WO2016040938A1

WO2016040938A1 - Rf-based gesture input device and associated method of use

Info

Publication number: WO2016040938A1
Application number: PCT/US2015/049963
Authority: WO
Inventors: Dana HUGHES; Halley PROFITA; Nikolaus CORRELL
Original assignee: University of Colorado System; University of Colorado Colorado Springs
Current assignee: University of Colorado System; University of Colorado Colorado Springs
Priority date: 2014-09-12
Filing date: 2015-09-14
Publication date: 2016-03-17
Anticipated expiration: 2017-03-12

Abstract

An RF-based gesture input device for sensing multiple forms of contact gestures, including tapping and bidirectional swiping, requiring minimal calibration. The RF-based gesture input device includes at least one RF (radio frequency) transmission line and an RF frequency domain measurement circuit coupled to the RF transmission line, the frequency domain measurement circuit using a single frequency RF signal to measure a complex reflection coefficient of the RF transmission line in response to one or more contact gestures performed on the RF transmission line. The reflection coefficient of the RF transmission line is affected by the dielectric properties of the surrounding material which changes in a predictable manner when touched by a user of the RF-based gesture input device.

Description

RF-BASED GESTURE INPUT DEVICE AND

ASSOCIATED METHOD OF USE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to currently co-pending U.S. Provisional Patent Application No. 62/049,801 , filed September 12, 2014 and entitled“ON-BODY RF-Based Gesture Input Device”, which is herein incorporated by reference.

FIELD OF INVENTION

This invention relates to electronic user interfaces. More specifically, this invention relates to a radio frequency-based gesture input device and associated method of use.

BACKGROUND OF THE INVENTION

Electronic textiles, or e-textiles, are known in the art to include fabrics having integrated electronics. A number of e-textile interfaces and input devices have been developed utilizing capacitive circuit completion, resistive circuit completion or hybrid resistive- capacitive sensing methods. These various interfaces allow for touch input and are conducive for wearable forms of technology as they can be directly sewn into garments. The e-textile interface methods currently known in the art offer particular advantages, wherein resistive implementations yield direct touching, capacitive implementations enable hovering activation and the hybrid resistive-capacitive implementations address the inherent deficiencies of independent resistive or capacitive sensing. However, current e-textile interface technologies also face a number of limitations. In the case of the hybrid resistive-capacitive sensing methodologies, elaborate interfaces are commonly necessary to avoid shorting and involuntary activation of the device by the user. Capacitive sensing interfaces are often nondiscriminatory with respect to the conducting agent, which can lead to false triggering. Resistive sensing techniques offer closed-circuit solutions, which are ideal for discrete touch, but localizing triggers typically require the integration of numerous leads. Additionally, the e-textile interfaces known in the art fall short in their ability to arbitrarily assess multipoint touch or continuous input without extensive individual lead construction, which creates a significant fabrication challenge. Known e- textile interfaces are also susceptible to malfunctioning when exposed to environmental elements.

Accordingly, what is needed in the art is an improved input device that overcomes the numerous deficiencies of the input devices currently known in the art. SUMMARY OF THE INVENTION

The present invention provide a novel RF-based gesture input device that can register multiple forms of input, including, but not limited to, tapping and bidirectional swiping, with minimal calibration.

In one embodiment, an RF-based gesture input device includes at least one RF (radio frequency) transmission line and an RF frequency domain measurement circuit coupled to the RF transmission line, the frequency domain measurement circuit using a single frequency RF signal to measure a complex reflection coefficient of the RF transmission line in response to one or more contact gestures performed on the RF transmission line. The contact gestures may include a tap, an upward swipe and a downward swipe.

In a particular embodiment, the RF transmission line may be a microstrip transmission line which is comprised of a conductive fabric ground plane layer, a conductive fabric sensing element, a dielectric layer positioned between the conductive fabric ground plane layer and the conductive fabric sensing element and a conductive thread coupled between a first end of the conductive fabric ground plane layer and a first end of the conductive fabric sensing layer. In a particular embodiment, the conductive fabric sensing element is a substantially planar one-dimensional strip. In an additional embodiment, the conductive fabric sensing element is a substantially planar two- dimension strip which may be fabricated in a serpentine shape to provide sensing of gestures in both the x and y directions.

