Microelectronic capacitance transducer for particle detection

This paper describes the CMOS circuit design of a sensor for detecting changes of capacitance due, for instance, to the incidence of particles or bubbles on the electrodes. The circuit is based on a simple design originating at the University of California, Berkeley, for measuring crosstalk on integrated circuits. The basic front-end sensor circuit comprises eight MOSFETs and has a sensitivity of 40 mV/fF. A differential amplifier receives the outputs from two sensor circuits each having 20-/spl mu/m square inter-digitated electrodes. The resulting sensitivity of the fabricated sensor is 1 V/fF with a noise level equivalent to 10 aF. Monte Carlo circuit simulations have been used to identify transistor dimensions to yield acceptable yield, and prototype custom silicon chips have been fabricated using a 0.8-/spl mu/m CMOS process. Static and dynamic tests, using polyamide particles as small as 10-/spl mu/m diameter, verify correct operation of the sensors. The sensor is now being developed for application in miniature electrical tomography systems.     

Multiplexing of optical fiber gas sensors with a frequency-modulated continuous-wave technique

We report on the use of a frequency-modulated continuous-wave technique for multiplexing optical fiber gas sensors. The sensor network is of a ladder topology and is interrogated by a tunable laser. The system performance in terms of detection sensitivity and cross talk between sensors was investigated and found to be limited by coherent mixing between signals from different channels. The system performance can be improved significantly by use of appropriate wavelength modulation-scanning coupled with low-pass filtering. Computer simulation shows that an array of 37 acetylene sensors with a detection accuracy of 2000 parts in 10(6) for each sensor may be realized. A two-sensor acetylene detection system was experimentally demonstrated that had a detection sensitivity of 165 parts in 10(6) for 2.5-cm gas cells (or a minimum detectable absorbance of 2.1 x 10(-4)) and a cross talk of -25 dB.     

Quantum cascade laser sensor for SO2 and SO3 for application to combustor exhaust streams

We have demonstrated a high-sensitivity, room-temperature quantum-cascade (QC) laser sensor for detection of SO2 and SO3 under conditions relevant to aircraft test combustor exhaust. Two QC lasers probe infrared absorption features at 7.50 and 7.16 microm for SO2 and SO3, respectively, with a common dual-beam detection system. We inferred a noise-equivalent absorbance of approximately 1 x 10(-4) Hz(-1/2). We have demonstrated detection limits for both SO2 and SO3 of 1-2 ppmv m/Hz(1/2) (where ppmv is parts in 10(6) by volume) for 300 torr, elevated temperature, and path lengths near 1 m. This level of sensitivity permits measurement of < 1 ppmv of SO2 and SO3 at these conditions with modest signal averaging.     

Electric field sensing with a hybrid polymer/glass fiber

We demonstrate the operation of an in-fiber electric field sensor. The sensor is fabricated with selective chemical etching of the core of a D-shaped optical fiber followed by the deposition of an electro-optic polymer (PMMA/DR1), which forms a hybrid core. The device demonstrates electromagnetic field sensitivity less than 100 V/m at a frequency of 2.9 GHz. Epi is estimated to be 60 MV/m with an insertion loss of 14.4 dB.     

Fluidic sensor based on the side-opened and suspended dual-core fiber

For accelerating the response and enhancing the sensitivity simultaneously, a novel fluidic sensor based on a side-opened and suspended dual-core fiber and dual-beam interference detection mechanism is first explored and analyzed here. The side opening ensures a fast response by allowing fluidic analyte to approach the fiber core laterally. The dual-beam Mach-Zehnder interferemetry provides a relative higher sensitivity. Calculation results show that a sensitivity of 2.1×10(-6) refractive index unit (RIU) within a response time of 10 s could be achievable, which reflects its potential impact on constructing a fluid refractometer for fast-response and high-sensitivity detection. Moreover, the relationship of the sensing sensitivity and the detected dynamic range of this suspended dual-core fiber structure, polarization, and the transmitting waveband are also analyzed.     

