Vehicle detection using a magnetic field sensor

The measurement of vehicle magnetic moments and the results from use of a fluxgate magnetic sensor to actuate a lighting system from the magnetic fields of passing vehicles is reported. A typical U.S. automobile has a magnetic moment of about 200 A-m²(Ampere-meters²), while for a school bus it is about 2000 A-m². When the vehicle is modeled as an ideal magnetic dipole with a moment of 200 A-m², the predicted results from an analysis of the sensor-vehicle geometry agree closely with observations of the system response to automobiles.     

A CMOS magnetic field sensor

The authors present a novel, fully integrated magnetic field sensor made in the standard, polysilicon-gate CMOS technology. The circuit shows a sensitivity of 1.2 V/T with 10 V supply voltage and 100 /spl mu/A current consumption. The circuit consists of a pair of split-drain MOS transistors in a CMOS-differential amplifier-like configuration.     

Two-dimensional numerical analysis of a silicon magnetic field sensor

We present two-dimensional numerical solutions of the coupled, nonlinear, partial differential equations governing the electric potential, carrier drift, diffusion, generation, and recombination in a finite semiconductor slab in the presence of a magnetic field. This enables device modeling for general geometries, doping levels, and injection conditions, where the effect of the magnetic field cannot be expressed simply in terms of Hall voltage, Lorentz deflection, or magnetoconcentration.     

Location and calculation-free node-scheduling schemes in large wireless sensor networks

In wireless sensor networks that consist of a large number of low-power, short-lived, unreliable sensors, one of the main design challenges is to obtain long system lifetime without sacrificing system original performance (sensing coverage and sensing reliability). To solve this problem, one of the potential approaches is to identify redundant nodes at the sensing interface and then assign them an off-duty operation mode that has lower energy consumption than the normal on-duty mode. In our previous work [J. Wireless Commun. Mobile Comput. 3 (2003) 271; Processing of ACM Wireless Sensor Network and Application Workshop 2002, September 2002], we proposed a node-scheduling scheme, which can provide a 100% sensing coverage preservation capability. This, however, requires each node to be aware of its own and its neighbors’ location information. Also, in that scheme, each node has to do accurate geometrical calculation to determine whether to take an off-duty status. In this paper, we propose and study several alternative node-scheduling schemes, which cannot completely preserve the original system coverage, but are nonetheless light-weighted and flexible compared with the previous one. Our simulation results compare these schemes with the previous one and demonstrate their effectiveness.     

新型Spindt阴极阵列磁敏传感器的研究

提出了一种检测三维磁场的真空微电子磁敏传感器。该传感器采用Ｓｐｉｎｄｔ阴极阵列作为电子源,阳极分为五个区域,以便检测发射电子在磁场作用下的偏移。通过不同阴极电压下电子束流的偏移量的国赤出器件所在位置磁场的三个分量。对传感器的灵敏度和误差进行了模拟计算,并研究了它们与阳极电压、阴－阳极间距及阳极电压变化步长的关系。结果表明该传感器的灵敏度约为８００％,相对误差为３％。     

Coiled-fiber sensor for vectorial measurement of magnetic field

New results on the polarization properties of a matched fiber-coil (i.e. one beat length per turn) immersed in a magnetic field are described. It is shown that both components H_y and H_z, perpendicular to the coil axis, can be simultaneously measured. Sensing coils of 1-cm diameter, with multiple turns of fiber, were fabricated. Using 100-turn heads, a sensitivity of 0.01 G was achieved for the vectorial fiber sensor     

Active magnetic field sensor for measurements of transients

An active magnetic field sensor consisting of an electrically small loop, two ferrite core transformers, and a balanced amplifier with a low input impedance is suitable for measurements of fields, in a broad range of frequencies, and transients. The sensor provides a flat transfer function from approximately 600 Hz to 200 MHz (3 dB roll-off frequencies) and high-fidelity reproduction of pulses with a risetime of 2 ns. The sensor can be used to measure fields from less than 0.2 mA/m to approximately 0.2 A/m. The sensor has a minimal response to the electric field (at least -20 dB). The sensor's dimensions are 6 cm×6 cm, and the electronic circuitry is contained in a box of approximately 5 cm×8 cm×3 cm     

A flame sensor with uniform sensitivity over a large field of view

The sensor is a gas-filled tube of the Geiger-Mueller type, in which an electron emitted from a photocathode is accelerated by an applied electric field to cause ionization of the fill gas. Although the operating principle is not new, this tube differs from others in that the cathode consists of a semitransparent layer of metal on the inside of the cylindrical tube envelope, which is applied by sputtering after filling and sealing. Used as a cathode during sputtering, the anode consists of a pin along the axis of the tube, providing the cylindrical symmetry for uniform wide-angle viewing. The performance of the tube is compared with that of a tube of the same external dimensions, but with more conventional parallel wire electrodes. The counting rate for the sputtered tube was a factor of 10 higher than the conventional tube, due to the larger sensitive cathode area, and uniform over 360° in a plane perpendicular to the tube axis, due to cylindrical symmetry. The counting rate for the sputtered tube was 2000/min in response to a flame 7 ft away burning natural gas at the rate of 138 cm³/min.     