In an additional embodiment, the RF transmission line may be a coaxial transmission line which is comprised of a conductive fabric axial sensing element, a conductive fabric outer axial ground conductor surrounding the conductive fabric inner axial sensing element and a dielectric layer positioned between the conductive fabric inner axial sensing element and the conductive fabric outer axial ground conductor.

A method of sensing one or more contact gestures performed on at least one RF transmission line of the present invention may include, performing one or more contact gestures on at least one RF transmission line and measuring, using a single frequency RF signal from an RF frequency domain measurement circuit coupled to the RF transmission line, a complex reflection coefficient of the RF transmission line in response to the one or more contact gestures performed on the RF transmission line. The contact gestures sensed by the method of the present invention may include a tap, an upward swipe and a downward swipe.

In various embodiments, the RF-based gesture input device can be integrated into an article of clothing and does not require direct contact with the skin of a user to be activated. The interface may be located underneath another piece of cloth, making it an imperceptible addition to a garment. Alternatively, the RF-based gesture input device may be covered with a thin coating of silicone rubber, making it weatherproof. Different forms of the RF-based gesture input device may also be developed or incorporated into existing clothing parts, such as a drawstring.

The RF-based gesture input device of the present invention is not limited to a single application or family of applications. Instead, the device can be used as a control mechanism suitable to the gestures capable of being perceived. Examples include using the device as an interface for MP3 players, phones, video game consoles, communication devices and remote operations. As the device can be easily weatherproofed or waterproofed, it can be incorporated into a variety of garments, including common articles of clothing, ski jackets, wetsuits and backpacks.

Accordingly, the RF-based gesture input device of the present invention overcomes many of the deficiencies inherent in the prior art interfaces known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: FIG. 1 is a block diagram of an RF-based gesture input device, in accordance with an embodiment of the present invention.

FIG. 2 is an illustration depicting transmission line theory, wherein a continuous, high- frequency incident signal is sent down the length of the line and the signal is reflected back due to the short circuit at the end of the line. The combination of the incident and reflected signal results in a standing wave.

FIG. 3a is an illustration depicting a standing wave on an untouched transmission line, in accordance with an embodiment of the present invention.

FIG. 3b is an illustration depicting a change in the standing wave resulting from the performance of a touching gesture on the transmission line, in accordance with an embodiment of the present invention.

FIG. 4a is an illustration of a cross-section of a microstrip RF transmission line, in accordance with an embodiment of the present invention.

FIG. 4b is an illustration of a substantially planar one-dimensional conductive sensing element of an RF transmission line, in accordance with an embodiment of the present invention. FIG. 4c is an illustration of a substantially planar two-dimensional serpentine-shaped conductive sensing element of an RF transmission line, in accordance with an embodiment of the present invention.

FIG. 5 is a pair of graphs illustrating the calculated magnitude and phase reflection coefficient of an RF-based gesture input device touched at various positions, in accordance with an embodiment of the present invention.

FIG. 6 is a set of nine graphs illustrating the characteristic gesture signals for downward swiping, upward swiping and tapping, for three configurations of the RF-based gesture input device, in accordance with an embodiment of the present invention. Horizontal axes are time (in seconds). Vertical axes are measured voltage (in millivolts).

FIG. 7 is an illustration depicting touch recognition and classification using a feed-forward neural network, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

On-body forms of technology continue to grow in both commercial and research sectors. As these devices become more prolific, they will benefit from novel interfaces and input devices that can more robustly support existing and new user interaction techniques. E- textiles and non-traditional forms of conductive materials, such as inks and tape, lend new opportunities for flexible and textile-based on-body input devices. The physical downsizing of hardware has allowed previously unrealized on-body form factors. The proliferation of wireless and cellular phone devices has resulted in cheap, robust and readily available surface mount components for RF circuits. Novel sensing devices can be created using RF circuits that integrate easily in existing e-textiles and extend to a number of different on-body and mobile applications.

