Conjugate Impedance Research Articles

Impedance Network for Power Optimisation in Piezoelectric Energy Harvesting Systems

Distributed wireless sensor network would be autonomous by scavenging energy from the ambience. The piezoelectric materials provide one of the promising transduction mechanisms for harvesting the ambient vibration energy. In the piezoelectric energy harvesting (PEH) systems, even it was claimed that the harvested power can be optimised with the impedance matching theory, several fundamental issues were still not thoroughly investigated or even misunderstood. Retrospecting to the origin of the impedance matching theory, the equivalent impedance network for PEH systems is proposed in this paper with emphases on its scope, as well as the definition, available range, and composition of the electrical part equivalent impedance. Due to the distinctions between the equivalent impedance network of the PEH systems and the unconstrained impedance network, the conventional complex conjugate and resistive impedance matching theories can no longer be directly used for the harvested power optimisation. Instead, constra...

Optimal design of a vibration-based energy harvester using magnetostrictive material(MsM)

In this study, an optimal vibration-based energy harvesting system using magnetostrictivematerial (MsM) was designed and tested to enable the powering of a wireless sensor. Inparticular, the conversion efficiency, converting from magnetic to electric energy, isapproximately modeled from the magnetic field induced by the beam vibration. A numberof factors that affect the output power such as the number of MsM layers, coil design andload matching are analyzed and explored in the design optimization. From themeasurements, the open-circuit voltage can reach 1.5 V when the MsM cantilever beamoperates at the second natural frequency 324 Hz. The AC output power is 970 µW, giving a powerdensity of 279 µW cm − 3. The attempt to use electrical reactive components (either inductors or capacitors) toresonate the system at any frequency has also been analyzed and tested experimentally.The results showed that this approach is not feasible to optimize the power. Since the MsMdevice has low output voltage characteristics, a full-wave quadrupler has beendesigned to boost the rectified output voltage. To deliver the maximum outputpower to the load, a complex conjugate impedance matching between the load andthe MsM device is implemented using a discontinuous conduction mode (DCM)buck-boost converter. The DC output power after the voltage quadrupler reaches 705 µW and the correspondingpower density is 202 µW cm − 3. The output power delivered to a lithium rechargeable battery is around 630 µW, independent of the load resistance.

Refined Processing and Two‐Dimensional Inversion of Magnetotelluric Data I: Impedance Tensor Decomposition and Analysis of Structural Dimensionality

AbstractA mathematical transformation, conjugate impedance transformation, is performed to magnetotelluric impedances data, which yields a special relationship between observed and regional impedance. It is independent of local galvanic distortion and does not require assumption of subsurface dimensionality. This relationship also holds to a three‐dimensional regional structure. Using the available Swift rotation method, the strike angle for the regional structure can be derived from the transformed impedance data. Then the phases, amplitudes and distortion factors can be resolved by the optimization technique. New structural dimensionality is defined based on the transformed impedance, which is not affected by local galvanic distortion. The correctness of this new algorithm is tested by using synthetic data. And a comparison with other methods, such as the Swift, Bahr, GB, phase tensor and WAL, is made analytically. Finally, these new procedures are applied to interpretation of real field data and a set of refined processing techniques are developed for removal of local distortion and determination of structural dimensionality. In the follow‐up work this new algorithm will be extended to multisite and multiple frequency cases and a new stable method based on optimization for impedance tensor decomposition will be developed.

Planar UHF RFID Tag Antenna With Open Stub Feed for Metallic Objects

An open stub feed planar patch antenna is proposed for UHF RFID tag mountable on metallic objects. Compared to conventional short stub feed patch antenna used for UHF RFID tag, the open stub feed patch antenna has planar structure which can decrease the manufacturing cost of the tags. Moreover, the open stub feed makes the impedance of the patch antenna be tuned in a large scale for conjugate impedance matching. Modeling and simulation results are presented which are in good agreement with the measurement data. Finally, differences between the open stub feed patch antenna and the short stub feed patch antenna for UHF RFID tag are discussed.

