Utilising the Piezoelectric Effect to Fight Battery Drain

Article By : Anne-Françoise Pelé

Smart devices, always listening, in aggregate consume kilowatt-hours of energy while idle. That's an opportunity Vesper Technologies is seizing.

PARIS — Microphones are virtually everywhere, and they are proliferating at an astonishing rate. It’s an inexorable trend attributed to the surging demand for smartphones, IoT devices, wearables, hearing aids, virtual reality headsets, and other consumer electronics. Those mics are always listening, always ready to switch on, so even while idle most of the time, in aggregate they consume kilowatt-hours of energy. That’s an opportunity Vesper Technologies Inc., a Boston-based provider of piezoelectric MEMS microphones, has seized.  

Vesper’s ZeroPower Listening (ZPL) technology uses the piezoelectric effect, first discovered by French physicists Paul-Jacques and Pierre Curie, to make the acoustic transducer operate as an acoustic switch. When a soundwave hits a piezoelectric cantilever, it moves the cantilever. This motion creates a voltage via the piezoelectric effect. This voltage is sensed by a very low-power comparator circuit, which sends a wake signal to the rest of the system. 


Vesper first introduced its ZPL technology in 2017. Two years later, “it has been adopted by large customers such as the Samsung, Amazon and Bose, and has become more mainstream,” said Matt Crowley, CEO of Vesper. The company reached a milestone that results from a combination of factors it had neither originally imagined nor planned on.

A market on the rise
Apple’s iPhone uses four microphones. Amazon Echo uses seven microphones. It is no surprise that today’s microphone market is robust. According to Yole Développement, the total MEMS microphone market (consumer, automotive, industrial, and defense) amounted to about $1.1 billion in 2018 and is expected to grow at a 5 percent annual rate up to $1.5 billion in 2024.  


Click here for larger image
(Source: Yole Developpement)
Click here for larger image

(Source: Yole Développement)

“An upcoming trend is piezoelectric technology,” said Dimitrios Damianos, Technology & Market Analyst, MEMS, Sensors, Photonics and Imaging at Yole Développement (Lyon, France). “In total, the thin-film piezoelectric-based device market reached more than $2.6 billion in 2018 and is expected to grow up to $6 billion in 2024. This includes all types of piezoelectric MEMS devices such as gyroscopes, inkjet printheads, microphones and BAW filters.” Asked about microphones specifically, Damianos said that “piezoelectric MEMS are disrupting the traditional capacitive microphone approach thanks to waterproof, dust-proof and ultra-low power consumption features.” 

All in all, piezoelectric technology is gaining momentum, and “piezoelectric MEMS technology has started rejuvenating the MEMS market, spreading to other devices such as micro-speakers, piezoelectric micromachined ultrasonic transducers, autofocus, etc.”  

On the global MEMS microphone market, Knowles Corp. and Goertek Inc., “have left their competitors far behind and competed against each other for market share.” As for piezoelectric MEMS microphones, Vesper was early in the game and remains today the only provider.  

Durability and sustainability at stake 
The global smart home market is projected to grow almost five times to $192 billion in 2023, according to IHS Markit. With the penetration of these always-listening devices comes the risk of ever-rising power consumption and adverse impact on the carbon footprint. “A typical smart speaker runs at 2.9 watts when idle, which is close to the energy use in active mode, 3 watts,” Vesper said. “In a smart home equipped with 10 devices, remote controls, speakers, home assistants and TVs increase electricity consumption by 262kWh per year, which represents a 7.5-percent rise on worldwide average household energy usage.” 

Dimitrios Damianos
Dimitrios Damianos

Here is where Vesper has a card to play.  

Smart devices with traditional microphones require constant flow of electricity to stay in listening mode, which is a constant drain on their batteries. Instead, Vesper claims its piezoelectric MEMS microphones let battery-powered devices stay in wake-on-sound mode without draining the battery. Power consumption is reduced. Durability is improved. “Vesper’s ZPL technology offers a unique low-power consumption, inherent to the piezoelectric effect,” Damianos said. “It is ideal for low-power always-listening consumer applications, where the battery life is of paramount importance and can be greatly extended.”   

For instance, Crowley said, “voice-activated TV remote controls survive about 4 weeks with the traditional microphone technology. With our technology, it is over 6 months, and up to 12 months if the user doesn’t watch TV that much.” Compared to other listening systems, the ZPL technology can extend microphone’s battery life from 5 to 20 times.  