Resolution limits of laser spectroscopic absorption measurements with hollow glass waveguides

In this paper, resolution limits of laser spectroscopy absorption measurements with hollow capillary fibers are investigated. Furthermore, a concept of sensitive near-infrared sensing utilizing hollow fiber directly coupled with vertical-cavity surface-emitting lasers is developed. By performing wavelength modulation spectroscopy, the smallest absorbance that can be detected by the fiber sensor was determined to be 10(-4), limited by a random modulation of the fiber transmission function (modal noise). By mechanically vibrating the fiber, a sensor resolution of 10(-5) in absorbance is achieved. Because the random modulation on the fiber transmission function limits the detection sensitivity, its physical reasons are analyzed. One contribution is found to be the partial integration of the far field, and the amplitude of the spectral features is inversely proportional to the square root of the integrated speckle points number. Therefore, careful design of the fiber-detector outcoupling is necessary. It turned out that incoupling alignment is not of much influence with respect to the spectral background. The residual spectral background is caused by mode-dependent effects and can be lowered by vibrating the fiber mechanically.     

Polymer MEMS-based Fabry-Perot shear stress sensor

This paper reports a novel optical fiber-based micro-shear stress sensor utilizing a flexible membrane and double SU-8 resist structures as a moving micro-mirror, together with an optical fiber as a micro-Fabry-Perot interferometer. This sensor can be employed in air or liquid environments with high sensitivity because of its waterproof design. Through UV lithography processes on thick SU-8 resist, the roughness of the reflection surface has approached 7 nm (Ra value), suitable for optical applications. A single-mode optical fiber is employed for detecting the displacement of the floating element induced by shear stress. Tests have been carried out successfully and a detection possibility of 10 nm-displacement of the floating element and a displacement sensitivity of 0.128 nm/nm (spectrum shift/floating element displacement) has been demonstrated. The temperature coefficient of this fiber-optic sensor has been characterized to be 3.4 nm/K linearly from 25 to 48/spl deg/C. Fluid tests have also been performed by placing the sensor inside the inner wall of a precisely machined rectangular channel and the result shows a sensitivity of 0.4 nm/ml/min (spectrum shift/flow rate), corresponding to a shear stress resolution of 0.65 Pa/nm (shear stress/spectrum shift). The minimum detectable shear stress is thereby estimated as 0.065 Pa from the reading resolution of the spectrometer of 0.1 nm, comparable to its counterparts with resolutions from 0.1-1 Pa.     

Study of a fiber optic humidity sensor based on agarose gel

An optical fiber humidity sensor was fabricated using a hydrophilic gel (agarose) deposited on the tapered plastic optical fiber (POF). The sensing element, agarose, can absorb and exude moisture from/to the ambience, thereby altering its refractive index and changing its ability to modulate the intensity of light that propagates through the fiber. Thus, the operating principle of the sensor is based on the intensity modulation technique, which utilizes a tapered POF probe coated with agarose that is sensitive to humidity. The POF, which was fabricated using an etching method, has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 80%, the output voltage of the sensor with agarose gel of 0.5% weight content decreases linearly from 2.24 mV to 1.55 mV. The agarose-based sensor produces a sensitivity of 0.0228 mV/%, with a slope linearity of more than 98.36%. The tapered fiber with agarose gel of 1% weight content produces a sensitivity of 0.0103 mV/% with a slope linearity of more than 94.95% and a limit of detection of 2.635%, while the tapered fiber with agarose gel of 1.5% weight content produces a sensitivity of 0.0079 mV/% with a slope linearity of more than 98.53% and a limit of detection of 6.853%. The fiber with agarose gel of 0.5% weight content shows higher sensitivity compared to that of 1% and 1.5% due to the effect of pore size, which changes with concentration. The results demonstrate that agarose-based optical fiber sensors are both sensitive and efficient for economical and flexible measurements of humidity.     

Strain-independent temperature measurement by use of a fluorescence intensity ratio technique in optical fiber

The strain sensitivity of the fluorescence intensity ratio temperature-sensing technique has been measured to be (2 +/- 3) x 10(-4)%/muepsilon in Yb3+-doped fiber, implying a temperature-to-strain cross sensitivity of (2 +/- 3) x 10(-4) degrees C/muepsilon. The near-zero strain sensitivity means that this optical-fiber sensor technique is well suited for temperature measurement in strain-affected environments.     

Optical deflection measurement for characterization of microelectromechanical systems (MEMS)

Nonintrusive measurement of small out-of-plane motions of microscale structures is critical to the development of microelectromechanical systems (MEMS). This paper presents a low-cost deflection measurement system for MEMS structures based on a fiber optic displacement sensor. The system is demonstrated in the characterization of a microwave switch. The deflection system had a demonstrated sensitivity of 290/spl plusmn/32 /spl mu/V/nm over a deflection range of 100 /spl mu/m. The calibration and linearity of the system are described, and the static and dynamic performance is compared to more elaborate systems.     

