System for motion sensing and energy harvesting

Abstract

A system for motion sensing and energy harvesting is described in an embodiment. The system comprising: a transductor adapted to convert a motion to an electric signal for motion sensing and energy harvesting, the transductor having a positive voltage terminal and a negative voltage terminal; an over-voltage protection circuit connected to the transductor, the over-voltage protection circuit being adapted to receive the electric signal in the form of a harvested voltage and to provide a supply voltage of less than or equal to 3.2 V peak-to-peak; a power rectifier connected to the over-voltage protection circuit for rectifying the supply voltage to generate an output voltage; a comparator circuit connected to the transductor for comparing voltages between the positive voltage terminal and the negative voltage terminal; and a processing chip connected to the comparator circuit, the processing chip having at least one logic circuit for use in processing an output from the comparator circuit for sensing the motion, wherein the output voltage of the power rectifier is used to supply power to the comparator circuit, and wherein the over-voltage protection circuit and the power rectifier are integrated onto the processing chip.

Description

[0001] System for motion sensing and energy harvesting

[0002] Technical Field

[0003] The present disclosure relates to a system for motion sensing and energy harvesting.

[0004] Electronic textiles (E-textiles) offer numerous benefits, primarily in areas like healthcare, safety and comfort, by integrating electronics into textiles. Typically, an E-textile system integrates electronic components, e.g. silicon dice, on a fabric as a substrate. Implementation of an E-textile system therefore requires conformability (e.g., use of a very small / thin die), minimization of off-chip components, low costs, and extremely low power requirements (e.g. in the range of pW). For self-powered operations, conformable and large-area in-textile harvesters such as triboelectric nanogenerators (TENGs), piezoelectric nanogenerators (PENGs), or other type of flexible or miniaturized harvesters are required.

[0005] Recent progress has been made in E-textile systems. For example, E-textile inter-chip data links without harvesting or sensing and with a mW-range power has been demonstrated. However, the required mW-range exceeds typical available harvesting power, for example, the tens of nWs of TENGs or the 1 -2 pW of PENGs. A fully energy- autonomous temperature-to-time converter (TTC) powered entirely by a TENG for biomedical applications was demonstrated, but it had utilised an external off-chip supply, sensing circuitry and off-the-shelf microcontroller whose form factor severely limits system conformability. The high-power consumption of the TTC in this case also prevents full-system sustainable operations. Harvesting energy from human motion using high-voltage-yielding TENGs which deliver high voltages, e.g. in the range of 70 V to 130 V, were demonstrated but these necessitate higher-cost high-voltage processes, die stacking, and / or off-chip over-voltage protections / rectifiers.

[0006] Further, a conventional E-textile system using a TENG energy harvester has shown limited level of on-chip integration as part of the sensor interface requires an external supply. Such a system is also capable of harvesting only, without demonstrating a fullsystem sustainable operation under a tight harvester power budget. Piezoelectric harvesting is another energy harvesting option which has a small form factor. Nevertheless, its mechanical rigidity prevents its exploitation over a large area typically available in E-textiles. In either case, several large off-chip components, such as large in-textile inductors (e.g. mH range, about 40 cm), high-voltage capacitors (e.g. 100 V, or in the 100-pF range) and batteries, are required. In addition, due to the nature of human motion which is generally much slower than a typical minimum allowable harvesting frequency of these energy harvesters (-75 Hz to 250 Hz), even larger off-chip components are required to lower the allowable harvesting frequency.

[0007] It is therefore desirable to provide a system for motion sensing and energy harvesting which address the aforementioned problems and / or provide a useful alternative. Further, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

[0008] Summary

[0009] Aspects of the present application relate to a system for motion sensing and energy harvesting.

[0010] In accordance with a first aspect, there is provided a system comprising: a transductor adapted to convert a motion to an electric signal for motion sensing and energy harvesting, the transductor having a positive voltage terminal and a negative voltage terminal; an over-voltage protection circuit connected to the transductor, the over-voltage protection circuit being adapted to receive the electric signal in the form of a harvested voltage and to provide a supply voltage of less than or equal to 3.2 V peak-to-peak; a power rectifier connected to the over-voltage protection circuit for rectifying the supply voltage to generate an output voltage; a comparator circuit connected to the transductor for comparing voltages between the positive voltage terminal and the negative voltage terminal; and a processing chip connected to the comparator circuit, the processing chip having at least one logic circuit for use in processing an output from the comparator circuit for sensing the motion, wherein the output voltage of the power rectifier is used to supply power to at least the comparator circuit, and wherein the over-voltage protection circuit and the power rectifier are integrated onto the processing chip.

[0011] By having the power rectifier connected to the transductor for rectifying the supply voltage, energy from a motion can be harvested from the transductor and output to at least the comparator circuit for powering the comparator circuit. At the same time, the comparator circuit provided is connected to the transductor and adapted to compare voltages between the positive voltage terminal and the negative voltage terminal of the transductor, and the output of the comparator circuit is provided to the processing chip for use in motion sensing. The aforementioned system is therefore able to use a same motion applied or detected by the transductor for both energy harvesting and motion sensing, minimising the number of components required for performing these actions, particularly when applied in an E-textile system. This dual-function of energy harvesting and motion sensing using the same transductor allows for just-in-time power provision as the transductor is able to generate more power in response to a larger or wider range motion, which in turn requires a higher system power e.g. to sense a higher level of motion activity. This means that the present system is able to provide self-sustained power on demand without the need for additional energy storage, for example, in the form of a battery. Further, the over-voltage protection circuit in the system is adapted to receive the electric signal from the transductor in the form of a harvested voltage and to provide a supply voltage of less than or equal to 3.2 V peak-to-peak. This allows the system to be adopted with common low-cost complementary metal-oxide-semiconductor (CMOS) technology having typically 3.3 V input / output (I / O) connections.

[0012] The over-voltage protection circuit may comprise N number of PNP bipolar junction transistors (BJTs) and N-2 number of NPN bipolar junction transistors (BJTs), wherein N-1 of the N number of PNP BJTs may be stacked laterally to form a first set of BJTs, wherein the N-2 number of NPN BJTs and a remaining one of the N number of PNP BJTs may be stacked laterally to form a second set of BJTs having at least a base of a last of the N-2 number of NPN BJTs being connected to a base of the remaining one of the N number of PNP BJTs at an end portion of the second set of BJTs, wherein a collector of a first of the N-1 of the N number of PNP BJTs of the first set of BJTs may be connected to ground and an emitter of a last of the N-1 of the N number of PNP BJTs of the first set of BJTs may be connected to an emitter of a first of the N-2 number of NPN BJTs of the second set of BJTs at the positive voltage terminal of the transductor, and wherein an emitter of the remaining one of the N number of PNP BJTs of the second set of BJTs may be connected to the negative voltage terminal of the transductor.

[0013] The motion may include walking and the over-voltage protection circuit may comprise three PNP bipolar junction transistors (BJTs) and one NPN bipolar junction transistor (BJT). The power rectifier may comprise a full-bridge rectifier comprising two of a first set of transistors and two of a second set of transistors, the first set of transistors being adapted to function as a p-channel metal-oxide-semiconductor (PMOS) diode and the second set of transistors being adapted to function as a n-channel metal-oxide-semiconductor (NMOS) diode, wherein the first set of transistors and the second set of transistors are connected to form each half of the full-bridge rectifier.

[0014] The first set of transistors may comprise a PMOS transistor and first and second subthreshold Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) sets, and the second set of transistors may comprise a NMOS transistor and third and fourth subthreshold MOSFET sets, wherein each of the first, second, third and fourth sub-threshold MOSFET sets may comprise two transistors connected in series, wherein the first subthreshold MOSFET set may comprise a first transistor and a second transistor, the first transistor having a drain connected to a drain of the PMOS transistor and a source connected to a second drain of the second transistor, the second transistor having a source connected to ground, wherein the second sub-threshold MOSFET set may comprise a third transistor and a fourth transistor, the third transistor having a drain connected to a source of the PMOS transistor and the output voltage of the power rectifier and a source connected to a drain of the fourth transistor, and the fourth transistor having a source connected to ground, wherein the third sub-threshold MOSFET set may comprise a fifth transistor and a sixth transistor, the fifth transistor having a source connected to ground and a source of the NMOS transistor and a drain connected to a source of the sixth transistor, and the sixth transistor having a drain connected to the output voltage of the power rectifier, and wherein the fourth subthreshold MOSFET set may comprise a seventh transistor and an eighth transistor, the seventh transistor having a source connected to a drain of the NMOS transistor and a drain connected to a source of the eighth transistor, and the eighth transistor having a drain connected to the output voltage of the power rectifier.

[0015] A gate of the PMOS transistor, a gate of the first transistor, and a gate of the third transistor may be connected to the source of the third transistor, a gate of the second transistor and a gate of the fourth transistor may be connected to ground, a gate of the NMOS transistor, a gate of the fifth transistor and a gate of the seventh transistor may be connected to a drain of the fifth transistor, and a gate of the sixth transistor and a gate of the eighth transistor may be connected to the output voltage of the power rectifier. The full-bridge rectifier may comprise a capacitor connected between the PMOS transistor and the NMOS transistor for each half of the full-bridge rectifier.

