Molex unveils automotive noise cancellation sensor

Molex has announced the first product in a new family of automotive active noise cancellation (ANC) sensors with the introduction of the MEMS accelerometer-based road noise cancelling (RNC) sensor. This noise cancellation sensor is designed to reduce road, wind, and HVAC car noise as well as low-frequency sounds that increase driver fatigue.

In-cabin noise reduction is becoming more important to customers of electric vehicles (EVs). Molex expects advancements in ANC technology, more commonly associated with high-end headphones, to transform how car manufacturers address road-based noises. Instead of installing sound-absorbing materials to insulate car interiors from excessive road noise, ANC sensors can be installed on a car’s chassis for higher accuracy, said Molex.

The Molex RNC sensor features a couple of key differentiators, which include pairing the accelerometer sensing element with the Automotive Audio Bus (A2B) technology from Analog Devices Inc. (ADI) for high-fidelity audio, the ability to daisy chain the sensors, and a ruggedized housing that enables the ANC sensors to be mounted on wheel wells and car frames.

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The combination of the A2B technology with the RNC sensor delivers several benefits, including the ability to transmit noise signals to the processing unit in less than two milliseconds. The pairing also delivers higher sensitivity, enabling the sensor to measure and cancel noise at slower speeds.

The low noise floor of the RNC sensor enables the devices to capture road noise, convert the vehicle chassis vibration into a signal that generates a cancellation sound wave, which reduces road noise in the vehicle cabin. The noise spec for the accelerometer is <100 µg/√Hz for x- and y-axes and <150 µg/√Hz for z-axis.

The ability to daisy chain the sensors that include integral connectors, using twisted-pair discrete cabling and Molex’s Mini50 sealed connectors, eliminates the need to be connected by parallel cables in a star pattern, simplifying integration and offering up to a 30% reduction in wire harness weight when compared to other systems, according to Molex. In addition, the Mini50 connectors offer up to a 50% space savings over traditional USCAR 0.64 connectors.

The A2B technology also allows a higher number of signals per chain to be processed. While the ability to daisy chain the sensor is not unique, it’s the number of channels, or nodes, on that network and the overall length of the network itself that ADI has been able to maximize, said Kurt Dekoski, business development engineer, at Molex. “You can have up to 32 channels with a maximum length of 40 meters.”

Since these sensors can be mounted to wheel wells and car frames, they also need to withstand harsh conditions. According to Molex’s recently commissioned The Future of Automotive Survey, conducted by Dimensional Research, one of the biggest barriers to innovation, cited by 36% of the automotive decision makers surveyed, is the need for electronics and software to operate in extreme scenarios. Sensor technology was reported as one of the most important innovations by 27% of the respondents.

To meet this challenge, the RNC sensor is available in different housings, including an IP6K9K enclosure that enables the sensors to be placed under the car’s chassis, much closer to the road noise for faster and more accurate noise cancellation. This also ensures greater protection from harsh weather and road conditions. The sensors are pothole and collision rated and provide an operating temperature range of -40°C to 115°C.

The Molex team was originally tasked with ensuring that the RNC sensors could withstand harsh conditions, including a direct impact such as a rock strike, said Dekoski. Initial feedback from customers indicates that the offering is more robust than competitive solutions for mounting in these areas [under the chassis], he said.

Detecting the sound at its source speeds processing of the noise-canceling signal, said Dekoski. “The closer you can get to the the source of the noise the more accurate and the clearer that sound is going to be.”

Reducing the design cycle

Electronic component manufacturers aren’t going alone anymore. Collaboration among the supply chain is becoming more the norm to bring a better product to market faster, while also helping to reduce the design or development cycle for the OEM customer.

In addition to working with ADI, Molex also tested and validated the RNC sensor with Silentium’s “Active Acoustics” software, which removes up to 90% of unwanted noises across a broad band of frequencies (from 20 Hz to 1 kHz). By integrating Molex’s RNC sensors with the Silentium’s noise cancelling software it can reduce automotive design cycles as well as engineering costs, reducing the effort to launch these sensors into a vehicle, said Dekoski.

“This is the way that a lot of business is starting to happen where you can form these relationships and it just accelerates the launch of new tech and how you’re able to do it,” he added. “You don’t necessarily need to have everything under one roof like we used to have. Now, we’re able to work together and come up with good solutions.”