Maximum likelihood estimation and Cramer-Rao bounds for directionof arrival parameters of a large sensor array

A maximum likelihood (ML) method is developed for estimation of direction of arrival (DOA) and associated parameters of narrowband signals based on the Taylor's series expansion of the inverse of the data covariance matrix R for large M, M specifying number of sensors in the array. The stochastic ML criterion function can thus be simplified resulting in a computationally efficient algorithm for DOA estimation. The more important result is the derivation of asymptotic (large M) expressions for the Cramer-Rao lower bound (CRB) on the covariance matrix of all unknown DOA angles for the general D source case. The derived bound is expressed explicitly as a function of snapshots, signal-to-noise ratio (SNR), sensors, separation, and correlation between signal sources. Using the condition of positive definiteness of the Fisher information matrix a resolution criterion is proposed which gives a tight lower limit on the minimum resolvable angle     

U型微弱梯度磁场检测传感器设计及应用

本文就U型微弱梯度磁场检测传感器的设计原理、结构、应用领域等进行了较为全面的叙述,并与其他检测方法在同一标准磁场条件下在测量灵敏度、重复性等方面进行了比较,结果表明各项指标均优于其他传感器。该传感器用于均匀变化磁场中测量非均匀直流梯度弱磁场,检测微弱磁场的变化,在实现微弱磁场的过零检测中具有独特性,且便于实现自动化测量,具有良好应用和开发空间。该传感器在开磁路软磁矫顽力测量中得到很好的应用。     

光纤微弱磁场传感技术研究进展

文章扼要评述了光纤微弱磁场传感器的工作原理及在换能器、信号处理、传感器等阵列等方面的研究进展。     

An integrated silicon magnetic field sensor using the magnetodiode principle

We report a novel integrated magnetic field sensitive device. Its structure is reminiscent of the bipolar transistor, but its operation is essentially that of a magnetodiode: a reverse-biased p-n (collector) junction plays a role similar to that of the high recombining surface of classical magnetodiodes. The device can be manufactured in standard bulk CMOS or bipolar technology. Sensitivity up to 25 V/T at 10-mA current is achieved. Voltage-current characteristics shows saturation and negative resistance regions, which are explained by JFET and UJT effects, respectively.     

Yield-enhancement of a large systolic array chip

This paper examines the feasibility of enhancing the yield of a very large VLSI circuit through the use of fault-tolerant circuitry. The example of a linear array architecture has been selected because it appears to be the next most promising candidate after memories. An example is presented which shows that with rather simple circuitry a chip 8 times larger than a conventional design could actually turn out to have a higher yield. This combined with economies of scale make the approach look attractive.     

A passive high sensitivity magnetic field sensor based on metallicglass wire

The responsitivity and sensitivity of fiber interferometric sensors based on magnetostrictive transducers consisting of up to 25 m of annealed metallic glass wire are reported. The frequency and temperature range of these sensors is examined both theoretically and experimentally. The performance of these sensors is acceptable for the transient electromagnetic method of geomagnetic surveying     

Blind beamforming on a randomly distributed sensor array system

We consider a digital signal processing sensor array system, based on randomly distributed sensor nodes, for surveillance and source localization applications. In most array processing the sensor array geometry is fixed and known and the steering array vector/manifold information is used in beamformation. In this system, array calibration may be impractical due to unknown placement and orientation of the sensors with unknown frequency/spatial responses. This paper proposes a blind beamforming technique, using only the measured sensor data, to form either a sample data or a sample correlation matrix. The maximum power collection criterion is used to obtain array weights from the dominant eigenvector associated with the largest eigenvalue of a matrix eigenvalue problem. Theoretical justification of this approach uses a generalization of Szego's (1958) theory of the asymptotic distribution of eigenvalues of the Toeplitz form. An efficient blind beamforming time delay estimate of the dominant source is proposed. Source localization based on a least squares (LS) method for time delay estimation is also given. Results based on analysis, simulation, and measured acoustical sensor data show the effectiveness of this beamforming technique for signal enhancement and space-time filtering     

Thermoelectric power of the n-InSb in a transverse quantizing magnetic field at a large temperature gradient

The thermoelectric power of the n-type indium antimonide was studied in the transverse magnetic field (0–80 kOe) at T _aV =160 K and different temperature gradients. It was found that the electron component of the thermoelectric power at a small temperature gradient is consistent with the theory that takes into account the electron spin, whereas, for a large temperature gradient, the value determined by the variation of the Benedicks thermoelectric power in the magnetic field is added to this component.     

Improvements to an electromagnetic near-field sensor forsimultaneous electric and magnetic field measurement

A sensor for simultaneous electric and magnetic field measurement has been described by M. Kanda (see ibid., vol.EMC-26, no.3, p.102-10, 1984). It relies upon measuring the voltage across precisely matched loads at opposite sides of a loop antenna. A modification to the theory is presented to account for unmatched loading of the loop. Measured results of wave impedance over a 10-400-MHz range demonstrate the accuracy of the modified theory as well as highlighting a novel calibration technique     

Hybrid magnetic tunnel junction/vertical cavity surface emittinglaser field sensor device

A hybrid magneto-optoelectronic device is demonstrated, composed of a magnetic tunnel junction and a vertical cavity surface emitting diode laser. External magnetic field changes are translated into amplitude modulation of the laser output power with sensitivity that suggests applications in wireless and remote sensing of magnetic fields