A.D. Drake

Fiber‐optic interferometer for remote subangstrom vibration measurement

A single‐mode fiber‐optic interferometer for measuring subangstrom vibrations has been designed and constructed. The interferometer is based on the Fizeau configuration and employs peak detection schemes in the signal processing. The instrument has been used to measure the displacement of a cricket’s tympanic membrane.

Development of an orthogonal-stripe CdZnTe gamma radiation imaging spectrometer

We report performance measurements of a sub-millimeter resolution CdZnTe strip detector developed as a prototype for astronomical instruments operating with good efficiency in the 30-300 keV photon energy range. The prototype is a 1.4 mm thick, 64/spl times/64 contact stripe CdZnTe array of 0.375 mm pitch in both dimensions. Pulse height spectra were recorded in orthogonal-stripe coincidence mode which demonstrate room-temperature energy resolution <10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio >5:1. Good response is also demonstrated at higher energies using a coplanar grid readout configuration. Spatial resolution capabilities finer than the stripe pitch are demonstrated. We present the image of a /sup 133/Ba source viewed through a collimator slit produced by a 4/spl times/4 stripe detector segment. Charge signals from electron and hole collecting contacts are also discussed.

Performance and simulation of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 strip region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals, and the photon detection efficiency. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results to the data. The data indicate that the cathode signal-as well as the anode signal-arises primarily from the conduction electrons rather than the holes. This presents a detection efficiency limitation which must be considered in the design of strip detector systems.

Performance of CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals, and the photon detection efficiency. We also present a technique for determining the location of the event in the third dimension (depth). We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that the cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes.

Interferometric measurement of the ocular pulse

An instrument which noninvasively and accurately measures the ocular pulse is described. To acquire this signal, a fiber Fizeau interferometer operating at a wavelength of 632 nm is used. A unique dithering and signal processing scheme allows standard FM demodulation techniques to recover the ocular pulse signal from the interference pattern. A detailed description of this data acquisition method is presented along with the results of test measurements made on a model eye.<<ETX>>

A Fiber Fizeau Interferometer for Measuring Minute Biological Displacements

A laser interferometer has been developed which was used to measure vibratory displacements of the crickets posterior tympanic membrane with a sensitivity of less than 0.1 A. A special feature is the incorporation of an optical fiber in two of its arms, which makes possible its use in hard-to-access areas. Another feature is its Fizeau configuration, which enables one to eliminate much undesirable noise by combining both the reference arm and the object arm within the same length of fiber. Numerical results are given over the auditory spectrum for two different conditions of the space behind the crickets posterior tympanic membrane.

A 5-bit 10GS/s 65nm flash ADC with feedthrough cancellation track-and-hold circuit

A 10GSamples/second (GS/s) 5-b flash analog-todigital converter (ADC) that includes a feedthrough cancellation track and hold amplifier (THA) is presented. The proposed 10GS/s switched source follower (SSF) THA removes the input feedthrough error during the hold mode, which dramatically improves the settling behavior than previous designs. The proposed track and hold circuit achieves a total harmonic distortion (THD) of −37.3dBc at 10GS/s and an input frequency of 4GHz, which is 4.5dBc lower than the THD of traditional SSF THAs. The THA core only consumes 26mW and this is the minimum power consumption of THA above 10GS/s ever reported. In addition, a proposed comparator array to address the overdrive recovery issue is implemented for very high speed ADC. A reference ladder with source followers is applied to reduce the pre-amplifier feedthrough distortion by 10 times. This design is implemented in IBM 65nm CMOS technology with 1.4V power supply, 1.2V peak-to-peak differential input amplitude, and 1V peak-to-peak clock swing.

Analog processing of signals from a CZT strip detector with orthogonal coplanar anodes

We present the requirements, design, and performance of an analog circuit for processing the non-collecting anode strip signals from a cadmium zinc telluride (CZT) strip detector with orthogonal coplanar anodes. Detector signal simulations and measurements with a prototype are used to define the range of signal characteristics as a function of location of the gamma interaction in the detector. The signals from the non- collecting anode strip electrodes are used to define two of the three spatial coordinates including the depth of interaction, the z dimension. Analog signal processing options are discussed. A circuit to process the signals from the non- collecting anode strips and extract from them the depth of interaction is described. The circuit employs a time-over- threshold (TOT) measurement. The performance of the detector prototype with a preliminary version of this circuit is presented, and future development work is outlined.

A two dimensional fiber optic eye position sensor for tracking and point-of-gaze measurements

The optical configuration of the presented sensor consists of three imaging lenses mounted on a pair of eyeglass frames around the field of vision. This allows normal eye movement and unobstructed vision without distracting the subject. The optical sensors gather light reflected from the area of the sclera to the immediate left and right of the iris and transmit this light through optical fibers to remote detectors. The device determines horizontal position by utilizing the difference in reflectivity between the iris and sclera. Vertical position of the eye is determined similarly by monitoring either the upper or lower eyelid. Point-of-gaze and short period tracking measurements have been made in two dimensions with an accuracy of better than half a degree in the horizontal direction and three degrees in the vertical direction.<<ETX>>

CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray measurements in the range of 20-600 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes.