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From the last 4-year, Apple phones are coming without the audio jack. Wireless headphones of all types promise to function like the wired headphones just without the twisted mess of cords. But in reality, they don’t function like wired headphones. Many times, when we are using our Bluetooth earbuds and our phone is in the pocket the connection cut out or there will be synchronization issues between audio and video. If one earbud sync separately with the other one, it may cause an echo effect.

Figure.1 The Size of AirPods are very small

Making good Airpods is a difficult task as “they are Tiny” unlike the other Bluetooth headphones which have bigger PCB sizes available.

However, size is not everything. Normally in wireless devices, the antenna size corresponds to the corresponding operating wavelength, but it doesn’t mean that a bigger antenna guarantees a better connection. To establish a good connection, the placement of the antenna, PCB, and other mechanical parts play important rules. In the case of AirPods, we get a very small space. This means, we need to make sure that we are using every millimeter space quite wisely and also all the components are placed properly. For this 3D EM simulation help efficiently.

Still, so many people think that 3D EM simulation cannot accurately predict the antenna performance. Many people consider that simulation is a secondary function, which can be performed after the initial prototyping of the product to see its real-world performance. But nowadays, the simulation has moved to the center of the product development process. So that the performance of the product can be evaluated at the early stage of design. “Simulation has become an entire part of the design process, saving time reducing physical prototyping cost and improve the quality of the product,” said Nicolas Tillet, Dassault systems. Also, by saving product development time through simulation, the design team can spend more time in innovation.

The discrepancies between simulation and measurement may arrive if the proper simulation of the model is not performed. The success of simulation depends on the resources available, and the best and proven practices you adopt during the simulation process. That is why, it is very important to perform simulation properly otherwise we will get misleading data.


AirPods Simulation with CST Microwave Studio







Fig2.  AirPods, the 2.4GHz Bluetooth antenna is designed inside the Tube portion. Figures show the antenna return loss and efficiency.


The above figure shows the results are with AirPods only, the human body effect is not considered in the above simulation. The antenna efficiency is about 77 percent at 2.44GHz.


As we know that the space for the AirPods components such as the battery, PCB, speaker, and antenna are very limited, so every component is placed near to each other and as a result, it affects the performance of others. For example, in the above figure, the effect of PCB on the antenna efficiency is presented. The current antenna efficiency is about 77 percent but if we move the PCB only 2.5mm from the current position the antenna efficiency drops to 45.43 percent at 2.44GHz. Also, the designer needs to consider every millimeter of glue they are using to keep the components together inside the AirPods because extra material may block the signal.

Fig3. Effect of PCB Position and 3D Radiation pattern at 2.4GHz and 2.45GHz


Human Body effect on antenna performance



Fig4.  AirPods with Human head phantom (provided by CST microwave studio)


Many times in the Bluetooth AirPods, the main issue every user experiences is the drop of the signal when they put their phone in the pocket. This happens because the signal gets bounce with the human body and also the liquids and solids in the human body offer more molecular resistance to the free air.

Fig5.  Antenna return loss and efficiency with human head phantom


 Fig6. Antenna 3D radiation patterns at 2.44GHz with human head phantom


As from the figure.2 it can be found that the antenna efficiency is about 77 percent when the AirPods are simulated alone. But, as soon you put the AirPods near to ears in human head phantom the efficiency drops to 54 percent it can be seen in the above figure 5.  Figure 6. shows the 3D radiation pattern at 2.44GHz, it is observed that the radiation pattern is going away from the human head this reduces the hazard of human exposure to the EM radiation.



With the 3D EM simulation in hand, we can try different versions of products even without making the prototype. Different prototypes can be created and tested making simulation as a part of the design process itself. Simulation can reduce the overall product cost and time.

At CoreIoT Technologies, we utilize the most up-to-date tools available in the market. We actively develop new methodologies to improve our efficiency. We provide lower cost, better accuracy, and fast service. We can simulate your wireless device to see how it will perform at the very early stage of product development with the aid of a powerful workstation. At CoreIoT Technologies, all the engineers are advanced users of simulation tools such as CST microwave studio, Altium, and KiCad.



Rehan Siddiqui

Antenna Design Engineer