Acoustical mechanism for the extraordinary sound transmission through subwavelength apertures

An acoustical theory is developed for sound transmitting through subwavelength apertures. We show that the excitation of evanescent high-order modes induces, on each end of an aperture (either a slit or a hole), an additional acoustical reactance, which is singular as incident wavelength approaches one of cutoff wavelengths of high modes. The anomaly of the induced reactance greatly changes the resonant behaviors of the aperture, and makes the conjugate impedance matching possible at a wavelength slightly longer than the cutoff, thus leading to the extraordinary full transmission.

Design of a wideband rectangular loop tag antenna for UHF RFID library management

AbstractIn this letter, we propose a wideband rectangular loop tag antenna for ultra‐high frequency radio frequency identification library management systems.The proposed antenna has a small matching loop for conjugate impedance matching with the impedance of a tag IC. The impedance bandwidth of the proposed antenna is broadened by lengthening the vertical sides of a rectangular loop. We considered the effects of books in designing the tag antenna. The optimized tag antenna, which is 35 mm × 90 mm in size, has a wide impedance bandwidth of 170 MHz for S11 less than −10 dB. The maximum reading distance of a single tag is about 5 m, and the concurrent reading distance of 19 arranged tags is 1 m. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1439–1445, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25219

Indirect coupling method for RFID tag antenna design

Proposed is an indirect coupling method for designing an RFID tag antenna, which can not only achieve broadband operation, but can also conveniently implement a complex conjugate impedance match between an antenna and an RFID chip. An equivalent circuit model of the proposed coupling method is presented to characterise the performance of the antenna. An example is included to demonstrate the coupling method for an antenna with half-power bandwidth of approximately 16% (840-985 MHz), and which covers the entire UHF RFID frequency band. Estimated and simulated results are shown to be in good agreement with measured ones.

An Electrically Small Spherical UHF RFID Tag Antenna With Quasi-Isotropic Patterns for Wireless Sensor Networks

An electrically small spherical UHF (911.25 MHz) radio frequency identification (RFID) tag antenna is proposed. A dipole-typed RFID tag antenna is wound into a spherical shape to achieve small size and quasi-isotropic pattern. The overall diameter of the antenna is 25 mm (0.076?), and the resulting electrical size is a kr of 0.24. A short stub is employed for good conjugate impedance matching with a RFID chip (Zchip = 14 - j145 ?). The designed antenna has a -10-dB bandwidth of 7 MHz (0.77%) and the maximum readable distance of 132 cm at 5.2 W EIRP.

A Capacitively Coupling Multifeed Slot Antenna for Metallic RFID Tag Design

This letter describes a capacitively coupling multifeed slot antenna, which is comprises a slot radiator and a small dipole coupling source for metallic plate radio frequency identification (RFID) tag design. The features of the design is that the tag can function effectively with three different RFID chips, whose impedances vary widely, and the design of the conjugate impedance match of the RFID tag can be easily achieved. The important advantages of the design are that the tag does not have to be redesigned to work with different RFID chips, and additionally, the indirect coupling mechanism helps solve the mounting issue encountered in the process of mass production of the RFID tag. The experimental tests carried out with tags in which the TI, Alien-H2, and Alien-H3 chips were incorporated show that the maximum read ranges we can achieve are 1.2, 2.8, and 4.2 m, respectively, which has been tested for an RFID reader with only 0.5 W of EIRP. The letter shows that the simulated and measured results are shown to be in good agreement with each other.

