mm). The measurement simulation is used, HFSS as modeling simulation and VNA as a measurement of the physical representation of the design results with parametric optimization methods. To verify the correlation and the expected sensitivity, media with different dielectrics were mounted on the surface of the sensor resonator with blood glucose levels of 1mg/dl, 72mg/dl, 126mg/dl, 162mg/dl and 216mg/dl. Reflection factor S11 was observed based on dielectric constant blood glucose levels (dB) fluctuations. Analysis of the data on the graph between the independent variables, namely blood glucose concentration and the dependent variable levels of S11 has an “R” correlation value of 0.97. The sensitivity level of the sensor on the S11 reflection factor with HFSS simulation averages 73.36mdB/mgdl-1 and VNA reaches 82.39mdB/mgdl-1. The results are interesting for developing a more optimal glucose sensor system.

Vascularized Toe Proximal Interphalangeal Joint Transfer in Posttraumatic Fingers: Analysis of Prognostic Factors for Suboptimal Outcomes.

Posttraumatic finger osteoarthritis of the proximal interphalangeal joint (PIPJ) is a difficult problem. Over the past decade, we have reported several methods for improving the outcomes of vascularized toe joint transfer (VJT). In this study, we focused on determining poor prognostic factors which lead to a suboptimal outcome. A consecutive series of patients with posttraumatic osteoarthritis of the PIPJ who received VJT between January 2008 and January 2021 were enrolled in this study. The senior surgeon (Y.-T.L.) performed the surgery in all cases. In this retrospective study, we reexamine the initial trauma-related soft tissue and bony structure injuries of the recipient finger, to assess the baseline tissue quality before VJT. The injuries were classified into five major categories according to their anatomic region. The functional outcome parameters (including range of motion, percentage of use, and extensor lag of the transferred PIPJ) were collected. Univariate and multivariate linear regression analyses were performed using the generalized estimated equation model to identify the correlation between the injury category involved and functional outcome. A total of 59 digits were enrolled. Our results revealed that the fingers with previous vascular injury that received revascularization procedures had relatively suboptimal functional outcomes. These fingers had a significantly lower percentage of use both before (β = -0.222, P = 0.006) and after (β = -0.177, P = 0.006) receiving secondary procedures to improve functional outcome. Patients with prior revascularization surgery were associated with a poor functional outcome after VJT.

Usefulness of the lateral arm free flap for hand defect reconstruction

Purpose: Although various surgical reconstruction methods are available for multidigit defects or soft tissue defects of the hand, they often require a thin flap due to the hand’s unique physical characteristics. We performed a total of 13 cases of lateral arm free flap surgery at our hospital. The purpose of this study was to report the usefulness of this technique. Methods: This study included the following cases: four cases of multiple digit amputations, seven cases of hand dorsum skin defects, one case of first web reconstruction due to web contracture, and one case of an index finger bone and soft tissue defect with only the ulnar-side neuro-vascular bundle remaining. After emergency simple debridement, subsequent reconstruction was performed using a lateral arm free flap. Results: All 13 cases healed without necrosis. Patients who underwent finger amputation were able to preserve the length of their fingers without any additional amputation. Patients who initially had hand dorsum defects were able to maintain grasping function after flap stabilization. The patient with web contracture was able to recover the lost pinching function, and the patient with a combined loss of osteoarticular and soft tissue of the index finger maintained the shape and length of the finger despite the absence of joint function. Conclusion: The lateral arm free flap is a useful reconstruction method that can be easily performed with a single session of regional anesthesia. Since the flap is thin, it is suitable for hand defect reconstruction. If necessary, vascularized bone grafting is possible.

Raspberry PI-Based Finger Vein Recognition System Using PCA NET

Despite simultaneously ignoring the intensity distribution that is formed by the finger tissue and, in some instances, processing it as background noise, the majority of finger vein feature extraction algorithms achieve satisfactory performance due to their ability to represent texture. This project makes use of two- directional two-dimensional Fisher Principal Component Analysis, also known as (2D) 2 FPCA, for feature extraction. This type of "noise" is presented as a novel soft biometric trait for improving finger vein recognition performance. In order to demonstrate that the intensity distribution that is formed by the finger tissue in the background can be extracted as a soft biometric trait for recognition, a comprehensive analysis of the finger vein imaging principle and the characteristics of the image are first presented.

