Recent Developments in the Remote Radio Control of Insect Flight
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FOCUSED REVIEW published: 08 December 2010 doi: 10.3389/fnins.2010.00199 Recent developments in the remote radio control of insect flight Hirotaka Sato* and Michel M. Maharbiz* Department of Electrical Engineering and Computer Science, University of California at Berkeley, Berkeley, CA, USA The continuing miniaturization of digital circuits and the development of low power radio systems coupled with continuing studies into the neurophysiology and dynamics of insect flight are enabling a new class of implantable interfaces capable of controlling insects in free flight for extended periods. We provide context for these developments, review the state-of-the-art and discuss future directions in this field. Keywords: insect flight, micro air vehicle (MAV), telemetry, cyborg insect, brain machine interface (BMI) Edited by: Rui M. Costa, Instituto Gulbenkian de Ciência, Portugal INTRODUCTION and Boettiger, 1965; Leston et al., 1965; Ellington, Reviewed by: Ty Hedrick, The University of North Insects exhibit some amazing modes of locomo- 1984; Tu and Dickinson, 1994, 1996; Ellington Carolina at Chapel Hill, USA tion. They float, swim, crawl, jump, run (even et al., 1996; Dickinson and Tu, 1997; Dickinson M. Eugenia Chiappe, Howard Hughes bipedally), and fly. They do this with such effi- et al., 1999, 2000; Josephson et al., 2000a,b) engi- Medical Institute, USA ciency, sophistication, and elegance of function neers are starting to build tiny, sub-gram scale, *Correspondence: across a vast size range (the smallest insect is flying robots. 1/5 of a millimeter across, the largest insects can Building very small flyers which can fly well weigh 100 g and be over 20 cm long) that they in real environments is a difficult task, however, have mastered locomotion on almost every ter- hampered not just by knowledge of insect flight, rain on Earth. but current technological limitations. A housefly The adaptations which enable insects to do is about 8 mm long and weighs 1 g; its wings beat Hirotaka Sato received his B.Sc. and these things have inspired human art, science, and approximately 200 times a second; during each Ph.D. in Chemistry from Waseda engineering for centuries (e.g., Tipton, 1976). On stroke, tiny muscles make subtle adjustments to University, Japan for his work on electrochemistry based nano-fabrication the ground, the science of insect locomotion has the trajectory of the wings to generate the forces processes under Professor Takayuki informed several generations of legged robots required to move it where it wants to go (Tu and Homma (Chem), Professor Shuichi Shoji (e.g., Full and Koditschek, 1999; Delcomyn, Dickinson, 1994, 1996; Dickinson and Tu, 1997; (EECS) and Professor Tetsuya Osaka 2004; Lehmann, 2004; Riztman et al., 2004), from Dickinson et al., 1999, 2000). As it does this, it (Chem). He started his postdoc work in the crawling machines of the 1980s (like MIT’s integrates data from a variety of sensors on its 2007 at University of Michigan and in 2008 at University of California at Ghengis; Brooks, 1991) to the more modern Rhex body which provide airflow information, gyro- Berkeley where he has been leading a capable of successfully traversing complex terrain scopic information, and visual flow information; research project demonstrating the remote (Altendorfer et al., 2001). In the air, a great deal of it computes and then compensates for the hori- radio control of insect flight (often research spanning decades is beginning to tease zon, for incoming obstacles, and for constantly referred to as “Cyborg Insects”). In 2009, out the complex interplay between aerodynam- changing wind gusts and does this so efficiently, his research was ranked in TR10 (MIT Tech Review) and selected as one of the ics, mechanical construction, and neurophysiol- that it can fly for hours a day and could fly a top 50 innovations by TIME magazine. ogy that enables something as small as a fruitfly mile or two in single stretch if really had to. By His research interests are in biochemistry, to fly so incredibly well. Enabled by advances in comparison, the Delfly Micro de( Croon et al., neuromuscular physiology, microfabrication techniques (Tanaka and Wood, 2009), arguably one of the smallest untethered, electrochemistry and MEMS (Micro Electro Mechanical Systems). 2010) and considerable progress in our under- instrumented air vehicles, weighs 3 g and has a [email protected] standing of insect flight (Pringle, 1957; Machin 10 cm wingspan, can fly for 3 min on a battery Web: http://hirotakasato.web.fc2.com/ and Pringle, 1959, 1960; Machin et al., 1962; Ikeda which constitutes 1/3 of its weight and requires Frontiers in Neuroscience www.frontiersin.org December 2010 | Volume 4 | Article 199 | 1 Sato and Maharbiz Development of insect flight control Telemetry a human operator to perform all flight func- dual channel telemetry backpack to measure and The science and technology of tions. To the authors’ knowledge, the smallest, compare EMG’s from a pair of flight muscles of measuring, transmitting, and storing non-autonomous flying machine is the micro- a male hawkmoth, Agrius convolvuli, during phe- signals of interest remotely. An instrument to measure and transduce robotic fly built at the Harvard Microrobotics romone-triggered zigzag flight (Kuwana et al., the phenomenon of interest into Laboratory, weighing in at 60 mg (Wood, 2008). 