Rajesh Rajamani's research while affiliated with University of Minnesota Twin Cities and other places

Publications (313)

Chapter
Optical wireless communication is emerging as a low-power, low-cost, and high data rate alternative to acoustic and radio-frequency communications in several short to medium-range applications. However, it requires a close-to-line-of-sight link between the transmitter and the receiver. Indeed, a severe misalignment can lead to intolerable signal fa...
Article
Light-Emitting Diode (LED) optical wireless communication is a potentially low-cost, sustainable approach for enabling high-speed free-space and underwater transmissions within a limited communication range. Establishing a tightly controlled line of sight (LOS) between transmitter and receiver is a significant challenge because the angle of the ali...
Article
This paper proposes a novel electromagnetic position estimation system suitable for piston-cylinder actuators using active current control. The inexpensive non-contacting position measurement system is composed of an electromagnet on the stationary cylinder and a magnetic sensor on the piston rod. The measured amplitude of an alternating magnetic f...
Article
This work aims to estimate severe fMRI scanning artifacts in extracellular neural recordings made at ultrahigh magnetic field strengths in order to remove the artifact interferences and uncover the complete neural electrophysiology signal. We build on previous work that used PCA to denoise EEG recorded during fMRI, adapting it to cover the much lar...
Article
This paper develops a machine-learning-based method for counting vehicles and classifying their maneuvers in a traffic intersection using inexpensive low-density Lidar sensors. First, each vehicle is automatically detected using hierarchical clustering and then its trajectory is tracked using a virtual point method that compensates for the low angu...
Article
This paper develops a novel algorithm for tracking closely-spaced road vehicles using a low-density flash lidar. Low-density flash lidars are recent to the automotive market and have attracted attention due to their low cost. However, these sensors have a poor angular resolution which makes tracking the lateral motion of targets challenging. One su...
Article
This paper focuses on step length estimation using inertial measurement sensors. Accurate step length estimation has a number of useful health applications, including its use in characterizing the postural instability of Parkinson’s disease patients. Three different sensor configurations are studied using sensors on the shank and/or thigh of a huma...
Article
This paper focuses on position estimation in smart actuators using non-contacting magnetic sensors. Magnetic position estimation in long-stroke actuators involves nonlinear non-monotonic measurement equations and the need to use more than one magnetic sensor. These challenges are addressed by developing a methodology for computing optimal sensor pl...
Preprint
This paper focuses on step length estimation using inertial measurement units. Accurate step length estimation has a number of useful health applications, including its use in characterizing the postural instability of Parkinson’s disease patients. Three different sensor configurations are studied using sensors on the shank and/or thigh of a human...
Article
This paper focuses on the removal of periodic artifacts from neural signals recorded in rats in ultra-high field (UHF) MRI scanners, using a reference free adaptive feedforward method. Recording extracellular neural signals in the UHF environment is motivated by the desire to combine neural recording and UHF functional magnetic resonance imaging (f...
Article
Bicycling is a healthy physical activity for all ages. It can provide both physical and mental health benefits, including reducing the risk of cancer [1], cutting the risk of heart disease by half [2], postponing Alzheimer’s disease [3, 4], and promoting mental alertness and memory [5].
Article
This paper addresses the problem of state estimation and simultaneous learning of the vehicles tire model on autonomous vehicles. The problem is motivated by the fact that lateral distance measurements are typically available on modern vehicles while tire models are difficult to identify and also vary with time. Tire forces are modeled in the estim...
Article
Traditional electrodes used for neural recording and stimulation generate large regions of signal void (no functional MRI signal) when used in ultrahigh field (UHF) MRI scanners. This is a significant disadvantage when simultaneous neural recording/stimulation and fMRI signal acquisition is desired, for example in understanding the functional mecha...
Article
This paper focuses on state-of-charge (SoC) estimation for a lithium-ion battery modeled using a recently developed nonlinear double-capacitor representation that has been shown to be highly accurate. The measurement equation of the model has two nonlinear functions, one of them being significant hysteresis in voltage as a function of the SoC. The...
Article
This paper deals with new finite-time estimation algorithms for Linear Parameter Varying (LPV) discrete-time systems and their application to output feedback stabilization. Two exact finite-time estimation schemes are proposed. The first scheme provides a direct and explicit estimation algorithm based on the use of delayed outputs, while the second...
Article
This article examines the problem of Lithium-Sulfur (Li-S) battery state estimation. Such estimation is important for the online management of this energy-dense chemistry. The literature uses equivalent circuit models (ECMs) for Li-S state estimation. This article’s main goal is to perform estimation using a physics-based model instead. This approa...
Article
This study uses a low-density solid-state flash lidar for estimating the trajectories of road vehicles in vehicle collision avoidance applications. Low-density flash lidars are inexpensive compared to the commonly used radars and pointcloud lidars, and have attracted the attention of vehicle manufacturers recently. However, tracking road vehicles u...
Article
This paper focuses on the dynamics of the COVID-19 pandemic and estimation of associated real-time variables characterizing disease spread. A nonlinear dynamic model is developed which enhances the traditional SEIR epidemic model to include additional variables of hospitalizations, ICU admissions, and deaths. A 6-month data set containing Minnesota...
Preprint
This article examines the problem of Lithium-Sulfur (Li-S) battery state estimation. Such estimation is important for the online management of this energy-dense chemistry. The literature uses equivalent circuit models (ECMs) for Li-S state estimation. This article's main goal is to perform estimation using a physics-based model instead. This approa...
Article
PURPOSE: Dupuytren disease (DD) has been associated with enlarged Pacinian corpuscles (PCs) and with PCs having a greater number of lamellae. Based on these associations, we hypothesized that subjects with DD would have altered sensitivity to high-frequency vibrations and that the changes would be more prominent at 250 Hz, where healthy subjects de...
Article
Objective: Removal of common mode noise and artifacts from extracellularly measured action potentials, herein referred to as spikes, recorded with multi-electrode arrays (MEAs) which included severe noise and artifacts generated by an ultrahigh field (UHF) 16.4 Tesla magnetic resonance imaging (MRI) scanner. Approach: An adaptive virtual referen...
Article
Full-text available
This paper focuses on state‐of‐charge (SOC) estimation in a lithium‐ion battery, using measurements of terminal voltage and bulk force. A nonlinear observer designed using Lyapunov analysis relying on lower and upper bounds of the Jacobian of the nonlinear output function is utilized. Rigorous analysis shows that the proposed observer has feasible...
Article
This paper focuses on the development of a thin normal-shear force sensor based on the use of a supercapacitive sensing mechanism. The sensor has a quad structure with four sensing units in which the bottom substrate has four pairs of electrodes while the top deformable portion has a solid-state electrolyte. The application of normal and shear forc...
Article
This paper focuses on the detection of cyber-attacks on a wireless communication channel and simultaneous radar sensor health monitoring for a connected vehicle. A semi-autonomous adaptive cruise control (SA-ACC) vehicle is considered which has wireless communication with its immediately preceding vehicle in the same lane. The wireless connectivity...
Article
This paper focuses on the development of a system to detect if any car poses a collision danger to a bicycle, and to sound a loud horn to alert the car driver if a collision danger is detected. A sensing and estimation system suitable for use on a bicycle is therefore developed in order to track the trajectories of vehicles in a traffic intersectio...
Article
This paper develops a novel instrumented urethral catheter with an array of force sensors for measuring the distributed pressure in a human urethra. The catheter and integrated portions of the force sensors are fabricated by the use of 3D printing using a combination of both soft and hard polymer substrates. Other portions of the force sensors cons...
Article
Estimating central aortic blood pressure is important for cardiovascular health and risk prediction purposes. Cardiovascular system is a multi-channel dynamical system that yields multiple blood pressures at various body sites in response to central aortic blood pressure. This paper concerns the development and analysis of an observer-based approac...
Patent
A pressure sensing catheter system includes a urethral catheter and a sensor array formed on the urethral catheter. The sensor array includes a plurality of pressure sensors distributed along a length of the urethral catheter. The sensor array is configured to produce a dynamic pressure distribution profile along a urethra.
Article
This paper focuses on the challenges in observer design for nonlinear systems which are non-monotonic. A class of nonlinear systems is considered in which the process dynamics and output equations are both composed of nonlinear vector functions of scalar combinations of the states. The nonlinear functions are assumed to be differentiable with bound...
Article
Alignment for maintaining Line-of-Sight (LoS) between the receiver and the transmitter in a LED optical communication system is a challenging problem due to the constant movement of the underlying optical platform that is caused by vibration effects and atmospheric turbulence. In this paper, we propose a robust switched-gain nonlinear observer to e...
Conference Paper
The focus of this paper is on the development of a vehicle-tracking algorithm using a solid-state LIDAR sensor for application to Collision Avoidance Systems (CAS) for Heavy Commercial Road Vehicles. Solid State LIDARs are relatively inexpensive compared to RADARs and point cloud LIDARs, and hence could accelerate commercialization of Advanced Driv...