“The first generation of smart devices consumed a large amount of power even if they were plugged in,” Vesper’s CEO said. “It is changing as large companies such as Amazon recognize it is not sustainable to have all these products consuming power all the time.” The first wave of adoption was driven by battery-powered products, but many other devices can use the technology and have an impact on household energy consumption.  

Manufacturing at scale 
“Even with a proper and superior technology, a killer application is needed,” Damianos reminded. “This was the case with Knowles in 2003. It took off by incorporating the MEMS microphones in Motorola Razr phones, which were sold in millions.” At the time, Knowles offered killer functionality by reducing microphone thickness and size. “Moreover, the capability of manufacturing and selling to one single client quantities in the order of one million units is very important for success.” 

“2019 is the first year of very high volumes,” Crowley claimed. “Our ZPL products have gotten good adoption, and volumes have grown from less than a million in 2018 to more than 10 million this year. It has been adopted by large customers such as Samsung, Amazon and Bose.” Anticipating the manufacturing demand, Vesper partnered with tier-one manufacturers GlobalFoundries and TSMC, as well as assembly and test services provider Unisem. 

The ZPL technology is not the only microphone technology Vesper offers. “It’s the customer’s choice to adopt it.” Today, over half of the customers use it, and “there are still a lot of adoptions for us to work on. We want to continue to tell people about this technology and explain its benefits.” Last year, “was about proving we could ship our technology in high volumes, which has always been difficult for MEMS. Next year will be about growing and expanding our product line with improved products.” 

In July, Vesper introduced its first digital piezoelectric MEMS microphone, the VM3000. “It could potentially be used in large arrays for 3D sound capture,” Damianos said. “Especially with the voice-based interaction becoming more popular, Vesper could enter the smart TV, remote control and smart speaker markets.”

The VM3000 achieves a typical 63db dB signal-to-noise ratio (SNR) at 1kHz signal and offers an acoustic overload point (AOP) of 122 db sound pressure level (SPL).  “In legacy capacitive technology, the protective mesh used for waterproof/dustproofing drops the SNR by 3 to 5 db, or more depending on the mesh thickness. So, in applications where robustness is needed, such as harsh environments, VM3000 would be an excellent choice.” 

Later this year, Crowley said Vesper will be sampling two additional ZPL products, including a version of the VM3000.  

Long-term vision and development plans 
“Our long-term vision comprises three things,” said Crowley. Unsurprisingly, the Boston-based company aims at becoming the number-one provider of sensors for microphones. A goal that can only be achieved by leveraging its core MEMS technology, improving the SNR and reducing the product size.  

Matt Crowley
Matt Crowley

Second, Vesper plans to manufacture other types of sensors, with the same manufacturing process, and combine microphones with accelerometers and temperature sensors. “Multi-sensor chips with microphones will come sooner than people realize. Our ambition is to quickly transform ourselves from a microphone company to a multi-sensor company on a single chip.”

Third, Vesper wants to increase the intelligence of the sensor. “We want to take the ZeroPower capability and do more signal processing to do more intelligent things such as identify specific keywords and have the system wake up from a specific keyword, not from other sounds.” Today, piezoelectric MEMS microphones are designed to only respond to sounds between 300 Hz and 6 kHz, which includes the human vocal range. Because they do not require a bias voltage, they start up at around 50 microseconds and do not miss the keyword. In comparison, capacitive MEMS microphones take about 1000X more time to start up because they require time to charge their MEMS to a high bias voltage. 

“We believe that, in the future, we will have sensors paired with some artificial intelligence embedded in the sensor. It will be able to learn the way humans and animals use their senses — not just sight, hearing, taste, smell and touch, but also motion or temperature — to learn about their environment. Our long-term vision is that objects will use multiple types of bio-inspired sensors to learn about their environment and respond the best way possible.” 

To support the company’s development, Vesper is expanding both engineering and sales teams and now employs over 40 people. It currently has offices in China, Korea and Singapore and is planning to open in Taiwan in the coming months. In 2020, it expects to expand its international footprint in other places like Korea, Japan and Europe. Vesper’s piezoelectric MEMS microphone design architecture is “so new and different that it takes time for people to understand the benefits. Now that large companies have gone through the adoption phase, people are more comfortable using it. It is time to start expanding.” 

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