1 Axetris Infrared Sources (IRS) Products
This is a collection of relevant questions regarding infrared sources manufactured by Axetris. Topics not included in this document are explained in Product Specifications and furthermore in Technical and Application Notes.
1.1 What is the Axetris IR Source?
Axetris IR sources are micro-machined, electrically modulated thermal infrared emitters featuring true black body radiation characteristics, low power consumption, high emissivity and a long lifetime. Axetris IR sources are ideally suited for compact IR gas detection modules where a high emissivity, high reliability and low power consumption are key requirements.
The appropriate design is based on a resistive heating element integrated onto a thin dielectric membrane which is suspended on a micro-machined silicon structure. Axetris sources are available with a protective cap or with a reflector. Axetris provides several different reflectors to fulfil different optical requirements. Reflectors can be fitted with Sapphire, CaF2 or BaF2 or Germanium windows.
1.2 What are the main advantages and benefits as compared to other IR Sources?
- True black body radiation
- Wide wavelength range (2 to 14 μ m)
- High emissivity
- Fast electrical modulation (no chopper wheel needed)
- High modulation depth
- High optical output to electrical input efficiency
- Low power consumption
- Long lifetime
- Robust MEMS design (passed the requirements of IEC 60721-3-7 Class 7M3, except for BaF2 and CaF2 windows
1.3 What are the differences between EMIRS200 and EMIRS50 Sources?
Axetris provides sources in two sizes: EMIRS200 IR Sources are larger with 2.1 x 1.8 mm2 active area and EMIRS50 sources are smaller with 0.8 x 0.8 mm2 active area. Both IR sources can be driven to maximum 500°C peak temperature. EMIRS200 sources have greater emission, whereas EMIRS50 sources are smaller, require lower power and can be driven with higher frequencies. Frequency range for EMIRS200 is from 5 to 50 Hz and for EMIRS50 from 10 to 100 Hz. The nominal cold resistance can vary from 35 up to 55 Ohm for EMIRS200 and 22 to 36 Ohm for EMIRS50.
EMIRS200 sources are packaged in compact TO-39 cans and EMIRS50 sources in TO-46 cans or SMD packages. Axetris sources are available as chip-on-header or with a protective cap or a reflector. Axetris provides several different reflectors to fulfil different optical requirements. Reflectors can be fitted with Sapphire, CaF2 or BaF2 or Germanium windows.
1.4 What is the actual design of Axetris MEMS IR Source?
The design consists of a solid-state hot plate on a thin micro-machined membrane. The system has low thermal mass enabling fast modulation. The emitting layer is black platinum, which enables emissivity close to theoretical maximum. See illustrated Figure:
1.5 What is the temperature distribution on the active area?
Please refer to image below. Maximum temperature is in the center part of the active area.
1.6 What kind of reflectors do you provide?
Axetris provides several types of reflectors, reflectors with simple cones, elliptical focusing reflectors and reflectors based on Winston Cone Design for collimation. Axetris is also capable of providing custom reflectors for special requirements.
1.7 What types of windows are available?
Sapphire, CaF2, BaF2 and Germanium windows are available as a standard product. The reflection loss of the Sapphire window is about 15%. The transmission range extends to about 6µm. The CaF2 window up to 10µm, BaF2 up to 12 µm and the Germanium with antireflection coating up to 16 µm.
Transmission vs Wavelengths comparison of different windows
1.8 What is the approximate efficiency of converting electrical power into light?
The efficiency of Axetris emitters is considerably larger compared to emitters based on filaments. The efficiency can be read from the plots below: emissivity of Axetris sources is stable across a broad wavelength range, varying between 85 and 90 %. This states that the design of Axetris sources is close to optimal.
Top: Emissive power of EMIRS50 and EMIRS200 compared to theoretical maximum.
Down: Emissivity of EMIRS200.
1.9 Regarding sources with reflectors: do you have any data on angular distribution differences between sources?
First, we define the two major influences to the pointing vector that could give variation on angular distribution.
- Tilt of the reflector (vs. header)
- Position deviation (chip vs reflector)
With these two impacting factors, variation of 1.5° (2σ) for the standard IRS production should be considered.
1.10 Do you have any data available that demonstrates the “tear out” strength of the joint?
Yes, in addition to the Shock & Vibration test that was done for the complete IRS family, there is also Pull Test in which the glue bond between reflectors and TO-39 headers was studied. The reflectors must pass the pull test with a load of 2 Kg equivalent to 20 N after 20 cycles according to IEC 60068-2-14. Please contact our Sales Manager or customer support to request for this complete document.
1.11 (From US customers) Is your IRS a compliant of Conflict Minerals Regulation?