차량 범퍼에 부착된 번호판용 태그 안테나의 설계

본 논문은 차량 범퍼에 부착된 번호판을 이용한 900 MHz 대역 RFID 태그 안테나의 설계를 기술하고 있다. 차량 번호판의 위쪽 중앙 지점에 위치한 제안된 태그 안테나의 크기는 162.5<TEX>${\times}$</TEX>40<TEX>${\times}$</TEX>1 <TEX>$mm^3$</TEX>이다. 설계 안테나의 공진 주파수와 - 10 dB 이하의 반사 손실을 가지는 대역폭은 각각 900 MHz와 약 720 MHz(640<TEX>${\sim}$</TEX>1,360 MHz)이다. 설계에 고려된 상용 칩의 임피던스는 16-j131<TEX>${\Omega}$</TEX>이었고, 칩의 복소 공액 임피던스가 태그 안테나의 입력 임피던스로써 사용되었다. 측정된 반사 손실과 방사 패턴은 계산된 결과들과 잘 일치하였다. 단지 차량 번호판 위에 설계된 태그 안테나의 측정된 인식 거리는 11.5 m였다. 또한, 번호판과 차량 범퍼가 볼트와 너트에 의해 고정되어진 제작된 태그 안테나의 인식 거리는 10.4 m로 관측되었다. 이 측정된 인식 거리는 상용 태그 안테나의 평균 인식 거리보다 약 5 m 이상 먼 거리였다. This paper describes a design for RFID(Radio Frequency Identification) tag antenna using license plate attached the vehicle bumper in 900 MHz band. The proposed tag antenna size which is located on upper center position of a vehicle license plate is 162.5<TEX>${\times}$</TEX>40<TEX>${\times}$</TEX>1 mm<TEX>$^3$</TEX>. A resonant frequency of design antenna and the bandwidth which has return loss of -10 dB below are 900 MHz and about 720 MHz(640<TEX>${\sim}$</TEX>1,360 MHz), respectively. The commercial chip impedance considered on design was 16- j131 <TEX>${\Omega}$</TEX> and the complex conjugate impedance of chip was used as input impedance of tag antenna. The measured return loss and radiation pattern were agreed well with the calculated results. The measured readable range of the proposed tag antenna designed on only the vehicle license plate was 11.5 m. Moreover, its range of the fabricated tag antenna that the license plate and the vehicle bumper were fixed by volt and nut was observed 10.4 m. These measured readable range showed about 5 m above far distance more than the average readable range of commercial tag antenna.

광대역에서 일정한 준 등방성 특성을 가지는 U-형태의 RFID 태그 안테나

본 논문에서는 UHF 대역에서 동작하는 광대역에서 일정한 준 등방성 특성을 가지는 U-형태의 RFID 태그 안테나를 제안하였다. 제안한 태그 안테나는 복사부에 해당하는 U-형태의 반파장 다이폴 안테나 본체에 상용 태그 칩과의 공액 정합이 용이하도록 사각형태의 급전부를 연결하였다. 또한, 본체 하단 중앙에 직사각형 슬릿을 삽입하여 동작 대역폭 안에서 태그 안테나가 일정한 준 등방성 특성을 가지도록 하였다. 태그 안테나는 VSWR<2를 기준으로 슬릿이 없을 경우 <TEX>$860.5{\sim}954.5\;MHz$</TEX>의 대역폭과 슬릿이 있을 경우 <TEX>$864.5{\sim}954\;MHz$</TEX>의 대역폭을 가졌다. VSWR<5.8을 기준으로 슬릿이 없을 경우와 슬릿이 있을 경우 각각 <TEX>$835.5{\sim}979.5\;MHz$</TEX>의 대역폭과 <TEX>$837{\sim}981.5\;MHz$</TEX>의 대역폭을 얻었다. 정합 주파수 대역 안에서 슬릿이 없는 태그 안테나의 치대 이득편차와 최소 이득편차는 각각 3.86 dB와 3.33 dB로 약 0.53 dB 차이를 가졌고, 슬릿이 있을 경우에는 최대 이득편차와 최소 이득편차가 각각 3.60 dB와 3.54 dB로 약 0.06 dB 차이의 매우 일정한 이득편차 특성을 가졌다. In this paper, we proposed a broadband U-shaped RFID tag antenna with near-isotropic characteristic at UHF band. The proposed tag antenna is composed of the U-shaped half wavelength dipole and a rectangular shaped feed. The rectangular shaped feed that is located inside U-shaped dipole is connected for conjugate impedance matching with the commercial tag chip. A better constant gain deviation characteristic in the operating frequency band is achieved by inserting a rectangular slit in the lower center of the U-shaped antenna body. On the condition of VSWR<2, the tag antenna had the measured bandwidth of 10.36%, from 860.5 to 954.5 MHz, and 9.84%, from 864.5 to 954 MHz, for antenna without slit and with slit, respectively. On the condition of VSWR<5.8, the tag antennas had the measured bandwidth of 15.78%, from 835.5 to 979.5 MHz, and 15.89%, from 837 to 981.5 MHz, for antenna without slit and with slit, respectively. The difference between the maximum and minimum gain deviations of tag antenna without slit in the operating frequency band is 0.53 dB since the maximum and minimum gain deviations are 3.86 dB and 3.33 dB, respectively. Whereas the difference between the maximum and minimum gain deviations of tag antenna with slit in the operating frequency is 0.06 dB since the maximum and minimum gain deviations are 3.60 dB and 3.54 dB, respectively.

