Some properties and applications of thin self-supporting polymer membranes.

Membranes as thin as 500 A were produced from many plastic materials and transferred to frames with dimensions of several centimeters. The self-supporting membranes were obtained using simple-dip-coating techniques. In some cases additional plasma polymerized layers were applied. These membranes can withstand several procedures of photolithography and chemical processing. The mechanical properties of the membranes are similar to that of the bulk material. Some typical applications are described. These applications include the use of the membranes as substrates for thermoelectric detectors and also as beamsplitters and windows for cells employed in CO(2) laser spectroscopy.

Acoustics of a flanged cylindrical pipe using singular basis functions

The problem of acoustic radiation from a cylindrical pipe with an infinite flange has been discussed in a number of papers. The most common approach is to decompose the field inside the pipe over a basis of Bessel functions. A very large number of basis functions is usually required, with a large degree of ripple appearing as an artifact in the solution. In this paper it is shown that a close analysis of the velocity field near the corner yields a new family of functions, which are called "edge functions." Using this set of functions as test functions and applying the moment method on the boundary between the waveguide and free space, a solution is obtained with greatly improved convergence properties and no ripple.

Optoacoustic detection of ethylene in the presence of interfering gases.

A study of the limitations of optoacoustic detection of ethylene in gas mixtures using a (12)C(16)O(2) laser is presented. Particular emphasis is given to the detection of ethylene in urban areas and in fruit storage chambers. Calculations indicate that in most cases of interest the practical minimum detectable and identifiable concentration of ethylene is about 5 ppb. A concentration of 1% of CO(2) may increase this limit to 50 ppb. These limits are primarily due to inaccuracy in a priori knowledge of ir spectral signatures of interfering gases. As a practical example of the monitoring of ethylene in a realistic environment, a meausrement with a sensitive resonant optoacoustic cell in an urban area is reported. The same cell is also used to demonstrate the effectiveness of NaOH scrubbers for the elimination of interfering CO(2). Measurements of absorption coefficients of ethylene for several (12)C(16)O(2) laser transitions are reported and compared with those given in the literature. Data are also given for the isotopic (13)C(16)O(2) laser transitions which may be useful in overcoming CO(2) interference.

Pyroelectric PVF(2) infrared detector arrays.

Linear arrays of thin membrane (0.5-0.8-microm) pyroelectric PVF(2) detectors have been constructed. The size of each element was 0.1 x 3 mm. The arrays were built with twenty-four channels of hybrid self-scanning electronics and packaged in vacuum containers, D* of 1.5 x 10(9) cm/Hz/W at 10 Hz and thermal cross talk of <15% at 50 Hz were obtained.

Thermoelectric needle probe for temperature measurements in biological materials.

In certain biological and medical applications it is important to measure and follow temperature changes inside a body or tissue. Any probe inserted into a tissue causes damage to tissue and distortion to the initial temperature distribution. To minimize this interference, a fine probe is needed. Thus, thin film technology is advantageous and was utilized by us to produce sensitive probes for these applications. The resulting probe is a small thermocouple at the tip of a thin needle (acupuncture stainless steel needle, approximately 0.26 mm in diameter and length in the range 5-10 cm was used). The junction was produced at the needle's tip by coating the needle with thin layers of insulating and thermoelectric materials. The first layer is an insulating one and is composed of polyacrylonitrile (PAN) and polymide produced by plasma polymerization and dip-coating respectively. This layer covers all the needle except the tip. The second layer is a vacuum deposited thermoelectric thin layer of Bi-5% Sb alloy coating also the tip. The third layer is for insulation and protection and is composed of PAN and polyimide. In this arrangement the junction is at the needle's tip, the needle is one conductor, the thermoelectric layer is the other and they are isolated by the plastic layer. The probe is handy and mechanically sturdy. The sensitivity is typically 77 microV/degrees C at room temperature and is constant to within 2% up to 90 degrees C. The response is fast (less than 1 sec) the noise is small, (less than 0.05 degrees C) and because of the small dimension, damage to tissue and disturbance to the measured temperature field are minimal.

Statistical properties of He-Ne laser radiation reflected through a turbulent atmosphere.

Statistical properties of a He-Ne laser beam (0.63 microm) propagating through atmospheric folded paths of 1 and 12 km were investigated experimentally using direct and heterodyne detection. Measured scintillation histograms, power spectra, time autocorrelations, and phase fluctuations are reported. The turbulence parameters derived from the optical measurements were found to be in good agreement with those obtained from measurements of in situ temperature fluctuations.