Low-cost Sensor System Research Articles

Posture estimation and human support using wearable sensors and walking-aid robot

In this paper, an omni-directional walking-aid robot is developed to assist the elderly in the daily living movements. A motion control strategy of walking-aid robot based on the observation of the human status through wearable sensors is proposed. During normal walking, the robot is controlled using a conventional admittance control scheme. When the tendency of a fall is detected, the robot will immediately react to prevent the user from falling down. The distance between the human Center of Pressure (COP) and the midpoint of the human feet is assumed to be a significant feature to detecting the fall events. When the user is in a quasi-static state or walking slowly, the COP can be approximated by the projection of Center of Gravity (COG) of the user’s body. A simple and low-cost wearable sensor system is proposed to measure online the COG of the user. A limitation of the proposed wearable sensor system is that the Head–Arms–Torso (HAT) of the user is assumed to be always in upright position, which may generate measurement error. From comparison experiments with a reference optical system it is found that the measurement error is acceptable especially at the early stage of fall event. Dubois possibility theory is applied to describe the membership function of “normal walking” state. A threshold based fall detection approach is obtained from online evaluation of the walking status. Finally, experiments demonstrate the validity of the proposed strategy.

Low cost packaging for gas sensors

MEMS technologies have enabled the development of various sensors including gas sensors in a miniaturized and cost effective way. Sensor systems are being developed using these sensor chips where chip packaging is still a major cost due to special requirements. This paper focuses on the packaging needs of a MEMS based gas sensor. These gas sensors have various applications in safety systems for fire and harmful gases detectors for automobiles, home, offices, factories, environment, etc. A low cost packaging solution for MEMS based gas sensors is elaborated which is suitable for the trace level detection of various lethal gases like H2S, PH3, CO, CO2, NH3 etc. To enable the vast and multiple applications of these gas sensors it is important to provide a low cost sensor system which is low power and can be operated on battery. Standard semiconductor device packages like TO headers are costly and not suitable for low cost devices. Proposed packaging scheme uses printed circuit board (PCB) as substrate material (FR4) where reliable low resistance (1---2 ohm) interconnects are provided by conducting epoxy. PCB based packages add very little extra power (3---5 mW) to the power required for micro-heater that heats gas sensor film up to 300 °C. Packaged gas sensors were tested for their reliability in two different conditions i.e. 1 h ON reliability test and repetitive ON/OFF (100 times) test. These packages have additional advantages of being more mechanically stable than wire bonded packages and easy processing in comparison to Transistor Outline (TO) headers. Infrared imaging of the packaged device in forced condition shows the stability of the package.

A Compact Low Cost Wearable Sensor System for Quantitative Gait Measurement

The demand for quantitative gait analysis increases due to increasing number of neurological disorder patients. Conventional gait analysis tools such as 3D motion capture systemsare relatively expensive. Therefore, there is a need to develop a low cost sensor system to obtain the spatial temporal gait parameters without compromising too much on the accuracy. This paper describesthe development of a wearable low cost sensor system which consists ofrelatively less sensing elements with 2 accelerometers, 4 force sensitive resistors (FSR) and 2 EMG electrodes. Thesensor output was validated by a vision system and the relative error was less than 5% formost of the gait parameters measured.

MEMS/GPS Integrated Navigation System Based on EKF

MEMS (Micro-electromechanical Systems) sensors have many advantages including fast response, low cost, small size and low power consumption. However, MEMS sensors suffer low accuracy and poor stability due to the limitations of the manufacturing process. the MEMS/GPS integrated navigation system based on EKF make up for these shortcomings. The system using a low-cost MEMS sensor system consists of tri-axis gyroscopes and accelerometers which also incorporates a tri-axis magnetometer, and it can provide a complete measurement of orientation relative to the direction of gravity and the earths magnetic field.Extended kalman filter is used to fuse informations from MEMS and GPSof UAV. Mathematical models of GPS and MEMS sensor system are constructed based on matlab/simulink. The experimental results indicate that the average attitude angle error obtained is less than 0.15° in simulation experiments while position error is less than 7m and the velocity error is less than 0.4m.