An RF-based contact gesture input device that can detect two-way swiping and tapping with minimal calibration is presented herein. In various embodiments, the RF-based gesture input device is wearable by a user and can be positioned as an on-body RF- based gesture input device. The RF-based gesture input device may be uncovered or covered by a layer of clothing. In an uncovered embodiment, the RF-based gesture input device may be affixed to the strap of a backpack or to the back of a tie. In a covered embodiment, the RF-based gesture input device of the present invention may be positioned underneath, or within, a layer of clothing, such as under a pant leg of a user. Additionally, the RF-based gesture input device may be a weatherproofed on-body RF- based gesture input device that is affixed to a sleeve of a user. In various embodiments, embedding and weatherproofing techniques are used to provide an on-body RF-based contact gesture input device that is not only resilient to the elements, but also functional in a number of different scenarios and contexts, offering flexibility for interface design.

The RF-based gesture input device taught herein provides an eyes-free, one-handed interface capable of discrete and multi-directional continuous input from a user of the device. The RF-based gesture input device disclosed herein is both fabrication-simplistic and competent when either conspicuously or inconspicuously embedded in clothing. The RF-based gesture input device of the present invention may additionally be extended to be off-body and into the environment, including placement of the device on dog leashes or embedding the device in the arms of furniture. Whether on-body or off-body, the RF-based gesture input device is eyes-free, unobtrusive, and supports multiple forms of input and one-handed access.

With reference to FIG. 1 , an RF-based gesture input device 100 is provided comprising an RF frequency domain measurement circuit 110 coupled to an RF transmission line 105. In one embodiment, the RF transmission line 105 of the present invention is fabricated utilizing conductive fabrics to form a transmission line. The RF frequency domain measurement circuit 110 of the preset invention measures a variation of changes to the properties of the transmission line in response to one or more contact gestures performed on the RF transmission line 105. In one embodiment, the RF frequency domain measurement circuit 110 may include a voltage controlled oscillator 115, a first directional coupler 120, a second directional coupler 125 and a gain phase detector 140. RF signals are alternating current signals with frequencies in the range of several hundred kHz to several hundred GHz. In this range, the wavelength of the signal is small enough that the phase of a signal varies significantly over the area of a circuit. An RF transmission line is schematically represented as a two-wire line and can be electrically described with a complex propagation constant, γ = α + jβ, and characteristic impedance, Z₀, for lines with negligible loss, as shown with reference to FIG. 2, wherein the two-wire line 200, 205 is terminated at location z = l with an arbitrary load Z_L 210. In accordance with transmission line theory, an incident RF signal injected at z = 0 propagates down the line, and may be partially or fully reflected at z = l, due to the mismatch of line and load impedances. The incident and reflected waves form a standing wave, as shown in FIG. 2. The standing wave represents the voltage on the line as a function of position. The maximum, minimum and phase of the standing wave vary as a function of the characteristic impedance of the two-wire line and the load 210 impedance. The input impedance of the line and reflection coefficient, measured at the input of the line, vary based on the value of the standing wave at that point. The reflection coefficient, Γ, is a complex value representing the ratio of the incident wave and the reflected wave. The standing wave, reflection coefficient and input impedance all change with variations in length, characteristic impedance or load impedance of the two-wire line.

The effect of touching the RF-based gesture input device of the present invention is illustrated with reference to FIG. 3, in which FIG. 3a depicts the reflection coefficient of an untouched line and FIG. 3b depicts reflections due to a touched region. The changes resulting from the touch can be measured by the reflection coefficient of the transmission line.

As previously described with reference to FIG. 1 , the RF frequency measurement circuit 100 is used to measure the input impedance of the RF transmission line 105 and may include a voltage-controlled oscillator (VCO) 115, and a gain phase detector 140. In this embodiment, it is assumed that circuit transmission lines have a characteristic impedance of 50Ω, to match the impedance of the components. In an additional embodiment, the gain phase detector 140 may be replaced with any component or circuit capable of measuring the phase difference between two signals, such as a mixer.