AN INDUCTIVE SELF-COMPLEMENTARY HILBERT-CURVE ANTENN FOR UHF RFID BROADBAND AND CIRCULAR POLARIZATION TAGS

A novel fractal tag antenna constructed with Hilbertcurve and self-complementary configuration is proposed for UHF RFID applications. The main aim of this paper is to merge the meander line and meandered-slot structure of the RFID tag antenna in order to obtain a good performance of compact, broadband, circular polarization and conjugate impedance matching. The tunable inductive and broadband (−10 dB BW = 115 MHz) characteristics Corresponding author: J. C. Liu (jichyun@cyu.edu.tw).

RFID 태그용 루프형 다이폴 안테나의 지향성 설계

이 논문은 차량용 사이드 미러에 적합한 광대역 RFID 태그안테나를 설계하고, 차체에 의한 지향성의 특성을 제시한다. 제안된 태그 안테나는 인식거리와 광대역 특성을 향상시키기 위해 대칭 구조로 설계되었다 제안된 태그 안테나(<TEX>$30\;mm{\times}24\;mm{\times}1\;mm$</TEX>)는 910 MHz에서 공진하며 대역폭은 780 MHz(<TEX>$540\;MHz{\sim}1320\;MHz$</TEX>)를 가진다. 칩 임피던스는 16 - <TEX>$j131\;{\Omega}$</TEX>이고, 상용 칩의 복소 공액 임피던스가 태그 안테나의 설계에 사용되었다. 제안된 태그 안테나는 차량의 사이드 미러의 내부에 위치한다. 사이드 미러의 유전율뿐만 아니라 차체(도체)에 대한 태그 안테나의 효과를 평가하기 위해, 지향패턴 측정과 인식거리가 계산되고 측정되었다. 차량용 RFID 시스템을 위한 최적의 위치가 사이드 미러 내부에서 관측되었으며, 계산된 결과들은 측정된 결과들과 잘 일치하였다. This paper presents a design of RFID(Radio Frequency Identification) tag antenna which is available for a vehicle's side mirror and directivity characteristics by mr body. The proposed Tag antenna is designed symmetrical structure to improve the broad bandwidth characteristic and the readable range. A proposed tag antenna(<TEX>$30\;mm{\times}24\;mm{\times}1\;mm$</TEX>) has resonant frequency at 910 MHz and bandwidth is 780 MHz (<TEX>$540\;MHz{\sim}1320\;MHz$</TEX>). The chip impedance is the 16 - <TEX>$j131\;{\Omega}$</TEX> and the complex conjugate impedance of commercial chip has been used for tag antenna design. In order to evaluate effects of tag antenna for side view mirror's permittivity as well as car body(conductor), radiation pattern characteristics and readable range have been calculated and measured. The optimized position for a vehicle's RFID system has been observed in the inside of a side mirror and the calculated results show good agreement with the measured results.

