[Advanced technology to watch in 2022] Technical introduction of JQA reverberation chamber Immunity test of in-vehicle equipment with high accuracy | Dempa Shimbun Digital

1. Introduction

　The Japan Quality Assurance Organization (JQA) introduced a reverberation chamber (hereinafter referred to as "RVC") for automotive equipment in anticipation of future immunity tests. ), the operating principle and technical features are introduced.

　The automotive industry is said to be entering a period of change, including manufacturing, in relation to IoT technology and energy policies. Electric vehicles (EVs) are expected to spread and expand not only as a role of mobility but also as one element to solve energy problems, and self-driving cars are incorporated as an important element in the grand design of future society.

As shown in Fig. 1, in a society where the use of radio waves is being promoted more and more, automobiles encounter various electromagnetic waves while moving. Vehicle resistance tests (immunity tests) against electromagnetic waves have been conducted with sufficient quality through repeated improvements in testing methods, but self-driving cars:

(1) The use of sophisticated electronic devices

② A large number of sensors such as cameras and radars are installed around the vehicle body

(3) A high-speed data communication network is installed throughout the vehicle.

There is a demand for an efficient and high-quality immunity test method suitable for this. Therefore, the RVC method has recently attracted attention.

　The RVC method can evenly irradiate automobiles and in-vehicle equipment with electromagnetic waves from various angles, and is expected to be a method that can maintain test quality even in the gigahertz high-frequency band. In 2010, ISO 11452-11, an in-vehicle component test based on the basic standard IEC 61000-4-21, was issued as a test standard for the RVC method for automobiles. ISO 11451-5 is being prepared (currently deliberating Committee Draft ) (Fig. 2).

2. Basic principles of the RVC method

There are various methods of the RVC method, but the currently commonly used method is specified in IEC 61000-4-21 Most of them have a mechanical stirrer (Fig. 3).

　The chamber has a structure of a shielded room made of metal with high conductivity, and is a three-dimensional cavity resonator designed with a large size so that it becomes multimode at the lowest operating frequency used in the test. For an ideal cavity resonator, the resonant frequency is given by equation (1).

L, W, H: size of RVC, C0: speed of light 2.998×108 m/s, m, n, p: mode order

If the size of the RVC owned by JQA (4.84 x 3.6 x 3.1 [m]) is applied to this formula, the eigenmode is shown in Fig. 4, and it can be seen that the higher the frequency, the denser the distribution.

The RVC has a stirrer (called a stirrer or tuner), and the rotation of it changes the boundary conditions of the chamber, so it is possible to change the mode distribution. By adjusting the input power based on the modal distribution and the Q value of each mode, an electromagnetic field is obtained in which the amplitude and polarization of the electric field within the test area are statistically uniform. Fig. 5 shows the measurement results of the electric field uniformity. Field uniformity is evaluated by taking the standard deviation of field strength measured by field probes placed at eight locations in the test area shown in FIG. Since the electric field components Ex, Ey, and Ez of each probe are handled independently, a total of 24 (=8×3) data are used for each angle of the stirrer in step rotation.

　Electric field uniformity is an important indicator for verifying whether the RVC functions as designed. Satisfying standard requirements for electric field uniformity is a condition for obtaining results with good correlation between different RVCs.

3. RVC method test procedure

Prior to executing the actual test, set up the test bench, test samples, and other items necessary for the test in the RVC that satisfies the requirements for electric field uniformity. Measure the loss due to The loss is obtained by measuring the received power using an antenna or electric field sensor placed in the test area and calculating the difference before and after the setup. This difference is called the chamber loading factor (CLF) and is used to determine the input power to the transmit antenna during testing. This is to consider changes in attenuation and Q due to test benches and test samples. Once CLF is determined, the input power PForw to the transmit antenna to obtain the test electric field ETest is determined by equation (2).

Here, FCLF and GRC are the load factor and chamber gain defined by ISO 11452-11, respectively.

4. RVC electromagnetic field

In the RVC of Fig. 3, the distribution of the electromagnetic field changes when the stirrer is rotated, from the constraints of the paper, the angles 0° and 60° , and only three points at 120° are shown in FIG. It can be seen that the magnitude of each component of the electric field changes, albeit only at three angles, and that it is stirred. In addition, since the arrow of the Poynting vector is a composite wave of scattered waves, it is not uniform on each cutting plane, and varies irregularly depending on the stirrer. It differs greatly from the ALSE method, which applies a quasi-plane wave from one direction.

5.RVC method characteristic application range

　ISO 11452-2 (ALSE method) has been widely used since the mid-1990s for immunity testing of in-vehicle equipment. A characteristic application example that the RVC method has compared with the law is given.

　Since the test area can be three-dimensional and large, it is possible to test large specimens. Since the effect of the placement of the harness on the results is small, long harnesses can also be laid out, so it can be applied to in-vehicle Ethernet cables in full size. In addition, EV in-vehicle equipment with three types of harnesses, DC high voltage, AC charging, and conventional 12V, can be affected by simultaneously applying electromagnetic fields without repeating the test by rearranging the harness. can see.

Since the RVC method generates a uniform electromagnetic field by stirring a large number of internally scattered reflected waves, it is possible to test multiple specimens at the same time if a certain interval is maintained. "N increase test" can be easily performed. Highly reliable judgments can be made with multiple specimens.

　You can test up to the high frequency band without worrying about the beam width of the irradiation antenna. It is expected that immunity tests will be required up to 6GHz in the near future, and this can be easily handled.

Unlike the ALSE method, there is no need to change the antenna position or polarization plane, so automatic measurement is possible without interrupting the test.

6. Conclusion

Around 2000, interest in the RVC method temporarily increased as many studies were conducted mainly in the United States and France to apply it to automobiles. Compared to the ALSE method, the RVC method, in which the stirrer is stepped and rotated, was avoided because it took more time to test than the ALSE method. However, with the increasing complexity of in-vehicle equipment due to autonomous driving, etc., high robustness against immunity is required, and the test time for the ALSE method is increasing.In addition, test quality requirements in the GHz band has come to be questioned, the RVC law is once again attracting attention.

JQA has introduced two RVCs (one at the Safety Electromagnetic Center and one at the Chubu Testing Center ). We are considering the possibility of new utilization of RVC, such as test setup considering the characteristics of the product and expansion of the application range of the test method.

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