摘要:

A system has been developed for investigating the piezoresistive effect in semiconducting solids and conductive polymers under different elastic and thermal boundary conditions. The system provides the necessary information needed for sensor design such as nonlinearity, hysteresis, and temperature dependence of the piezoresistance coefficient. The system operates under full computer control for both data acquisition and data reduction cycles. The temperature dependence of the hydrostatic piezoresistance coefficient of a donor‐doped polycrystalline semiconducting barium titanate below and above its ferroelectric–paraelectric Curie point will be presented for the first time. The nonlinear and hysteretic behavior of an electrically conductive polymer over the pressure range of 0–30 MPa will also be demonstrated.

ISSN:0034-6748    

DOI:10.1063/1.1139657

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We describe high‐performance successive approximation amplitude and phase digitizers capable of resolving 1 part in 4096 in amplitude and 0.1° in phase at a rate of 50 000 points per second. They communicate with a computer workstation by DMA over a GPIO bus. The phase digitizer exhibits negligible AM to PM conversion and an input amplitude range of 70 dB. Both digitizers reside on one thick 7×9‐in. card module. The system is currently used in an electronically scanned laser microscope. We also describe a high‐precision phase calibrator and associated calibration software.

ISSN:0034-6748    

DOI:10.1063/1.1139391

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We developed a pulse generator that uses high‐voltage step recovery diodes to produce 400‐ to 500‐V pulses with rise and fall times of 0.8 ns. The output pulse width is continuously adjustable. For a pulse width of 0.8‐ns FWHM, the amplitude into 50 &OHgr; is 400 V. With the pulse‐width control set at maximum, the output pulse amplitude is about 500 V and the width is 3.5‐ns FWHM. The delay of the output pulse with respect to the input trigger is 38 ns with a jitter of about ±30 ps. An unusual feature of the pulse generator is that the 38‐ns delay time to the centroid of the output pulse is approximately constant and independent of the pulse width.

ISSN:0034-6748    

DOI:10.1063/1.1139392

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A low‐cost multichannel scaler and signal‐averaging system with user selectable channel widths ranging from 1 to 255 &mgr;s has been developed for molecular beam time‐of‐flight (TOF) experiments. It has the ability to collect up to 255 channels and has a programmable delay of up to 0.65 s. On‐board logic can accommodate a 15‐MHz count rate. Completely contained on a 7×2 3/4 ‐in. Apple II prototyping board (with the exception of a 5‐A, 5‐V external power supply), the interface fits into a peripheral port of the Apple II. The interface was tested by measuring the TOF distribution of Ar metastables from a supersonic nozzle beam source.

ISSN:0034-6748    

DOI:10.1063/1.1139393

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This note describes an inexpensive and expendable molybdenum heater that can be used as a direct replacement for much more expensive heaters in the smaller commercial resistance heated furnaces.

ISSN:0034-6748    

DOI:10.1063/1.1139394

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We describe some techniques for making reliable and stable electrical contact to thin films using a gold wire bonding machine. Applications of these techniques to specific low‐temperature experiments are given.

ISSN:0034-6748    

DOI:10.1063/1.1139395

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A simple atomic beam oven is described. It uses a modified commercially available all metal sealed valve to break a glass cesium ampoule. Standard fittings are used to provide modularity and cost efficiency. Although designed for use with cesium ampoules, application to any volatile material is straightforward.

ISSN:0034-6748    

DOI:10.1063/1.1139396

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Intere´talon feedback in a tandem Fabry–Perot spectrometer will often be manifested by a frequency‐modulated spectrum. This undesirable modulation can be removed in a simple and consistent manner without significant loss of signal.

ISSN:0034-6748    

DOI:10.1063/1.1139397

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This fast, low‐current integrator uses an active feedback circuit to eliminate the effects of reset/offset error and switch leakage. Sensitivity is 200 pC per volt, response time is <1 &mgr;s, input bias current (ib) is <0.5 fA, signal source background current can be subtracted and built‐in calibration is provided. It is well suited to capacitance versus voltage measurements.

ISSN:0034-6748    

DOI:10.1063/1.1139398

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A displacement sensor based on the ratio of fiber‐optic light emitted from two fixed position optical fibers into a third, movable fiber connected to a photodetector is described. Square‐wave modulated light of opposite phases produces a corresponding square wave at the detector which has zero ac amplitude at the center position and an amplitude proportional to displacement on either side of the detection fiber. A phase‐sensitive detector produces a positive dc output voltage for positive displacements and negative for negative displacements.

ISSN:0034-6748    

DOI:10.1063/1.1139399

出版商:AIP    

年代:1987

数据来源: AIP