New approaches for rapid setpoint determination and uninterrupted tracking in non-invasive continuous blood pressure monitoring based on volume-clamp method

The volume-clamp method (VCM) is a widely used non-invasive continuous blood pressure (BP) monitoring technique, but determining the volume setpoint (V0) in the open-loop phase can be time-consuming and may cause finger tissue displacement. Additionally, frequent interruptions in BP measurement are required during the closed-loop phase to reset V0. We proposed two new approaches: the proportional value method (PVM) for rapid V0 determination in the open-loop phase and the uninterrupted V0 tracking method (UVTM) in the closed-loop phase. PVM adaptively searches for V0 by analyzing the shape index (Prop) of the plethysmographic (PG) signal under constant cuff pressure, while UVTM introduces a new vascular compliance calculation method in closed-loop phase to track changes in V0 without interrupting BP measurement. We describe the non-invasive continuous BP monitor (NC-BPM) based on these methods. Experimental results show that PVM can accurately determine V0, with a mean arterial pressure error of −1.72 ± 2.80 mmHg when compared to oscillometric method (OSCM). UVTM in NC-BPM produced a mean absolute error (MAE) of 2.44 ± 2.91 mmHg for mean arterial pressure (MAP) in induced BP fluctuation test compared to the Nexfin monitor. In the clinical study with invasive reference, the MAE in measuring MAP by NC-BPM was 4.69 ± 5.39 mmHg. Our results show that PVM and UVTM are highly accurate and reliable, with the potential to integrate effectively into VCM-based BP monitoring devices that could benefit patients, healthcare providers, and researchers.

Development of a wearable cybernic glove that enables object grasping and gripping force measurement with open finger pad

Patients with hand paralysis have motor and sensory dysfunction of their hands. They can neither flex/extend their fingers nor feel the gripping force. To enable the gripping motion with sensory information, sensory information has to be acquired simultaneously as the fingers are assisted. Since the skin plays a role in increasing friction with the grasped object in addition to acquiring sensory information, it is important for the skin to be in direct contact with the object. Therefore, it is necessary to enable gripping motion and measure the gripping force with an open finger pad. In this study, a wearable system was developed to enable gripping motion and gripping force measurements with an open finger pad. A tendon-driven finger-assist glove assisted the flexion/extension of the fingers and adduction/abduction of the thumb; moreover, a sensor was developed to estimate the fingertip force by measuring the lateral expansion force of the finger tissue. We conducted an evaluation experiment for the developed sensor and object grasping experiments for the developed wearable system with the sensor. The root mean square error (RMSE) in force estimation was approximately 0.2 N. In addition, the system could assist the motions of the thumb/index/middle finger in grasping objects.

A novel rat-tail model for studying human finger vibration health effects.

It has been hypothesized that the biodynamic responses of the human finger tissues to vibration are among the major stimuli that cause vibration health effects. Furthermore, the finger contact pressure can alter these effects. It is difficult to test these hypotheses using human subjects or existing animal models. The objective of this study was to develop a new rat-tail vibration model to investigate the combined effects of vibration and contact pressure and to identify their relationships with the biodynamic responses. Physically, the new exposure system was developed by adding a loading device to an existing rat-tail model. An analytical model of the rat-tail exposure system was proposed and used to formulate the methods for quantifying the biodynamic responses. A series of tests with six tails dissected from rat cadavers were conducted to test and evaluate the new model. The experimental and modeling results demonstrate that the new model behaves as predicted. Unlike the previous model, the vibration strain and stress of the rat tail does not depend primarily on the vibration response of the tail itself but on that of the loading device. This makes it possible to quantify and control the biodynamic responses conveniently and reliably by measuring the loading device response. This study also identified the basic characteristics of the tail biodynamic responses in the exposure system, which can be used to help design the experiments for studying vibration biological effects.

