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Search for plant biomagnetism with a sensitive atomic magnetometer
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Image of FIG. 1.
FIG. 1.

(Color online) The titan arum (or Amorphophallus titanum), nicknamed “Trudy,” in full bloom on June 23, 2009, at the University of California Botanical Garden. The Geometrics G858 magnetometer sensors are visible behind the plant on the left.

Image of FIG. 2.
FIG. 2.

(Color online) Experimental setup: The Geometrics G858 atomic gradiometer is positioned with one sensor near the spathe where pollination occurs. The other sensor is used to subtract the ambient magnetic field noise. [Inset: Each sensor’s dead sensing zones lie within of the sensors axis and within of the plane perpendicular to it. The downward pointing arrow indicates the direction of the ambient magnetic field.] The sensor axes are parallel and to the ambient magnetic field, which is inclined to the vertical and commensurate to the local earth magnetic field (Ref. 28).

Image of FIG. 3.
FIG. 3.

(Color online) Data from the two magnetometer channels spanning 3 days. The local earth magnetic field is mG. The three rectangular boxes indicate the magnetically quiet periods when the BART operations are suspended from –5 a.m. Discontinuities in the data correspond to shifting of the plant and/or the magnetometer sensor heads. Large magnetic-field fluctuations are seen during the U.C. Botanical Garden open hours (9 a.m.–5 p.m.). The difference between the two magnetometer channels depends on their position relative to the ambient magnetic field gradients.

Image of FIG. 4.
FIG. 4.

(Color online) Gradiometer signal (difference magnetic field). (a) 9 h segment: night of bloom. (b),(c): for comparison, same 9 h segments on the following two nights. Data averaged over one minute intervals. We attribute the overall magnetic field increase to a gradual change in temperature and corresponding residual temperature dependence of the sensor (°C). The time scale of that drift is significantly longer then the time scale we expect from the plant biomagnetic activity. On each of the three nights, the magnetic field noise at 1 mHz, in a 0.5 mHz bandwidth (corresponding to events lasting –30 min), is 0.6 .

Image of FIG. 5.
FIG. 5.

(Color online) Frequency spectra of data shown in Fig. 4. Dark (blue): night of bloom [Fig. 4(a)]. Light (gray): average of subsequent two nights [Figs. 4(b), 4(c)]. A biomagnetic event of a magnitude larger than 0.6 and lasting 10–30 min would appear as a feature between 0.5 and 1.5 mHz rising above the overall 1/f noise.


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Scitation: Search for plant biomagnetism with a sensitive atomic magnetometer