205 research outputs found
Rail-to-Rail Timer-Based Demodulator for AM Sensor Signals
© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper proposes a novel timer-based demodulator for low-frequency amplitude-modulated (AM) sensor signals with a rail-to-rail operating range. The demodulator extracts the amplitude of the AM signal by measuring the period of a reference signal that is altered by the AM signal itself, as already suggested in a previous paper. The rail-to-rail operation, which is the main contribution of the novel circuit, is achieved by simply but cleverly incorporating a multiplexer that enables the comparison between the two signals (reference and AM) just at the beginning and at the end of the period measurement. This new topology offers an operating range that is up to more than four times wider than that reported in the literature. The input-output characteristic in such a wider operating range is not linear, but it can be accurately modeled by a second-degree polynomial.Peer ReviewedPostprint (author's final draft
Demodulating AM square signals via a digital timer for sensor applications
This paper evaluates theoretically and
experimentally the performance of a timer-based demodulator
applied to low-frequency amplitude-modulated (AM) square
signals coming from sensor circuits. The demodulator extracts
the amplitude of the AM square signal by measuring the period
of a reference triangular signal that is altered by the AM signal
itself, as already suggested in a previous paper but for AM
sinusoidal signals.Postprint (published version
Wearable impedance plethysmography and electrocardiography sensor
Wearable technology has become increasingly popular in the last few years. This project describes the design and implementation of a wearable impedance plethysmography and electrocardiography sensor. This sensor is developed to be compact and lightweight while having a very extended battery life. This way, it can be easily integrated into other wearable devices or into clothing or shoes. The acquired IPG and ECG data will be transmitted in real-time to a receiving host for further storage and processing by using the Bluetooth Low Energy protocol. By using a so widespread low energy wireless protocol, the data can be received into any compatible device, such as smartphones, laptops or even specialized systems. An android application showing a real-time graphic of the measured signals is also developed for demonstration purposes. To meet the low power consumption requirements of the analog front-end circuitry, multiple techniques were used, such as using low power versions of components such as operational amplifiers and even taking advantage of their limitations to improve circuit performance characteristics. Other techniques such as sensing the correct placement of electrodes or disabling parts of the circuitry when not needed or the signal is not available were also used. A current consumption for the analog frontend in the order of only 100 µA to 200 µA at 3V was achieved while continuously providing both IPG and ECG data. For the digital circuitry, consisting mainly of the nRF51822 System on Chip from Nordic Semiconductor and some peripherals, multiple techniques of power consumption minimization were also used. A current consumption of around 200 µA to 300 µA was achieved, again at 3V, during continuous data processing and transmission. A prototype was implemented on a PCB. Unfortunately, full functionality was not achieved mainly due to some hardware failures and time constraints, however, as multiple innovative solutions were implemented, this work will provide useful information to improve other research projects in this area.Objectius de Desenvolupament Sostenible::3 - Salut i Benesta
Digital control for automating feed distribution in feedlots
An investigation was conducted to determine the feasibility of automatic controls to automate feed distribution in feedlots. The control approach was restricted to compatibility with conventional feeding equipment. Input control signals were taken to originate from commonly available mechanical and electronic sensors. The control system was implemented with standard digital logic components;The proposed digital control system is based on a railguided, self-propelled automatic vehicle capable of delivering feed sequentially to 255 pens located on both sides of a single feeding path. A manual, closed-loop control system consisting of the following functions was developed: (1) pen identification, (2) initialization control, (3) feeding mode, (4) exit from feeding mode, (5) re-entry into feeding mode, (6) end of feeding cycle, (7) ground drive and conveyor control, (8) interface and auto/manual mode, (9) monitoring of automated system and (10) data and failure display and alarm. The control system allows either automatic or manual operation of the feeding vehicle. Digital electronic circuits capable of implementing the desired control functions were designed;The feeding cycle is manually initiated and automatically terminated when feed has been delivered to all pens requiring feed. It can be partially programmed to enable feed delivery to sections of the feedlot. Two feed rations can be delivered. The feeding status of each pen is recorded. The pen feed rations are stored in reprogrammable memories;The operation of the automated feeding system is based on the automatic identification of the feedlot pens. The number assigned to a pen is coded, using binary pulse-code modulation. Frequency-shift keying is used to transmit the coded number. The received coded number is recovered by specialized communication circuits and then validated;The control system monitors the vehicle components and the major electronic circuits to detect failures, prevent damage and produce a safe operation. Furthermore, it incorporates safety sensors and logic circuitry to meet the basic safety requirements pertaining to automated vehicles;The proposed automated feed distribution system for feedlots is expected to: (1) reduce management requirements through automatic distribution of feed to cattle raised in pens, (2) increase efficiency of feeding operation by eliminating time losses associated with secondary feed transfer, (3) eliminate damage to feedbunks through positive guidance of the vehicle by rails, and (4) save energy by eliminating secondary feed transfer