128 Development of a low cost sensor system for determination of glass transition temperatures during cooling and warming

Ice nucleation and glass transition (Tg) temperatures influence cell viability during cryopreservation. Knowledge of these phase changes for cryoprotectant mixtures is an essential step in optimising cryopreservation protocols for cell survival. Differential scanning calorimetry (DSC) is the conventional device used to determine Tg, but the expensive nature of such instrumentation limits its widespread use. A cost-effective sensor system has been designed to monitor ice nucleation and Tg events in cryoprotectant solutions. Glycerol was used a test solution and Tg values were measured (with and without NaCl supplement) in cryotubes and cryostraws, using RTD temperature and screen-printed impedance sensors. The effect of changes to ice-nucleation temperature on Tg was also investigated using ice nucleators. Cooling rates of (a) 5 °C min −1 , (b) 0.1 °C min −1 and (c) direct plunge into liquid nitrogen were set using a Grant Asymptote (EF600) controlled rate freezer. Protocols (a) and (b) were run from 0 °C to −90 °C followed by rapid plunge into liquid nitrogen. The warming event of the three protocols was monitored during slow warming of the samples in air at room temperature. The Tg values during warming events compared favourably with the values obtained by DSC reported in the literature. The reported DSC derived Tg values (Morris et al., 2006) for 10% glycerol +0.15 M NaCl (−55 °C) are close to the values obtained in the current work (−52 to −57 °C). The availability of low cost sensor systems to monitor changes in impedance allows the determination of Tg of cryopreservation media during both cooling and warming cycles, and should enable such measurements to become routine in laboratories. Source of funding: University of Bedfordshire Research Development funds. Conflict of interest: None declared. jahanbeen.jahangir@beds.ac.uk

A fast response intrinsic humidity sensor based on an etched singlemode polymer fiber Bragg grating

A simple, low cost and fast response time intrinsic relative humidity sensor system based on an etched singlemode polymer fiber Bragg (POFBG) is presented in this paper. A macro-bend linear edge filter which converts the humidity induced wavelength shift into an intensity change is used as the interrogation technique. The singlemode POFBG is etched to micro-meters in diameter to improve the response time of the humidity sensor. A response time of 4.5s is observed for a polymer FBG with a cladding diameter of 25μm. The overall sensor system sensitivity was 0.23mV/%RH. The etched POFBG humidity sensor shows anexponential decrease in response time with a decrease in fiber diameter. The developed sensor might have potential applications in a wide range of applications where fast and accurate real time humidity control is required.

Simultaneous Single Detector Measurement of Multiple Fluorescent Sources

In many applications it is desirable to simultaneously measure the concentration of multiple fluorescent sources. In this paper, a simple robust technique for accomplishing this is realized by illuminating the fluorescent elements by excitation light modulated at different frequencies. A single microprocessor is used to drive the excitation sources (different color LEDs), and analyze the detector response at the two different frequencies. The excitation light at both colors is filtered by a single set of cross-polarized filters, and the signal from the single detector is locked-in to the different excitation light frequencies to simultaneously measure the response of different dyes. As proof-of-concept, this approach is demonstrated on two distinct systems. First, mixtures of concentrations of the fluorescent dyes trisodium 8-methoxypyrene-1, 3,6-trisulfonate and Rhodamine 6G in water are simultaneously measured in a standard fluorescence measurement. Then, the system is used for simultaneous detection of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in a mixture of gases using two different gas-sensitive fluorescent films. The detection of oxygen is based on the fluorescence quenching of platinum octaethylporphine lumiphore in the presence of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The detection of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is based on fluorescence quenching of hydroxypyrene trisulfonic acid trisodium salt in presence of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The whole arrangement is a compact and low-cost simultaneous multicolor fluorescent sensor system that is suitable for many biological, chemical, and gas-monitoring applications.

