• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

MassDevice

The Medical Device Business Journal — Medical Device News & Articles | MassDevice

  • Latest News
    • Cardiovascular
    • Orthopedics
  • Wall Street Beat
    • Funding Roundup
    • Mergers & Acquisitions
  • Podcasts & Webinars
    • Podcasts
    • Webinars
  • Resources
    • About MassDevice
    • Newsletter Signup
    • Leadership in Medtech
    • Manufacturers & Suppliers Search
    • MedTech 100 Index
    • Videos
    • Whitepapers
  • DeviceTalks Tuesdays
  • Coronavirus: Live updates
Home » Teardown: Inside the Neurometrix Quell TENS device

Teardown: Inside the Neurometrix Quell TENS device

June 12, 2018 By MassDevice

A TENS device for transcutaneous electrical nerve stimulation wraps around the upper calf much like a wristwatch wraps around the wrist. Here are some of its operational secrets.

quell

By Lee Teschler

A medical device called a Quell performs what’s called transcutaneous electrical nerve stimulation on the lower leg. This technique is said to relieve diabetic pain. None of us here are diabetic so we can’t say whether the Quell actually does what its manufacturer — Neurometrix Inc. of Waltham, Mass. — claims it can do. What we can do is describe how the Quell is supposed to work and what we found when we disassembled it.

Neurometrix filed several patents on the Quell technology. The patents include block diagrams that explain the device’s functions. So our commentary here draws upon the explanations we found in the patent as well as what we discovered when we disassembled the components.

The Quell consists of a circuit pack that fits in a fabric holster. It stimulates the leg through a stick-on set of electrodes. The electrodes have a backing of a gel-like material that firmly touches the skin. Two snaps on the electrode form both the electrical connection to the Quell electronics and the mechanical connection to the electronics housing. The housing is plastic. It holds a two-sided circuit board and the lithium-ion rechargeable battery.

quell components
The Quell electrode material, top, elastic band, middle, and electronics enclosure, bottom.

The functions of the electronics are spelled out in one of the Neurometrix patents. The electrodes use hydrogel to create a low-impedance interface between the skin and the electrode. If the portion of the electrode touching the skin peels away at all, the current density and power density rises because there’s less area of contact between the electrode and the skin. The extra power density can be painful and in extreme cases can cause thermal burns. So the unit monitors the integrity of the skin-to-electrode interface by checking the impedance of the connection continuously. If the impedance rises beyond a certain threshold, the circuit stops delivering power to the electrodes.

The hydrogel has effectively zero impedance. The electrode-to-skin impedance is generally much larger than the body’s internal tissue impedance, so dividing the anode-cathode voltage difference by the stimulation current yields the electrode-to-skin impedance.

The Quell is designed so the person using it can walk around. Of course, walking around can induce some mechanical shocks and bumps, particularly if you happen to bump into anything. But this sort of jostling can cause momentary changes in how much of the electrode touches the skin.

The Quell block diagram as given in the Neurometrix patent.

You don’t want the device switching off when these momentary interruptions happen. So the electronics includes an accelerometer to provide a measurement of shock impact that indicates when the electrode impedance has changed simply because the wearer is walking or has stumbled into something. According to the patent, the accelerometer is sampled at a 400 Hz rate, and processor is programmed to ignore pulses from the accelerometer that are shorter than about 50 msec.

The accelerometer on the board is a three-axis 14-bit NXP device. It sits on the back of the PCB along with one other chip, a USB 2.0 controller from Silicon Labs. We should note we bought this Quell device second hand, so it’s likely that newer versions of the Quell use a more current version of a USB chip.

One interesting bit from its data sheet is that it provides access to both low-pass filtered data as well as high-pass filtered data, which is said to minimize the data analysis required for jolt detection – something we suppose would come in handy for filtering out things that happen when the wearer walks. The accelerometer can also monitor events and remain in a low-power mode during periods of inactivity.

The patent also describes how the Quell distinguishes impedance changes arising from walking or other transient conditions from those that could be more permanent. It’s all done with software flags and timers. The processor monitors the accelerometer. If the accelerometer generates a pulse, a flag gets set. The processor also monitors another flag that gets set if there’s an indication that the impedance between the electrode and the skin has risen. If the two events coincide long enough, the processor powers down the electrodes.

Plastic covers removed from the enclosure revealing the Li-ion battery andPCB

One Neurometrix patent shows a functional diagram of the TENS device that includes blocks for detection of pulses, transient motion, and electrode-skin contact, as well as a means of measuring and controlling the current and voltage of the two electrodes. You can be sure all these functions happen within the onboard processor. The processor on the Quell is a mixed-signal microcontroller from Texas Instruments. It is a 16-bit RISC CPU that has some features that let it wake up quickly from low-power modes.

