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Silicon Menagerie ANTS – A Sensor Perspec/ve MAS.S63 JoeP Ants Make Sounds • Stridula/on – ‘Rubbing parts of their rear sec/on or gaster together’ – hCp://home.olemiss.edu/~hickling – hCp://blog.wildaboutants.com/2010/01/28/ant-‐ stridula/on/ • Nobody knows exactly how they ‘hear’ – probably with legs or hair on antennae – Only contact or near-‐field vibra/on R. Hickling and R. L. Brown, "Analysis of acous/c communica/on by ants" Journ. Acoust. Soc. Amer.,Vol. 108, No. 4, pp 1920-‐1929, 2000. 2/04 JAP Acoustic Transducers • Measure dynamic range to moving diaphragm • Carbon mic • Condensor mic • Electret mic – Foil electret mic – FEP material polarized with corona discharge – Wideband • 10-3 Hz to hundreds of MHz – Usually have integrated FET http://www.openmusiclabs.com/learning/sensors/electret-microphones 3 2/04 JAP MEMs Microphones • Many Manufacturers – Akustica (direct digital output), Infineon, Panasonic, etc. • Very small - surface-mount chip • Have integrated amplifier and sometimes ADC 4 Ants are Endocrinal Adepts blog.wildaboutants.com Pheromone Trails… Town ant workers following an ar/ficial trail made by drawing a very dilute solu/on of the ant's trail pheromone methyl 4-‐methylpyrrole-‐2-‐carboxylate. (USDA.gov) Chemical Markers…. • Probably need to lay down a vola/le, and sniff for vapors just above… – What type? – Generally put an agent on a sensor and look for a reac/on, or s/mulate material and look for response – Electrochemical, resis/ve, cataly/c, op/cal (color to spectroscopy), resonant (mass perturba/on), molecular size/weight… (see presenta/on that follows) – E.g., hCp://www.sensorsmag.com/list/sensors/chemical-‐ gas-‐129 – You can try ‘wild ideas’ here, but stay safe (e.g., no radioisotopes, carcinogens, or toxins) Ideas for other marker types… • Drop a paint, ink, or colored dust… – Will need to search to acquire trail; op/cal sensors might be noisy, but could employ florescence s/mulated by a UV LED, for example… • Drop magne/c or ferrous par/cles – Use a magne/c sensor or metal detector • Deposit other kinds of detectable markers… 2/04 JAP Color Sensors Color Light Sensor - Avago ADJD-S371-Q999" http://www.sparkfun.com/commerce/product_info.php?products_id=8618" Features: • 10 bit per channel resolution • Independent gain selection for each channel • Wide sensitivity: 0.1k - 100k lux • Two wire serial communication • Built in oscillator/selectable external clock • Low power mode (sleep mode) • Integrated solution with sensor, LED and separator in module for ease of design 9 2/04 JAP Magnetic Field Sensors 10 2/04 JAP Permalloy Differential strapping for compasses +/- 2 Gauss max range 11 2/04 JAP Integrated Magnetometers 12 2/04 JAP Beat frequency metal detector Wireless “boot” coil and AM radio 13 2/04 JAP Flux Transmission Metal Detector 14 2/04 JAP Pulse Induction Metal Detector 15 2/04 JAP The Wiegand Effect Weigand pulses tend to be short (HF components!) Shaft encoder w. alternating poles on disk Shaft encoder w. distributed Weigand wires • Metal wire made with large Magnitization hysteresis – At a certain magnetic field strength, all domains reverse together – Produces a voltage pulse (e.g., 2-6 V into 24K Ohms) when domains switch. • Also produces a magnetic field pulse (J-Wires for library-book antitheft systems) – Pulse can be readout for magnetic field switch – Products exist… 16 Ringdown Tag Readers • Very simple, inexpensive prototype tag reader detects Magnetostrictor (Sensormatic) shoplifting tags – In-store sysems can reach circa 12 feet in range – High-Q mechanical structures (not so good with LC) – By cutting tag to different lengths, we get several (4-6) bits of very cheap ID • Slow – Must sit at frequencies of interest and interrogate Media Lab Ringdown Prototypes Paradiso & Hsiao 1997 Prototype, running 30-150 kHz Potentially good range, but slow Response (e.g., 10 ms/tag) Triac-switched capacitor ladder for tuning search coil on transmit, Comp. MOSFET drivers Special Nodes – “Breadcrumb” Relay Geqng RF penetra/on down tunnels or into spaces where no link exists • Nodes carried by worker in “bag” • System prompts worker to drop a new relay node when at range limit of RF link • Worker is also prompted to collect nodes when returning • System can alert if link spontaneously breaks 2/04 JAP Synchronous Detection - Also called a “Lock-in” Amplifier - Also a “Matched Filter” of sorts - Can regenerate carrier with PLL if no connection f Quadrature demodulation eliminates need to chase phase 4-Quadrant multiplication suppresses the carrier Tight low-pass filter gives extremely high noise rejection! 