Sewer inspection and comparison of acoustic and CCTV methods

In the UK, the majority of sewer pipe inspections are carried out using closed-circuit television (CCTV) technology. This inspection technology is expensive; given the size of the UK sewer network, this means that only a small sample of network is inspected regularly. Up-to-date condition information on individual sewers is required to minimise sewer network operation failures and, ultimately, to eliminate flooding. There is therefore a need for a quicker and cheaper inspection method. This paper reports on a novel low-cost acoustic sensor system that can be used for the rapid detection of various defects in sewer pipes. It is shown that a large number of pipe defects can be classified and validated against CCTV images by way of visual examination of the acoustical data presented in the form of spectrograms. An overview of the technological principles used by the acoustic inspection method is presented in this paper together with the results of field trial surveys. The new method was tested in operational sewers in Austria and the acoustic inspection results compared with available CCTV reports: 79% of the defects identified by CCTV were also detected using the acoustic technique.

Determining Maximum Push-off Velocity in Swimming Using Accelerometers

The ability to unobtrusively measure velocity in the aquatic environment is a fundamental challenge for engineers and sport scientists. In the past video systems were the first choice to monitor the athletes during training. With the acceptance of small inertial sensors new ways of investigating the athletes movements have arisen. These small systems are light, easy to use and do not hinder the athlete during training, allowing an easy tracking of training improvements. This research used a self developed low-cost inertial sensor system, attached to the lower back, to record the acceleration of swimmers performing sub-surface wall push-offs. The recorded data were downloaded to MATLAB for data analysis. Using seven swimmers, the wall push-off velocity at three different efforts was analysed and compared to a tethered cable velocity meter (criterion measure) using Regression and Bland-Altman analysis. The maximum velocity determined from the accelerometer unit was linearly related to the benchmark criteria (r2=0.89). A biomechanical technique for the determination of the maximum glide velocity from acceleration data has been verified.

VIBRATIONS OF A GYROCOPTER – AN ANALYSIS USING IMUS

Abstract. As a part of a research project on the development of a low-cost sensor system for use on gyrocopters several investigations on the recording of aerial image blocks have been carried out during the last two years. The vibration of the gyrocopter platform is one of the critical factors that should be mitigated during the data collection. Apart from the wind-induced oscillation, the vibration induced by the motor, the propeller and the main rotor are prominent. To prevent negative impact to the imaging process, vibration absorbers are to be implemented on the sensor platform. One focus of this research is a comparison between the vibrations within the passenger area and the vibrations at the undercarriage of the gyrocopter. The comparison is based on the use of three synchronized micro-electro mechanical motion trackers (MEMS IMUs), one fixed on the gyrocopter floor and the others fixed on the struts of the gyrocopter. The results indicate that the propeller and rotorinduced vibrations are somewhat bigger within the passenger area. Fourier analysis shows that the rotor-induced vibration at a frequency of 12 Hz is predominant in all signals; its amplitude may vary strongly in time. Whereas the translational vibrations have negligible impact on the image quality, rotational vibrations around all three axes may effect significant blurring of aerial images according to common quality standards.

Portable RF-Sensor System for the Monitoring of Air Pollution and Water Contamination

Monitoring air pollution including the contents of VOC, O3, NO2, and dusts has attracted a lot of interest in addition to the monitoring of water contamination because it affects directly to the quality of living conditions. Most of the current air pollution monitoring stations use the expensive and bulky instruments and are only installed in the very limited area. To bring the information of the air and water quality to the public in real time, it is important to construct portable monitoring systems and distribute them close to our everyday living places. In this work, we have constructed a low-cost portable RF sensor system by using 400 MHz transceiver to achieve this goal. Accuracy of the measurement was comparable to the ones used in the expensive and bulky commercial air pollution forecast systems.