Sweat Gland Extraction From Optical Coherence Tomography Using Convolutional Neural Network

As the Level 3 features of fingerprint, sweat pores have attracted attention in the field of fingerprint recognition and have been successfully applied to automatic fingerprint recognition systems. Traditional surface sweat pores become unclear or disappeared when the finger is contaminated, dried, or damaged. These unstable factors create major challenges in collecting sweat pores. Subcutaneous sweat glands belong to the internal tissues of fingers, which are stable and immune to external disturbances. This study investigated the extraction of subcutaneous sweat glands from fingertip volume data collected by optical coherence tomography (OCT). First, an improved multitask V-Net is proposed to extract subcutaneous sweat glands from OCT volume data. The network has an encoding path for features extraction and two decoding paths for extracting sweat gland boundaries and regions, respectively. The multitask scheme is designed to enhance the boundary and shape information of sweat glands and to prevent false extraction caused by interference from other tissues. Second, three mapping methods are proposed to address the problem of different spatial orientations of sweat glands. These three mapping methods, namely, global direct mapping (GDM), local direct mapping (LDM), and cylindrical fitting mapping (CFM), are used to map sweat glands to the surface fingerprint. Experiments are conducted in terms of sweat gland extraction, mapping, and matching. The qualitative and quantitative results show that the proposed network for sweat glands extraction outperforms other methods and that the LDM and CFM methods derive more accurate positions of sweat glands on the surface fingerprint than GDM. In the matching experiment, the equal error rate (EER) of dual-decoding V-Net (DDVN) reached 0.58%, which verified the recognition ability of sweat glands and the effectiveness of the proposed network.

The neglected background cues can facilitate finger vein recognition

Recently, finger vein based biometric authentication has attracted considerable attention due to its high efficiency and high security. However, most existing finger vein representation methods focus on vein traits while ignoring background cues, although background cues also convey identity information specific to each individual. In this paper, we leverage background intensity variations in finger vein images as new features to enrich discriminative representation, and accordingly propose a new descriptor named Intensity Orientation Vector (IOV). IOV, scaleable to reflect characteristics of finger tissues, offers additional informative cues for finger vein representation. Furthermore, we propose a new learning scheme named Semantic Similarity Preserved Discrete Binary Feature Learning (SSP-DBFL) for finger vein recognition. Unlike the most bimodal binary feature representation methods, SSP-DBFL preserves high-level semantic similarity in a common Hamming space to exploit the consensus between vein traits and background cues. Specifically, given a finger vein image, we first extract the direction difference vectors (DDV) as the main vein traits and the IOV as the auxiliary background cues. Subsequently, we jointly learn projection functions from these two types of features in a supervised manner, converting the two features into discriminative binary codes with their semantic similarity preserved. Finally, the binary codes are pooled into histogram-based vectors for finger vein representation. Extensive experiments are conducted on five widely used finger vein databases and demonstrate the effectiveness of our proposed IOV and SSP-DBFL.

A Robust Approach for Reproducing the Haptic Sensation of Sandpaper With Different Roughness During Bare Fingertip Interaction

When reproducing realistic virtual textures for bare finger interaction, an accelerometer attached to a fingernail is commonly used. This measurement depends on the dynamic conditions during the exploration action, and slight differences in roughness are difficult to acquire accurately because of masking by shivering, low-pass filtering by the finger tissue, and sensor accuracy. We propose a simpler yet robust approach based on the 3D measurement of the surface and compare it with the conventional approach. The 3D surface images of sandpaper with different degrees of roughness were captured using a 3D microscope, and the line roughness curve was transformed into an acceleration curve by quadratic differential transformation. The real-time acceleration and frictional force were measured by an accelerometer and force sensor for comparison. A haptic device replaying acceleration-based vibrations by two audio speakers and producing tangential force by a motor-controlled liner slide was developed for reproduction. We conducted experiments with participants to evaluate the reproduction approach. Experimental results showed that the conventional approach obtained sufficient discriminability with the assistance of force, whereas the proposed approach achieved higher reproducibility and discriminability by sole vibration. Thus, our approach provides a new reference for studies of bare finger interaction with rough surfaces.

