Excess low frequency noises in some electronic materials and components
We devised burst noise eliminating equipment and characterized the 1/f and burst noise in some electronic materials, components, electric contacts and bipolar transistors. The burst-eliminated noise spectrum is the 1/f type. The noise intensity is proportional to the square of the current and to the fifth power of the contact resistance. This contact resistance dependence of the noise is analyzed with the constriction resistance of the contact surface material. The measured results are also shown in the amplitude and phase fluctuations in the transistor collector current. They are also of 1/f type and correlate each other. On the other hand, we did not find this correlation in another transistor with burst noise. Hence, the 1/f fluctuation is considered to be due to diffusion or mobility fluctuation and the burst noise is not due to the diffusion process in the solid.
1/f Noise in Metal Contacts and Granular Resistors
To measure the current noise in metal contacts and granular resistors, we arranged a noise measuring system with a switched-capacitor filter. The samples are crossbar contacts and grphite thick-film resistors. All noise spectra are the 1/f type. The noise of crossbar contacts and thick-film resistors increases in proportion to the fifth and third power of the resistance, respectively. A model for the noise of metal contacts and granular resistors is proposed. It is based on the spontaneous fluctuation of temperature of the small Conducting spots between metal surfaces and granular boundaries, respectively. The results of the analysis are qualitatively in agreement with those of measurement.
The effect of collimation on image quality and radiation safety in digital radiography of small animals
Collimating the primary x-ray beam to the specific area of anatomic interest has traditionally been strongly recommended to produce high quality radiographic images, even though some small animal patients can fit their entire torso on a single radiographic casette or detector. However, modern digital radiography may allow for whole-body projections for these patients at similar quality to specific collimated projections. Lateral and ventrodorsal projections of 31 small dogs were obtained to evaluate the effect of collimation on the quality of the resulting digital radiograph. Each projection was performed using both a collimated and whole-body technique. Scatter radiation was detected during each exposure as well to determine the effect of collimation on radiation safety for veterinary personnel. The resulting images were cropped to portray only the thorax, and were evaluated by five radiologists blinded to the procedure used for each image. Visual grading characteristics analysis was performed. An overall trend towards higher image quality was found in the collimated approach compared to the whole-body, but in most cases this change was not significant. Overall image quality for the ventrodorsal images was found to be significantly better in the collimated approach compared to the whole-body. Evaluation of image histograms suggests that the application of digital processing and the look-up table differs between them, and this may account for a large portion of any quality difference. Over twice as much scatter radiation was detected during the whole-body images as during the collimated images. Overall image quality was rated as adequate to high for almost all images with both approaches. Adequate collimation remains recommended to provide the highest quality images with the lowest exposure to veterinary personnel.