3-Axis Magnetometer on a Chip. Philip Keller

Size: px

Start display at page:

Download "3-Axis Magnetometer on a Chip. Philip Keller"

Elmer Tucker
5 years ago
Views:

1 3-Axis Magnetometer on a Chip Philip Keller

2 Why magnetometers? You can only make as well as you can measure Joseph Whitworth Engineer, entrepreneur, inventor, philanthropist Credit: Grace s Guide to British Industrial History

3 3-Axis Hall Magnetometers Advantages: All vector components Any probe orientation Limitations: Orthogonality Sensor separation Planar Hall Effect Cost Credits: - LakeShore Cryotronics (Model 460) - Magnetic Sciences Inc. (F.W. Bell 8030) - Metrolab (THM7025)

4 The first revolution Vertical Hall sensor Ø Integrated 3-axis sensors V Hall B Advantages: I Simplified construction ~100 µm active volume V Hall Limitations: +++ Si: lower sensitivity, higher noise I B I

5 Additional advantages Integrated current source and amplifier Integrated temperature sensor Spinning current to minimize offset, Planar Hall Effect, and noise Credit: presentation by D. Popovic (Senis) at IMMW-14 + R-DR R+DR R-DR I V = -IDR - I R+DR + R+DR R-DR R+DR R-DR - V = +IDR

cost Minimize errors from inductive voltages

6 The second revolution Integrated ADC Ø Digital interface Advantages: Minimize system complexity & cost Minimize errors from inductive voltages Additional controls Sensor arrays feasible Disadvantages: ADC performance

7 Architecture VCC (3.3 V) VDD GND OM LP 3.3 V regulator Digital control DR MODUL 3-Axis Hall devices S/H ADC Temperature sensor Biasing + Spin Box x y z M U X A S/H S/H ADC ADC SPI interface MOSI MISO SCLK CS T A S/H ADC R0 R1 AS0 AS1 ANA_REF TEMP ANA_X ANA_Y ANA_Z INIT

8 CSN Sensor arrays Communication: SPI bus with individual Chip Select lines Controller CS MV2 0 SCLK MOSI MISO CS MV2 1 SCLK MOSI MISO CS MV2 N SCLK MOSI MISO CS0 CS1 SCLK MOSI MISO Synchronization: INIT 1 0: reinitialize and start ADC conversion

9 Example: magnetron sputtering Magnets degraded by heat, radiation Causes uneven deposition Periodic mapping of magnets Sensor array: Minimize downtime! Simplify scanning robot Credits: - Wikipedia: Sputter deposition - Dep. of Physics of Politecnico di Milano

10 Example: Accelerator magnet mapping Facility for Antiproton and Ion Research (FAIR), Darmstadt, DE Dipoles of High-Energy Storage Ring (HESR) 44 bent dipoles, 4.2 m long, T Credit:

11 Accelerator magnet mapper Angular map along entire magnet length 0.17, 0.5, 1.7 T 10-4 resolution 8 sensors Rotary motor for additional angles Sled for lengthwise motion 82 mm free gap Credit: Forschungszentrum Jülich

Accelerator magnet mapper 8 sensors @ 76 mm diameter Radial layout, ± 0.1 mm Precision mounting holes Temperature stabilization ~0.

12 Accelerator magnet mapper 8 76 mm diameter Radial layout, ± 0.1 mm Precision mounting holes Temperature stabilization ~0.01C: Thermal vias Cu-core PCB Heater Current regulator Insulation On-board electronics: µp Temperature sensor Voltage regulator USB power & communication LabVIEW API

$Heater Refractory metals: NiCr, FeCrAl, CuNi Mo, W, Ta, Nb, Cr 0.5 mm NiCr plate, 1.7 T : -0.6 µt (0.$

13 Heater Refractory metals: NiCr, FeCrAl, CuNi Mo, W, Ta, Nb, Cr 0.5 mm NiCr plate, 1.7 T : -0.6 µt (0.4 ppm) : -5 µt (3 ppm) Field from heater current: ~4 ADC bits Use AC no DC offset Coil inductance roll-off ADC integration negligible > ~400 Hz

14 Resolution & stability Noise: ±4.7 µt (100 mt range) Drift: Bx, By: 0.07 bits/hour Bz: 0.4 bits/hour Conditions: 4 hour preheat 16 hours measurement 80 mt ± 0.5 µt 35 ± axis mode

15 Zero Gauss Chamber Measure initial & final zero-offset; interpolate in time Enclose mapper, including drive shaft Attenuation goal: ~50 µt < 1 µt Measured: µt µt Maximum (orientation) ~6 mm below sensor

Conclusions Logical evolution of 3- axis Hall magnetometers Size, performance, cost embedded / custom applications, e.g. mappers Calibration, UIF not a cheap gaussmeter Unsuitable for special conditions (e.

16 Conclusions Logical evolution of 3- axis Hall magnetometers Size, performance, cost embedded / custom applications, e.g. mappers Calibration, UIF not a cheap gaussmeter Unsuitable for special conditions (e.g. high precision, low fields, cryogenic temperatures)

F3A Magnetic Field Transducers

F3A Magnetic Field Transducers DESCRIPTION: The F3A denotes a range of SENIS Magnetic Fieldto-Voltage Transducers with fully integrated 3-axis Hall Probe. The Hall Probe contains a CMOS integrated circuit, which incorporates three groups