Rectenna from Dengyo (via Dengyo)
A rectenna is a type of antenna that converts microwave energy into DC. Usually arranged in a "multi element phased array with a mesh pattern reflector element," a rectenna ends up being directional. RFID is a common use of rectenna tech. (Side note: a Schottky diode is placed across dipole antenna elements, rectifying the AC current induced by microwaves.)
Japanese company Nihon Dengyo Kosaku Co Ltd (Dengyo) has created a rectennas for the 2.4GHz band of microwave energy. Although the rectenna could pick up 6mW from Tokyo Tower at 4 km away, the device is being pushed as a great way to recover lost energy in microwave heating products, such as a microwave-oven. The rectenna re-collects energy not used to heat the food.
The team claims that foods with a low-water content have a high regeneration efficiency, meaning they recover more energy. The microwave oven rectenna formula breaks down as follows (From Dengyo):
ηt = ηm x (1 - ηh) x (1 - LC) x ηr x ηC
ηm is the efficiency of converting alternating-current power into microwaves with a microwave oven
ηh (heating efficiency) is the ratio of the energy used for heating food or materials to the energy of the generated microwaves
LC is the loss of the transmission circuit
ηr is the efficiency of the rectifier
ηC is the efficiency of the boost circuit or superposed circuit
Case 1: ηm = 70%, LC = 10%, ηr = 80%, ηC = 90% ηh = 50% yields ηt = 22.7%
Case 2: ηm = 70%, LC = 10%, ηr = 80%, ηC = 90% ηh = 10% yields ηt = 40.9%
Up to 100W can be reclaimed from the 103 x 93 x 17mm rectenna. Time to extend our planet's resources while cooking the usually dry dinners we end up stomaching.
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