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March, 2020

Lensless Microscopy Shows Samples in Full View...

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record the pattern created by the dif- fracted light. To recover an entire complex image, like a tissue sample, for viewing, ptychography requires thousands of patterns to be recorded, while scanning the sample to differ- ent positions. “Although ptychography has

been of increasing interest to scien- tists around the world, broad imple- mentation of the method has been hampered by its slow speed and the requirement of precise mechanical scanning,” says Shaowei Jiang, UConn graduate student and lead author of the study. Zheng’s new ptychographic tech-

nology addresses these issues by bringing the sample close to the image sensor. This new configuration allows the team to have the entire image sen- sor area as the imaging field of view. Also, it no longer requires the precise mechanical scanning needed for tradi- tional ptychography. This is because the new configu-

ration has the highest Fresnel num- ber ever tested for ptychography, ap- proximately 50,000. The Fresnel number characterizes how a light wave travels over a distance after passing through an opening, such as

a pinhole. The ultra-high Fresnel number used in Zheng’s experiments indicates that there is very little light diffraction from the object plane to the sensor plane. Low levels of dif- fraction mean that the motion of the diffuser can be directly traced from the captured raw images, eliminat- ing the need for a precise motion stage, which is critical for conven- tional ptychography. With traditional lensed mi-

croscopy, users can only view a small portion of a slide. Zheng’s current platform offers a 0.05 in.2 (30 mm2) field of view, compared with the stan- dard 0.003 in.2 (2 mm2). By using a full-frame image sensor in a regular photography camera, Zheng’s tech- nology allows researchers to analyze two entire slides at once. “Imagine being able to read an

entire book at once, instead of just a page at a time,” says Zheng. “That’s essentially what we hope our tech- nology will allow clinicians to do.” Due to its compact configura-

tion and robust performance, Zheng and his team envision their platform to be a good fit for use in range of point-of-care, global health and telemedicine applications. The tech- nology can also be useful for X-ray and electron microscopy. Web: r

Ultra-Low Power Wi-Fi Connectivity

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videos) over a range of up to 70 ft (21m).

“You can connect your phone,

your smart devices, even small cam- eras or various sensors to this chip, and it can directly send data from these devices to a Wi-Fi access point near you,” says Dinesh Bharadia, a professor of electrical and computer engineering at the UC San Diego Ja- cobs School of Engineering. “You don’t need to buy anything else. And it could last for years on a single coin cell battery.”

Commercial Wi-Fi radios typi-

cally consume hundreds of milliwatts to connect IoT devices with Wi-Fi transceivers. As a result, these de- vices need large batteries, frequent recharging or other external power sources to run. “This Wi-Fi radio is low enough

power that we can start thinking about new application spaces where you no longer need to plug IoT de- vices into the wall. This could un- leash smaller, fully wireless IoT se- tups,” says UC San Diego electrical and computer engineering professor Patrick Mercier, who co-led the work with Bharadia. “It could also allow you to connect devices that are not currently connected — things that cannot meet power demands of cur- rent Wi-Fi radios, like a smoke alarm — and not have a huge burden on battery replacement.” The Wi-Fi radio runs on extreme-

ly low power by transmitting data by a technique called backscattering. It takes incoming Wi-Fi signals from a nearby device (like a smartphone) or Wi-Fi access point, modifies the sig- nals and encodes its own data onto them, then reflects the new signals on-

to a different Wi-Fi channel to another device or access point. This work builds on low-power

Wi-Fi radio technology that Bhara- dia helped to develop as a Ph.D. stu- dent at Stanford. In this project, he teamed up with Mercier to develop an even lower-power Wi-Fi radio. They accomplished this by building in a component called a wakeup re- ceiver. This “wakes up” the Wi-Fi ra- dio only when it needs to communi- cate with Wi-Fi signals, so it can stay in low-power sleep mode the rest of the time, during which it consumes only 3 µW of power. The UC San Diego team’s im-

provements to the technology also in- clude a custom IC for backscattering data, which makes the whole system

Wi-Fi radios integrated in small chips next to a grain of rice (Credit: David Baillot/UC San Diego Jacobs School of Engineering).

smaller and more efficient and en- ables the Wi-Fi radio to operate over its long communication range. Its range of 70 ft (21m) is a practical dis- tance for operating in a smart home environment. “Here, we demonstrate the first

pragmatic chip design that can actu- ally be deployed in a small, low-pow- er device,” says Mercier. Web: r

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