The scientists from Tokyo Institute of Technology are pioneering a cutting-edge technique using diamond quantum sensors that accurately estimate electric vehicle mileage.

A current drawback of some electric vehicles (EVs) is the inaccuracy of their battery charge, which can be wrong by as much as 10%. Japanese researchers now appear to have introduced an innovative solution to this problem, developing a detection technique based on a diamond quantum sensor that can accurately quantify the mileage of an electric vehicle.

Limits on battery efficiency of electric vehicles

Electric vehicles have seen a significant surge in demand as the world shifts from emissions-producing internal combustion engines to a greener, battery-powered, emission-free alternative. This has led to efforts to improve the efficiency of batteries for electric vehicles; however, a major drawback is that their calculated fee can be very inaccurate.

The battery charge of an electric vehicle is measured based on the current output of the battery, which then estimates the remaining range of the vehicle. Electric vehicle battery current can typically reach hundreds of amperes; however, commercial sensors that detect these currents cannot measure small current changes at milliamp levels. This can lead to inaccuracies in electric vehicle battery range of up to 10%

Improving efficiency with quantum sensors

To overcome these limitations, researchers at the Tokyo Institute of Technology have developed a detection technique based on a diamond quantum sensor that can estimate the battery charge of an electric vehicle with 99% accuracy.

Professor Mutsuko Hatano, head of the research from the Tokyo Institute of Technology, said: “We have developed diamond sensors that are sensitive to milliamp currents and compact enough to be implemented in cars. Besides, we measures currents over a wide range and detects milliamp currents in noisy environments.

The team developed their sensor prototype using two diamond quantum sensors placed on either side of the busbar – the electrical connection for input and output currents – in the car. They then used differential detection to remove the noise detected by the sensors and keep only the actual signal. This allowed them to identify a small current of 10 mA in the ambient background noise.

The team then used mixed analog digital control of the frequencies generated by two microwave generators to track the magnetic resonance frequencies of the quantum sensors in a one gigahertz bandwidth. This facilitates a large dynamic range of ±1000 and a wide operating temperature range from −40 to + 85 °C.

For the final stage, the researchers tested driving with the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) – the standard test for energy consumption in electric vehicles. Quantum sensors accurately track charge and discharge current from -50 A to 130 A and battery charge estimation accuracy within 1%.

Professor Hatano concludes: “Increasing battery efficiency by 10% would reduce battery weight by 10%, reducing 3.5% energy for propulsion and 5% energy to produce 20 million new EVs in 2030 worldwide.” This in turn corresponds to a 0.2% reduction in CO2 global transport emissions in 2030.’

Quantum sensors accurately predict electric vehicle range capacity

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