Article
This paper develops an electromagnet-based position measurement system for industrial actuators which offers significant advantages compared to traditional position measurement systems. These advantages include low cost, non-contacting operation, easy installation and robustness to magnetic disturbances. In the first embodiment of the sensor, the e...
Article
This paper addresses the problem of observer-based stabilization of discrete-time linear systems in presence of parameter uncertainties and ℓ2-bounded disturbances. We propose a new variant of the classical two-step LMI approach. In the first step, we use a slack variable technique to solve the optimization problem resulting from stabilization by a...
Article
This article develops a fundamental new sensing principle for measuring the position of a moving object. The moving object is equipped with a thin film of high magnetic permeability. A stationary electromagnet and a magnetic sensor are located nearby. As the moving object’s position changes, the coupling between the electromagnet and the magnetic s...
Article
This paper uses an inexpensive laser sensor mounted on a rotationally controlled platform to simultaneously search for and track vehicles that are behind a bicycle. Vehicles in the bicycle's lane and in the adjacent left lane are both considered. The tasks involved are searching both lanes to detect presence of vehicles, tracking a vehicle's trajec...
Article
This paper develops a robust gain-scheduled proportional–integral–derivative (PID) controller design method for a linear-parameter-varying (LPV) system with parametric uncertainty. It is recognized in the literature that the robust fixed-order controller design can be formulated as a feasibility problem of a bilinear matrix inequality (BMI) constra...
Article
This paper discusses a novel algorithm to automatically identify the position of a smartphone inside a moving vehicle, so as to detect whether it is being used by the driver or just a passenger of the car. This detection has applications to the prevention of distracted driving and can be used to automatically disable phone features such as texting...
Article
This paper deals with nonlinear observer design for a class of nonlinear systems with nonlinear output measurements. The proposed methodology is based on the use of Linear Matrix Inequalities (LMIs) to handle a problem of convergence criterion. Some new assumptions and convenient Young’s formulation are used to get less conservative LMI conditions...
Article
This letter develops a novel strain sensor with ultra-high sensitivity and range that can be easily fabricated using a paper-based electrolyte and two metal pins bought from a local hardware store. No cleanroom facilities are needed. The sensor utilizes a fundamentally new sensing principle consisting of a paper-based solid-state electrolyte which...
Article
This paper focuses on the development and use of a nonlinear observer for tracking of vehicle motion trajectories while using a radar or laser sensor. Previous results on vehicle tracking have typically used an interacting multiple model filter that needs different models for different modes of vehicle motion. This paper uses a single nonlinear veh...
Article
This paper develops a new high-gain observer design method for nonlinear systems that has a lower gain compared to the standard high-gain observer. This new observer, called HG/LMI observer is obtained by combining the standard high gain methodology with the LMI-based observer design technique. Through analytical developments, the paper shows how t...
Article
Full-text available
Abstract Paper has been pursued as an interesting substrate material for sensors in applications such as microfluidics, bio-sensing of analytes and printed microelectronics. It offers advantages of being inexpensive, lightweight, environmentally friendly and easy to use. However, currently available paper-based mechanical sensors suffer from inadeq...
Conference Paper
Urinary incontinence can be due to neuromuscular or structural problems in either the bladder or the urethra. Urodynamics is often used to analyze the patient-specific cause of urinary incontinence. In urodynamics, a challenging part of the studies involves measurement of the urethral (contact) pressure profile. Here we present an instrumented uret...
Conference Paper
The exact localization of signal recording probes or deep stimulation probes by magnetic resonance imaging (MRI) has significant importance in studying and understanding how the brain functions. But the magnetic susceptibility of the probes itself distorts the MRI image and creates error in position measurement. In this paper we propose an MRI comp...
Article
Estimating attitude using an inexpensive MEMS inertial measurement unit has many applications in smart phones, wearable sensors, rehabilitation medicine and robots. Traditional approaches to attitude estimation from the aerospace world focus on the use of either Euler angles or quaternions. These approaches suffer from disadvantages including singu...
Article
An observer for a nonlinear system may be required to satisfy multiple performance criteria such as minimum convergence rate and disturbance rejection, in addition to asymptotic stability. In such cases, the observer can no longer be designed using a linear matrix inequality. A bilinear matrix inequality (BMI) is needed instead and involves a non-s...
Article
Full-text available
Fluid accumulation in the lower extremities is an early indicator of disease deterioration in cardiac failure, chronic venous insufficiency and lymphedema. At-home wearable monitoring and early detection of fluid accumulation can potentially lead to prompt medical intervention and avoidance of hospitalization. Current methods of fluid accumulation...