[0016] The system may comprise: a further transductor adapted to convert a further motion to a further electric signal for energy harvesting, the further transductor having a further positive voltage terminal and a further negative voltage terminal; a further over-voltage protection circuit connected to the further transductor, the further over-voltage protection circuit being adapted to receive the further electric signal in the form of a further harvested voltage and to provide a further supply voltage of less than or equal to 3.2 V peak-to-peak; and a further power rectifier connected to the further over-voltage protection circuit for rectifying the further supply voltage to generate a further output voltage, the further power rectifier adapted to keep an off-state leakage of the system to below 1.5 pW, wherein the further output voltage is used to supply power to the processing chip, and wherein the further over-voltage protection circuit and the further power rectifier are integrated onto the processing chip.

[0017] The further power rectifier may have a same circuit architecture as the power rectifier.

[0018] The further over-voltage protection circuit may comprise four PNP bipolar junction transistors (BJTs) and two NPN bipolar junction transistors (BJTs), wherein three of the four PNP BJTs are stacked laterally and formed a further first set of BJTs, wherein the two NPN BJTs and a remaining one of the four PNP BJTs formed a further second set of BJTs having at least a base of a last of the two NPN BJTs being connected to a base of the remaining one of the four PNP BJTs at an end portion of the further second set of BJTs, wherein a collector of a first of the four PNP BJTs of the first set of BJTs is connected to ground and an emitter of a last of the four PNP BJTs of the further first set of BJTs is connected to an emitter of a first of the two NPN BJTs of the further second set of BJTs at the further positive voltage terminal of the further transductor, and wherein an emitter of the remaining one of the four PNP BJTs of the further second set of BJTs is connected to the further negative voltage terminal of the further transductor.

[0019] The system may comprise a capacitor connected to the further power rectifier and the processing chip, the capacitor adapted to provide back-up energy to the processing chip in case of sparse energy harvesting. The further motion may have a frequency of less than 1 Hz. The further motion may include breathing.

[0020] The further transductor may include a plurality of transductors connected in parallel.

[0021] The system may comprise a communication module configured to transmit data from the processing chip to an external device. The communication module may include a backscattered near field communication (NFC) transmission module.

[0022] The system may be formed on a textile substrate. The transductor may include a triboelectric nanogenerator or a piezoelectric transductor. The power rectifier may be adapted to keep an off-state leakage of the system to below 1 .5 pW.

[0023] In accordance with a second aspect, there is provided an electronic textile (E-textile) comprising a textile and any one of the aforementioned systems, the system being integrated with the textile.

[0024] It should be appreciated that features relating to one aspect may be applicable to the other aspects. Embodiments provide a system for motion sensing and energy harvesting. Particularly, by having the power rectifier connected to the transductor for rectifying the supply voltage, energy from a motion can be harvested from the transductor and output to at least the comparator circuit. At the same time, the comparator circuit provided is connected to the transductor and adapted to compare voltages between the positive voltage terminal and the negative voltage terminal of the transductor, and the output of the comparator circuit is used in motion sensing. The aforementioned system is therefore able to use a same motion applied or detected by the transductor for both energy harvesting and motion sensing, minimising the number of components required for performing these actions, particularly when applied in an E-textile system. This dualfunction of energy harvesting and motion sensing using the same transductor allows for just-in-time power provision as the transductor is able to generate more power in response to a larger or wider range motion, which in turn requires a higher system power e.g. to sense a higher level of motion activity. This means that the present system is able to provide self-sustained power on demand without the need for additional energy storage, for example, in the form of a battery. Further, the over-voltage protection circuit in the system is adapted to receive the electric signal from the transductor in the form of a harvested voltage and to provide a supply voltage of less than or equal to 3.2 V peak- to-peak. This allows the system to be adopted with common low-cost complementary metal-oxide-semiconductor (CMOS) technology having typically 3.3 V input / output (I / O) connections. In an embodiment, the system comprises a communication module adapted to transmit data (e.g. step counts) from the processing chip to an external device. A backscattered near field communication (NFC) transmission module can for example be used where wireless power can be received from the external device and therefore does not require additional power provision for data transmission internally from the system. Further, in an embodiment, the power rectifier and the over-protection circuit can be adapted to have ultra-low leakages which allow power reductions down to about pW. This enables uninterrupted operation of the system even during down-time when the sole power harvested can be from the breathing of the user.

[0025] Brief description of the

[0026] Embodiments will now be described, by way of example only, with reference to the following drawings, in which:

[0027] Figure 1 shows a schematic of a system for energy harvesting in accordance with an embodiment;

[0028] Figure 2 shows a series of schematics to illustrate electric signals generated by a transductor of the system of Figure 1 in response to motions in accordance with an embodiment;

[0029] Figure 3 shows a schematic of four transductors being connected in parallel for use in the system of Figure 1 in accordance with an embodiment;

[0030] Figure 4 shows a schematic of a system having two different modes for motion sensing and energy harvesting in accordance with an embodiment;

[0031] Figure 5 shows a plot of harvested power versus time to illustrate power harvested during a breathing mode of the system of Figure 4 in accordance with an embodiment;

[0032] Figure 6 shows a plot of harvested power versus time to illustrate power harvested during a walking / running mode of the system of Figure 4 in accordance with an embodiment;

[0033] Figures 7A and 7B show schematics of parts of a full bridge rectifier for use in the system of Figure 4 in accordance with an embodiment, where Figure 7A shows a schematic of a first set of transistors for use in the full-bridge rectifier and Figure 7B shows a schematic of a second set of transistors for use in the full-bridge rectifier;

[0034] Figure 8 shows a schematic of the full bridge rectifier comprising first and second halves of the full-bridge rectifier in accordance with an embodiment;

[0035] Figure 9 shows a schematic of an over-voltage protection circuit for use in the system of Figure 4 in accordance with an embodiment;

[0036] Figure 10 shows a schematic of a communication module for use in the system of Figure 4 in accordance with an embodiment;

[0037] Figure 11 shows a schematic of a logic circuit with super cut-off for use in the system of Figure 4 in accordance with an embodiment;

[0038] Figure 12 shows a schematic of an analogue circuit with super cut-off for use in the system of Figure 4 in accordance with an embodiment;

[0039] Figure 13 shows a plot of harvested voltage versus time with a 100 MQ load in response to a hand touch motion in accordance with an embodiment;

[0040] Figure 14 shows a plot of harvested voltage versus time with a 100 MQ load in response to a walking motion in accordance with an embodiment;

[0041] Figure 15 shows a plot of harvested voltage versus time with a 100 MQ load in response to a breathing motion in accordance with an embodiment;

[0042] Figure 16 shows a bar graph of total system power and power rectifier leakage power in a breathing mode for six different die samples in accordance with an embodiment;

[0043] Figure 17 shows a plot of power rectifier power efficiency versus load current obtained using the full-bridge rectifier of Figure 8 in accordance with an embodiment;

[0044] Figure 18 shows a plot of power rectifier power efficiency versus input power obtained using the full-bridge rectifier of Figure 8 in accordance with an embodiment;

[0045] Figure 19 shows a plot of power rectifier voltage efficiency versus load current obtained using the full-bridge rectifier of Figure 8 in accordance with an embodiment; Figure 20 shows a plot of voltage versus time of the over-voltage protection circuit obtained using the over-voltage protection circuit of Figure 9 in accordance with an embodiment;

[0046] Figure 21 shows a plot of gain (dB) versus frequency for a bandpass filter used in a comparator circuit of the system of Figure 4 in accordance with an embodiment;

[0047] Figure 22 shows a timing diagram to illustrate a walking step event and responses obtained by various components of the system of Figure 4 in accordance with an embodiment;

[0048] Figure 23 shows a plot of voltage versus time to illustrate a transient response of the transductor of the system of Figure 4 in a walking mode in accordance with an embodiment;

[0049] Figure 24 shows a plot of voltage versus time to illustrate a transient response of the power rectifier of the system of Figure 4 in a walking mode in accordance with an embodiment;

[0050] Figure 25 shows a plot of voltage versus time to illustrate a transient response of the comparator of the comparator circuit of the system of Figure 4 in a walking mode event in accordance with an embodiment;

[0051] Figure 26 shows a plot of voltage versus time to illustrate a transient response of step count information read from Dynamic Leakage Suppression (DLS) on-chip memory using the system of Figure 4 in a walking mode in accordance with an embodiment;

[0052] Figure 27 shows a pie chart of measured system power breakdown for a breathing mode of the system of Figure 4 in accordance with an embodiment; and

[0053] Figure 28 shows a pie chart of measured system power breakdown for a walking mode of the system of Figure 4 in accordance with an embodiment.

[0054] Detailed description

[0055] Exemplary embodiments relate to a system for motion sensing and energy harvesting.

