2.3. Electrical Stimulation
Figure 1 shows the experimental setup for the pulsed voltage stimulation of the bed-log and sawdust
substrate cultivation systems. The pulsed power generator was constructed based on an IES system
and was used to generate pulsed high voltages as electrical stimulation for mushrooms. The IES
pulsed power generator basically consisted of primary energy storage capacitors, closing switches,
a secondary energy storage inductor, and an opening switch [7,11,12]. The four primary energy
storage 0.22 μF capacitors were connected in parallel and were charged up using a high-voltage dc
power supply (50 kV maximum voltage). The charging voltage of the each primary energy storage
capacitor was controlled in the range from 5 to 7 kV. After charging up the capacitor, the closing
switch changed the connection of the capacitors from parallel to series. As a result, the voltage was
stepped-up in the same manner as in a Marx generator [12]. The output voltage of the primary circuit
was compressed and multiplied by the secondary energy storage inductor and the fuse-type opening
switch. The output voltage of the pulsed power generator was varied from 50 to 130 kV with a 100 ns
pulse width to determine the optimum amplitude. A needle electrode 3 mm in diameter and 9 cm in
length was driven into the logs to a depth of 7 cm, and subsequently, a pulsed voltage was applied by
the IES pulsed power generator as a form of electrical stimulation. The temperature rise of the bed-log
and the sawdust block by applying voltage was estimated to be several milli-Kelvins using 5.39 J
stored energy and 1.3 J/kg specific heat capacity.
2.4. Fruiting Body Yield
The fruiting season of the mushroom species is mainly early autumn, with some fruiting also
occurring in spring. The experiment was carried out from 2007 to 2008 as an attempt to increase the
yields. After the inoculation, the fungi matured on the logs under environmentally controlled
conditions. The fruit bodies of mushrooms were cropped every day, and their weight was measured to
obtain the yield. Twenty sawdust substrate beds were grouped under the same experimental conditions
to obtain as averaged value. Fifteen bed-logs of L. edodes were also grouped under the same
conditions to study the statistical distribution. The voltage amplitude for the bed-logs was changed to
obtain an optimum amplitude for improving mushroom yield, as mentioned in Section 2.3.