Designing the ANSYS Wristband - Ozen Engineering · Designing the ANSYS Wristband By: ... Dependent...

1 © 2014 ANSYS, Inc. April 23, 2015 ANSYS Confidential

Designing the ANSYS Wristband

By:

MingYao Ding

Mahmoud Mahmoud


Smart Wearable Design Process

System Design Goals

Electronics System • Antenna Performance • PCB Performance • Charger Performance

Mechanical System • Mechanical Durability • User Experience • Manufacturability

Control Design • Wireless Control • Data Processing

Final Product

Tools needed: • HFSS • SIwave • Maxwell • SpaceClaim

Tools needed: • Scade Systems

Tools needed: • ANSYS Mechanical • SpaceClaim

• Performance • Durability • User Experience • Cost

System simulation


ANSYS Wristband will:

• Perform Health Tracking (Blood pressure, Pulse rate, etc…)

• Stream music via Bluetooth speakers,

• Display Smart Watch functions on LCD

– Key Electronics Systems

• Omni-directional Antennas

• 3 layers board within 4X4cm

• Wireless power charging

– Key Mechanical Challenges

• Impact resistant

• Manufacturability

• Comfortable to wear

– Control System

• Control two wireless systems simultaneously

• Generate a robust code to ensure accurate measurement and display of health data.

System Design Goals


• Antenna Design – Start with a basic design

– Wrap antenna around the wristband

– Tune Antenna to vastly improve performance

• Power and Signal Integrity – Start with an initial layout

– Verify critical paths in pcb layout

• RF & Critical Digital interconnects

– Improve layout to handle high speed data

• Wireless Power charger – Design and Optimization of the Wireless power charger

Electronics System - Optimized

•Omni-directional Antennas •3 layers board within 4X4cm •Wireless power charging


Antenna Design


1. Bluetooth Antenna

• Frequency = 2.4GHz to 2.485GHz

• Return Loss = less than -10 dB

• Flexible Substrate

2. Bio-Sensor Antenna

• Frequency = 400-450 MHz

• Return Loss = less than -10 dB

• Flexible Substrate

Antenna Design

Bluetooth

Bio-Sensor Antenna and PCB


– Ant1_L1

– Ant1_L2

– Ant1_W

– Ant2_L1

– Ant2_L2

– Ant2_W

Antenna Design > Parameters

Ant1_L1

Ant1_L2

Ant1_W

Ant2_L1

Ant2_L2

Ant2_W


• The first step should be to solve the nominal variation using Analytic Derivatives

• The Analytic Derivatives can be used to reduce the number of necessary design variables. Eliminate variables that minimally affect the Return Loss over the band of interest!

• Plot the Derivatives of the Return Loss of each Variable with Respect to Frequency

– Ant1_L1

– Ant1_L2

– Ant1_W

– Ant2_L1

– Ant2_L2

– Ant2_W

Antenna Design


Dependent Solve Setup in HFSS

Multiple Solution Frequencies

2400 MHz 400MHz

Excitation

PCB

900MHz 2400MHz

Each frequency band excites a different part of the antenna. Meshing at a single frequency will not guarantee accuracy.

Setup 1: 2400MHz

Dependent Mesh Setup: 400MHz

Sweep Converged Adaptive Meshing


Antenna Design > Results

Optimized Planer Antenna Performance


Antenna Wrapping - Optimized

Both antennas performance is effected by wrapping

Bio-sensor Bluetooth

Problem fixed using parametric optimization!


PCB Power and Signal Integrity


PCB description

Schematic Layout

Layout work was done in Eagle


Critical RF Path and Interconnects

Bluetooth Antenna Feed

Bio-sensor Antenna Feed

SD Memory Card Interconnects

USB 3.0Interconnects


Checking Critical RF Path • Bio-sensor Interconnect

• Bluetooth Interconnect

• Bluetooth RF Module added to boost the signal Problem fixed!


Critical Interconnects > USB

1GBs

USB Interconnects fails the specs at

2GBs

2GBs

4GBs

Fixed!

1GBs

6GBs

3GBs

USB Interconnects

passed at 6GBs

Original Design New Design


Wireless Charging


Wireless charger > Transformer Design

Optimize the performance of Wireless Power Transformer


Optimized Transformer in Maxwell

Coupling Coefficient Vs Gap Vs Slide

Wireless charger in operation

Charger Sliding

Charger Gap


Addressing Mechanical Challenges


• The #1 failure mode for wearable devices is due to drop/impact.

• Simulations can help to determine the effect of an impact on the device before prototyping.

• This allows designers to improve the durability and reliability of the device.

ANSYS Wristband reliability

Deformation of the ANSYS Wristband due to impact

Damage of the LCD screen due to the impact. This is prevented with design modifications.


Manufacturing challenges


• In the ANSYS Wristband, the antenna need to be wrapped around curved wristband.

• This introduces stress in the antenna and can be a cause failure.

• In the initial design, the stress around the bend was too high. This was adjusted to improve reliability during manufacturing.