In an exemplary embodiment, the VCO 115 generates a 900MHz signal at -3dBm (500μW). The first directional coupler 120 is used to maintain a -23dBm reference signal, V_ref 145. The remaining signal power is passed through the second directional coupler 125 and provides an input signal at the measurement port, V_L 135. The reflected signal from the RF transmission line 105, V_R 130, is then transmitted back to the second directional coupler 125, which provides a measurement signal Vm 150 as an input to the gain phase detector 140. The reference and measurement signals, V_r 130 and V_m 150 are used as inputs to the gain phase detector 140. The gain phase detector 140 generates two DC voltages, V_Mag 155 and V_Phase 160. V_Mag 155 is based on the gain of the measured signal to the reference signal (|V_m|/|V_r|) and V_Phase 160 is based on the phase difference between the two signals (angle V_m - angle V_r). As such, the RF frequency domain measurement circuit 110 provides a measurement of the coherent reflection coefficient measured at the input of the RF transmission line 105. This reflection coefficient consists of the superposition of the static reflection coefficient internal to the circuit, and a dynamic reflection coefficient due to interaction with the RF transmission line 105.

As such, the RF frequency domain measurement circuit 110 measures a complex (magnitude and phase) reflection coefficient at the input of the transmission line 105 using a continuous, single frequency RF signal provided by the VCO 115. In accordance with transmission line theory, in the frequency domain, each multiple reflection resulting from the single continuous RF signal initiated on the transmission line 105 contributes to the measured steady-state reflected signal. The position of a contact gesture or touch on the e-textile RF transmission line 105 is determined based upon the near linear relationship that exists between the location of the touch and the phase of the reflection coefficient of the e-textile RF transmission line 105.

In order to ensure that a unique measurement is made for any touch location on the RF- based gesture input device 100, the length of the RF transmission line 105 is limited by the frequency of the transmitted wave. Despite this limitation, the frequency range of the circuit components (100MHz - 2.7GHz) allows for RF transmission lines up to 75cm in length, making them suitable for most wearable sensors.

With reference to FIG. 4a, in one embodiment, the RF transmission line of the RF-based gesture input device 100 is a microstrip line 400. In general, a microstrip line consists of a conducting strip 405, or sensing element, separated from a ground plane 410 using a dielectric substrate 415, as shown in FIG. 3. The characteristic impedance of a microstrip line 400 with line width w 420, thickness t 425, dielectric height d 430 and relative (to free space) dielectric constant ε_r 435 can be calculated by various means known in the art. Touching the microstrip 400 is equivalent to covering the sensing element 405 with a layer of generally lossy dielectric. Because human skin has a very high permittivity (relative to free space), and the average thickness of an adult fingertip is much thicker than the layer of dielectric 410, analysis can be simplified by treating the layer of human skin as an infinite dielectric layer. The characteristic impedance of a microstrip 400 is known to drastically change when the microstrip 400 is covered by an infinite dielectric layer.

As shown with reference to FIG. 4b, in one embodiment, the sensing element 405 of the RF transmission line may be a substantially planar strip of conductive material that is positioned on the surface of the dielectric layer 410 to extend in only one direction. In an additional embodiment, as shown with reference to FIG. 4c, the sensing element 450 of the RF transmission line may be a substantially planar strip of conductive material that is arranged to fill a two-dimensional region. In this illustrated embodiment, the sensing element 450 is formed into a serpentine shape. By arranging the sensing element to extend in both the x and y directions, the coordinates of a gesture performed on the sensing element 450 can be calculated from the position of the gesture from the measurement port of the transmission line 400 in two dimensions.