20 2/04 JAP Synchronous Detection Note: synchronous detection works only if signal stays linear (and doesn’t saturate). A bandpass filter can be inserted here to limit noise sensitivity Phase Shifter Mixer Mixer can be switched system as at left, or 4-quadrant multiplier like an AD633 21 2/04 JAP Ant Antennae Chemical, Tactile, vibratory, airflow, inertial, thermal(?) sensors… Plus they are actuated! 22 The “Tribble” Electronic “skin” as a dense sensor network Over 500 sensing channels Whisker, pressure, light, sound Each of 32 tiles actuates RGB LED, speaker, vibrator All tiles talk only to neighbors Inhibition/excitation, compression algorithms Josh Lifton, Mike Broxton - Demo at 1CC Sensor Net Array, Kapton Embedded (SNAKE) Skin • All on flex • Embedded strain gauges • Covered by a layer of QTC pressure-measuring material • Piezo whiskers • Optical sensors, microphones, temperature • Peer-Peer network • High-Speed I2C backbone • Scalable! Jerry Barroeta-Perez 4/08 ChainMail - Scalable Sensate Surface JAP • Rigid nodes, flex connects • Multimodal: – Light – Sound – Whiskers – Pressure – Temperature – Bend • Videos on YouTube BehramShort.mov Behram Mistree 25 4/08 Other Whiskers in Research JAP Also MEMs whisker arrays (see IEEE Sensors) MIT Seal Whisker (note the taper) Heather Beem, Matthew Hildner and Michael Triantafyllou UC Berkeley carbon nanotube & silver nanoparticles on polymer fiber whisker 26 4/08 Capacitive Whisker? JAP • Use loading mode – can sense proximity and contact of conducting objects (or wet dielectric ones) • Not in terrestrial animals so far as I know… 27 2/04 JAP Loading Mode Sensing Most common “capacitive” sensing (e.g., “elevator buttons”) 1- Set pin to output, and pull down 2- After brief wait, declare as logic input 3- Measure T until input goes to “1” 28 2/04 JAP Minimal Capacitive loading circuit 1 Pin 1 Output >1 Meg Ohm R PIC or other uP δt δt 2 Sense Plate User C Pin 2 Input • Pin 1 is digital output, pin 2 is digital input • Toggle state of pin 1 and measure time needed for state of pin 2 to flip – Time difference increases with R and C • Fix R, hence C is measured • Loading mode measurement – range typically few cm 29 2/04 JAP Conductive Polymers and FSR’s • Microphotograph, showing conductive ink and metalization from Interlink FSR 30 2/04 JAP Force Sensitive Resistors • Composite structure – Top, ink, electrodes • Flat, but can be fragile to shear force (delamination) and sensitive to bend 31 2/04 JAP The FlexiForce (from TekScan) 32 2/04 JAP FSR Bendy Sensors Available from the Images Co. (for PowerGlove - made by “Abrams-Gentile) High-end versions made by Immersion for their CyberGlove - 0.5° resolution, 1° repeatability, 0.6% max nonlinearity, 2-cm min bend radius These only measure bend in one dimension (expanding the FSR’s on surface) - Conduction saturates quickly when contracted - Can measure bidirectional bend with 2 FSR’s back-to-back (and diff amp) 33 2/04 JAP Data Glove by Tom Zimmerman (VPL) • Cladding of a Graded Index Optical Fiber is abraded at point where sensitivity is desired • When fiber bent, light leaks out as a function of bend angle – Drop in signal at detector Emitter Detector • Patented by Tom Zimmerman (lab alum) at VPL in 1985 & 1990. 34 2/04 JAP Measurand’s Shape Tape 35 2/04 JAP How ShapeTape Measures Twist Bend fibers near center of strip Twist fibers near edges Can also wrap fibers around center? 