Analog Single Sideband-Pulse Width Modulation Processor for Parametric Acoustic Arrays
Parametric acoustic arrays are ultrasonic-based loudspeakers that produce highly directive audio. The audio must first be preprocessed and modulated into an ultrasonic carrier before being emitted into the air, where it will self-demodulate in the far field. The resulting audio wave is proportional to the double time-derivative of the square of the modulation envelope. This thesis presents a fully analog processor which encodes the audio into two Pulse Width Modulated (PWM) signals in quadrature phase and sums them together to produce a Single Sideband (SSB) spectrum around the fundamental frequency of the PWM signals. The two signals are modulated between 8% and 24% duty cycle to maintain a quasi-linear relationship between the duty cycle and the output signal level. This also allows the signals to sum without overlapping each other, maintaining a two-level output. The system drives a network of narrowband transducers with a center frequency equal to the PWM fundamental. Because the transducers are voltage driven, they have a bandpass frequency response which behaves as a first-order integrator on the SSB signal, eliminating the need for two integrators in the processor. Results show that the “SSB-PWM” output wave has a consistent 20-30dB difference in magnitude between the upper sideband and lower sideband. In simulation, a single tone test shows higher total harmonic distortion for lower frequencies and higher modulation depth. A two-tone test creates a 2nd order intermodulation term that increases with the frequencies of the input signals
A long-range and long-life telemetry data-acquisition system for heart rate and multiple body temperatures from free-ranging animals
The system includes an implantable transmitter, external receiver-retransmitter collar, and a microprocessor-controlled demodulator. The size of the implant is suitable for animals with body weights of a few kilograms or more; further size reduction of the implant is possible. The ECG is sensed by electrodes designed for internal telemetry and to reduce movement artifacts. The R-wave characteristics are then specifically selected to trigger a short radio frequency pulse. Temperatures are sensed at desired locations by thermistors and then, based on a heartbeat counter, transmitted intermittently via pulse interval modulation. This modulation scheme includes first and last calibration intervals for a reference by ratios with the temperature intervals to achieve good accuracy even over long periods. Pulse duration and pulse sequencing are used to discriminate between heart rate and temperature pulses as well as RF interference
Electrical-Impedance biofeedback instrument for swallowing rehabilitation
Dysphagia is the difficulty or abnormality of swallowing. It is usually a consequence of another health condition and may be present in any of the phases of swallowing. The cause may be structural or neurological. The effects of dysphagia range in severity; milder symptoms range from discomfort to difficulty swallowing. More severe effects include expelling food or liquid out through the mouth and nose or aspiration of material into the lungs, resulting in heavy bouts of coughing and increasing the risk of developing pneumonia.
Treatment for dysphagia, if applicable, therefore depends on the type and cause of dysphagia. Evaluation charts, barium swallow, pharyngeal manometry, and endoscopy are some of the available tools in the diagnosis and classification of dysphagia.
Patients diagnosed with neurogenic dysphagia may undergo motor-training exercises for swallowing rehabilitation. However, literature suggests that motor-training exercises are more effective when the patient is presented with some form of interpretable feedback of their motor activity – known as biofeedback. Patients themselves have expressed the view that biofeedback gives something to aim for. To this end various techniques for biofeedback have been formally reviewed, including surface electromyography, acoustic, endoscopy and ultrasound amongst others.
Pharyngeal manometry is an invasive procedure which measures pressure along specific sections of an endoscopic-style probe and provides measurements that identify pharyngeal muscle activity sequencing. These measurements have been used as biofeedback information in rehabilitative treatment. However, such techniques are typically performed in a clinical setting and only administered by suitably trained staff.
Bio-impedance has been researched and demonstrated in other literature to be a suitable tool for assessing swallowing function, comparisons have been made to manometry with mixed results.
Previous Masters students in the University of Canterbury have investigated the suitability of a bio- impedance sensing device to perform as an easy-to-use, non-invasive alternative to intrusive pharyngeal sequence measuring devices. Though impedance measurement changes were obtained from a human subject, the research concluded that the number of measuring channels must be expanded. The device concept was named GULPS (Guided Utility for Latency in Pharyngeal Swallowing).
This project aims to expand the number of channels of the GULPS prototype whilst retaining the sensitivity and signal gain of the original.