In a specific embodiment, the microstrip RF transmission line 400 can be designed using a layering construction of conductive and non-conductive fabric. In this embodiment, the base layer 415 may be a 3.8cm x 12.7cm Rip-Stop Conductive Metallized Nylon fabric, which serves as the ground plane for the microstrip line 400. A 2mm layer of iron-on adhesive denim may constitute the middle layer 410 and may be ironed directly to the conductive base 415. The top layer sensing element 405 may consist of a 10cm x 0.635cm strip of Rip-Stop conductive fabric that is centered and adhered to the denim layer 410 using fabric glue. At a first end of the e-textile RF transmission line 400, the sensing element 405 and base 415 may be connected using 117/17 2-ply conductive thread (not shown), thereby forming a short-circuit. On a second end of the e-textile RF transmission line 400, the base 415 and the conductive top strip 405 may be coupled to the measurement port and ground plane of the RF frequency domain measurement circuit 110 using copper tape. The e-textile input device 400 is designed to attach to a number of on-body clothing articles or other textile-based items. The length of the interface and frequency of operation can be adjusted so that the interface is the ideal length of 1 /4 of the wavelength of the RF signal from the RF frequency domain measurement circuit 110. The thickness of the dielectric layer 410, and width and thickness of the microstrip sensing element 405 are independent of frequency.

In an additional embodiment, the RF transmission line 105 may be fabricated as coaxial transmission line, and may comprise a conductive fabric axial sensing element, a conductive fabric outer axial ground conductor surrounding the conductive fabric inner axial sensing element and a dielectric layer positioned between the conductive fabric inner axial sensing element and the conductive fabric outer axial ground conductor. Designing the e-textile RF transmission line 105 of the e-textile input device 100 as a coaxial line can make it less sensitive to indirect touching and less susceptible to accidental triggering.

In additional embodiment, the RF-based gesture input device may be comprised of conductive and dielectric materials that are not specifically integrated into fabric, textiles or cloth, but instead, the RF-based gesture input device may be at least partially enclosed in such a fabric or textile after it has been fabricated. As such the device can be integrated into standard articles of clothing.

As shown with reference to FIG. 5, the magnitudes 500 and phases 505 of reflection coefficients were calculated for fingertips of different widths (1.6 cm, 1.8 cm, and 2.0 cm) located at different positions along the RF-based gesture input device. The magnitude 500 and phase 505 of the microstrip line, when untouched, vary greatly from the values calculated when touched and the calculated phases are unique for the given line properties. Upon measuring the reflection coefficient of the RF transmission line 105 using the RF frequency domain measurement circuit 110, the position and/or gesture performed by a fingertip on the RF transmission line 105 can be uniquely determined by either the magnitude of the reflection coefficient 500 or the phase of the reflection coefficient 505. By continuously monitoring the phase of the RF transmission line 105, a tapping gesture will be shown to result in a sudden jump in the phase of the reflection coefficient, an upward swipe will result in an increase in the phase of the reflection coefficient and a downward swipe will result in a decrease in phase of the reflection coefficient. In this embodiment, an upward swipe gesture is defined as being initiated proximate to the measurement port interface between the RF transmission line 105 and the RF frequency domain measurement circuit 110 and moving away from the measurement port interface. In addition, a downward swipe gesture is define as being initiated distal to the measurement port interface between the RF transmission line 105 and the RF frequency domain measurement circuit 110 and toward the measurement port interface.

In an exemplary embodiment, experiments were performed by measuring the voltage output of the magnitude of the reflection coefficient of the RF transmission line 105 while performing three different contact gestures (downward swipe, upward swipe and tap) on the RF-based gesture input device. Three sets of experiments were performed on the RF- based gesture input device using three different swatch configurations, including: (1 ) uncovered (2) covered by a layer of cotton/polyester canvas and (3) weatherproofed using EcoFlex silicone rubber. FIG. 6 shows the measurement results for these three sets of experiments. As shown in 600, for each of the swatch configurations, downward swipe gestures are represented by a jump in voltage when the finger touches the measurement port end of the RF-based gesture input device, and the voltage declines as the finger slides down the RF-based gesture input device. As shown in 605, for each of the swatch configurations, upward swipe gestures are represented by a jump in voltage when the finger touches the RF-based gesture input device and a location distal to the measurement port, followed by a steady increase in voltage and then by a sharp return to baseline as the finger is released. As shown in 610, for each of the swatch configurations, taps on the RF-based gesture input device result in a simple spike as the finger touches and releases the RF-based gesture input device.

