KEYWORDS: Infrared detectors, Interference (communication), Sensors, Signal detection, Amplifiers, Signal to noise ratio, Field effect transistors, Crystals, Thermography, Resistors
Pyroelectric infrared detectors are used in many commercial and industrial applications. Typically these devices have been “single ended” and thus any electronic perturbation from a non-detector related noise source such as line frequency interference or microprocessor clock and other sources of electronic noise can be coupled onto the detector’s output signal. We have solved this problem by employing a rather unique connection which also provides an increase in the signal to noise of any pyroelectric detector by a factor of the square root of 2 or by about 1.41 times greater than devices not utilizing this connection.
Many devices using this connection have been built, fully tested and the data analyzed which provide a true differential or double ended output and the increase in D* as predicted. This scheme will work with any pyroelectric material (LTO, DLATGS, PLZT, PVDF etc.) with current or voltage mode impedance conversion and configurations such as parallel or series with and without temperature fluctuation compensation and of course with standard single elements. This talk will present this data and conclusions regarding the approach.
KEYWORDS: Infrared detectors, Interference (communication), Sensors, Amplifiers, Field effect transistors, Crystals, Electrodes, Capacitors, Signal detection, Signal to noise ratio
Pyroelectric infrared detectors are used in many commercial and industrial applications. These by nature are “single ended” and thus any electronic perturbation from an external or internal source such as AC pickup or from a nearby RF or other sources of noise can be coupled onto the detector’s output signal. This is in contrast to other IR detectors such as thermopiles, thermistor bolometers and others which are much lower impedance and don’t require these impedance converters are often used in the differential mode. In practice each electrode forming the capacitor is directly connected to an impedance converting amplifier. While exposed to a changing IR signal the capacitor produces current which flows out of one electrode and must be balanced by an equal but opposite current from the other electrode. When these two signals are connected to separate impedance converters the outputs are the same but of opposite sense. When these are connected to a differential amplifier the output is doubled while all the common mode artifact is canceled out. (Patent Pending) The noise in this configuration is primarily from the impedance converters. However as this noise is random it only RMS’s, thus it is only increased by a factor of 1.41 thus the D* of a detector connected will be increased by this factor This connection will work with any pyroelectric material with current or voltage mode impedance conversion and configurations such as parallel or series with and without temperature fluctuation compensation and of course with standard single elements.
Mn1.56Co0.96Ni0.48 is RF magnetron sputtered in a series of oxygen partial pressures, and non-stoichiometric films are produced. Conduction is small polaron hopping for all stoichiometries as evidenced by near temperature independent thermopower, and decreasing conduction activation energy with decreasing temperature. The carrier type transitions from p to n type with a decrease in the ratio of Mn3+ to Mn4+ concentration. The resistivity, and conduction activation energy are decreasing functions of the oxygen partial pressure. The Debye frequency increases with oxygen partial pressure as measured from the resistivity, and this is consistent with the observed shift of both the Raman and IR active lattice vibrations. The material has the spinel crystal structure, and as such is an optical window with the 3 phonon cutoff occurring at 17 micrometer. The material is transparent between 6 micrometer to 17 micrometer.
The identification of gases and the measurement of their concentration in a mixture is important in a variety of applications such as gas leak detection, process monitoring and control, and pollution control. Many gases can be uniquely identified by their optical absorption spectra. In a mix of gases, the individual species can be identified by measurements at several wavelengths and the knowledge of the absorption strengths. The advantages of these optical absorption techniques can often be utilized to the fullest only if the technology used is capable of measurements over a wide wavelength range. Instruments based on pyroelectric array detectors can utilize both dispersive and nondispersive techniques, and operate over the entire infrared region since the detectors themselves are not intrinsically wavelength sensitive. In this paper, the construction and use of infrared pyroelectric arrays suitable for gas detection and monitoring are described.
In the last 10 years passive IR based (8 to 12 microns) motion sensing has matured to become the dominant method of volumetric space protection and surveillance. These systems currently cost less than $25 to produce and yet use traditionally expensive IR optics, filters, sensors, and electronic circuitry. This IR application is quite interesting in that the volumes of systems produced and the costs and performance level required prove that this is potential for large scale commercial applications of IR technology. This paper will develop the basis and principles of operation of a staring motion sensor system using a technical approach. A model for the motion of the target is developed and compared to the background. The IR power difference between the target and the background as well as the optical requirements are determined from basic principles and used to determine the performance of the system. Low cost reflective and refractive IR optics and bandpass IR filters are discussed. The pyroelectric IR detector commonly used is fully discussed and characterized. Various schemes for `false alarms' have been developed and are also explained. This technology is also used in passive IR based motion sensors for other applications such as lighting control. These applications are also discussed. In addition the paper will discuss new developments in IR surveillance technology such as the use of linear motion sensing arrays. This presentation can be considered a `primer' on the art of passive IR motion sensing as applied to surveillance technology.
The thermistor infrared detector or bolometer is the detector of choice in many classical remote sensing applications such as horizon sensing, noncontact thermometry, and industrial applications. In recent years, the authors have developed a thin film process where the thermistor material is deposited from a target directly onto the substrate. This is an advance over the labor intensive ceramic technology, where sintered flakes of the thermistor are bonded to the substrate. The thin film technique permits a variety of device constructions and configurations. Detectors fabricated on heat-sunk ceramic substrates can withstand high operating temperatures and large incident optical power, in both pulsed and CW laser measurements. For dc or low frequency measurements, the films can be deposited onto a thermally isolated membrane with applications in motion sensing, gas detection, and temperature measurement. Utilizing advances in micromachining a 2D array of thermally isolated microbolometer sensors, integrated onto a silicon wafer containing readout circuitry may be achieved. This paper describes the construction of the sputtered film thermistor detectors, their operation, and applications.
Earth horizon sensors utilizing pyroelectric detectors are finding increasing use in infrared horizon sensing systems. These detectors, like the earlier thermistor bolometer sensors, observe the Earth's carbon-dioxide emission in the 15 micron wavelength band. This paper describes the design, construction and performance of a pyroelectric detector suitable for use in horizon scanner systems. The procedures being developed to ensure the space qualification of this detector will be described. The design of more advanced staring arrays which have been developed will also be discussed.
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