The previous implementations of GULPS took a multi-frequency approach as a means to create channels with 40 kHz and 70 kHz as the selected nominal current injection frequencies. This approach makes adding further channels very challenging as each channel is in effect a complete impedance measurement device, each with their own signal injection circuit, amplifiers, filters and detectors. Each signal injection circuit must have its power supply isolated from the rest posing further design considerations.
Channel multiplexing was determined to be the most efficient method by which to add additional channels to the bio-impedance module. This presents its own set of challenges, specifically the amplitude detector board must settle on a steady output considerably faster than the channel multiplexing rate, to allow sufficient time for multiple samples of the channel value to be taken for averaging.
A tetrapolar electrode measuring scheme was selected as this approach has proven successful in previous implementations of GULPS, as well as other bio-impedance projects. The number of channels was expanded to sixteen and comparable sensitivity was demonstrated on simulated loads of 120 Ω subjected to a 10% drop in nominal impedance. A test chamber was constructed with channel electrodes spaced vertically along a column filled with saline solution to simulate conditions comparable to that of a human neck. A narrow conductive cylinder attached to an insulating rod was lowered and raised through the path of the current injection and voltage measurement electrodes. This resulted in sufficiently large voltage swings in the corresponding channel with minimal cross- talk or interference to other channels.
Though the settling time for the new detector was measured to be sufficiently fast for the desired sampling rate of 1000 Hz per channel, the sampling rate had to be lowered to 700 Hz in the final implementation of the GULPS hardware. The cumulative effect of series-connected resistances meant filtering capacitors had to be lowered to almost parasitic values to try to maintain the required time constants, until the delays could be reduced no further. The per-channel bandwidth is limited to 10 Hz after additional filtering at the output stage.
The prototype is initiated and configured via USB by an application developed in Visual Studio. The application allows for frequency selection for the constant current source from 70 kHz to 2 MHz so that the most suitable injection frequency could be determined experimentally.
Due to time constraints the prototype was not tested on a test subject nor comparisons made to manometry readings. Testing with a simulated load designed to mimic human tissue demonstrated sufficient signal gain and low inter-channel interference, suggesting the device would be suitable to go to human trials
Informe mensual d'articles publicats. Campus Baix Llobregat. Base de dades Scopus. Gener 2019
Informe bibliomètric mensual Campus Baix Llobregat. Base de dades Scopus. Gener 2019Postprint (published version
An energy-efficient wireless data link for implantable electronics
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 101-103).Low-power wireless links are important for the development of long-term implantable neural prostheses. Furthermore, in implanted systems with many neural recording electrodes, the data rate of the wireless link will need to be quite high since each recording electrode can produce about 120 kbps of data. For low-power operation, inductively-coupled near-field wireless links have shown great promise and were used to develop a power-efficient data link for biomedical implants. A prototype bi-directional, half-duplex wireless link based on inductive coupling was designed in a 0.18 [mu]m process. The uplink (i.e. data transmission from the internal transceiver) was designed to use an impedance modulation strategy. Since this technique only requires a single local oscillator (LO) in the external transceiver, the energy expenditure of the implanted transceiver is minimized. Simulated uplink data transfer rates of up to 10 Mbps has been shown. A PWM based ASK coding strategy was used for the downlink (i.e. data transmission to the implanted device). The downlink is able to achieve a data transfer rate of up to 1.5 Mbps. A technique to reduce BER of inductive coupling links due to pulse-width distortion effects by pre-distorting the transmitted data is also presented. A calibration technique to reduce the resonant frequency mismatch between the two magnetically coupled resonators is also shown.by Daniel Prashanth Kumar.S.M
Measuring moisture content of biofilter media using capacitance
A biofilter operates by passing contaminated air through a moist medium like woodchips, saw dust, soil or artificial material. Maintaining moisture content within this medium is critical for biofilter operation. To date, most biofilters use a timer system and sprinklers to apply water to the medium which may lead to under-watering or over-watering. The moisture content of the filter medium in small and in research biofilters has been controlled gravimetrically using load cells. However, for full scale application of biofilters, this technique would be overly expensive and impractical. Some research is being undertaken to develop capacitor plates to monitor moisture levels within the biofilter medium. This technique shows promise and needs further development. This project will reviews the literature on biofilters and biofilter control methods, and also on capacitance-based and other possible moisture measurement techniques. Based on this research, designs are developed for the measurement of the moisture content of the selected biofilter media such as wood chips and soil. It is concluded that the completion of this project has demonstrated the advantages of using the capacitive sensor as the basis for the design and proved the feasibility of the capacitive sensing system in determining the moisture content of the biofilter media
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