SENSORS, 2002 IEEE

The basic principles of a new surface acoustic wave (SAW) gas sensor are described. Being essentially a sensor of the mass-sensitive type, the proposed device possesses certain features of the thermometric SAW sensors and is not only sensitive to the vapors of volatile substances, but capable of detecting gases by their thermal properties as well. This principles consists of making a certain delay of heat fluxes between the substrate of sensitive SAW element (SAW delay line or SAW resonator) and working surface of the sensor's temperature stabilization system. In contrast to the known thermometric SAW sensors, the proposed sensor is characterized by high temperature stability and fast response. A variant of the sensor based on a LiNbO/sub 3/ is described and some results on detecting propane-butane mixtures are presented, glass spacers being a means providing heat flux delay between LiNbO/sub 3/ substrate and working surface of the sensor's temperature stabilization system.

A gas sensor based on off-null ellipsometric readout is presented. It includes miniaturization of a null ellipsometer facilitating multisensing. and small optical components are used. Some experimental results on low concentration alcoholic gases (methanol, ethanol and 2-propanol) with porous silicon and chemically modified porous silicon as sensing layers are shown. Currently, the lower detection limit for these gases is about 1 ppm. Optimization of the sensor system and improvement of sensitivity or alteration of selectivity by modification of the sensing layer is also discussed.

Posture and gesture analysis and body kinematics monitoring is a field of increasing interest in bioengineering and several connected disciplines. We propose wearable systems able to read and record posture and movements of a subject wearing them. We used strain gage sensors, deposited directly onto textile fibers realizing, in contrast with different strategies, truly wearable and unintrusive systems.

This paper presents the design concept, fabrication and calibration of a six-degree of freedom (6-DOF) turbulent flow micro sensor utilizing the piezoresistive effects in silicon. The proposed sensor can independently detect six components of force and moment on a test particle in a turbulent flow. By combining p-type conventional and shear piezoresistors in Si [111], and arranging them suitably on the sensing area, the total number of piezoresistors used in this sensing chip is only eighteen, much fewer than that of the prior art piezoresistive 6-DOF force sensors. Calibration for six components of force versus output voltages was completed. The sensitivities are linear close to the design values, and high enough to measure the forces and moments expected to act on the particles in turbulent flow in geophysics.

This paper presents an application of networked sensors that offers a reusable design pattern for a class of sensor-based appliances. It deals with an integrated, sensor networking framework stemming from the IEEE 1451 smart transducer interface standard, an object-based networking model, complemented by the Virtual Interface Architecture (VIA), a Compaq-Intel-Microsoft approach to Internet messaging, and by the Internet Protocol (IP) multicast communication, mediating efficient and unified access from Internet to smart sensors. The kernel of the paper focuses on utilization of this framework for a computer-based pressure measurement systems development environment as a real-world project while stressing smart pressure sensor and Internet connectivity architectures.

Presents a theoretical description, fabrication and experimental investigation of miniature optical fiber pressure sensor for invasive measurement of blood pressure. Sensor measures only 125 /spl mu/m in diameter. The essential element is thin polymer diaphragm that is positioned inside a hollow end of the optical fiber. The cavity at the fiber end is made by wet etching in diluted HF acid. Thus the Fabry-Perot interferometer is formed between the inner fiber-cavity interface and the diaphragm. Deflection of the diaphragm and so pressure magnitude is determined by reading the reflectance spectrum of the sensing Fabry-Perot interferometer using broadband illumination. The configuration of Fabry-Perot interferometer at the optical fiber end makes sensor immune from bending of optical fiber and optical power fluctuations of light source. We deployed sensor prototype from 125 /spl mu/m-diameter optical fiber. It is optimized for human blood pressure range, namely from 0 to 40 kPa (0 to 300 mmHg) with 1 mmHg resolution. Our fabrication technique offers simple and low-cost disposable medical pressure sensor production.

We discuss the realization of tactile sensor based on the principle of change in piezoelectric resonance frequency with applied pressure. An array of electrodes has been adopted on either side of the PZT material to achieve independent resonators. The common areas sandwiched between the electrodes and excitable at the resonance frequency of the PZT material are used to form the sensitive area of the tactile sensor. The electrodes were deposited using a sputtering technique. Tactile sensors with 3/spl times/3, 7/spl times/7 and 15/spl times/15 array of electrodes are developed with different electrode dimensions and separation between the electrodes. The tactile sensor has been interfaced to a computer for the convenience of automatic scanning and making it more user interactive. The tactile sensors developed with different spatial resolution were tested for different shaped objects placed in contact with the sensor. The 3/spl times/3 matrix tactile sensor showed relatively poor spatial resolution whereas 15/spl times/15-matrix tactile sensor showed improved spatial resolution. The sensor with 7/spl times/7 matrix elements was tested for its sensitivity to different extents of applied force/pressure. The output response study carried out on the sensors indicated that these sensors can provide information not only about the extent of force/pressure applied on the object, but also the contour of the object which is in contact with the sensor.

The vacuum packaged differential resonant accelerometer (DRXL) using gap sensitive electrostatic change effect is proposed by using the reverse surface micromachining (RSM) process based on the single crystal silicon. The differential frequency output is achieved by subtracting the resonant frequency between the two independent resonators, which has advantages with the wide input range and the good linearity. But the resonant accelerometer is fabricated using the epi-polysilicon surface micromachining process in the previous work. The residual and shear stress of the polysilicon result in the mismatch of the mechanical resonant frequency. The mismatch of the resonant frequency may demolish the advantages of the differential scheme because of the mechanical resonance characteristics. So, the single-crystal silicon was chosen for the accelerometer structure material because it has better mechanical properties than the polysilicon. The fabricated resonant accelerometer shows the nominal frequency of 6928 Hz and the sensitivity is about 10Hz in the /spl plusmn/10 G range. The bandwidth is more than 100 Hz.

Users of tele-operated assistive robots, much like their counter-parts in other applications, have indicated concern about the lack of tactile feedback. While remarkable developments have been made in eliciting viable neuronal control of a robotic arm, the sensation of touch is needed in order to close the sensorimotor loop and enhance control of movement. We have developed a novel assistive robotic system that provides tactile feedback from a robotic gripper via a haptic interface to the user's tongue. In this paper we focus on the sensors suitable for inclusion in such a system. We explore the requirements for tactile sensors used in assistive robotics. A prototype sensor system with force (both normal and shear) and shape sensing capabilities is presented. This system is being used to evaluate the utility of various tactile sensing capabilities (e.g. normal vs. shear force, force distributions) in assistive robot applications.

As the safety in the food supply becomes critical, the demand for rapid, low volume, sensitive, and economic biosensing devices has dramatically increased. An immunosensor based on electrochemical sandwich immunoassay using polyaniline has been developed for detecting foodborne pathogens, such as Escherichia coli 0157:H7. The immunosensor design is based primarily upon the specific nature of labeled antibody-antigen binding. The architecture of the biosensor demonstrates the advantages of using lateral flow formal strip attached to a portable circuitry for signal measurement. The ability to change the specificity of the antibodies enables the biosensor to be used as a semi-quantitative detection device for other types of foodborne pathogens. Results show that the biosensor could detect as low as 10/sup 1/ bacterial cells per milliliter in less than 10 minutes. Additionally, the biosensor yields faster results, and is cheaper than conventional approaches. Details on the device fabrication and performance of the biosensor in detecting E. coli 0157:H7 are presented.