Fabrication and calibration of oxazine-based optic fiber sensor for detection of ammonia in water

This paper presented the fabrication and calibration of a clad-modified evanescent based plastic optical fiber (POF) sensor for the detection of ammonia in both stagnant and dynamic aqueous media. This optochemical sensor was based on Oxazine 170 perchlorate (sensing material) and polydimethylsiloxane (PDMS) (protective material) thin layers. A special chemical solution was developed for the etching removal of cladding and a methodology for trapping moisture was exercised. Experimental results on dissolved ammonia detection exhibited short response time (≤10 s), low detection limit (minimum detection limit 1.4 ppm), high sensitivity, and excellent reversibility (over 99%).     

Highly Sensitive Fiber-Optic Faraday-Effect Magnetic Field Sensor Based on Yttrium Iron Garnet

1. IntroductionFaraday-effect sensors have been developed during the past 15 years to measure electric current andmagnetic fi.ldllL31. In these sensors) much attentionhas been given to enhance their sensitivity. Available optical materials providing a Faraday effect largeenough to be seriously considered for sensitive measuremellts of small magnetic field can be classified intwo groups. In one group are the paramagnetic anddiamagnetic doped glasses. In the other class are therare earth iron …     

Optical response of a d-fiber antenna in a finite-element analysis intended for radio-over-fiber applications

An all-fiber antenna with a piezoelectric polymer-coated circular-core D fiber has been characterized by finite-element analysis. The response of the D-fiber antenna was determined over a wide frequency range from 1 to 500 MHz. The modeling predicts an electric-field-induced phase shift of 2.43 x 10(-5) rad/(V/m)/m at 5 MHz. At frequencies higher than 8 MHz the optical response is dominated by radial resonances of the D-fiber-coating composite. From the simulation results a minimum detectable electric field of 41-muV/m has been achieved with a 1-km length of coated D fiber. In addition, a D-fiber antenna network intended for microcellular communications has been analyzed by shot-noise-limited detection.     

A Novel Vector Hydrophone Based on the Piezoresistive Effect of Resonant Tunneling Diode

This letter reports a novel vector hydrophone based on the piezoresistive effect of resonant tunneling diode (RTD). An external pressure introduces stress in the layers of RTD and induces its current-voltage (I-V) curves change. This effect has been applied to designing new sensor. By control-hole technology, the sensor is processed integrated with GaAs/In_xGa_1-xAs/AlAs double barrier structures posited on its strain-sensitive region. The fabricated sensor is packaged for watertight solution, and underwater measurements are conducted in RTD's negative differential resistance (NDR) region. Directivity curve of the sensor follows ";8"; cosine functional form, which shows its vector sound signal detection ability, and its sensitivity reaches -184.6 dB (0 dB = 1 V/muPa) at 1 KHz.     

Ammonia detection by use of quartz-enhanced photoacoustic spectroscopy with a near-IR telecommunication diode laser

A gas sensor based on quartz-enhanced photoacoustic detection and a fiber-coupled telecommunication distributed-feedback diode laser was designed and characterized for trace NH3 monitoring at a 1.53-microm wavelength (overtone absorption region). Signal and noise dependence on gas pressure were studied to optimize sensor performance. The ammonia concentration resulting in a noise-equivalent signal was found to be 0.65 parts per million by volume with 38-mW optical excitation power and a lock-in amplifier time constant of 1 s. This corresponds to a normalized absorption sensitivity of 7.2 x 10(-9) cm(-1) W/Hz1/2, comparable with detection sensitivity achieved in conventional photoacoustic spectroscopy. The sensor architecture can be the basis for a portable gas analyzer.     