1999; Ando et al., 2002; Ando and Kanzaki, 2004; electrical signals is attached on a target While these systems are rapidly evolving, they Wang et al., 2008). and the electrical signals are modulated are currently hampered by the energy and power To our best knowledge, three different groups and transmitted to the users’ receiver, which demodulates the electrical density of existing fuel sources and the difficulty have recently developed wireless systems that signals. in replicating the flight dynamics and mechani- can both transmit and receive data from free- cal efficiencies of very small flyers. Insects have flying insects flight control (Figures 1–3). Flight flight performance (as measured by distance and control requiring multiple-channel stimula- speed vs. payload and maneuverability) as-yet tion, during complex, long-duration control- unmatched by man-made craft of similar size. led flight requires on-board digital processing, Very recently, several groups have attempted to memory, and programmability in addition to circumvent such problems by merging synthetic efficient radio systems. Each group developed control and communication systems into living systems with different trade-off choices in terms insects with the aim to control free flight. of functionality, weight, and complexity. Sato et al. describe an 8-channel system built around TECHNOLOGY the Texas Instruments CC2431 microcontroller WIRELESS TELEMETRY AND CONTROL with built-in transceiver; careful programming The development of wireless telemetry systems of the microcontroller allows for half hour of for small, free-flying, and walking insects began flight time and approximately 24 h of battery in the early 1990s with applications ranging from life in sleep mode (Figure 1, Sato et al., 2009a,b; neuromuscular recording (Kutsch et al., 1993, Maharbiz and Sato, 2010). The use of surface 2003; Kuwana et al., 1995, 1999; Fischer et al., mount ceramic antennas results in a very small 1996; Holzer and Shimoyama, 1997; Fischer package in terms of size, mass, and inertial effect and Ebert, 1999; Fischer and Kutsch, 1999; on the flying insect (Figure 1B). Bozkurt et al. Ando et al., 2002; Kutsch, 2002; Ando and (2009b) developed a custom-built, 2 channel Kanzaki, 2004; Colot et al., 2004; Cooke et al., AM receiver which used pulse-position mod- 2004; Takeuchi and Shimoyama, 2004; Mohseni ulation via a super-regenerative architecture et al., 2005; Lemmerhirt et al., 2006; Wang et al., which was fed into a PIC12F615 microcontrol- 2008) to using radio transmitters to study the ler (Figure 2). Daly et al. (2009, 2010) devel- long-range movements of insects (Hedin and oped a custom silicon system-on-chip receiver Ranius, 2002; Sword et al., 2005; Holland, 2006; operating at 3–5 GHz on the 802.15.4a wireless Wikelski et al., 2006, 2010; Pasquet et al., 2008). standard which interfaced with an on-board Table 1 shows the wireless systems used for neu- Texas Instruments MP430 microcontroller; the *Correspondence: romuscular recording and stimulation of free- receiver was remarkable for its extremely low- flying insects. All of the early devices employed power operation (2.5 mW, 1.4 nJ/bit) for a data custom-made radios hand-assembled from sur- rate of 16 Mb/s (Figure 3). Driven primarily by face mount electronics components and lacked technological developments in ultra-low power digital processing, on-board memory or pro- distributed sensor networks, low power micro- grammability. Detection of emitted signals was controllers equipped with internal radios are Michel M. Maharbiz is an Associate usually carried out using complimentary radio now very accessible. Professor with the Department of receivers or spectrum analyzers (and the rel- Electrical Engineering and Computer evant biological information was de-convolved STIMULATION PROTOCOLS Science at the University of California, Berkeley. He received his Ph.D. from the from the analog radio signals). Kutsch et al. Flight control of insects ideally requires the trig- University of California at Berkeley for (1993) developed a 0.42 g telemetry backpack gering of flight initiation and cessation as well as his work on microbioreactor systems (including battery) for a locust (Schistocerca the free-flight adjustment of orientation with 3 under Professor Roger T. Howe (EECS) gregaria, 3.0–3.5 g, payload capacity 0.5 g). The degrees of freedom (Dudley, 2000; Taylor, 2001). and Professor Jay D. Keasling (ChemE). backpack had a single channel transmitter to It is important to note that all published attempts Professor Maharbiz’s current research interests include building micro/nano wirelessly acquire electromyograms (EMG) of at free flight control rely on the insect to “fly itself” interfaces to cells and organisms and a single flight muscle of interest.