Pyroelectric Multi-Channel Detectors | SIMTRUM Photonics Store

The Multi-Channel Element Detectors are developed for use in gas analysis, spectroscopy, pyrometry and security applications. Many types of infrared sensors manufactured in volume production are available. Beyond customized infrared sensors solutions are possible. Very high values of specific detectivity D* (up to 109 cm√Hz/W) are achieved by using modern ion beam etching technology for extremely thin elements. The great variety of infrared sensor constructions makes it possible to realize custom-made solutions for both small and large quantities with an excellent price-performance payoff. 

• Coated silicon or germanium as infrared window

• Broad band windows (>1.3 μm) or special filters

• Customized filters and integrated optics

Many gases absorb infrared radiation in a characteristic absorption spectrum, which is determined by the specific molecular structure of the respective gas. Non-dispersive infrared gas analysis (NDIR gas analysis) is a comparatively inexpensive method for an exact determination of the concentration of individual gases, which utilizes individual substance-typical absorption bands of the gases to be detected.

Principle of gas concentration measurement using NDIR gas analysis

The gas mixture to be analyzed is located in a defined volume between a broadband IR emitter and an infrared sensor. The broadband absorbing IR sensor is equipped with a narrowband filter which has its peak transmission exactly at a typical absorption band of the gas to be analyzed. If a sensor with multiple spectral channels is used instead of a single-element sensor, several discrete gases can be detected simultaneously. The emission spectrum of the emitter must cover at least the spectral range of the absorption bands used. If there is no gas to be detected between the emitter and the sensor, the emitted radiation hits the sensor almost unhindered and generates the maximum possible signal there. With increasing concentration of a gas to be measured, the absorption on its typical absorption spectrum increases and thus the sensor with the narrowband filter tuned to it emits a lower signal. The other channels, if any, react accordingly only to other gases.

For standard measurement tasks, the sensors of the type series PYROSENS LTA and LTM are perfectly suitable. With the type series PYROSENS LTMI and LTSI DIAS Infrared GmbH offers highly developed pyroelectric IR sensors which allow NDIR gas analysis even for lowest gas concentrations in the single digit ppm range. The respective detection limit depends on the construction of the measuring cell as well as on the gas to be detected. The typical spectral range is between approx. 1 µm and 20 µm, but our sensors can even be used at wavelengths far above 100 µm.

PYROSENS sensors are used for leak detection or leak testing of refrigerators and air conditioning systems as well as for highly accurate and temperature stable concentration measurements of gases such as CO, CO2 and CH4 with very low cross sensitivity between CO and CO2, which are used especially in human and veterinary medicine. In the semiconductor industry, they are used, among other things, for gas monitoring in the end-point monitoring of vacuum chamber cleaning processes.

A wide range of gases, liquids, powders and solids can be analyzed very precisely in the mid-infrared range, as they exhibit substance-typical absorption behavior at these wavelengths due to characteristic molecular vibrations. The energy of the IR radiation stimulates the molecular bonds to substance-typical vibrational modes, resulting in a unique „fingerprint“. Using IR sensors, spectroscopic techniques can give a wide range of information from corresponding measurement samples. Thus, composition, impurities and concentration of various constituents can be determined and detected.

Various physical principles are available for the detection of radiation in the mid-IR range. Pyroelectric detectors PYROSENS of Infrared GmbH based on lithium tantalate rank themselves in terms of their signal-to-noise ratio between the cooled MCT sensors and the less sensitive and slower thermopiles and bolometers. They also exhibit significantly higher specific detectivity compared to pyroelectric sensors with ceramic thin films, e.g. based on PZT.

PYROSENS line sensors are available with 128, 256 and 510 pixels, among others. This makes them suitable for high-resolution detection over a wider wavelength range together with dispersive optical assemblies and/or linear variable filters (LVF). Linear variable filters are currently available up to a wavelength of about 11 µm, for IR spectroscopy divided into the ranges 1.3-2.6 µm, 2.5-5 µm and 5.5-11 µm.

The spectrometers in which our linear arrays are used are essentially based on three operating principles.

NDIR transmission spectrometer  

The setup of a linear array NDIR transmission spectrometer is similar to the setup with single element sensors known from gas analysis. However, by using linearly variable filters, not only individual substances but also mixtures of substances can be analyzed (basic principle in Fig. 1).

Fig. 2 shows a simple demonstrator for this type of spectrometer, which allows very cost-effective and compact spectrometers for general applications. Its core component is our Evaluation Kit which can be used for all PYROSENS arrays.

ATR Spectrometer 

Attenuated total reflection (ATR) spectroscopy uses the IR array with LVF in conjunction with an ATR crystal (waveguide) and an IR radiation source. The IR radiation is guided through the waveguide in total reflection, whereby the liquid or solid sample to be measured at the surface of the waveguide spectrally influences its reflection behavior. This measurement method enables compact, precise, fast and versatile systems that can also be used in mobile devices. The operating principle of ATR spectroscopy using line sensors with linear graduated filters is shown in Fig. 3.

Grating Spectrometer

In the grating spectrometer (principle in Fig. 4), the IR radiation enters through a slit or fiber and first hits a spherical mirror. This parallelizes this radiation, which is then diffracted and reflected at an optical grating. This causes different wavelengths to be directed in different directions. A second mirror now focuses the radiation onto the line sensor, whose pixels now detect radiation of different wavelengths. The wavelength range that can be measured over the entire sensor length is defined by the specific optical arrangement.