The Quell also uses a current source, rather than a voltage source, to drive the electrodes. A Neurometrix patent indicates that driving the electrodes with pulses of current, rather than pulses of voltage, is preferable because stimulation current is independent of the impedance between the electrode and the skin, which changes while the device is in use. The voltage, of course, will change if the impedance changes.

quell electrodes
The two connections to the electrodes visible on the plastic enclosure.

The patent also indicates the maximum output voltage is 100 V and the maximum output current is 100 mA. The device generates a pulse pattern with intervals between the pulses that vary randomly in a 60 to 100-Hz interval. The reason for this variation is that it minimizes the tendency of the nerves in the skin to stop responding to the stimulation.

It’s pretty easy to see what the Quell uses to drive the electrodes. It is a big n-channel power MOSFET from ON Semiconductor. You normally find it in things like ac/dc power supplies. In this application, it seems over-specified because it can handle nine amps and 200 V. Though the patent talks about current pulses that are only 100 mA at most, the size of this MOSFET makes us suspect that the real Quell device uses current pulses that are a lot bigger than what the patent describes.

The MOSFET along with one sizeable 3.3 µH inductor and three ceramic capacitors seem to make up the main part of the drive circuit for the electrodes.

The main board. Note the size of that power MOSFET.

The processor, MOSFET, and accelerometer are the key semiconductors that handle the essential functions of the Quell. There are several other chips on the Quell that are interesting. Bluetooth communications are handled by a Silicon Labs BLE113. This is a Bluetooth Smart module that includes a host processor designed to also host end-user applications.

What’s interesting about this is that we can surmise that the software running the Quell functions was too big to fit in this Bluetooth module. Otherwise, Neurometrix would most certainly have squeezed it in and avoided the cost of the TI processor we found.

 

back board
The other side of the PCB.

References – chips on the Quell
Silicon Labs cp2102

NXP accelerometer 8451

Maxim fuel gage 17201

Silicon Labs Blue Giga

TI LP55231 LED driver

TI A40A op amps

TI MSP430F261x mixed signal MCU

On Semi FQD12N20L: N-Channel QFET

Filed Under: Neuromodulation/Neurostimulation, Pain Management Tagged With: Neurometrix

In case you missed it

  • Calyxo raises $32.7M for kidney stone treatment
  • Getinge anesthesia systems recall is Class I
  • RefleXion closes $125M debt facility
  • Senseonics announces equity grants to employees
  • New data backs Aerin’s RhinAer for treating chronic rhinitis
  • Enovis completes Insight Medical acquisition
  • Orchestra BioMed to go public, partner with Medtronic on cardiac neuromodulation therapy
  • Memic Innovative Surgery is now Momentis Surgical
  • Lyra Therapeutics appoints new chief medical officer
  • Masimo’s SafetyNet monitoring reduced length of COVID-19 hospital stays, study says
  • CeQur is launching a discreet, convenient ‘wearable insulin pen’
  • Teva appoints former Vertex exec as new head of R&D, CMO
  • Enovis partners with Kelvi on hot and cold therapies
  • West Pharmaceutical Services debuts new needle syringe system
  • Titan Medical names Cary G. Vance as new president, CEO
  • Acutus completes first closing in left-heart access portfolio sale to Medtronic
  • FDA clears Intuitive, Siemens Healthineers imaging integration for robotic bronchoscopy