Piezoelectric Energy Harvesting Improvement with Complex Conjugate Impedance Matching

One way to enhance the efficiency of energy harvesting systems is complex conjugate impedance matching of its electrical impedance. In Piezoelectric energy Harvesting systems the match is done to increment the energy flows from a vibration energy source to an energy storage electrical circuit. In this article, we compare the power generated using the modulus impedance matching with the power generated using the complex conjugate impedance matching. We present the power ratio between both types of matching methods. The novelty of this article consists of a piezoelectric transducer completely adapted with a complex conjugate impedance match. The theory developed is validated on a commercial piezoelectric transducer QP40w from Midé Technology. The transducer model is first identified by means of a system identification step based on a novel two-port Lumped-Electromechanical Model. The QP40w is complex conjugate matched at its fourth resonant mode increasing the generated power by up to 20% more compared with the modulus match.

Inductively Coupled Compact RFID Tag Antenna at 910 MHz With Near-Isotropic Radar Cross-Section (RCS) Patterns

This letter presents a compact (0.12 x 0.14lambda) RFID tag antenna which has near-isotropic radar cross-section (RCS) patterns and easy conjugate impedance matching property by virtue of an inductively coupled feeding. Its measured maximum and minimum RCS' are -17.3 dBm2 and -20.4 dBm2, respectively, with a difference of only 3.1 dB in all incident angles. The measured RCS' have been found to be in good agreement with simulation.

RFID Antennas for the UHF Remote Monitoring of Human Subjects

This paper addresses the design of passive and semi- passive transponder antennas for radio frequency identification applications involving the human body as the object to be tagged or bio-monitored. A planar tag antenna geometry, that is based on a suspended patch fed via a nested slot and is able to host sensors and electronics, is here introduced. Guidelines for conjugate impedance matching are given for different kinds of microchip transmitters, within power limitations as well as space constraints. Finally, the antenna matching performance is experimentally evaluated utilizing a body-tissue phantom.

Impedance matching with lossy components

Impedance matching networks couple a generator to a load. When lossless matching elements are used, the load power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</tex> and the power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P'</tex> extracted from the generator terminals are the same. Then the familiar conjugate impedance match condition maximizes <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P'</tex> , and hence <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</tex> . But if the matching elements are lossy <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P \neq P'</tex> ; the power difference <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P' - P</tex> is wasted in the matching network. Maximizing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P'</tex> does not maximize <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</tex> . Suppose the load is purely resistive and that the quality factors of all elements used in the matching network must not exceed a prescribed value <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> . If the load resistance value <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</tex> is not prescribed, but can be adjusted to facilitate matching, then the maximum obtainable load power is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_m</tex> , given by Theorem 1. When <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</tex> is prescribed, the maximum power may be less than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_m</tex> . However, there is a range of load resistance values, wide in many cases, for which Theorem 2 applies to deliver the same maximum power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_m</tex> . <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_m</tex> depends on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> and on another quality factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</tex> of the generator. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_m</tex> is small if <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q \ll q</tex> , as may be the case if the generator is a short receiving antenna.

Conjugate-Image Impedances

A load having the conjugate impedance of the signal generator to which it is connected receives the maximum amount of power and is said to be matched on the conjugate-image basis. This method of impedance matching, when applied to active and passive four-terminal networks, is shown to be especially suitable for determining the limits of power amplification or loss. In contrast, an analysis on the usual image basis gives these results only if the image impedances happen to be pure resistances. The maximum power gain of a given network and the impedance terminations for achieving it are derived and are expressed in-concise form. The effects of impedance mismatching are likewise treated.