C. S. Anoop

Electronic Scheme for Computing Inverse-Cosine and its Application to a GMR Based Angle Sensor

This paper presents a new, simple but effective, electronic method to obtain inverse-cosine of an electrical variable. The proposed method is very useful for linearization of sensors whose output is a cosine or sine function of the physical quantity being sensed. The inverse-cosine of the variable is obtained by comparing it with a reference sinusoidal wave. The proposed method is easy to implement using electronic components. Using the new technique, a giant magneto-resistance-based angle sensor that provides an output linearly proportional to the angle being sensed has been developed, and the details are reported in this paper. A prototype of the angle sensor has been built, and the practicality of the new method has been tested successfully. The developed sensor provides a linear output for a range of 0° to 180°. The worst case error was found to be less than 0.35° for a range of 10°-170°.

A health monitoring system using multiple non-contact ECG sensors for automotive drivers

Health and alert-level monitoring of automotive driver is very important to reduce the number of vehicle accidents and associated fatalities. The proposed work focuses on the development of a reliable and low-cost health monitoring system for automotive drivers. It is based on non-contact electrocardiogram (ECG) principle. Multiple signal acquisition ECG electrodes are placed on the seat and seat-belt of the automotive. The signals from the different electrodes are interfaced to simple analog and digital signal processing units through a switching logic. The frequency domain-based digital processing and the switching logic ensures that best quality ECG signal is selected for heart rate (HR) estimation. A prototype of the proposed system is build and tested on several volunteers. These tests show that the accuracy is 2 bpm. Additional tests to determine the system performance in various conditions was conducted and results reported.

A real-time heart-rate monitor using non-contact electrocardiogram for automotive drivers

A large number of vehicle accidents and its associated human fatalities occur throughout the world due to drowsiness or health-related issues of the driver. Such mis-happenings can be reduced by integrating a driver-health monitor into the automotive. Different techniques such as camera-based image processing, photoplethysmograph, electroencephalograph, etc. have been employed to develop driver-state monitors. They use either multiple electrodes or require direct optical contact with the human body or need complex signal conditioning algorithms. In this paper, we develop a basic framework in the direction of developing a simple real-time heart-rate (HR) monitoring system using non-contact capacitive electrocardiograph (ECG). The system uses of an electrode structure which can be integrated within a steering wheel and simple, low-cost signal processing blocks. The system efficiency is verified through extensive testing on a number of volunteers in multiple scenarios and multiple electrode configurations with respect to the steering wheel. These tests show that the proposed system gives good quality ECG signals and estimates HR with good accuracy. The capability of the system as a reliable drowsiness monitor is also tested and encouraging results are obtained.

Non-invasive heart rate monitoring system using giant magneto resistance sensor

A simple heart rate (HR) monitoring system designed and developed using the Giant Magneto-Resistance (GMR) sensor is presented in this paper. The GMR sensor is placed on the wrist of the human and it provides the magneto-plethysmographic signal. This signal is processed by the simple analog and digital instrumentation stages to render the heart rate indication. A prototype of the system has been built and test results on 26 volunteers have been reported. The error in HR estimation of the system is merely 1 beat per minute. The performance of the system when layer of cloth is present between the sensor and the human body is investigated. The capability of the system as a HR variability estimator has also been established through experimentation. The proposed technique can be used as an efficient alternative to conventional HR monitors and is well suited for remote and continuous monitoring of HR.

A reluctance-Hall Effect based linear digital angle sensor

A new angle sensor based on a combination of a reluctance technique and Hall-Effect principle is presented in this paper. The proposed sensor provides a linear, digital output proportional to the angle being sensed. The sensor consists of two identical ring shaped sheets, in parallel, and a permanent magnet, placed between the rings. This unit rotates in unison with the target. Two fixed Hall-Effect sensor ICs, which are 180° apart, are kept in the air gap between the rings. An analysis shows that the flux density seen by these fixed Hall-Effect ICs vary as a third order polynomial function of the angle being sensed. A new signal conditioning method that provides a linear digital output from the proposed sensor is presented. A prototype angle sensor and signal conditioning unit have been built and tested. Output of the prototype unit was linear across 0 - 110° and worst-case error was less than 1.2%. The proposed sensor is suitable for automotive and industrial applications, especially where center of the target is not easily accessible to employ the conventional magnetic sensors directly.