Forming of the Antenna

Antenna Deformation

Antenna Stress

Adjusting the radius of curvature helps to reduce the stress during the forming of the antenna


Electronics Assembly


• The use of lead free solder and flexible PCB introduces many challenges during electronics assembly.

• Lead free solder requires high soldering temperature while flexible PCB can not tolerate high temperatures. This means soldering process need to be designed carefully in order to insure good connections while minimizing damage to the PCB.

• The goal is to ensure that solder paste is heated to the right temperature for the manufacture recommended duration while other components doe not exceed the manufacture recommended temperatures.

Electronics Assembly Process

Soldering Assembly

Heater

Solder Paste

PCB


Electronics Assembly Process

Solder Temperature

Solder melting

PCB Temperature

PCB OK

Adjust heating profile to insure PCB is protected

• Simulation of the soldering process allows designers to predict the temperature of each component through out the solder process.

• By adjusting the duration of and heat load for each soldering step, a high quality assembly process can be maintained.

Solder process temperature


User Experience


• Wearable electronics industry is highly competitive and the user experience can play a large role in the success and failure of any product.

• The ANSYS Wristband need to stay cool during use because excessive heat during use has been shown to lead to perceived problems and discomfort by users.

User Experience


• The ANSYS Wristband is not expected to operate at high power for extended periods of time.

• A transient simulation shows that the device can operate at high power mode for 500 seconds before the temperature exceed desirable values.

• This is deemed acceptable.

User Experience

This graph shows the temperature on the bottom of the watch. It shows this watch can be run for 500s before the temperature exceeds 45C.


System Verification


Adding human body model


Simulation in a realistic noisy environment

Noise Source 1

Noise Source 2

Transmitter

Receiver


Let the best product win!!


In a noisy environment, the ANSYS Wristband performs dramatically better than a standard off the shelf antenna!

On the shelf Antenna > Poorly designed

-16dB difference 0dB difference

The Antenna designed in ANSYS can receive signals 16dB lower than commercially available ones


Wrap up


Appendix and backup slides


SpaceClaim is used to create and prepare the simulation geometry


– Ant1_L1

– Ant1_L2

– Ant1_W

– Ant2_L1

– Ant2_L2

– Ant2_W

Antenna Design Parameters

Ant1_L1

Ant1_L2

Ant1_W

Ant2_L1

Ant2_L2

Ant2_W


• The first step should be to solve the nominal variation using Analytic Derivatives

• The Analytic Derivatives can be used to reduce the number of necessary design variables. Eliminate variables that minimally affect the Return Loss over the band of interest!

• Plot the Derivatives of the Return Loss of each Variable with Respect to Frequency

– Ant1_L1

– Ant1_L2

– Ant1_W

– Ant2_L1

– Ant2_L2

– Ant2_W

Antenna Design


Dependent Solve Setup in HFSS

Multiple Solution Frequencies

2400 MHz 400MHz

Excitation

PCB

900MHz 2400MHz

Each frequency band excites a different part of the antenna. Meshing at a single frequency will not guarantee accuracy.

Setup 1: 2400MHz

Dependent Mesh Setup: 400MHz

Sweep Converged Adaptive Meshing


PCB Layout

4cm

Bluetooth

Biosensor

Display

Micro controller

Batteries

Memory

BT circuit BS circuit

Crystal

I/O

Voltage

Reg


PCB description

Schematic Layout

Layout work was done in Eagle


Critical Interconnects

SDXC Memory card should support signals at 450MBs


Critical Interconnects > SD Memory

500MBs

2GBs

4GBs

1GBs

Memory Interconnects meet the specs up to 1GBs Target = 450MBs


Near-Field (Inductive coupling, resonant)

• Do not rely on propagating EM waves.

• Operate at distances less than a wavelength of transmission signal

• Resonance obtained by use of external circuit capacitor, tuned farad for resonance

• Can be solved using separate Magnetic Solver – Magnetic coupling between the coils

Far-Field (resonant)

• Operating range to ~10 meters

• Tradeoff between directionality and transmission efficiency.

• Self capacitance of coil turns are of importance

• Requires full wave solver with coupled electric and magnetic field equations

Wireless Power Transfer (WPT)


• Simulating the whole Electrical Module – Effect of PCB on Antenna simulations

– Effect of Power Transformer on System performance

• Adding human body model – How will the device performs after wearing it on hand?

• Drop Impact Simulations – What happens when you drop the watch?

• Wearable Device Thermal – Will the user feels the pcb heating?

• Simulating the watch in a realistic environment – Taking noise in consideration

– Lots of interference

System Verification


Simulating the whole Electrical Module

Including the PCB has minimal impact on Antenna performance


Let the best Design Win!!!!

Lots of Interferences!!!

-40dBm What is the received power?

-80dBm

-60dBm

-40dBm

-20dBm


Lots of Interferences!!! Input Signal = -40dB

Received Noise = -164dB

Input Noise = -80dB

Input Noise = -60dB

Input Noise = -30dB

Input Noise = -10dB




Received Signal = -62dB

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Designing the ANSYS Wristband - Ozen Engineering · Designing the ANSYS Wristband By: ... Dependent...

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