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Name of experiment：Application of power amplifier in the detection of foreign body in wireless power transmission

Experimental equipment：inverter, resonant circuit, Tx coil, signal generator, power amplifier, speaker, circuit breaker

Experimental purpose：aiming at the wireless power transmission system of electric vehicle, the detection method which can quickly, effectively and accurately identify the intruding metal foreign body is studied.

Content of experiment：in a complete magnetic resonance wireless power transmission system, the DC excitation is converted into the standard sinusoidal excitation by the inverter and resonant circuit and then applied to the Tx coil. The method of sinusoidal excitation directly applied to the Tx coil is used to simulate the actual situation.

Experimental process：

（1）Set up the experimental system

The Tx coil requires a sinusoidal excitation generated by a signal generator and a power amplifier. As shown in the figure, the signal generator model is Agilent 33522A and the power amplifier model is ATA-4014, which can amplify the input signal without distortion.

（2）Feasibility verification of horizontal gradiometer detection

Firstly, the feasibility of horizontal gradiometer detection of metallic foreign bodies was tested. In the experiment, a sinusoidal excitation current was applied to the Tx coil with an excitation frequency of 100kHz and an amplitude of 1.2A.

Using a one yuan coin as a metal foreign body, the Tx magnetic field is not uniform, resulting in the presence of an initial induced voltage on the gradiometer. When the foreign body is present, the induced voltage amplitude increases. Although the induced voltage waveform varies, the initial voltage will vary with the Tx magnetic field amplitude.

（3）Verify the feasibility of vertical gradiometer detection

Place the rectangular gradiometer upright parallel to the Tx magnetic field as shown.

Result of experiment：

（1）Excitation and induction voltage waveform at initial placement

（2）The gradiometer has no induced voltage under normal conditions. In the presence of a metallic foreign body, the induced voltage waveform on the gradiometer is shown, with the voltage amplitude no longer zero. Therefore, it is feasible to use vertical gradiometer for metal foreign body detection.

Conclusion of experiment ：

Both horizontal and vertical gradiometer can complete the basic metal foreign body detection function. For the horizontal gradiometer, the initial induced voltage amplitude of the gradiometer is close to zero when the magnetic field is distributed symmetrically along Tx. For the vertical gradiometer, the Tx magnetic field can be circumvented by a simple radial arrangement along the magnetic field so that the initial induced voltage is zero. The detection blind spots exist in both coils, and the induced voltage increases with the increase of the foreign body area.