WiththedevelopmentofCMOSandMEMStechnologies,theimplementationofalargenumberofwirelessdistributedmicro-sensorsthatcanbeeasilyandrapidlydeployedtoformhighlyredundant,self-configuring,andadhocsensornetworks.Tofacilitateeaseofdeployment,thesesensorsoperateonbatteryforextendedperiodsoftime.Aparticularchallengeinmaintainingextendedbatterylifetimeliesinachievingcommunicationswithlowpower.Forbetterunderstandingofthedesigntradeoffsofwirelesssensornetwork(WSN),amoreaccurateenergymodelforwirelesssensornodeisproposed,andanoptimaldesignmethodofenergyeffcientwirelesssensornodeisdescribedaswell.DifferentfrompowermodelsevershownwhichassumethepowercostofeachcomponentinWSNnodeisconstant,thenewonetakesintoaccounttheenergydissipationofcircuitsinpracticalphysicallayer.Itshowsthattherearesomeparameters,suchasdatarate,carrierfrequency,bandwidth,Tsw,etc,whichhaveasignificanteffectontheWSNnodeenergyconsumptionperusefulbit(EPUB).Foragivenqualityspecification,howenergyconsumptioncanbereducedbyadjustingoneormoreoftheseparametersisshown.