[0056] It is appreciated that in the present application, the use of the singular includes the plural unless specifically stated otherwise. It should be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Further, the use of the term “including”, “comprising”, and “having” as well as other forms, such as “include”, “comprise”, “have” are not considered limiting.

[0057] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0058] As used herein, the term “comprising” or “including” is to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps or components, or groups thereof. However, in context with the present disclosure, the term “comprising” or “including” also includes “consisting of’. The variations of the word “comprising”, such as “comprise” and “comprises”, and “including”, such as “include” and “includes”, have correspondingly varied meanings.

[0059] To implement a suitable system in an electronic textile, it is desirable for the system to include conformable components that use ultra-low power, that can be manufactured cheaply and can be used to harvest energy in a sustainable way. It is also desirable that the system is self-sustainable so that no battery is required for the system. This translates to a system which can preferably harvest energy in any condition. It is also desirable that the system has a high-level of integration with minimal off-chip discrete components, and that the system is compatible to standard CMOS components or processes to minimise manufacturing costs.

[0060] The present disclosure relates to a system for motion sensing and energy harvesting to fulfil at least some of the above system properties. In an exemplary embodiment, an always-on walking step counting system for e-textile applications is described. The system can be integrated on a textile substrate, e.g. a T-shirt, and is solely powered by transductors. The exemplary embodiment provides a system which includes sub- systems / components configured to provide motion sensing, power management and on- demand wireless communications (e.g. NFC communications). The system of the exemplary embodiment is battery-less, inductor-less, and requires minimal off-chip discrete components. In the present embodiment, a triboelectric nanogenerator (TENG) is used as a physical transductor, but it should be appreciated that other suitable transductors e.g. a piezoelectric-based transductor may be used. As will be shown in relation to later Figures, only an off-chip component (an optional feature) comprising a mm-sized 1 -pF bondable capacitor is implemented in the exemplary system for enhancing robustness against noise or mechanical solicitations. The present system is also designed to work within typical I / O voltage ratings of a silicon chip, so that off-chip protection, rectifier, or high-voltage process are not required. This lowers a cost of the system while minimising a form factor of the system. The present system provides a much higher level of integration with low-area and low costs, and is compatible with non- high voltage standard CMOS processes to meet the requirements of E-textile applications at scale.

[0061] Figure 1 shows a schematic of a system 100 for energy harvesting in accordance with an embodiment.

[0062] The system 100 comprises a transductor 102 or a Motion Harvesting Sensor (MoHSr) adapted to convert a motion to an electric signal for motion sensing and / or energy harvesting. A motion can be an action such as breathing, walking, running and / or touching which exerts pressure or a force 103 onto the transductor 102. In the present embodiment, the transductor 102 includes a triboelectric nanogenerator (TENG). It should be appreciated that in other embodiments, the transductor 102 includes other types of motion harvester or combination of different types of motion harvesters. For example, in an embodiment, a piezo-electric nanogenerator (PENG) or a combination of TENG and PENG, or any other suitable motion harvesters can be used. The transductor 102 has a positive voltage terminal (VTENG+) 104 and a negative voltage terminal (VTENG-) 106. As shown in Figure 1 , the system 100 further comprises an over-voltage protection circuit 108 connected to the transductor 102 and a power rectifier 110 connected to the over-voltage protection circuit 108. The over-voltage protection circuit 108 is adapted to receive the electric signal in the form of a harvested voltage from the transductor 102 and in the present embodiment, to provide a supply voltage of less than or equal to 3.2 V peak-to-peak to the power rectifier 1 10. The power rectifier 110 is connected to the over-voltage protection circuit 108 and is adapted to rectify the supply voltage to generate an output voltage for feeding into a silicon system 112 in the present embodiment. Figure 1 therefore shows energy harvested using the transductor 102 which can be provided to power the silicon system 1 12. The system 100 of Figure 1 forms a sub-system or sub-component to a system for motion sensing and energy harvesting as discussed below in relation to Figure 4. As would be made clearer later in Figure 4, the transductor 102 / TENG can also be connected to a comparator circuit for comparing voltages between the positive voltage terminal 104 and the negative voltage terminal 106. The comparator circuit is in turn connected to a processing chip (which may form part of the silicon system 112) having at least one logic circuit and is adapted to process an output from the comparator circuit for sensing the motion. Output relating to the motion sensing can later be transmitted externally to an external device via a built-in communication module. In this case, the output voltage of the power rectifier can be used to supply power to the comparator circuit to eliminate any requirement for an external power source.

[0063] Referring back to Figure 1 , the over-voltage protection circuit 108 and the power rectifier 1 10 in the present embodiment are integrated with the silicon system 1 12 (or onto the processing chip to form a system-on-chip) as shown by the box 114. In the present embodiment, the system 100 can be formed on or integrated with a textile to form an E- textile.

[0064] Figure 2 shows a series 200 of schematics to illustrate electric signals generated by the transductor 102 of the system 100 of Figure 1 in response to motions in accordance with an embodiment. Periodic changes in potential difference between inner surfaces of the two sheets 202, 204 induced by cycled separation and re-contact generate an alternating current (AC) as illustrated by the series 200 of schematics.

[0065] As shown in relation to the schematic 210, when a pressure or a force 206 is applied to the transductor 102, the inner surfaces of the two sheets 202, 204 will come into close contact, leaving one surface of the sheet 202 with positive charges and an opposing surface of the other sheet 204 with negative charges. The potential difference generated by the opposite charges generates a current in a clockwise direction 222 across a load 224 in the present embodiment as shown in the schematic 220.

[0066] When the pressure or force is released 232, the two surfaces with opposite charges separate, generating an electric field and inducing a potential difference across the top and bottom electrodes. A current in an opposite direction 234 flowing through the load 224 is generated, as shown in the schematic 230. The current 234 generated in this process will continue until the potentials of the top and bottom electrodes are the same as shown in the schematic 240. The cycle as shown in relation to the schematics 210, 220, 230, 240 is repeated in response to a periodic mechanical deformation (e.g. in a periodic motion) and alternating current signals can be continuously generated.

[0067] Figure 3 shows a schematic 300 of four transductors 302, 304, 306, 308 being connected in parallel for use in the system 100 of Figure 1 in accordance with an embodiment. This is also applicable to the system of Figure 4 as described later.

[0068] As shown in Figure 3, each of the four transductors 302, 304, 306, 308 is patterned as a tile and each of these tiles 302, 304, 306, 308 includes a top triboelectric electrode 310, a bottom triboelectric electrode 312 and a polyimide film 314 sandwiched between the top triboelectric electrode 310 and the bottom triboelectric electrode 312. In the present embodiment, four tile-shaped transductors are connected in parallel using patterned electrodes 316 but it should be appreciated that any other number of transductors can be used. Further, the transductor tiles may also be connected either in series or in parallel, or a combination of both, to maximise an input current at a targeted harvesting voltage. Having a transductor in tile-shaped is useful as these transductor tiles can be stacked in layers for more efficient e-textile area usage. It should, however, be appreciated that the transductor can be formed in other shapes.

[0069] Figure 3 also shows the positive voltage terminal (VTENG+) 318 and the negative voltage terminal (VTENG-) 320. As the four transductors 302, 304, 306, 308 are connected in parallel, each of the top electrode 310 of the four transductors 302, 304, 306, 308 is connected to the positive voltage terminal (VTENG+) 318 and each of the bottom electrode 312 of the four transductors 302, 304, 306, 308 is connected to the negative voltage terminal (VTENG ) 320. In the present embodiment, the transductors 302, 304, 306, 308 used are then connected to an over-voltage protection circuit which keeps a supply voltage to the silicon system to lower than 3.2 V peak to peak, allowing its adoption with common low-cost CMOS technology having typically 3.3 V I / O connections. In the present embodiment, the four transductors 302, 304, 306, 308 are formed on a flexible substrate 322, such as a cloth or T-shirt.

[0070] Figure 4 shows a schematic of a system 400 having two different modes for motion sensing and energy harvesting in accordance with an embodiment. This system 400 uses the components of the system 100 as discussed in relation to Figure 1 . In the present system 400, a plurality of transductor tiles is used and these transductor tiles are split into two sets, one set for use with a walking harvesting module 402 and another set for use with a breathing harvesting module 404. As shown in the system 400 of Figure 4, transductors 406 for the walking harvesting module 402 are connected to an over-voltage protection circuit 408 which in turn is connected to a power rectifier 410. These components have been described in relation to Figure 1 and so their descriptions are not repeated here for succinctness. Similarly, transductors 412 for the breathing harvesting module 404 are connected to an over-voltage protection circuit 414 which in turn is connected to a power rectifier 416 as shown in Figure 4. In the present embodiment, the transductors 406 of the walking harvesting module 402 are configured to harvest energy from a walking motion of the user, while the transductors 412 of the breathing harvesting module 404 are configured to harvest energy from a breathing motion of the user. In the present embodiment, the over-voltage protection circuit 408 of the walking harvesting module 402 and the over-voltage protection circuit 414 of the breathing harvesting module 404 has a capped voltage output of ±0.6V and ±1.6V, respectively.