As shown in FIG. 6, the characteristic signals vary little between the three swatch configurations. When embedded in EcoFlex, however, the dynamic range of the signal is reduced some, though not enough to affect detection. This is likely due to EcoFlex soaking into the denim, resulting in a change in the permittivity of the dielectric layer and an increase in the static reflection of the line at the port of the RF domain measurement circuit.

The RF-based gesture input device of the present invention may be used to control various other electronic devices, including, but not limited to, MP3 players, phones, video game consoles, communication devices and remote operations. As such, an output of the RF frequency domain reflectometer of the RF-based gesture input device may be coupled to a controllable device, wherein the controllable device is configured to be controlled by the measured complex reflection coefficient of at least one RF transmission line in response to one or more contact gesture performed on at least one RF transmission line. As shown with reference to FIG. 7, classification of the touch recognition on the RF-based gesture input device 100 may be implemented utilizing a gesture identification circuit, such as a neural network. In this embodiment, the magnitude and phase voltage resulting from the performance of sample touches on the RF transmission line can be measured by the gain phase detector 700 using a 1 kHz input signal, as previously described. The measurements may then be stored in a sample buffer 705. A feed-forward neural network 710 may then analyze the stored sample measurements to classify the samples. Using this method, the output of the neural network 710 would be representative of a current gesture being performed on the e-textile transmission line, including, (1 ) no touch, (2) upward swipe, (3) downward swipe and (4) tap gesture. In one embodiment, the output of the gesture identification circuit can be used to control a controllable electronic device, such as an MP3 player or phone.

In accordance with the present invention, the use of RF in an gesture input device lends to an eyes-free, one-handed interface capable of multiple types of input. Because the RF signal is only sensitive to dielectric and geometric properties, textile substitutions can be made without altering the circuitry or the sensing mechanism. The experimental results demonstrate a handful of possible usage scenarios for the RF-based gesture input device. The weatherproofed system tackles the issue of susceptibility to the elements. The ability to use the interface in a covered, uncovered, or weatherproofed state lends to the optional conspicuity of the device and permits for flexibility in usage scenarios. While the embodiments described herein have discussed only three types of input gestures, by modifying the interface with an additional conductive layer or elastic conductive fabric additional functionality can be built into the system, including pressure detection, multi- touch, and twist recognition.

The on-body or off-body, RF-based gesture input device has been described which demonstrates the use of RF and non-traditional conductive materials to create interfaces capable of multiple forms of eyes-free, one-handed input. The manufacturing simplicity of the on-body RF-based gesture input device has been shown, as well as its ability to perform reliably in exposed, embedded, and weatherproofed scenarios. The RF-based gesture input device is just one possible example of novel interfaces, which could be designed by combining RF technology with wearable technology.

The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

All references cited in the present application are incorporated in their entirety herein by reference to the extent not inconsistent herewith.

It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Claims

What is claimed is:

1. An RF-based gesture input device comprising:

at least one RF (radio frequency) transmission line; and

an RF frequency domain measurement circuit coupled to the at least one RF transmission line, the frequency domain measurement circuit using a single frequency RF signal to measure a complex reflection coefficient of the at least one RF transmission line in response to one or more contact gestures performed on the at least one RF transmission line.

2. The RF-based gesture input device of claim 1 , wherein the at least one RF

transmission line is at least partially integrated into or surrounded by a fabric.

3. The RF-based gesture input device of claim 1 , wherein the at least one RF frequency domain measurement circuit is at least partially integrated into or surrounded by a fabric.

4. The RF-based gesture input device of claim 1 , wherein the at least one RF

transmission line is a microstrip transmission line.

5. The RF-based gesture input device of claim 2, wherein the microstrip transmission line further comprises:

a conductive ground plane layer;

a conductive sensing element;

a dielectric layer positioned between the conductive ground plane layer and the conductive strip element; and

a conductor coupled between a first end of the conductive ground plane layer and a first end of the conductive strip element .

6. The RF-based gesture input device of claim 5, wherein the conductive ground plane layer is a conductive fabric ground plane layer.The RF-based gesture input device of claim 5, wherein the conductive sensing element is a conductive fabric sensing element.