Purulent-necrotic lesions of finger tissues in cows and their effect on the physicochemical and biochemical properties of blood

A study was made of the prevalence, species structure and localization of purulent-necrotic ulcerative lesions of the tissues of the fingers in cows with a non-walking technology of keeping on a leash in stalls and loose in boxes, as well as an assessment of their effect on the physico-chemical and biochemical properties of blood. It was found that in conditions of loose housing, the number of cases of registration of purulent-necrotic defects in the tissues of the fingers of cows is 4.30% more than in conditions of tethered housing. The species structure of purulent-necrotic ulcers in loose keeping technology is represented by ulcerative defects in the tissues of the corolla and the arch of the interdigital fissure, the incidence of diagnosing which is higher by 7.14% and 4.76% than in the conditions of tethered keeping, and in the conditions of tethered technology, the most common are ulcerative defects in the tissues of the crumb and the base of the skin of the sole, the frequency of registration of which is higher by 7.16% and 7.24% than with loose technology. When evaluating the effect of registered forms of purulent-necrotic ulcerative lesions of the tissues of the fingers on the physical and chemical properties, it was found that the lowest concentration of hemoglobin is recorded with a purulent-necrotic ulcer of the base of the skin of the sole, which is less than with ulcerative defects of the crumb by 3.37%, with ulcerative defects in tissues of the interdigital fissure by 7.63%, with ulcerative defects of the corolla by 17.06%. In cows with ulcers of the base of the skin of the sole, crumb and tissues of the interdigital gap, hypochromic anemia was recorded, which is expressed in a decrease in the average hemoglobin content in the erythrocyte relative to the physiological norm by 20.70%, 14.42% and 3.51%, respectively. The revealed hypochromic anemia reduced the digital indicator of blood hematocrit relative to the threshold values of the physiological norm by 6.43%, 5.56%, 2.80%. When evaluating the effect of the established species structure of purulent-necrotic ulcerative defects in the tissues of the fingers on the biochemical composition of blood serum, it was determined that the highest concentration of total protein, aspartate aminotransferase and alanine aminotransferase is recorded in cows with purulent-necrotic ulcers in the tissues of the hoof corolla, total bilirubin - with purulent-necrotic ulcers of the base of the skin of the sole, alkaline phosphatase - with purulent-necrotic ulcers of the tissues of the interdigital fissure.

Функциональная оценка эндотелиальной дисфункции с помощью модифицированной пробы на основе постокклюзионной реактивной гиперемии

The purpose — to develop a modification of the functional test for assessing vascular reactivity using post-occlusive reactive hyperemia (PORH). The test should be suitable for diagnosing endothelial dysfunction (ED) in clinical practice. Material and methods. A modification of the test is proposed: 1) a local thermometry by commonly used non-contact infrared thermometer is proposed to assess local blood flow, 2) standardization of cooling the examined finger tissues during complete vascular occlusion is also proposed by immersing it in an aqueous medium cooled to a given temperature. Results. A preliminary criterion for the ED diagnosis was established. If the local temperature of the examined hand finger is < 32.0⁰C at the time point 90 sec after the end of arterial occlusion then it is as sign of ED (sensitivity — 75%, specificity — 96%).

A 3D-Printed Soft Fingertip Sensor for Providing Information about Normal and Shear Components of Interaction Forces

Sensing of the interaction forces at fingertips is of great value in assessment and rehabilitation therapy. Current force sensors are not compliant to the fingertip tissue and result in loss of touch sensation of the user. This work shows the development and characterization of a flexible fully-3D-printed piezoresistive shear and normal force sensor that uses the mechanical deformation of the finger tissue. Two prototypes of the sensing structure are evaluated using a finite element model and a measurement setup that applies normal and shear forces up to 10 N on a fingertip phantom placed inside the sensing structure, which is fixed to prevent slippage. Furthermore, the relation between strain (rate) and resistance of the conductive TPU, used for the strain gauges, is characterized. The applied normal and shear force components of the 3D-printed sensing structure can be partly separated. FEM analysis showed that the output of the sensor is largely related to the sensor geometry and location of the strain gauges. Furthermore, the conductive TPU that was used has a negative gauge factor for the strain range used in this study and might cause non-linear behaviors in the sensor output.