Simple Low-Cost System for Thickness Measurement of Metallic Plates Using Laser Mouse Navigation Sensor

A simple low-cost sensor system for thickness measurement of metallic plates by means of a high-resolution laser mouse navigation sensor and a lightweight displacement probe is presented in this paper. An experimental prototype was developed, which involves release of the probe freely on the plain surface of metallic plates under test. A signal is generated from the laser mouse during the release of the probe. The first minima of the signals are related to the thickness of the metallic plates.

2 DOF resolution adjustment laser position sensor

A low cost sensor system is envisaged that has 2 distinct routes for resolution enhancement in position detection. The main area for application of the sensor design would be in the food processing and packaging industry where position resolution of the end effector is in the millimetre to sub-millimetre range. The sensor concept consists of a grid of laser light detectors attached to the stationary base and a grid of lasers attached to the mobile end effector. The photo detectors on the base provide one level for position detection enhancement, that is, the density of the sensor array. The second degree of freedom in improvement comes from the strategic positioning of a set of lasers attached to the end effector.

Low-Cost QCM Sensor System for Screening Semen Samples

Artificial insemination is a well-established part of modern agricultural practice. A viable semen sample is judged by the total number of spermatozoa (sperm) in the sample and the motility of the sperm. In this paper, we report the development of a reusable measurement cell and electronics for screening semen samples based on the Quartz Crystal Microbalance (QCM) and Universal Frequency to Digital Converter (UFDC-1) to produce a low-cost sensor system. After introducing the semen sample at one end of the measurement cell, sperm swim down a channel before causing a frequency change on the QCM. Data is presented that shows the different frequency changes using a commercial frequency counter caused by porcine semen samples, one two days old and one twenty one days old. Similar data is presented for a motile semen sample measurement using the low-cost UFDC-1.

Highly sensitive digital optical sensor based on cascaded high-Q ring-resonators

A digital optical sensor based on two cascaded rings with different free spectral ranges (FSRs) is proposed. Because of their different FSRs, the major peak of the spectral response from the output port shifts digitally when the effective refractive index of ring #1 changes. And the shift of the major peak is equal to multiple FSRs of ring #2. Since it is easy to design a ring with a FSR of nanometers, the present digital optical sensor shows an ultra-high sensitivity (at the order of 10(5) nm/RIU) which is over two orders higher than that of a regular single-ring sensor. By using the present digital optical sensor, it becomes convenient to use an integrated optical micro-spectrometer (even with a low resolution) to monitor the peak shift of the spectral response. Therefore, it is promising to realize a low-cost and portable highly-sensitive optical sensor system on a single chip.

Development of an Automated Wireless Tension Force Estimation System for Cable-stayed Bridges

Cable-supported bridges rely on the use of steel cables to support the bridge deck and load on it. Cable tension forces are monitored during construction to assist the alignment of cables and to ensure no cables are overloaded. Given that the cables are critical load carrying elements, it is prudent to routinely monitor the levels of cable tensions during operation. With current measurement methods being costly and labor-intensive, this article proposes an automated and low-cost wireless sensor system for continuous monitoring of the cable tension based on the vibration signature of the cable. A vibration-based tension force estimation method using a peak picking algorithm is explored by embedding it in the computational core of a wireless sensor. Welch’s method to average Fourier spectra from the segments of a long time history signal is employed to remove the non-stationarity of a short-duration acceleration record, which is a limit of the memory-constrained wireless sensor. A series of laboratory tests are conducted on a slender braided steel cable with a variety of cable sags and tension forces. Excellent agreements have been found between the actual tensions and those estimated by the present wireless system.