Article
A two-step numerical computation of T2∗ signal weighting maps in gradient echo magnetic resonance imaging in the presence of an object with varied susceptibility property is presented. In the first step, the magnetic scalar potential is computed for an arbitrary 2D magnetic susceptibility distribution using an algebraic solver. The corresponding ma...
Article
The proximity of a magnetic sensor to a magnet has been utilized for position measurement in many applications involving small ranges of motion. However, such position measurement becomes challenging when the application involves a ferromagnetic environment and larger ranges of motion. The movement of a magnet magnetizes and demagnetizes the ferrom...
Conference Paper
Electrical stimulation of neural tissue is a promising therapy for a variety of neurological diseases. For example, electrical stimulation of deep thalamic nuclei has been used extensively to treat symptoms of Parkinson’s disease, and there is growing interest in treating other conditions including epilepsy and depression with similar techniques. H...
Conference Paper
Urinary incontinence (UI), defined by the International Continence Society as “the complaint of any involuntary leakage of urine” [1], is believed to affect at least 13 million people in the United States. Around 80% of people affected are women [2,3]. The most common type of UI in women is stress urinary incontinence (SUI) [4]. Although not identi...
Article
This paper presents an observer design technique for a newly developed non-intrusive position estimation system based on magnetic sensors. Typically, the magnetic field of an object as a function of position needs to be represented by a highly nonlinear measurement equation. Previous results on observer design for nonlinear systems have mostly assu...
Article
This paper focuses on the development of an active sensing system for a bicycle to accurately detect and track rear vehicles. A collision detection sensor on a bicycle is required to be inexpensive, small, and lightweight. A single beam laser sensor that meets these constraints is mounted on a rotationally controlled platform for this sensing missi...
Article
A new LMI design technique is developed to address the problem of circle criterion-based ℋ∞ observer design for nonlinear systems. The developed technique applies to both locally Lipschitz as well as monotonic nonlinear systems, and allows for nonlinear functions in both the process dynamics and output equations. The LMI design condition obtained i...
Article
Traditional capacitive sensors suffer from significant parasitic noise when used in liquid environments or inside the human body. The parasitic noise overwhelms the force response of the sensor and makes it impossible to calculate the absolute force experienced by the sensor. This article focuses on the development of a supercapacitor based force s...
Article
Objective: Previous animal studies have demonstrated that carbon nanotube (CNT) electrodes provide several advantages of preferential cell growth and better signal-to-noise ratio when interfacing with brain neural tissue. This work explores another advantage of CNT electrodes, namely their MRI compatibility. MRI-compatible neural electrodes that d...
Conference Paper
This paper aims at developing a robust gain-scheduled proportional-integral-derivative (PID) control design method for a linear-parameter-varying (LPV) system. It is recognized in the literature that robust fixed-order controller design can be formulated as a feasibility problem of a bilinear matrix inequality (BMI) constraint. Unfortunately, the s...
Article
Capacitive micro-sensors such as accelerometers, gyroscopes and pressure sensors are increasingly used in the modern electronic world. However, the in vivo use of capacitive sensing for measurement of pressure or other variables inside a human body suffers from significant errors due to stray capacitance. This paper proposes a solution consisting o...
Article
This paper aims at developing a robust observer–based estimated state feedback control design method for an uncertain dynamical system that can be represented as a linear time-invariant system connected with an integral quadratic constraint–type nonlinear uncertainty. Traditionally, in existing design methodologies, a convex semidefinite constraint...
Article
This paper examines the performance of bounded Jacobian and Lipschitz observer design techniques for nonlinear estimation applications. The bounded Jacobian observer technique utilizes the mean value theorem to express the nonlinear estimation error dynamics as a convex combination of known matrices with time varying coefficients. The Lipschitz bas...
Article
This paper examines the performance of bounded Jacobian and Lipschitz observer design techniques for nonlinear estimation applications. The bounded Jacobian observer technique utilizes the mean value theorem to express the nonlinear estimation error dynamics as a convex combination of known matrices with time varying coefficients. The Lipschitz bas...
Article
The presence of two eyes, ears, and nostrils endows mammals with many benefits that go beyond just having a second (spare) sensory organ. The spatial separation between two similar sensory organs enables enhanced sensory perception. For instance, in the case of the eyes, it is well known that the presence of two spatially separated eyes enables ste...
Article
Most geometric control design methods for nonlinear systems assume that all state variables are available for feedback in real time. Unfortunately, the entire state is usually too expensive or impossible to measure, and some form of estimation is necessary. Unlike linear timeinvariant systems where the state estimation problem is analogous to the c...