Development and analysis of a PCB vector 2-D magnetic field sensor system for electronic compasses

A high-sensitivity vector two-dimensional (2-D) magnetic sensor system for low magnetic field measurements has been realized and tested. The system, made in PCB technology, consists of a double-axis Fluxgate magnetic sensor and the readout electronic circuitry, based on second-harmonic detection. The amorphous magnetic materials Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick) were used as the ferromagnetic core of the sensor. By applying a sinusoidal excitation current having a 450-mA peak at 10 kHz with Vitrovac 6025Z, the measured magnetic sensitivity was about 1.25 mV//spl mu/T. This value seems to be adequate for the Earth's magnetic field detection (/spl plusmn/60 /spl mu/T). The full-scale linearity error was about 1.5%. By using the thicker Vitrovac 6025X and a sinusoidal excitation current having a 600-mA peak at 10 kHz, a maximum sensitivity of approximately 1.68 mV//spl mu/T with a linearity error of about 1.55% full scale in the range of /spl plusmn/60 /spl mu/T were measured. Due to the use of commercially available ferromagnetic materials, the vector 2-D magnetic sensor system presented is characterized by a very simple fabrication process, thus allowing low-cost devices to be designed.     

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 16. Sensing by fluorescence

A fluorescence spectroelectrochemical sensor capable of detecting very low concentrations of metal complexes is described. The sensor is based on a novel spectroelectrochemical sensor that incorporates multiple internal reflection spectroscopy at an optically transparent electrode (OTE) coated with a selective film to enhance detection limits by preconcentrating the analyte at the OTE surface. Nafion was used as the selective cation exchange film for detecting Ru(bpy)(3)(2+), the model analyte, which fluoresces at 605 nm when excited with a 441.6-nm HeCd laser. The unoptimized linear dynamic range of the sensor for Ru(bpy)(3)(2+) is between 1 x 10(-)(11) and 1 x 10(-)(7) M with a calculated 2 x 10(-)(13) M detection limit. The sensor employs extremely thin films ( approximately 12 nm) without significantly sacrificing its sensitivity. The sensor response is demonstrated with varying film thicknesses. A state-of-the-art flow cell design allows variable cell volumes as low as approximately 4 microL. Fluorescence of the sample can be controlled by electromodulation between 0.7 and 1.3 V. Sensor operation is not reversible for the chosen model film (Nafion) and sample (Ru(bpy)(3)(2+)) but it can be regenerated with ethanol for multiple uses.     

Fiber-optic cavity sensing of hydrogen diffusion

A novel type of fiber-optic cavity sensor for hydrogen diffusion into and out of fibers is presented. The sensor is an implementation of a cavity ringdown scheme in a silica-based single-mode fiber that has been exposed to gaseous hydrogen at normal pressure. The measured ringdown times during the H2 diffusion show good agreement with a theoretical diffusion model. This model allows the determination of the diffusion coefficient of hydrogen in silica, resulting in D = (3.02 +/- 0.07) x 10(-15) m2/s at 30 degrees C.     

High-resolution photoelastic pressure sensor using low-birefringence fiber

The effect of birefringence induced in a single-mode fiber by a lateral force has been applied to measure the absolute value of force or pressure with high resolution. A sensor configuration with an extended detecting surface has been investigated by means of calibrated weights. The sensor is sensitive to an incremental force of 2 x 10(-3) N, independently of the length of the fiber. The maximum force applied was 10 N/m of fiber length.     

Interface for MEMS-based rotational accelerometer for HDD applications with 2.5 rad/s/sup 2/ resolution and digital output

A 0.6 /spl mu/m BiCMOS interface for microelectromechanical systems (MEMS) based rotational accelerometers is presented. It is housed in an inexpensive standard SO-24 plastic package with a capacitive rotational accelerometer sensor produced using MEMS technology. This sensitive interface chip includes the analog-to-digital conversion, filtering, and interface functions. The analog-to-digital conversion is realized through a single-bit electromechanical /spl Sigma/-/spl Delta/ loop able to detect capacitive unbalancing as low as 50 aF (50/spl times/10/sup -18/ F). The produced bitstream is then processed by a digital chain and made available through a standard 3.3 V (5 V tolerant) three-wire serial bus. The signal bandwidth is about 800 Hz, the sensitivity is 2.5 rad/s/sup 2/, with a full-scale sinewave of 200 rad/s/sup 2/ and a signal-to-noise ratio peak of 38 dB over 30-800 Hz. Through the serial bus, it is also possible to program device characteristics including gain, offset, filter performance, and phase delay. The complete sensor is used in a feed-forward compensation scheme to cancel external disturbances acting on computer hard-disk drives so as to steadily keep the read-write heads on track: this allows greater track densities and better speed performance.