A Low-Cost Wireless Sensor System and Its Application in Dental Retainers

In this paper, a wireless interrogable sensor device based on an ultra low-power microcontroller for data collection and a radio frequency identification (RFID) interface for data transmission is presented. Wireless sensor systems utilizing RFID transponders offer a new and exciting means of measurement and identification suitable for many biomedical applications. For the majority of these applications, small, inexpensive radio request sensor systems are desirable. In this paper, an ultra-low-power and low-cost wireless temperature data logger system is presented with its application in observing dental retainer use. For this purpose, the retainer's ambient temperature is measured by an integrated sensor and recorded using a microcontroller which acts like a temperature data logger storing the thermal history of several months. For a self powered wireless data transmission from the sensor to the interrogation unit a RFID transponder, operating in the 13.56 MHz ISM band, is used. The presented sensor system includes hard- and software power saving modes reducing the sensor idle current consumption to 1 muA. This allows a battery powered operation of the device for up to two years. For dental and biomedical applications, the device is hermetically sealed using a biocompatible polymeric encapsulation. Results of the first clinical trials observing the patient's dental retainer usage by a set of retainers equipped with the RFID temperature sensor/data logger device are presented. The stored temperature values are analyzed and a clear temperature characteristic indicating the retainer usage was found.

Development of a sensor system for traffic data collection

AbstractAlthough many types of traffic sensors are currently in use, all have some drawbacks, and widespread deployment of such sensor systems has been difficult due to high costs. Due to these deficiencies, there is a need to design and evaluate a low cost sensor system that measures both vehicle speed and counts. Fulfilling this need is the primary objective of this research. Compared to the many existing infrared‐based concepts that have been developed for traffic data collection, the proposed method uses a transmission‐based type of optical sensor rather than a reflection‐based type. Vehicles passing between sensors block transmission of the infrared signal, thus indicating the presence of a vehicle. Vehicle speeds are then determined using the known distance between multiple pairs of sensors. A prototype of the sensor system, which uses laser diode and photo detector pairs with the laser directly projected onto the photo detector, was first developed and tested in the laboratory. Subsequently this experimental prototype was implemented for field testing. The traffic flow data collected were compared to manually collected vehicle speed and traffic counts and a statistical analysis was done to evaluate the accuracy of the sensor system. The analysis found no significant difference between the data generated by the sensor system and the data collected manually at a 95% confidence interval. However, the testing scenarios were limited and so further analysis is necessary to determine the applicability in more congested urban areas. The proposed sensor system, with its simple technology and low cost, will be suitable for saturated deployment to form a densely distributed sensor network and can provide unique support for efficient traffic incident management. Additionally, because it may be quickly installed in the field without the need of elaborate fixtures, it may be deployed for use in temporary traffic management applications such as traffic management in road work zones or during special events.

Response of Local Evanescent Array-Coupled Biosensors to Organic Nanofilms

A label-free planar optical waveguide immunosensor that operates on the novel principle of local evanescent field shift is demonstrated in this paper. Increased local refractive index at the waveguide's upper surface due to the formation of an organic adlayer shifts the evanescent field distribution up, and hence, changes the light intensity both above and below the waveguide structure. Beam propagation simulations show increased modulation ratio sensitivity to adlayer thickness with increasing detection distance below the waveguide. The local nature of detection allows sensors to be implemented in array formats on a single waveguide for multiple-analyte sensing. Both near-field scanning optical microscopy and integrated buried detector arrays are employed to study the response to patterned organic nanofilms including immunocomplexes, photoresist, and adsorbed bovine serum albumin (BSA) layers. Buried polysilicon detector arrays integrated with silicon nitride waveguides in a commercial CMOS process exhibit a 15% photocurrent modulation ratio response to an approximately 1-nm-thick adsorbed film of BSA. CMOS compatibility enables a low-cost sensor system on a chip. Temperature dependence measurements show that sensor has a 0.3%/degC change in modulation ratio, which is thousands of times less than traditional resonant biosensors.

A Near Field Focused Microstrip Array for a Radiometric Temperature Sensor

A low-cost radiometric temperature sensor system is described, with emphasis on the use of a 12.5 GHz near-field focused microstrip array to provide a low-profile compact product suitable for commercial and industrial applications. An overview of the temperature sensor system is given, followed by design details of the focused microstrip array, including near-field patterns and antenna efficiency measurements. Temperature measurements made with the radiometric system in a food-processing plant field test show that the antenna can resolve individual hamburger patties at a practical measurement distance