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For powering small wireless IoT nodes, compact, efficient rectifying antennas have been realized. A first design for 868 and 915 MHz is described. Based on the lessons learned, a new design for 2.45 GHz is realized that is a factor 13 smaller in size.
The position of radiative Wireless Power Transfer (WPT) in the spectrum of power harvesting is given and a brief history of radiative WPT, starting with the work of Faraday is presented. The challenges in increasing the received dc power level or the transfer distance are outlined and possible directions for a solution are indicated.
The use of an array antenna, transmitting pulsed signals and applying time-delays between the elements to create an area of high power density in front of the array at a prescribed position at a chosen moment in time is discussed. Using realistic bandwidths and pulse repetition frequencies leads to the creation of undesirable hot spots. Replacing the array elements with small phased array antennas...
A reconfigurable monopole array antenna consists of one or a few driven monopole elements, surrounded by passive monopole elements that can be switched to be connected to ground. Thus, the antenna radiation pattern can be discretely adjusted by choosing different subsets of parasitic monopole elements connected to ground. This switching can be performed by PIN diodes. Here we will look at the alternative...
An accurate equivalent circuit model to predict the power conversion efficiency (PCE) of a Schottky Barrier Diode (SBD) is presented in this paper. By making use of good insight into the used SBD models and careful analysis of circuit behavior, more efficient rectifier circuits have been identified. An increase in circuit efficiency of 18–25% is shown compared to state of the art, resulting in 20–180%...
The use of a linear array of half-wave dipole antennas, excited by intermittent CW signals is discussed. Time delays are introduced between the transmitted signals so that at prescribed instances of time, a power density maximum is created at a desired position in front of the array. The power density increase at the desired location relative to that of a single element is equal the number of elements...
A new, reliable and inherently safe nasogastric feeding tube position determination system has been developed. The system is particularly useful for preterm born infants. The system uses low-frequency transmit, reflection and receive coils. Transmit and receive coils are positioned in a handheld detection module in such a way that the mutual coupling is minimized, resulting in a good spatial resolution...
This paper reports first results in applying CST Microwave Studio in combination with a human voxel model and a dedicatedly developed equivalent cardiac cycle source. Based on first coarse-meshing simulation results it may be concluded that it is feasible to model the heart in a three-dimensional anthropomorphic voxel model of a human being by an equivalent fixed dipole volume source. Through changing...
To realize a sufficiently high dc voltage for a realistic load impedance with a rectenna we may increase the receiving aperture or employ a voltage boost circuit. A gridded, square loop FSS, loaded with Schottky diodes is demonstrated as an example of the first solution. For the second solution we have employed a Texas Instruments TI BQ22570 Power Management circuit combined with a miniaturized rectenna...
This chapter deals with radio frequency (RF) energy transfer over a distance. After explaining the differences between nonradiative and radiative RF energy transfer, the chapter gives definitions for transfer and harvesting. Nonradiative RF energy transfer is mostly employed in inductive systems, obeying the Qi standard. The chapter also identifies the subcomponents of an RF energy transfer system,...
Electromagnetic Band Gap (EBG) structures may be used to create magnetic conductors that can be used as ground planes for dipole and loop-like antennas without annihilating the radiation as electrically conducting ground planes would do. An EBG ground plane may be created by placing a Frequency Selective Surface (FSS) on a grounded dielectric slab. Since RF harvesting FSS structures have been demonstrated...
For practical use of radiative wireless power transfer (WPT), it is necessary to design a system which is able to supply circuits with a dynamic loading characteristic. In this paper we present a practical way to obtain efficiency and dc output power characteristics of a WPT system. An Avago HSMS-2852 Schottky diode pair is used to rectify the RF power. The diode pair is matched to a 50 Ω input impedance...
For a near-field focused wireless power transfer system a parasitically coupled dipole transmit array antenna must be designed. To speed up the analysis time, an approximate input impedance model for parasitically coupled, dipole array antennas has been extended to include the mutual coupling between two active dipole antennas, using input impedances only. The analysis procedure is explained and comparisons...
Two rectennas are presented. One consists of a printed 5Ω antenna, connected to a loaded voltage doubling rectifier through a LC impedance matching network. The other one consists of a printed loop antenna, complex conjugately impedance-matched to the same rectifier. The second rectenna is reduced in size by a factor of more than four with respect to the first rectenna and showing a 55% RF-to-DC power...
Through analysis it is found that the only steps available to maximize the voltage at the input of a rectifying and voltage multiplication circuit for a given low level of power available from the antenna are: Design the rectifier/multiplier circuit for a minimum real part of the input admittance and conjugate match the antenna to the rectifier / multiplier circuit. Use antenna miniaturization up...
For wireless sensor networks, network life time is a critical aspect to the success of the system. Due to high maintenance costs, energy autonomous sensor networks are highly desirable. RF powering provides such a solution by charging the sensor nodes on the field. However, how to deploy such a kind of system efficiently is still left as an open question. This paper is motivated to formulate an answer...
A method for the fast creation of antenna and Frequency Selective Surface (FSS) prototypes is discussed. The method is suited for printed structures on planar and singly curved surfaces and avoids the use of photo-etching techniques. Furthermore, it allows for creating printed metallic structures on non-microwave-specific substrates. The method uses adhesive copper tape, common adhesive tape, a paper...
An approximate or engineering model for a modified, asymmetric strip folded dipole antenna is discussed. The modification consists of adding short-circuit strips in the folded dipole arms, thereby giving means for input impedance tuning. This tuning is necessary for directly matching the antenna to the complex input impedance of the rectifier that is connected to the antenna to form a rectifying antenna...
For Smart Building Integration many wireless sensors are needed. Far-field RF energy transport may be used to charge the batteries of these sensors. Due to path loss and transmit power limitations the RF power available at the sensors will be very low. By optimizing not only the receiving rectifying antenna, but also the transmitter radiation pattern, based on the propagation channel characteristics,...
For powering wireless sensors in buildings rechargeable batteries may be used, being charged remotely by dedicated RF sources. RF energy transport suffers from path loss and therefore the RF power available on a rectenna will be very low. As a consequence, the RF-to-DC conversion efficiency will also be very low. By optimizing not only the subsystems of a rectenna but also taking the propagation channel...
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