SAR（Specific Absorption Rate），electromagnetic wave energy absorption ratio of cell phone or wireless product. The meaning of SAR is that the body mass of the human body is absorbed or consumed by the electromagnetic power, the unit is W/kg. Wireless communication terminal of the electromagnetic radiation is too meeting on human health caused by certain effect, long term electromagnetic radiation exposure makes people feel physical fatigue, eye fatigue, shoulder pain, headache, somnolence, uneasiness. Government departments, telecommunications regulatory agencies, and other relevant regulations for the promulgation of electromagnetic radiation. Such as 1644.1-2007 YD-T and 62209-1 EN, etc.. Below we introduce the requirements of the national standard.
Basic requirements for testing
- The temperature of the environment can not exceed 2 in the measurement of the temperature at 18 -25.
- Environmental electromagnetic noise can not exceed 0.012W/Kg.
- The wireless communication device is not connected to the local public communication network.
- The effect of reflection and auxiliary radio frequency transmitter should be less than 3% of the SAR value.
The above 4 points, such as temperature, power and other factors that affect the SAR test, make it control in a certain range, reduce the error of the test.
- The SAM standard model should be used for the 62209-1 SAR standard for the use of handheld wireless communication devices for IEC measurements.
The dielectric constant and conductivity of tissue simulation solution
Requirements: the shell of the model should be used in the formulation of the chemical composition of the tissue simulation solution which has the resistance, the dielectric constant and the low loss of the material.
SAR measurement equipment specifications
1. Scan system specification
1.1 The position accuracy of the probe tip is better than that of the 0.2mm.
1.2 The positioning resolution is a measurement system that can be performed on each measurement system, and the resolution should be 1mm or less. The requirements for the robot arm and probe positioning to ensure the accuracy of the test position.
2. Equipment fixture
2.1 The effects of environmental (e.g., floor, fixture, liquid surface) on the reflection and absorption of SAR measurements.
2.2 The fixture must be made of low loss and low dielectric constant material (loss tangent is less than 0.05, the relative dielectric constant is less than or equal to 5)
As shown in the picture, the SAR system’s fixture is usually made of plastic.
3.1 In the SAR test, the dielectric properties of the tissue fluid should be measured, and the temperature of the tissue should be the same as that of the SAR.
3.2 Calibration of the tissue fluid (to ensure that the measured two dielectric parameters are in the table 1. 5%).
3.3 For the horizontal layout of the human body model, the depth of the tissue should be at least 15cm above ERP, and there is no bubble.
System check is usually the signal source input 1W power, through the measurement and system check target value comparison. Must be within 10%
Ready to test the wireless equipment
1. The transmitter, antenna, battery, and accessories used in the wireless device itself should be specified by the manufacturer. The battery should be charged with electricity and there should not be any other external cable links in the process.
2. From the base station to control the output power and operating frequency of the device, the wireless device should be set at the highest power level to transmit.
3. The prototype of the test must be verified to be identical to the commercial version of the machine and the electrical characteristics.
Localization of wireless devices relative to the model
The standard set up two test locations on the head of the phone in the head model, “stick” and “tilt””. Mobile phones should be tested on the left and right of the SAM model in these two positions.
SAR test required
1. SAM model on the left and right side of the stick face and tilt position
2. In the completion of the post face and tilt test of colleagues, but also to consider the different state of the device itself. Such as sliding cover models and retractable antennas, etc..
3. After the completion of the above two points, but also to the different state of the system and frequency bands.
SAR scan area
1、Area scan for maximum values
In the range of the 8mm, the SAR value of the fixed distance from the surface of the model, the scanning area should cover the entire area of the cell phone. It is necessary to maintain the fixed distance between the probe and the model surface of the model in the whole scanning process. The error of the fixed distance between the 8mm and the model is 1mm.
A local scan can be selected from the center of the region of the peak SAR in the process of scanning, and the volume of 32mm x 32mm x 30mm by 5 x 5 x 7g points is scanned.
After two stages, the electric field intensity of the unit tissue is ensured.
The difference American Standard and GB
1. The calculating method of SAR value is not the same, American Standard is 1g units calculated peak, GB is 10g units to calculate average value.
2. American Standard has on the body of the test requirements. Such as mobile phones, data in addition, FCC will be a description of the document, specific testing for individual products to do guidance documents.
A place to be noted before testing SAR
At the present stage, the mobile phone antenna is characterized by Monopole and PIFA antennas, and the two antennas have some characteristics, so the two antennas should be recognized before using. In order to meet the requirements of SAR, the placement, material and direction of the antenna is controlled.
If the product is not easy to form an antenna and PCB board, we need to adjust the mobile power to lower the SAR value. Especially when testing GPRS, due to a number of upstream channel, if the power is not adjusted, SAR is very easy to exceed.