RSS From Medical Design & Outsourcing

  • FDA can’t explain drop in device recalls, but experts point to COVID disruptions
    The FDA acknowledged interruptions with notifications from recalling firms during the pandemic, while regulatory experts point to fewer inspections and fewer procedures. FDA medical device product recalls dropped last year to their lowest level since 2013, according to a Medical Design & Outsourcing analysis of recall data from the regulatory agency. Medtech regulatory experts said the COVID-19… […]
  • DeviceTalks Boston 2022: Here’s what you missed on the show floor
    At DeviceTalks Boston 2022, there was a wealth of expertise to be had from exhibitors including Viant, ICS, PSN Labs, Propel and more. From stories of overcoming challenges during the COVID-19 pandemic to medical device materials pitfalls to avoid, MassDevice and MDO executive editor Chris Newmarker hit the DeviceTalks Boston show floor to discover insights. […]
  • Supply Chain EVP Greg Smith sees fewer suppliers in Medtronic’s future
    All eyes are on Medtronic’s global operations and supply chain leader as he works to modernize its operations and scrutinize suppliers. EVP of Global Operations and Supply Chain Greg Smith anticipates fewer suppliers in Medtronic’s future, he said in an interview this week. Smith spoke with DeviceTalks Editorial Director Tom Salemi in his first published… […]
  • CeQur is launching a discreet, convenient ‘wearable insulin pen’
    CeQur designed its Simplicity device to make insulin delivery as seamless as possible for people with diabetes. When it comes to managing diabetes, CeQur wants to make insulin therapy as convenient as possible. For those who prefer to manage their own insulin delivery, the Simplicity device might just do exactly that. Simplicity, a wearable, disposable… […]
  • Meddux opens new facility in Colorado
    Engineering, design, development and manufacturing company Meddux announced that it opened a new facility in Boulder, Colorado. The new, 22,000-square-foot facility doubles the overall square footage from its previous location in Colorado. According to a news release, it helps the company to quadruple its product development area and double its manufacturing footprint. Meddux’s new facility… […]
  • Reducing the Overall Cost of Validation
    By PTI Engineered Plastics Reliable medical devices and equipment are essential for researchers and doctors to accurately diagnose and treat a wide range of diseases. That is why there is such stringent oversight from the FDA to ensure these products meet the necessary requirements and specifications. To ensure compliance with regulators, manufacturers follow installation qualification… […]
  • BBS Automation has a deal to buy medtech supplier Kahle Automation
    BBS Automation said it plans to purchase high-speed automation supplier Kahle Automation to expand its medtech and life sciences business. Kahle will operate as Kahle – a BBS Company, according to a news release from Munich, Germany-based BBS and Lombardy, Italy-based Kahle. The deal is subject to regulatory approval. Terms were not disclosed. Kahle’s co-owners —… […]
  • How safe is health information after the overturning of Roe?
    The U.S. Department of Health and Human Services today issued guidance meant to better protect women’s health information as state abortion bans kick in after the U.S. Supreme Court’s overturning of Roe v. Wade. Despite the HHS actions, women may still wonder whether their health information is entirely safe going forward — a potential challenge… […]
  • Dexcom focuses on early diabetes diagnosis as COVID links emerge
    New evidence is showing that COVID-19 may increase a person’s risk of diabetes, but it could be years until we know for sure. In the meantime, Dexcom (Nasdaq:DXCM) is getting ready, VP of Global Clinical Initiatives Tomas Walker said. Walker recently spoke with Medical Design & Outsourcing to discuss the San Diego-based diabetes device developer’s… […]
  • Blackrock Neurotech and Pitt work on first at-home BCI system for remote trials
    Blackrock Neurotech and the University of Pittsburgh’s Rehab Neural Engineering Labs (Pitt RNEL) are working together on the first portable brain-computer interface (BCI) to allow patients to participate in research trials from home. A Blackrock representative said it’s the final step as the company prepares to launch its first commercial product early next year. Salt… […]
  • How medical device companies are responding to abortion bans
    Days after the U.S. Supreme Court’s decision to overturn Roe v. Wade’s protection of abortion rights, medical device companies are among those reassuring workers about healthcare access. Corporate communications to employees and the public at large come as trigger laws in nearly half of the states outlaw abortion immediately. Some medtech companies are not using… […]

Primary Sidebar

DeviceTalks Weekly

July 1, 2022
Boston Scientific CEO Mike Mahoney on building a corporate culture that drives high growth results
See More >

MEDTECH 100 INDEX

Medtech 100 logo
Market Summary > Current Price
The MedTech 100 is a financial index calculated using the BIG100 companies covered in Medical Design and Outsourcing.
Need Medtech news in a minute?
We Deliver!

MassDevice Enewsletters get you caught up on all the mission critical news you need in med tech. Sign up today.

MDO ad

Footer

MASSDEVICE MEDICAL NETWORK

DeviceTalks
Drug Delivery Business News
Medical Design & Outsourcing
Medical Tubing + Extrusion
Drug Discovery & Development
Pharmaceutical Processing World
MedTech 100 Index
R&D World

Device Talks Webinars, Podcasts, & Discussions

Attend our Monthly Webinars
Listen to our Weekly Podcasts
Join our Device Talks Tuesdays Discussion

MASSDEVICE

Subscribe to MassDevice E-Newsletter
Advertise with us
About
Contact us
Add us on Facebook Follow us on Twitter Connect with us on LinkedIn Follow us on YouTube

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Advertise | Privacy Policy | RSS