A linear Tunneling Magneto-Resistance angle transducer

A new Tunneling Magneto-Resistance (TMR) based angle transducer realized with a novel Signal Conditioning (SC) scheme that accepts TMR angle sensing elements possessing sine/cosine output characteristics and provides a final output that changes linearly with the angle being sensed over a full-circle range (0-360°) is presented in this paper. The proposed scheme converts the angle being sensed by the TMR sensing elements into an equivalent phase shift of a sinusoid, whose amplitude is dictated by the flux produced by the permanent magnet employed in the transducer. The phase of the sinusoid is then converted as an output voltage that is dependent only on the phase angle and not on the magnetic strength. Thus even over a long period, over which the strength of the permanent magnet may decay, the accuracy of angle sensing is preserved. A prototype angle sensor, using a TMR IC, and proposed SC circuit has been built and tested. The output of the transducer was found to be linear across the entire 0-360°. The worst-case error observed for the transducer was less than ± 0.85 % of the full-scale while that for the SC unit alone was less than ± 0.1 %.

Study and analysis of two GMR-based eddy-current probes for defect-detection

This paper presents the study and detailed analysis of two different eddy-current probe configurations based on giant-magnetoresistance (GMR) sensors for characterization of defects in metallic plates. The probes have an excitation coil that induces eddy-currents in metallic test-plate and a suitably-aligned GMR sensor as main components. When the probe is near a defect, the eddy-current loops get disturbed, leading to a change in magnetic field distribution seen by the GMR sensor. Latters output-signal is processed to obtain the defect characteristics. The working-principles of the probes are initially derived using basic principles and later validated using finite element analysis. It is shown that output of the probes can directly reveal important features of a rectangular-type defect. A compensation method is developed next to minimize sensor-coil misplacement errors. Prototype hardware probe-models was developed and tested. Test results show fair degree of agreement with simulation studies. Finally, a basic study is presented to estimate the nature and dimensions of some typical defects.

Feasibility study of a giant Magneto-Resistance based respiration rate monitor

This paper reports a simple and reliable electronic technique for the estimation of respiration rate (RR). Giant Magneto-Resistance (GMR) based sensors are employed to extract a plethysmograph signal from the subject. This signal is filtered and processed further through simple signal processing stages to obtain RR indication. The feasibility of the system has been studied on a prototype built and associated experimentation on 20 volunteers. The developed system provided clean plethysmographic signals, whose relevant features are shown to possess a relation with RR. Test results shows that the worst-case error in RR estimation of the system is merely 2 breaths per minute. Further, the capability of the system for detecting breathing cessations is studied and results reported. The system can be extended to function as a heart-rate (HR) monitor. Some basic results which proves the working and accuracy of system as a HR estimator is also given in the paper. The proposed system can be used for effective estimation of the above two vital signs in clinics, automotives, wearable devices, etc.

A simple direct-digitizer for Giant magneto-resistance based sensors

A Direct Digitizer suitable for Giant magneto-resistive (GMR) sensors is proposed in this paper. The proffered digitizer integrates a GMR sensor, in the form of a full-bridge, with a novel circuit based on enhanced dual-slope technique and obtains a linear digital indication of the magnetic field being measured. The scheme does not use a separate ADC for digitization. A detailed mathematical methodology of the scheme has been reported to validate the linear transfer relation of the proposed scheme. Simulation study of the proposed circuit has been performed and the results show that output-non linearity is as small as 0.004 %. Further, the performance is validated by experimentation with emulated and actual GMR sensor bridges and results are reported. Output is found to be linear with-respect-to the magnetic field and the worst-case error is within acceptable limits. The proposed scheme can be employed as a superior alternative to conventional (instrumentation amplifier) based interface circuits for GMR sensors.

A non-contact capacitance based electrocardiograph and associated heart-rate detection using enhanced Fourier interpolation method.

Cardio-vascular health monitoring has gained considerable attention in the recent years. Principle of non-contact capacitive electrocardiograph (ECG) and its applicability as a valuable, low-cost, easy-to-use scheme for cardio-vascular health monitoring has been demonstrated in some recent research papers. In this paper, we develop a complete non-contact ECG system using a suitable front-end electronic circuit and a heart-rate (HR) measurement unit using enhanced Fourier interpolation technique. The front-end electronic circuit is realized using low-cost, readily available components and the proposed HR measurement unit is designed to achieve fairly accurate results. The entire system has been extensively tested to verify its efficacy and test results show that the developed system can estimate HR with an accuracy of ±2 beats. Detailed tests have been conducted to validate the performance of the system for different cloth thicknesses of the subject. Some basic tests which illustrate the application of the proposed system for heart-rate variability estimation has been conducted and results reported. The developed system can be used as a portable, reliable, long-term cardiac health monitoring device and can be extended to human drowsiness detection.