36 2/04 JAP Strain Gauges Many manufacturers (e.g., JP Technologies), many patterns... Simple strain gauge Torsional strain gauge 37 2/04 JAP Strain Gauge Patterns Strain Gauges want to be bonded onto a hard surface, so they can be forced into strain when the surface is deflected. Soft materials won’t strain the gauge enough 38 2/04 JAP Load Cells 20 Ton load cell for truck weight Simple, “naked” load cell from Ohio State • Bond strain gauge to cantilevered beam – Force deflects beam, bends strain gauge, creates signal • Can be quite accurate – Compensate temperature effects Load Cell assortment from DHS 39 2/04 JAP Silicon Pressure Sensors • Piezoresistors diffused onto silicon at R1, R2 – Boron doping typical… • Piezoresistors couple into longitudinal & transverse stress – Coupling is opposite for each mode • R1 and R2 essentially subtract in a half-bridge 40 2/04 JAP Piezo Foil (PVDF) http://www.meas-spec.com/myMeas/sensors/piezo.asp 41 2/04 JAP Compound Eyes Great for detecting motion – see transitions from one eyelet to the other, large FOV 42 2/04 JAP The Ommatidia Collimated – narrow FOV – up to 30,000 per eye in some insects 43 2/04 JAP Not a light-field camera! • http://askabiologist.asu.edu/content/ hollywood-misconception 44 2/04 JAP Ants also have simple eyes atop their head • The Ocelli – sense light levels & polarization, UV on some insects (e.g., bees) • Ants can have 3 45 2/04 JAP Compound Eye Research Prototypes • John Rogers & group, University of Illinois UC • Uses stretchy interconnects 46 2/04 JAP Photodetectors http://www.engr.udayton.edu/faculty/jloomis/ece445/topics/egginc/tp4.html Speed Ex Vg/Ex G Poor G/Pr G ? ? 47 Photoresistors CdS tends to like Yellow... Photons knock electrons into conduction band 1 photon can release 900 electrons Acceptor band keeps electron lifetime high -> Lower Resistance with increasing light Slow response... Goes from MΩ to Ohms • CdS (Cadmium Sulfide) and CdSe (Cadmium Selenide) cells are common ( I ) Directly beneath the conduction band of the CdS crystal is a donor level and there is an acceptor level above the valence band. In darkness, the electrons and holes in each level are almost crammed in place in the crystal and the photoconductor is at high resistance.! ( II ) When light illuminates the CdS crystal and is absorbed by the crystal, the electrons in the valence band are excited into the conduction band. This creates pairs of free holes in the valence band and free electrons in the conduction band, increasing the conductance.! ( III ) Furthermore, near the valence band is a separate acceptor level that can capture free electrons only with difficulty, but captures free holes easily. This lowers the recombination probability of the electrons and holes and increases the number for electrons in the conduction band for N-type conductance Condition like FSR’s (voltage divider, transimpedance amp, etc.) 2/04 JAP Photodiodes Solar Cells - Big (optimized) versions Photodiodes - (Smaller) • Photons interacting in the depletion region produce electron-hole pairs – Electrons diffuse through depletion region, driven by the E-field, to arrive at the N layer and electrode, producing current. – Make depletion region bigger (more reverse bias) • More efficient (higher probability of photon interaction) • Faster (charge doesn’t have to diffuse across longer lengths before it hits Efield, hence less charge stored, hence smaller capacitance) • PIN diodes increase the collection area - faster response 49 2/04 JAP Photodiode IC’s 50 2/04 JAP The Phototransistor • Like diodes, all transistors are light-sensitive. Phototransistors are designed specifically to take advantage of this fact. The most-common variant is an NPN bipolar transistor with an exposed base region. Here, light striking the base replaces what would ordinarily be voltage applied to the base -- so, a phototransistor amplifies variations in the light striking it. Note that phototransistors may or may not have a base lead (if they do, the base lead allows you to bias the phototransistor's light response). • Phototransistors run in the photoconductive mode • They’re pretty slow, on average (e.g., Khz response) • …But give a fair amount of gain and are very easy to use. – Generally ground emitter and provide a collector resistor to set gain • Photodarlingtons give more gain, but can be slower… http://encyclobeamia.solarbotics.net/articles/phototransistor.html 51 Phoresis Parasitic Mobility in Mobile Sensor Networks Best Paper Award Active Innovations and Architecture Passive - Interpretation of Energy Harvesting in mobile networks - Three flavors: - The Tick (e.g., jumps onto a host, attaches, then disengages) - The Bur (e.g., sticks to passing object, then shakes off) - The Symbiote (an appliance you want to carry while it works) - Contains GPS, RF, basic sensor suite Paradiso & Laibowitz 2005 Symbiotic