7. The RF-based gesture input device of claim 5, wherein the dielectric layer is a

dielectric fabric layer.

8. The RF-based gesture input device of claim 5, wherein the conductor is a conductive thread.

9. The RF-based gesture input device of claim 5, wherein the conductive sensing

element is a substantially planar one-dimensional conductive sensing element.

10. The RF-based gesture input device of claim 5, wherein the conductive sensing element is a substantially planar two-dimensional conductive sensing element.

11. The RF-based gesture input device of claim 5, wherein the conductive sensing

element is a substantially planar serpentine-shaped conductive sensing element.

12. The RF-based gesture input device of claim 1 , wherein the at least one RF

transmission line is a coaxial transmission line.

13. The RF-based gesture input device of claim 12, wherein the coaxial transmission line further comprises:

a conductive axial sensing element;

a conductive outer axial ground conductor surrounding the conductive inner axial sensing element; and

a dielectric layer positioned between the conductive inner axial sensing element and the conductive outer axial ground conductor.

14. The RF-based gesture input device of claim 13, wherein the conductive axial sensing element is a conductive fabric axial sensing element.

15. The RF-based gesture input device of claim 13, wherein the conductive outer axial ground conductor is a conductive fabric outer axial ground conductor.

16. The RF-based gesture input device of claim 13, wherein the dielectric layer is a dielectric fabric layer.

17. The RF-based gesture input device of claim 1 , wherein the RF frequency domain measurement circuit comprises an oscillator circuit for generating the single frequency RF signal.

18. The RF-based gesture input device of claim 17, wherein the RF frequency domain measurement circuit comprises an RF gain phase detector circuit coupled to the oscillator circuit, the RF gain phase detector circuit to measure the complex reflection coefficient in response to one or more contact gestures performed on the e-textile RF transmission line.

19. The RF-based gesture input device of claim 17, wherein the RF frequency domain measurement circuit comprises a mixer circuit coupled to the oscillator circuit, the mixer circuit to measure the complex reflection coefficient in response to one or more contact gestures performed on the e-textile RF transmission line.

20. The RF-based gesture input device of claim 1 , wherein the RF frequency domain measurement circuit is an RF frequency domain reflectometer.

21. The RF-based gesture input device of claim 1 , wherein the contact gesture is selected from a tap gesture, an upward swipe gesture and a downward swipe gesture.

22. The RF-based gesture input device of claim 1 , further comprising a gesture identification circuit coupled to the RF frequency domain measurement circuit, the gesture identification circuit to identify the one or more contact gestures based upon the measured complex reflection coefficient of the at least one RF transmission line.

23. The RF-based gesture input device of claim 1 , further comprising a controllable

device, coupled to an output of the RF frequency domain reflectometer, the controllable device configured to be controlled by the measured complex reflection coefficient of the at least one RF transmission line in response to one or more contact gesture performed on the at least one RF transmission line.

24. A system comprising:

an RF-based gesture input device comprising;

at least one RF transmission line;

an RF frequency domain reflectometer coupled to the at least one RF transmission line, the RF frequency domain reflectometer to measure a complex reflection coefficient of the at least one RF transmission line in response to one or more contact gestures performed on the at least one RF transmission line; and

a controllable device coupled to an output of the RF frequency domain reflectometer, the controllable device configured to be controlled by the measured complex reflection coefficient of the at least one RF transmission line in response to one or more contact gesture performed on the at least one RF transmission line.

25. A method of sensing one or more contact gestures performed on an RF transmission line, the method comprising:

performing one or more contact gestures on an RF transmission line; and measuring, using a single frequency RF signal from an RF frequency domain measurement circuit coupled to the RF transmission line, a complex reflection coefficient of the RF transmission line in response to the one or more contact gestures performed on the RF transmission line.

26. The method of claim 25, wherein the RF transmission line is selected from a one- dimensional microstrip RF transmission line, a two-dimensional RF transmission line and a coaxial RF transmission line.

27. The method of claim 25, wherein the contact gesture is selected from a tap gesture, an upward swipe gesture and a downward swipe gesture.