Yes, our material is compliant. This is available as per customer’s request.It’s all about the legislation “The United States Dodd Frank Act, Section 1502”. It requires manufacturing companies to identify and disclose to the U.S. Securities and Exchange Commission (SEC) the source of 3TG minerals (tin, tantalum, tungsten and gold) used in their products when those minerals originate from or around the war-torn region of the Democratic Republic of the Congo (DRC).
2 Driving Axetris IR Sources
2.1 What are the Pin assignments? How to connect the EMIRS200 or EMIRS50 correctly?
Please see Pin assignment illustration below.
Pin Assignments for EMIRS200 and EMIRS50, top and base vented
NOTE: The Pin-assignment is dependent from your order
Heating resistor Rh
Bidirectional element, Pin is isolated from TO-case
Heating resistor Rh
Pin is connected with TO-Case.
Hole in the TO-Case.
2.2 How to drive your emitter? Recommendation?
The IR sources can be driven in pulsed voltage or electrical power mode. The applied frequency needs to be above the cut-off frequency fco, which is fco ≈ 5Hz for EMIRS200 and fco ≈ 10Hz for EMIRS50. Driving the sources in DC mode is under constraints possible. Please contact us for further information. The voltage or power depends on desired peak temperature, cold resistance and duty-cycle. Detailed walk-though is presented in our Technical Note "Driving Mode Recommendation" and more detailed information in our datasheets.
Suggested drive circuit uses a conventional control loop. The power on the load is to be measured and fed back into the feedback loop. Please refer to the Technical Note "Driving Mode Recommendation" for a complete explanation about drive modes and implementation.
For an easy start, Axetris provides a LabKit (Figure 3) to run the sources up to 100 Hz. The LabKit can also be used to provide 5V synchronization signal.
Axetris IRS Labkit G1 and GUI
2.3 Can the On-State power be increased when using high frequencies and or short duty cycles?
Yes, the power for the on-state power can be increased accordingly but it must be verified that the maximum achieved membrane temperature is not above a critical value of 500°C. The figure 6 below explains the function compensated power and voltage versus modulation frequency.
Top: Relative (to RO) electrical drive values heater voltage PH versus frequency f for compensation Down: Relative (to RO) electrical drive values heater voltage VH and power PH versus duty cycle D for compensation.
2.4 Is the behavior of EMIRS200 influenced by ambient temperature?
The behavior of EMIRS200 can be influenced by ambient temperature. The influence is a combination of the gas volume that is directly in contact with the chip (open package) and the thermal gas interaction with the EMIRS200 package. The second interaction is difficult to predict if the EMIRS200 is integrated in different devices with different conductive/convective properties.
2.5 What is the best practice to switch On & Off the IRS?
In an application in which the IR Source is not constantly in use and often powered off, a special warm-up and cool-down cycle should be applied (see Figure 4). The cool-down should be conducted with voltage or power and not with duty-cycle. In case the sensor module is not always powered up, and measurements are carried only at irregular intervals, a stand-by mode can be considered. Such implementation would reduce the warm-up time and reduce the time until the system is stabilized.
Soft switch feature
3 IR Measurement Methods
3.1 What is Non-Dispersive Infrared Spectroscopy (NDIR)
Non-Dispersive Infrared (NDIR) method is based on principle that gas molecule absorbs IR light and absorption of a certain gas occurs at a certain wavelength. This technology utilizes a broadband infrared (IR) emitter, which covers all of the wavelengths of interest for a given set of gases to be measured. Depending on the measured gas, Optical Band Pass filter chosen and set between the source and detector. The filter allows only relevant IR wavelengths through at which a specific gas absorbs IR energy.
The detector produces a signal that is proportional to the amount of IR energy absorbed by the gas of interest. This signal is electronically processed to develop gas concentration information reported in engineering units of interest.
3.2 What is Photoacoustic infrared spectroscopy (PAS)
Photoacoustic spectroscopy is the measurement of the effect of absorbed electromagnetic energy on matter by means of acoustic detection. The absorbed energy from the light is transformed into kinetic energy of the sample by energy exchange processes. This results in local heating and thus a pressure wave or sound. The measurement setup is similar as with NDIR: case-dependant Band Pass Filter is set after the light source to have only wavelengths corresponding to molecular vibrations of interest in the gas.
Photo Accoustic Infrared Spectroscopy principle
3.3 What is Attenuated Total Reflectance (ATR) FTIR spectroscopy
Attenuated total reflectance (ATR) is a sampling technique used in conjunction with infrared spectroscopy which enables samples to be examined directly in the solid or liquid state with little or no sample preparation. Light undergoes one or multiple internal reflections in the crystal of high refractive index meeting the sample on the other side. Molecule specific wavelengths will get absorbed and absorbance spectrum can be recorded with a detector.
For other questions and technical inquiries not discussed in this FAQ, please write us on firstname.lastname@example.org.