[0071] Differing from the breathing harvesting module 404, the walking harvesting module 402 also includes a comparator circuit 418. The comparator circuit 418 is connected to the transductor 406 at its positive voltage terminal (VTENG+) and its negative voltage terminal (VTENG-) (see e.g. dotted line 419), and is adapted to compare voltages between VTENG+ and VTENG- for use in step detection or step counting. The comparator circuit 418 comprises a bandpass filter 420 for filtering the voltages received from the positive voltage terminal (TENG+) and the negative voltage terminal (VTENG ), a comparator 422 configured to compare the filtered voltages Vout, filter and Vout, filter- received from the bandpass filter 420, and a level shifter 424 adapted to translate the output voltage Vcomparator to Vstepfor use in logic circuits of the processing chip or on-chip memory 426. The processing chip 426 has at least one logic circuit for use in processing the output Vstep from the comparator circuit 418 for sensing the walking motion and to generate a step count. In the present embodiment, the system 400 includes a communication module 428 configured to transmit data from the processing chip 426 to an external device. In the present embodiment, the communication module 428 includes a backscattered near field communication (NFC) transmission module. In the present embodiment, the transductors 406 are configured to harvest energy from the walking motion and to provide motion sensing in a dual-function. Particularly, as shown in Figure 4, harvested power provided by the transductors 406 is provided to the components 420, 422, 424 of the comparator circuit 418 via the over-voltage circuit 408 and the power rectifier 410 for powering the comparator circuit 418. At the same time, the comparator circuit 418 is connected to the transductors 406 via its positive voltage terminal (VTENG+) and its negative voltage terminal (VTENG-) for use in comparing voltages between VTENG+ and VTENG to provide an output to the processing chip 426 for step counting. In this way, the transductors 406 can use a same motion for both energy harvesting and motion sensing, thereby minimising the number of components required for performing these actions. Further, this dual-function of energy harvesting and motion sensing using the same transductors 406 allow for just-in-time power provision as the transductors 406 are able to generate more power in response to larger or wider range motions which in turn require a higher system power e.g. to sense higher levels of motion activities. By using the transductors 406 for both energy harvesting and motion sensing (e.g., walking), the number of in-textile components and hence costs can be minimised. This also improves conformability of the present system.

[0072] Referring to the breathing harvesting module 404, the transductors 412 are adapted to harvest energy or power from the breathing motion of the user. The harvested power from the transductors 412 is then provided to the processing chip 426 and the level shifter 424 of the comparator circuit 418 as shown by the path 432. In this embodiment, the breathing module 404 is configured to harvest power from the breathing motion, which is a sustainable motion (i.e. happens all the time), for providing sufficient power to the present pW system 400 even when no motion sensing by the walking harvesting module 402 is required. Energy harvesting using breathing motion (typically in the pWs) is enabled in the present embodiment, for example, by limiting system power to the pW range by circuit techniques keeping transistors in logic and analogue circuits (e.g. components of the processing chip 426) in the super-cutoff region (i.e., NMOS with VGg<0). In the present embodiment, the over-voltage protection circuit 414 and the power rectifier 416 are also designed to have ultra-low leakages. Details of the over-voltage protection circuit 414 and the power rectifier 416 are provided later in relation to Figure 9 and Figures 7A, 7B and 8, respectively. With the ultra-low leakage provision obtained, conventionally large off-chip inductor or capacitor to reduce resonance frequency for harvesting energy from breathing motion (i.e. having a frequency of less than 1 Hz) is not necessary. This makes harvesting energy from breathing feasible for an E-textile integrated system.

[0073] In the present embodiment, discrete off-chip components for the system are limited to a single bondable capacitor 434 of 1 pF provided at an output of the power rectifier 416. The capacitor 434 acts as an energy buffer in the breathing harvesting module 404 adapted to provide back-up energy to the processing chip in case of sparse energy harvesting, thereby allowing sustained operation and data retention for much longer than the respiratory period (e.g. 16 minutes). The bondable nature of the capacitor 434 allows stacking it with the processing chip 426 (e.g. a silicon die), making its impact on form factor and conformability negligible. It should be appreciated that the capacitor 434 is not strictly needed (i.e. it is optional), and it is added for robustness against noise and mechanical solicitations. In the present embodiment, an on-chip capacitor 436 is also provided between the output of the power rectifier 410 and ground. In an embodiment, the on-chip capacitor 436 has a capacitance of in the nF range, and optionally about 1 .7 nF. The on-chip capacitor 436 is adapted to store energy harvested by the transductors 406 from physical activities to provide energy storage during just-in-time harvesting for just-in-time power provision.

[0074] In the present embodiment, components having ultra-low leakages are also applied to the walking harvesting module 402. For example, the same or similar circuits can be used for the over-voltage protection circuit 408 and the power rectifier 410 as those for the breathing harvesting module 404, and the comparator circuit 418 can be designed with components having ultra-low leakages. This enables the system 400 of the present embodiment to reduce the system power to ~20 pW via super-cutoff transistor operation which can be entirely provided just-in-time by the transductors 406 as discussed above thanks to its sufficiently rapid start-up. Such very low and sustainable power usage of the system in both the breathing mode and at higher levels of motion activity thereby suppresses the need for a battery, while still retaining the counted steps and providing power to always-on circuitry to retain a previous state without explicit energy storage.

[0075] The present system 400 therefore provides a battery-less and inductor-less system with sustained operation under any practical motion situations. Practically, given that the user (e.g. a human) is required to breath all the time, the operation of this system 400 can be sustain at all time. This provides an always-on system that can be integrated in an E- textile for always-ready motion sensing. Further, the present system 400 simultaneously uses the same dual-function transductors for both harvesting and sensing, is inductorless and has near-zero minimum harvesting frequency, thereby eliminating large traditional resonant LC passives from the harvesting sub-system. In the present embodiment, a combination of (i) aggressive system power reductions (~pW for step data retention and basic always-on functions) which enable uninterrupted operation by harvesting from breathing, (ii) just-in-time event-driven power provision provided by the dual function of the transductors, and (iii) nearly zero-power provision for near-field communications (NFC) due to backscattered operation powered by the external device, allow for sustainable energy harvesting and operation of the system without battery under any practical motion condition.

[0076] Figure 5 shows a plot 500 of harvested power versus time to illustrate power harvested during a breathing mode of the system 400 of Figure 4 in accordance with an embodiment.

[0077] The plot 500 shows that nearly-constant power 502 Pm n can be harvested from breathing using the breathing harvesting module 404 of the system 400 to provide a minimum always-on system power (in pW) for sustained operation and data-retention of the system.

[0078] Figure 6 shows a plot 600 of harvested power versus time to illustrate power harvested during a walking / running mode of the system 400 of Figure 4 in accordance with an embodiment.

[0079] The plot 600 shows just-in-time power provision from two different higher levels of motion activity, namely running and walking. For these cases, a higher level of harvested power is provided by the walking harvesting module 402 in response to a higher levels of motion activity as shown by the power peaks 602, 604 to provide sufficient power to the system 400 for motion sensing (e.g. step counting).

[0080] Details of the components of the system 400 are provided in relation to Figures 7A to 12 below. These components provide ultra-low leakages which help to preserve power conversion efficiency and reliability under even very low harvested powers (e.g. during breathing mode). Figures 7A and 7B show schematics of parts of a full-bridge rectifier for use in the system 400 of Figure 4 in accordance with an embodiment. The full-bridge rectifier can be used for the power rectifier 410 and / or the power rectifier 416 of the system 400 as shown in relation to Figure 4.

[0081] Figure 7A shows a schematic of a first set of transistors 700 for use in the full-bridge rectifier. The first set of transistors 700 is adapted to function as one PMOS diode in the full-bridge rectifier. The first set of transistors 700 comprises a p-channel metal-oxide- semiconductor (PMOS) transistor 702 and two sub-threshold MOSFET sets 708, 710. As shown in Figure 7A, a drain 704 of the PMOS transistor 702 is connected, e.g. via the over-voltage protection circuit 408, to the positive terminal VTENG+ of a transductor, and a source 706 of the PMOS transistor 702 is at a potential VDc of the output of the full-bridge rectifier. Also shown in Figure 7A are the two sub-threshold MOSFET sets 708, 710. The first sub-threshold MOSFET set 708 comprises a first transistor 712 and a second transistor 714. The first transistor 712 has a drain connected to the drain 704 of the PMOS transistor 702 and the positive voltage terminal VTENG+, and a source connected to a drain of the second transistor 714. The second transistor 714 has a source connected to ground 716. A second sub-threshold MOSFET set 710 comprises a third transistor 718 and a fourth transistor 720. The third transistor 718 has a drain connected to the source 706 of the PMOS transistor 702 and the output of the full-bridge rectifier, and a source connected to a drain of the fourth transistor 720. The fourth transistor 720 has a source connected to ground 722. Also shown in Figure 7A is that a gate of the PMOS transistor 702, a gate of the first transistor 712, and a gate of the third transistor 718 are connected to VGi724 at a potential of the source of the third transistor 718, and a gate of the second transistor 714 and a gate of the fourth transistor 720 are connected to ground 726.

[0082] Figure 7B shows a schematic of a second set of transistors 730 for use in the full-bridge rectifier. The second set of transistors 730 is adapted to function as one NMOS diode in the full-bridge rectifier. The second set of transistors 730 comprises a n-channel metal- oxide-semiconductor (NMOS) transistor 732 and two sub-threshold MOSFET sets 738, 740. As shown in Figure 7B, a drain 734 of the NMOS transistor 732 is connected, e.g. via the over-voltage protection circuit 408, to the negative terminal VTENG- of a transductor, and a source 736 of the NMOS transistor 732 is at a potential 1 ® (e.g. at ground). Also shown in Figure 7B are the two sub-threshold MOSFET sets 738, 740 (or third and fourth sub-threshold MOSFET sets for the full-bridge rectifier). The third sub-threshold MOSFET set 738 comprises a fifth transistor 742 and a sixth transistor 744. The fifth transistor 742 has a source connected to the potential l / ssand the source 736 of the NMOS transistor 732, and a drain connected to a source of the sixth transistor 744. The sixth transistor 744 has a drain connected to the output of the full-bridge rectifier at VDc 750. The fourth sub-threshold MOSFET set comprises a seventh transistor 746 and an eighth transistor 748. The seventh transistor 746 has a source connected to the drain 734 of the NMOS transistor 732, and a drain connected to a source of the eighth transistor 748. The eighth transistor 748 has a drain connected to the output of the fullbridge rectifier at VDc 750. The drain of the sixth transistor 744 and the drain of the eighth transistor 748 are therefore connected and at the same potential VDc 750. Also shown in Figure 7B is that a gate of the NMOS transistor 732, a gate of the fifth transistor 742 and a gate of the seventh transistor 746 are connected to I / GZ 752 at a drain of the fifth transistor 742, and a gate of the sixth transistor 744 and a gate of the eighth transistor 748 are connected to the output voltage of the full-bridge rectifier at VDc 750.

[0083] Figure 8 shows a schematic of the full-bridge rectifier 800 for use in the system 400 of Figure 4 comprising a first half 801 and a second half 820 of the full-bridge rectifier. Each of the first half 801 and the second half 820 of the full-bridge rectifier includes the first set of transistors 700 and the second set of transistors 730 as shown in Figure 8. For the first half 801 , the second set of transistors 730 as shown in relation to Figure 7B has been rotated 180 degrees so that the third sub-threshold MOSFET set 738 is next to the first set of transistors 700. For the second half 820, the drain of the NMOS transistor 732 of the second set of transistors 730 is connected to the positive terminal VTENG+, and the first set of transistors 700 as shown in relation to Figure 7A has been rotated 180 degrees with the drain 704 of the PMOS transistor 702 being connected to the negative terminal VTENG in this second half 820. For each of the first and second halves 801 , 820, the first set of transistors 700 and the second set of transistors 730 are connected via a capacitor 802 to form each half of the full-bridge rectifier 800. The first half 801 and the second half 802 are then connected together, e.g. the positive terminal VTENG+ and the negative terminal VTENG- as shown for each half 801 , 820 are connected together, to form the fullbridge rectifier 800. Inputs 822, 824 to the full-bridge rectifier 800 are also shown in Figure 8. The presence of the four sub-threshold MOSFET sets 708, 710, 738, 740 of each half 801 , 820 helps the full-bridge rectifier 800 keeps an OFF current to well below regular transistor leakage, which would otherwise be comparable with the very low current provided by the transductors in the breathing mode of the system 400. The sub-threshold MOSFET sets 708, 710, 738, 740 of each half 801 , 820 also aid to avoid having floating transductors.

[0084] During a positive transductor voltage half-wave 822 (i.e. when VTENG+ increases due to pressure on the transductor), current passes through the first half 801 of the full-bridge rectifier 800 while no current passes through the second half 820 of the full-bridge rectifier 800. In relation to the first half 801 of the full-bridge rectifier, the PMOS transistor (Mi) 702 turns on and conducts a current that raises the VDc voltage. This in turn increases the drain potential (VSGS) of the third transistor (M5) 718 and hence the current through the third transistor 718. As a consequence, VGi724 increases and turns off the PMOS transistor (Mi) 702 at the peak of the positive transductor voltage. After the peak, the PMOS transistor (Mi) 702 remains OFF and VGi724 remains at the same voltage (stored by a node capacitance of a capacitor 802 connected between the PMOS transistor 702 and the NMOS transistor 732), making a potential difference between the source and the gate of the PMOS transistor 702 to be less than zero (VgGi< 0) and hence turning off the PMOS transistor (Mi ) 702 strongly, making its current even lower than its regular leakage (i.e., the capacitor 802 is not drained by the full-bridge rectifier 800). The current path 804 and the leakage current paths 806, 808, 810, 812 for the positive transductor voltage half-wave are also shown in Figure 8. In the negative half-wave 824 when the pressure on the transductor is released, the potential difference of VTENG+ - VTENG- is less than zero (i.e. VTENG+ - VTENG- < 0), and the opposite behaviour takes place. Current passes through the second half 820 of the full-bridge rectifier 800 while no current passes through the first half 801 of the full-bridge rectifier 800. The current flow 826 across the second half 820 of the full-bridge rectifier 800 for the negative half-wave 824 is shown in relation to Figure 8. Leakage current flows are similarly shown in relation to the second half 820. It is noted that the transistors used in the first half 801 are complementary to that of the second half 820 of the full-bridge rectifier 800.

[0085] Figure 9 shows a schematic of an over-voltage protection circuit 900 for use in the system 400 of Figure 4 in accordance with an embodiment. The over-voltage protection circuit 900 is adapted to safeguard the always-on domain keeping the supply voltage to the processing chip to less than or equal to 3.2 V peak-to- peak (i.e. <3.2 Vpp). Consideration taken for the over-voltage protection circuit 900 is that the clipped voltages need to be symmetric with respect to the positive and negative halfwaves (see e.g. Figure 8) to: (i) assure a same level of reliability for both the positive and negative half-waves and (ii) allow correct subsequent full-wave rectification without unintentionally limiting one side (i.e. one of the positive or negative half-waves). In principle, three stacked p-n junctions would suffice for use in an over-voltage protection circuit by clamping an input voltage of the subsequent power rectifier to 3VDOn = 1 .5 to 1 .6 V, where VDonis a voltage of ON junction under pA-level currents). However, on-chip p-n junction diodes cannot be arbitrarily stacked since one terminal is either connected to a P-type substrate (e.g., for a n+ / P-sub diode) or has parasitic junctions that unintentionally turn on before the harvested transductor voltage reaches the limit, thereby prematurely clamping the input voltage.

[0086] To clamp the input voltage at 3VDon for both half-waves, the over-voltage protection circuit 900 in the present embodiment comprises laterally stacked PNP and NPN bi-polar junction transistors (BJTs).

[0087] The over-voltage protection circuit 900 as shown in Figure 9 is used for the breathing harvesting module 404 in the present embodiment. The over-voltage protection circuit 900 comprises four PNP bipolar junction transistors (BJTs) 902, 904, 906, 908 and two NPN bipolar junction transistors (BJTs) 910, 912, where three of the four PNP BJTs 902, 904, 906 are stacked laterally and formed a first set 914 of BJTs, and where the two NPN BJTs 910, 912 and the remaining one 908 of the four PNP BJTs formed a second set 916 of BJTs.

[0088] Referring to the first set 914 of the BJTs, a collector, C, of the PNP BJT 902 is connected to ground 903 and an emitter, E, of the PNP BJT 902 is connected to a base, B, of the PNP BJT 904 so that they are laterally stacked. This is similarly applied to the PNP BJT 906 where an emitter, E, of the PNP BJT 904 is connected to a base, B, of the PNP BJT 906. Therefore, as shown in Figure 9, the PNP BJTs 902, 904, 906 are laterally stacked. The emitter, E, of the PNP BJT 906 is connected to the positive voltage terminal VTENG+of the transductor. The collectors of the PNP BJTs 902, 904, 906 are all connected to ground 903. Referring to the second set 916 of the BJTs, an emitter, E, of the NPN BJT 910 is connected to the positive voltage terminal VTENG+O^ the transductor and a collector, C, of the NPN BJT 910 is connected to ground 911. A base, B, of the NPN BJT 910 is connected to the emitter, E, of the NPN BJT 912, and a base, B, of the NPN BJT 912 is connected to a base, B, of the PNP 908 so that these BJTs 910, 912, 908 are stacked laterally on the other side of the positive voltage terminal VTENG+ to form the second set 916 of the BJTs symmetrically to the first set 914 of the BJTs. An emitter, E, of the PNP BJT 908 of this second set 916 is connected to the negative voltage terminal VTENG of the transductor. The collectors of the BJTs 910, 912, 908 of the second set 916 are all connected to ground 91 1. It is noted that these BJTs can be formed on a P-substrate, where an additional diode is shown in the circuit diagram of Figure 9 for each of the NPN BJTs 910, 912. The VTENG+ positive current path 918 and the VTENG- negative current path 920 are also shown in Figure 9. Parasitic junctions of this over-voltage are always OFF as they are either connected back-to-back, or are individually reverse-biased. The overvoltage protection circuit 900 therefore has an ultra-low leakage.

[0089] For the walking harvesting module 402, the clamp to the input voltage is at 2VDOn and hence two stacked junctions are required. (VDOn is the on-voltage of an on-chip p-n junction). This means that for this walking harvesting module 402, a first set of BJTs includes two PNP BJTs and a second set of BJTs includes one NPN BJT and one PNP BJT. Referring to Figure 9, for the over-voltage protection circuit of the walking harvesting module 402, the middle BJT for each set (i.e. 904 and 912) can therefore be removed so that the emitter of the PNP BJT 902 is connected to the base of the PNP BJT 906 and the base of the NPN BJT 910 is connected to the base of the PNP BJT 908.

[0090] To generalise the number of BJTs required for the proposed over-voltage protection circuit for the present disclosure, it can therefore be said that an over-voltage protection circuit of the present disclosure comprises N number of PNP bipolar junction transistors (BJTs) and N-2 number of NPN bipolar junction transistors (BJTs), where N-1 of the N number of PNP BJTs are stacked laterally to form a first set of BJTs and the N-2 number of NPN BJTs and a remaining one of the N number of PNP BJTs are stacked laterally to form a second set of BJTs. N is equal to or more than 3 for the present disclosure. A base of a last of the N-2 number of NPN BJTs connected to a base of the remaining one of the N number of PNP BJTs at an end portion of the second set of BJTs, a collector of a first of the N-1 of the N number of PNP BJTs of the first set of BJTs is connected to ground, and an emitter of a last of the N-1 of the N number of PNP BJTs of the first set of BJTs is connected to an emitter of a first of the N-2 number of NPN BJTs of the second set of BJTs at the positive voltage terminal of the transductor. An emitter of the remaining one of the N number of PNP BJTs of the second set of BJTs is connected to the negative voltage terminal of the transductor.

[0091] Figure 10 shows a schematic of a communication module 1000 for use in the system 400 of Figure 4 in accordance with an embodiment.

[0092] The communication module 1000 includes a backscattered near field communication (NFC) transmission module as shown in relation to Figure 10. NFC communications can be triggered by an external device 1002 or reader (e.g. a smartphone) via the raised voltage detected across an in-textile coil or inductor 1004. In this case, the external device 1002 provides both command / data and wireless power. The rest of the communication module 1000, which includes a transistor MbaCkscatter for use in a conventional backscattering process in modulating a load, can be formed on-chip 1006 to minimise use of off-chip components. An on-chip logic circuit 1008 which is used to provide step count information is also shown in relation to Figure 10. The wireless power provided by the external device 1002 is sufficient to support the whole wireless interface in the present embodiment and thus does not count into the system power budget provided through the power harvested from the transductors.

[0093] Figures 1 1 and 12 show examples of logic and analogue circuits which can be used or designed in a super-cutoff scheme for pW operation.

[0094] Figure 11 shows a schematic of a logic circuit 1 100 with super cut-off for use in the system 400 of Figure 4 in accordance with an embodiment. The logic circuit 1100 utilises Dynamic Leakage Suppression (DLS) logic style to minimise leakage. Details for this can be found in “W. Lim st. al., ”8.2 Batteryless Sub-nW Cortex-M0+ processor with dynamic leakage-suppression logic," 2015 IEEE Internationa! Solid-State Circuits Conference (ISSCC) Digest of Technical Papers, USA, 2015, pp. 1 -3, doi: 10.1 109 / ISSCC.2015.7062968” and the content of which is incorporated herein in its entirety. It should be appreciated other forms of a super cut-off logic circuit or suitable variations of this can be used as long as leakage is minimised. Figure 12 shows a schematic of an analogue circuit 1200 with super cut-off for use in the system 400 of Figure 4 in accordance with an embodiment. The analogue circuit 1200 includes transistors in super-cutoff for < pA bias currents. Details for this can be found in “Systems and methods for low power circuits”, PCT patent application no. PCT / SG2024 / 050381 and the content of which is incorporated herein in its entirety. It should be appreciated other forms of a super cut-off analogue circuit or suitable variations of this can be used as long as leakage is minimised.

[0095] The harvested voltage and power of transductor(s) are shown in relation to Figures 13 to 16 below in terms of transient responses during a hand touch motion, a walking motion and a breathing motion.

[0096] Figure 13 shows a plot 1300 of harvested voltage versus time with a 100 MG load in response to a hand touch motion in accordance with an embodiment. Harvested voltage using a single transductor (or a single transductor tile) is shown by a data line 1302 and harvested voltage using four transductors connected in parallel (or 4 parallelly connected transductor tiles) is shown by a data line 1304.

[0097] Figure 14 shows a plot 1400 of harvested voltage versus time with a 100 MG load in response to a walking motion in accordance with an embodiment. Harvested voltage using a single transductor (or a single transductor tile) is shown by a data line 1402 and harvested voltage using two transductors connected in parallel (or 2 parallelly connected transductor tiles) is shown by a data line 1404. It is shown that harvested power from two transductor tiles is sufficient to provide system power during a walking motion.

[0098] Figure 15 shows a plot 1500 of harvested voltage versus time with a 100 MG load in response to a breathing motion in accordance with an embodiment. Harvested voltage using four transductors connected in parallel (or 4 parallelly connected transductor tiles) is shown by a data line 1502. The plot 1500 shows that harvested energy / power from four transductor tiles connected in parallel is sufficient to provide system power during a breathing motion.

[0099] From the plots 1300, 1400, 1500, it is shown that breathing motion expectedly generates the lowest voltage of about 1 -1.2 V peak-to-peak among the three motion activities in view of the lower mechanical energy harvested during breathing. The maximum opencircuitvoltage generated relates to walking, which is about 3.2 V peak to peak as targeted This is thus compliant with a typical voltage rating of low-cost silicon chips having 3.3V of I / O voltage.

[0100] Figure 16 shows a bar graph 1600 of total system power and power rectifier leakage power in breathing mode for six different die samples tested under various PVT corners in accordance with an embodiment. “TT” refers to a typical-typical corner, “SS” refers to a Slow-Slow corner and “SF” refers to a Slow-Fast corner. The value of the total system power 1602 is 3.42 pW, 3.33 pW, 3.45 pW, 3.41 pW, 4,27 pW, 4.44 pW for die samples 1 , 2, 3, 4, 5 and 6, respectively. An expected power of conventional diodes (if used as a power rectifier) is shown by the dotted line 1604. Therefore, if conventional diodes are used in the power rectifier for the system, they would dominate the system power and thus is not feasible. Leakage power 1606 of the power rectifier 800 of the present disclosure as shown in Figure 8 is also shown for each of the die samplesl , 2, 3, 4, 5 and 6. The power rectifier 800 of the present disclosure significantly reduces leakages over power rectifier based on conventional diodes, and becomes a minor percentage of the system power as shown.

[0101] Table 1 below summarises means and standard deviations of the total system power in the breathing mode and the leakage power of the power rectifier as shown in Figure 16.

[0102] Table 1 : Total system power and leakage power of rectifier

[0103] From the plot 1600 of Figure 16, it can be shown that the always-on system power in the breathing mode is consistently in the pW range, which has a mean of 3.72 pW across the different die samples. The always-on system power reaches 4.7 pW when margined at 2 standard deviations.

[0104] Performances of the power rectifier and the over-voltage protection of the present disclosure are further investigated and described in relation to Figures 17 to 20 below.

[0105] Figure 17 shows a plot 1700 of power rectifier power efficiency versus load current obtained using the full-bridge rectifier of Figure 8 in accordance with an embodiment. The data lines 1702, 1704, 1706 correspond to peak-to-peak alternating current (AC) voltages of 1 .5 V, 1 V and 0.6 V, respectively. The measurements were performed at a temperature of 25 °C. From the plot 1700, a power efficiency 1708 of 63.7% is obtained during walking (at a load current of about 20 pA), while a maximum power efficiency 1710 of 80.2% is obtained at a load current of about 160 pA. The results as shown in the plot 1700 confirm the power rectifier's capability to operate effectively even with a minimal supply voltage (VDD) (e.g. with a AC_PEAK of 0.6 V) and with a good power efficiency. Furthermore, the ability for the power rectifier to operate under these supply voltages also confirm that it is able to be used in the breathing harvesting mode of the system 400 as shown in relation to Figure 4.

[0106] Figure 18 shows a plot 1800 of power rectifier power efficiency versus input power obtained using the full-bridge rectifier of Figure 8 in accordance with an embodiment. The data lines 1802, 1804, 1806 correspond to peak-to-peak alternating current (AC) voltages of 1 .5 V, 1 V and 0.6 V, respectively. The measurements were performed at a temperature of 25 °C. From the plot 1800, a power efficiency 1808 of 63.6% is obtained when loaded with the full system during walking (at a current load of about 20 pA, input power of about 12 pW), while a maximum power efficiency 1810 of 80.1% is obtained.

[0107] Figure 19 shows a plot 1900 of power rectifier voltage efficiency versus load current obtained using the full-bridge rectifier of Figure 8 in accordance with an embodiment. The data lines 1902, 1904, 1906 correspond to peak-to-peak alternating current (AC) voltages of 1 .5 V, 1 V and 0.6 V, respectively. The measurements were performed at a temperature of 25 °C. From the plot 1900, a maximum voltage 1908 of 0.51 V is obtained when an input voltage to the power rectifier is 0.6V, and a maximum voltage efficiency 1910 of 99.6% is obtained when the input voltage to the power rectifier is 1 .5 V.

[0108] Figure 20 shows a plot 2000 of voltage versus time of the over-voltage protection circuit obtained using the over-protection circuit of Figure 9 in accordance with an embodiment. The data line 2002 relates to voltage obtained with no over-voltage protection, which shows that the peak to peak voltage exceeded the typical 3.3 V of common low-cost CMOS technology. Measured voltage with over-voltage protection for the breathing harvesting module 404 is also shown. With over-voltage protection, peak voltages 2004, 2006 obtained by the breathing harvesting module 404 is clipped at ±1 .6 V. This is about 3.2 V peak to peak as shown by the double-arrow 2008. Figure 21 shows a plot 2100 of gain (dB) versus frequency for the analogue bandpass filter 420 used in the comparator circuit 418 of the system of Figure 4 in accordance with an embodiment. The plot 2100 provides a measured response of the bandpass filter 420 for walking step event detection and shows a minimum, analogue filter-limited, harvesting frequency 2102, fmin of < 0.1 Hz. Typical walking cadence 2104 is also provided in the plot 2100 which shows that walking motions lie well within the bandwidth of the bandpass filter 420 used in the comparator circuit 418 and that the bandpass filter 420 covers most if not all practical stride frequencies. It is noted that the low fminof the proposed architecture is not constrained by resonant inductor-capacitor (LC) passives, thereby eliminating the need for large-valued components to bring fmin close to the walking cadence.

[0109] Figure 22 shows a timing diagram 2200 to illustrate a walking step event and responses obtained by various components of the system 400 of Figure 4 in accordance with an embodiment. The y-axis (or vertical axis) relates to voltage while the x-axis (or horizontal axis) denotes a timing sequence of the walking step event.

[0110] The harvested voltages output by the transductors 406 are illustrated by the graph 2202. Output voltage Vrectifier as outputted by the power rectifier 410 is illustrated by the graph 2204. The filtered voltage Vfiiter obtained as an output of the bandpass filter 420 is shown by the graph 2206. The graph 2208 shows an output voltage of the comparator circuit 418 and data is subsequently written to the DLS memory as triggered by a negative edge of the comparator circuit’s output voltage as shown by the graph 2210.

[0111] Measured voltages obtained from the various components during the walking step event are shown in relation to Figures 23 to 26.

[0112] Figure 23 shows a plot 2300 of voltage versus time to illustrate a transient response of the transductors 406 of the system 400 of Figure 4 in a walking mode in accordance with an embodiment. Each set 2302 of a voltage peak and a voltage trough corresponds to a step in a walking motion.

[0113] Figure 24 shows a plot 2400 of voltage versus time to illustrate a transient response of the power rectifier 410 of the system 400 of Figure 4 in a walking mode in accordance with an embodiment. The plot 2400 shows an immediate ramp-up in the rectified voltage waveform with sustained voltage when walking. After a first step in the walking motion, the voltage supply becomes and remains stable for immediate power delivery to the comparator circuit 418. This illustrates the “just-in-time” power provisioning as afore- described. The on-chip capacitor 436 is rapidly charged to VDDfor sustained power delivery to the comparator circuit 418.

[0114] Figure 25 shows a plot 2500 of voltage versus time to illustrate a transient response of the comparator 422 of the system 400 of Figure 4 in a walking mode event in accordance with an embodiment. The harvested voltages obtained from the transductors 406 are filtered and compared at the comparator 422 to generate the transient voltage response of the plot 2500. The plot 2500 shows that the first two steps at 2502 are not captured or are missed in this case.

[0115] Figure 26 shows a plot 2600 of voltage versus time to illustrate a transient response of step count information (or number of steps counted) read from DLS on-chip memory using the system 400 of Figure 4 in a walking mode in accordance with an embodiment. The plot 2600 is used for step counting. The steps in the present embodiment are encoded using three-bits as shown in the plot 2600 with a 16-bit data. The bits for B0, B1 , B2 are shown as 2602, 2604, 2606, respectively. The plateau 2608 corresponds to the non-response 2502 of the comparator 422.

[0116] As shown by Figures 23 to 26, just-in-time harvester power provisioning is enabled by the short start-up time of the walking event-activated domain, which was experimentally found to miss at most the first two steps and most commonly one step. This relates to a very minor fraction of steps / day in realistic walking patterns, and can be recoverable by over-incrementing the step count at start-up time. The conversion time of 353 ms also allows the system 400 to capture any feasible walking cadence.

[0117] Measured system power breakdowns for the breathing mode and the walking mode are shown in relation to Figures 27 and 28, respectively.

[0118] Figure 27 shows a pie chart 2700 of measured system power breakdown for a breathing mode of the system 400 of Figure 4 in accordance with an embodiment. The main components taking up system power during the breathing mode includes (i) the off-chip 1 pF capacitor 434 which takes up 41% 2702 of the total system power, (ii) the power rectifier 416 which takes up 25% 2704 of the total system power, (iii) the level shifter 424 which takes up 17% 2706 of the total system power, and (iv) the DLS logic (i.e. the processing chip 426) which takes up 17% 2708 of the total system power. The total system power for this pie chart 2700 is 3.4 pW.

[0119] Figure 28 shows a pie chart 2800 of measured system power breakdown for a walking mode of the system 400 of Figure 4 in accordance with an embodiment. The main components taking up system power during the breathing mode includes (i) the bandpass filter 420 which takes up 55% 2802 of the total system power, (ii) the comparator 422 which takes up 27% 2804 of the total system power, (iii) the bias circuit (in-built in the bandpass filter 420 and the comparator 422 of the comparator circuit 418) which takes up 9% 2806 of the total system power, and (iv) the power rectifier 410 which takes up 9% 2808 of the total system power. The total system power for this pie chart 2800 is 23 pW.

[0120] Table 2 below highlights some of the features of the system of the present disclosure together with their associated benefits or advantages.

[0121] Table 2: Selected features of the system and their benefits / advantages

[0122] The system of the present disclosure provides an in-textile motion and walking step counting system on a chip that seamlessly integrates the full signal chain from sensing to wireless communications. The in-textile system, exemplified by a smart T-shirt, acts as an unconventional substrate for pervasive and unobtrusive electronics. The present system operates efficiently by utilizing a motion harvesting sensor (or a transductor) printed on textile (e.g., a triboelectric nanogenerator, a piezoelectric nanogenerator).

[0123] The transductors of the present disclosure as incorporated in the present system is configured to function as both a motion energy harvester and a motion sensor. The system of the present embodiment enables battery-less and inductor-less system integration for in-textile system with improved conformability and form factor, at lower costs, and is adapted to have a near-zero minimum harvesting frequency for extracting power from the environment which enables energy harvesting for very slow motion (e.g. breathing). The present system enables on-chip integration of an ultra-low leakage power rectifier and an over-voltage protection circuit to minimise off-chip components for improved conformability and lower costs.

[0124] To enable always-on operation without a battery or equivalent energy storage, the always-on domain / portion of the system on chip employs a dynamic leakage suppression (DLS) logic style for always-on power reduction down to 3.4 pW so that the always-on portion of the system can be sustained by energy harvested from breathing. The leakage suppression utilised in components of the system also enable a peak total system power requirement of 23 pW during walking motion sensing. In addition, the system for motion sensing and energy harvesting of the present disclosure exhibits a total system power requirement of 1.4 pW for data retention. The system power reduction of the present system represents at least a 230-times improvement over prior partial system demonstrations reporting their consumption, and even a greater improvement over non- backscattered wired or wireless communications. The minimum harvesting frequency is also lowest known by far, and is one to two orders of magnitude lower than known systems. The system of the present disclosure also exhibits one of the highest levels of integration with only a mm-sized bondable capacitor and having improved conformability and at low costs.

[0125] Further, in the system of the present disclosure, the dual-function transductor is adapted to provide higher harvested power when higher levels of motion activity take place (e.g., walking instead of breathing), meeting the higher power consumption needs of the system during monitoring and sensing of higher-frequency motion. This provides the “just-in-time” power provision at higher levels of power consumption without the need for energy storage.

[0126] The system of the present disclosure can be used, for example, in an end-to-end intextile walking step counter for e-textile based applications such as health wearables, human wellness monitoring, and virtual tailoring that can work without battery. In an embodiment, at least the transductors, the over-voltage protection circuit and the power rectifier are fully-integrated to form an on-chip system.

[0127] Although the exemplary embodiment described primarily breathing mode and walking mode, it should be appreciated that the system is also applicable to other types of motions. A user of the system may be a human, an animal or other living being for which an E-textile comprising the system can be applied. It should also be appreciated that although step counting has been used in the exemplary embodiment as an example for motion sensing, the system may be modified to include other appropriate circuits for other forms of motion sensing, e.g. a number of moves / jumps etc.

[0128] The breathing harvesting module and the walking harvesting module of the system may be adapted to function independently. Therefore, it can be envisaged that in an embodiment, the system comprises only the walking harvesting module or the breathing harvesting module. For example, the walking harvesting module as described can be part of a system which has an alternative stand-by power source that provides power to the components of the system that are required to be always-on (e.g. for data retention etc.). In an embodiment, the breathing harvest module as described can form part of a system to provide stand-by power to the system (and not necessarily together with the walking harvesting module as described in the exemplary embodiment). It should also be appreciated that the ultra-low leakage power rectifier and / or the over-voltage protection circuit may be used independently in a system for motion sensing and / or energy harvesting which requires ultra-low leakages.

[0129] Alternative embodiments may include: (i) an electronic textile comprising a textile and the afore-described system for energy harvesting and motion sensing; (ii) the afore- described system being integrated with a textile; and (iii) the system being able to harvest energy and detect motion for a motion / activity with a frequency of less than 1 Hz.

[0130] Although only certain embodiments of the present invention have been described in detail, many variations are possible in accordance with the appended claims. For example, features described in relation to one embodiment may be incorporated into one or more other embodiments and vice versa.

Claims

Claims1 . A system for motion sensing and energy harvesting, the system comprising: a transductor adapted to convert a motion to an electric signal for motion sensing and energy harvesting, the transductor having a positive voltage terminal and a negative voltage terminal; an over-voltage protection circuit connected to the transductor, the over-voltage protection circuit being adapted to receive the electric signal in the form of a harvested voltage and to provide a supply voltage of less than or equal to 3.2 V peak-to-peak; a power rectifier connected to the over-voltage protection circuit for rectifying the supply voltage to generate an output voltage; a comparator circuit connected to the transductor for comparing voltages between the positive voltage terminal and the negative voltage terminal; and a processing chip connected to the comparator circuit, the processing chip having at least one logic circuit for use in processing an output from the comparator circuit for sensing the motion, wherein the output voltage of the power rectifier is used to supply power to at least the comparator circuit, and wherein the over-voltage protection circuit and the power rectifier are integrated onto the processing chip.

2. The system of claim 1 , wherein the over-voltage protection circuit comprises N number of PNP bipolar junction transistors (BJTs) and N-2 number of NPN bipolar junction transistors (BJTs), wherein N-1 of the N number of PNP BJTs are stacked laterally to form a first set of BJTs, wherein the N-2 number of NPN BJTs and a remaining one of the N number of PNP BJTs are stacked laterally to form a second set of BJTs having at least a base of a last of the N-2 number of NPN BJTs being connected to a base of the remaining one of the N number of PNP BJTs at an end portion of the second set of BJTs, wherein a collector of a first of the N-1 of the N number of PNP BJTs of the first set of BJTs is connected to ground and an emitter of a last of the N-1 of the N number of PNP BJTs of the first set of BJTs is connected to an emitter of a first of the N-2 number of NPN BJTs of the second set of BJTs at the positive voltage terminal of the transductor, and wherein an emitter of the remaining one of the N number of PNP BJTs of the second set of BJTs is connected to the negative voltage terminal of the transductor.

3. The system of claim 2, wherein the motion includes walking and the over-voltage protection circuit comprises three PNP bipolar junction transistors (BJTs) and one NPN bipolar junction transistor (BJT).

4. The system of any one of claims 1 to 3, wherein the power rectifier comprises a fullbridge rectifier comprising two of a first set of transistors and two of a second set of transistors, the first set of transistors being adapted to function as a p-channel metal- oxide-semiconductor (PMOS) diode and the second set of transistors being adapted to function as a n-channel metal-oxide-semiconductor (NMOS) diode, wherein the first set of transistors and the second set of transistors are connected to form each half of the full-bridge rectifier.

5. The system of claim 4, wherein the first set of transistors comprises a PMOS transistor and first and second sub-threshold Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) sets, and the second set of transistors comprises a NMOS transistor and third and fourth sub-threshold MOSFET sets, wherein each of the first, second, third and fourth sub-threshold MOSFET sets comprises two transistors connected in series, wherein the first sub-threshold MOSFET set comprises a first transistor and a second transistor, the first transistor having a drain connected to a drain of the PMOS transistor and a source connected to a second drain of the second transistor, the second transistor having a source connected to ground, wherein the second sub-threshold MOSFET set comprises a third transistor and a fourth transistor, the third transistor having a drain connected to a source of the PMOS transistor and the output voltage of the power rectifier and a source connected to a drain of the fourth transistor, and the fourth transistor having a source connected to ground, wherein the third sub-threshold MOSFET set comprises a fifth transistor and a sixth transistor, the fifth transistor having a source connected to ground and a source of the NMOS transistor and a drain connected to a source of the sixth transistor, and the sixth transistor having a drain connected to the output voltage of the power rectifier, and wherein the fourth sub-threshold MOSFET set comprises a seventh transistor and an eighth transistor, the seventh transistor having a source connected to a drain of the NMOS transistor and a drain connected to a source of the eighth transistor, and the eighth transistor having a drain connected to the output voltage of the power rectifier.

6. The system of claim 5, wherein a gate of the PMOS transistor, a gate of the first transistor, and a gate of the third transistor are connected to the source of the third transistor, wherein a gate of the second transistor and a gate of the fourth transistor are connected to ground, wherein a gate of the NMOS transistor, a gate of the fifth transistor and a gate of the seventh transistor are connected to a drain of the fifth transistor, and wherein a gate of the sixth transistor and a gate of the eighth transistor are connected to the output voltage of the power rectifier.

7. The system of claim 5 or claim 6, wherein the full-bridge rectifier further comprises a capacitor connected between the PMOS transistor and the NMOS transistor for each half of the full-bridge rectifier.

8. The system of any one of claims 1 to 7, further comprising: a further transductor adapted to convert a further motion to a further electric signal for energy harvesting, the further transductor having a further positive voltage terminal and a further negative voltage terminal; a further over-voltage protection circuit connected to the further transductor, the further over-voltage protection circuit being adapted to receive the further electric signal in the form of a further harvested voltage and to provide a further supply voltage of less than or equal to 3.2 V peak-to-peak; and a further power rectifier connected to the further over-voltage protection circuit for rectifying the further supply voltage to generate a further output voltage, the further power rectifier adapted to keep an off-state leakage of the system to below 1 .5 pW, wherein the further output voltage is used to supply power to the processing chip, and wherein the further over-voltage protection circuit and the further power rectifier are integrated onto the processing chip.

9. The system of claim 8, wherein the further power rectifier has a same circuit architecture as the power rectifier.

10. The system of claim 8 or claim 9, wherein the further over-voltage protection circuit comprises four PNP bipolar junction transistors (BJTs) and two NPN bipolar junction transistors (BJTs), wherein three of the four PNP BJTs are stacked laterally and formed a further first set of BJTs, wherein the two NPN BJTs and a remaining one of the fourPNP BJTs formed a further second set of BJTs having at least a base of a last of the two NPN BJTs being connected to a base of the remaining one of the four PNP BJTs at an end portion of the further second set of BJTs, wherein a collector of a first of the four PNP BJTs of the first set of BJTs is connected to ground and an emitter of a last of the four PNP BJTs of the further first set of BJTs is connected to an emitter of a first of the two NPN BJTs of the further second set of BJTs at the further positive voltage terminal of the further transductor, and wherein an emitter of the remaining one of the four PNP BJTs of the further second set of BJTs is connected to the further negative voltage terminal of the further transductor.1 1. The system of any one of claims 8 to 10, further comprising a capacitor connected to the further power rectifier and the processing chip, the capacitor adapted to provide back-up energy to the processing chip in case of sparse energy harvesting.

12. The system of any one of claims 8 to 11 , wherein the further motion has a frequency of less than 1 Hz.

13. The system of claim 12, wherein the further motion includes breathing.

14. The system of any one of the preceding claims, wherein the further transductor includes a plurality of transductors connected in parallel.

15. The system of any one of the preceding claims, further comprising a communication module configured to transmit data from the processing chip to an external device.

16. The system of claim 15, wherein the communication module includes a backscattered near field communication (NFC) transmission module.

17. The system of any one of the preceding claims, wherein the system is formed on a textile substrate.

18. The system of any one of the preceding claims, wherein the transductor includes a triboelectric nanogenerator or a piezoelectric transductor.

19. The system of any one of the preceding claims, wherein the power rectifier is adapted to keep an off-state leakage of the system to below 1 .5 pW.

20. An electronic textile comprising a textile and the system of any one of claims 1 to 19, wherein the system is integrated with the textile.

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